ftp.cc.uoc.gr
rfc5546
This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 2097, EID 2331, EID 3932
Network Working Group                                      C. Daboo, Ed.
Request for Comments: 5546                                    Apple Inc.
Obsoletes: 2446                                            December 2009
Updates: 5545
Category: Standards Track


    iCalendar Transport-Independent Interoperability Protocol (iTIP)

Abstract

   This document specifies a protocol that uses the iCalendar object
   specification to provide scheduling interoperability between
   different calendaring systems.  This is done without reference to a
   specific transport protocol so as to allow multiple methods of
   communication between systems.  Subsequent documents will define
   profiles of this protocol that use specific, interoperable methods of
   communication between systems.

   The iCalendar Transport-Independent Interoperability Protocol (iTIP)
   complements the iCalendar object specification by adding semantics
   for group scheduling methods commonly available in current
   calendaring systems.  These scheduling methods permit two or more
   calendaring systems to perform transactions such as publishing,
   scheduling, rescheduling, responding to scheduling requests,
   negotiating changes, or canceling.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must

   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction and Overview .......................................5
      1.1. Formatting Conventions .....................................5
      1.2. Related Documents ..........................................6
      1.3. Roles ......................................................6
      1.4. Methods ....................................................7
   2. Interoperability Models .........................................9
      2.1. Application Protocol ......................................10
           2.1.1. Scheduling State ...................................10
           2.1.2. Delegation .........................................10
           2.1.3. Acting on Behalf of Other Calendar Users ...........11
           2.1.4. Component Revisions ................................11
           2.1.5. Message Sequencing .................................12
   3. Application Protocol Elements ..................................13
      3.1. Common Component Restriction Tables .......................15
           3.1.1. VCALENDAR ..........................................15
           3.1.2. VTIMEZONE ..........................................15
           3.1.3. VALARM .............................................17
      3.2. Methods for VEVENT Calendar Components ....................17
           3.2.1. PUBLISH ............................................18
           3.2.2. REQUEST ............................................20
           3.2.3. REPLY ..............................................25
           3.2.4. ADD ................................................27
           3.2.5. CANCEL .............................................29
           3.2.6. REFRESH ............................................31
           3.2.7. COUNTER ............................................33
           3.2.8. DECLINECOUNTER .....................................35
      3.3. Methods for VFREEBUSY Components ..........................37
           3.3.1. PUBLISH ............................................37
           3.3.2. REQUEST ............................................40
           3.3.3. REPLY ..............................................42

      3.4. Methods for VTODO Components ..............................44
           3.4.1. PUBLISH ............................................44
           3.4.2. REQUEST ............................................46
           3.4.3. REPLY ..............................................51
           3.4.4. ADD ................................................53
           3.4.5. CANCEL .............................................55
           3.4.6. REFRESH ............................................57
           3.4.7. COUNTER ............................................59
           3.4.8. DECLINECOUNTER .....................................61
      3.5. Methods for VJOURNAL Components ...........................62
           3.5.1. PUBLISH ............................................63
           3.5.2. ADD ................................................64
           3.5.3. CANCEL .............................................66
      3.6. Status Replies ............................................68
      3.7. Implementation Considerations .............................77
           3.7.1. Working With Recurrence Instances ..................77
           3.7.2. Attendee Property Considerations ...................78
           3.7.3. Extension Tokens ...................................79
   4. Examples .......................................................79
      4.1. Published Event Examples ..................................79
           4.1.1. A Minimal Published Event ..........................80
           4.1.2. Changing a Published Event .........................80
           4.1.3. Canceling a Published Event ........................81
           4.1.4. A Rich Published Event .............................81
           4.1.5. Anniversaries or Events Attached to Entire Days ....83
      4.2. Group Event Examples ......................................83
           4.2.1. A Group Event Request ..............................84
           4.2.2. Reply to a Group Event Request .....................85
           4.2.3. Update an Event ....................................85
           4.2.4. Countering an Event Proposal .......................86
           4.2.5. Delegating an Event ................................88
           4.2.6. Delegate Accepts the Meeting .......................90
           4.2.7. Delegate Declines the Meeting ......................91
           4.2.8. Forwarding an Event Request ........................92
           4.2.9. Cancel a Group Event ...............................92
           4.2.10. Removing Attendees ................................93
           4.2.11. Replacing the Organizer ...........................95
      4.3. Busy Time Examples ........................................96
           4.3.1. Publish Busy Time ..................................96
           4.3.2. Request Busy Time ..................................96
           4.3.3. Reply to a Busy Time Request .......................97
      4.4. Recurring Event and Time Zone Examples ....................98
           4.4.1. A Recurring Event Spanning Time Zones ..............98
           4.4.2. Modify a Recurring Instance ........................99
           4.4.3. Cancel an Instance ................................101
           4.4.4. Cancel a Recurring Event ..........................101
           4.4.5. Change All Future Instances .......................102
           4.4.6. Add a New Instance to a Recurring Event ...........102

           4.4.7. Add a New Series of Instances to a
                  Recurring Event ...................................103
           4.4.8. Refreshing a Recurring Event ......................104
           4.4.9. Counter an Instance of a Recurring Event ..........106
           4.4.10. Error Reply to a Request .........................107
      4.5. Group To-Do Examples .....................................108
           4.5.1. A VTODO Request ...................................109
           4.5.2. A VTODO Reply .....................................110
           4.5.3. A VTODO Request for Updated Status ................110
           4.5.4. A Reply: Percent-Complete .........................111
           4.5.5. A Reply: Completed ................................111
           4.5.6. An Updated VTODO Request ..........................112
           4.5.7. Recurring VTODOs ..................................112
      4.6. Journal Examples .........................................113
      4.7. Other Examples ...........................................114
           4.7.1. Event Refresh .....................................114
           4.7.2. Bad RECURRENCE-ID .................................114
   5. Application Protocol Fallbacks ................................116
      5.1. Partial Implementation ...................................116
           5.1.1. Event-Related Fallbacks ...........................117
           5.1.2. Free/Busy-Related Fallbacks .......................119
           5.1.3. To-Do-Related Fallbacks ...........................120
           5.1.4. Journal-Related Fallbacks .........................122
      5.2. Latency Issues ...........................................123
           5.2.1. Cancellation of an Unknown Calendar Component .....123
           5.2.2. Unexpected Reply from an Unknown Delegate .........124
      5.3. Sequence Number ..........................................124
   6. Security Considerations .......................................124
      6.1. Security Threats .........................................124
           6.1.1. Spoofing the Organizer ............................124
           6.1.2. Spoofing the Attendee .............................124
           6.1.3. Unauthorized Replacement of the Organizer .........125
           6.1.4. Eavesdropping and Data Integrity ..................125
           6.1.5. Flooding a Calendar ...............................125
           6.1.6. Unauthorized REFRESH Requests .....................125
      6.2. Recommendations ..........................................125
           6.2.1. Securing iTIP transactions ........................125
           6.2.2. Implementation Controls ...........................126
           6.2.3. Access Controls and Filtering .....................126
      6.3. Privacy Issues ...........................................126
   7. IANA Considerations ...........................................127
      7.1. Registration Template for REQUEST-STATUS Values ..........127
      7.2. Additions to iCalendar METHOD Registry ...................127
      7.3. REQUEST-STATUS Value Registry ............................129
   8. Acknowledgments ...............................................130
   9. References ....................................................131
      9.1. Normative References .....................................131
      9.2. Informative References ...................................131

   Appendix A.  Differences from RFC 2446 ...........................132
     A.1.  Changed Restrictions .....................................132
     A.2.  Deprecated Features ......................................133

1.  Introduction and Overview

   This document specifies how calendaring systems use iCalendar
   [RFC5545] objects to interoperate with other calendaring systems.  In
   particular, it specifies how to schedule events, to-dos, or daily
   journal entries.  It further specifies how to search for available
   busy time information.  It does so in a general way, without
   specifying how communication between different systems actually takes
   place.  Subsequent documents will specify transport bindings between
   systems that use this protocol.

   This protocol is based on messages sent from an originator to one or
   more recipients.  For certain types of messages, a recipient may
   reply in order to update their status and may also return
   transaction/request status information.  The protocol supports the
   ability for the message originator to modify or cancel the original
   message.  The protocol also supports the ability for recipients to
   suggest changes to the originator of a message.  The elements of the
   protocol also define the user roles for its transactions.

   This specification obsoletes RFC 2446 - a list of important changes
   is provided in Appendix A.

1.1.  Formatting Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Calendaring and scheduling roles are referred to in quoted-strings of
   text with the first character of each word in upper case.  For
   example, "Organizer" refers to a role of a "Calendar User" (CU)
   within the scheduling protocol.

   Calendar components defined by [RFC5545] are referred to with
   capitalized, quoted-strings of text.  All calendar components start
   with the letter "V".  For example, "VEVENT" refers to the event
   calendar component, "VTODO" refers to the to-do calendar component,
   and "VJOURNAL" refers to the daily journal calendar component.

   Scheduling methods are referred to with capitalized, quoted-strings
   of text.  For example, "REQUEST" refers to the method for requesting
   a scheduling calendar component be created or modified; "REPLY"
   refers to the method a recipient of a request uses to update their
   status with the "Organizer" of the calendar component.

   Properties defined by [RFC5545] are referred to with capitalized,
   quoted-strings of text, followed by the word "property".  For
   example, "ATTENDEE" property refers to the iCalendar property used to
   convey the calendar address of a "Calendar User".

   Property parameters defined by this specification are referred to
   with capitalized, quoted-strings of text, followed by the word
   "parameter".  For example, "VALUE" parameter refers to the iCalendar
   property parameter used to override the default data type for a
   property value.

   Enumerated values defined by this specification are referred to with
   capitalized text, either alone or followed by the word "value".

   In tables, the quoted-string text is specified without quotes in
   order to minimize the table length.

1.2.  Related Documents

   Implementers will need to be familiar with several other
   specifications that, along with this one, describe the Internet
   calendaring and scheduling standards.  The related documents are:

      [RFC5545] - specifies the objects, data types, properties, and
      property parameters used in the protocols, along with the methods
      for representing and encoding them.

      [iMIP] - specifies an Internet email binding for iTIP.

   This specification does not attempt to repeat the concepts or
   definitions from these other specifications.  Where possible,
   explicit references are made to the other specifications.

1.3.  Roles

   Exchanges of iCalendar objects for the purposes of group calendaring
   and scheduling occur between "Calendar Users" (CUs).  CUs take on
   several roles in iTIP:

   +-----------+-------------------------------------------------------+
   | Role      | Description                                           |
   +-----------+-------------------------------------------------------+
   | Organizer | The CU who initiates an exchange takes on the role of |
   |           | Organizer.  For example, the CU who proposes a group  |
   |           | meeting is the Organizer.                             |
   |           |                                                       |
   | Attendee  | CUs who are included in the scheduling message as     |
   |           | possible recipients of that scheduling message.  For  |
   |           | example, the CUs asked to participate in a group      |
   |           | meeting by the Organizer take on the role of          |
   |           | Attendee.                                             |
   |           |                                                       |
   | Other CU  | A CU that is not explicitly included in a scheduling  |
   |           | message, i.e., not the Organizer or an Attendee.      |
   +-----------+-------------------------------------------------------+

   Note that "ROLE" is also a descriptive parameter to the iCalendar
   "ATTENDEE" property.  Its use is to convey descriptive context about
   an "Attendee" -- such as "chair", "required participant", or "non-
   required participant" -- and has nothing to do with the calendaring
   workflow.

1.4.  Methods

   The iTIP methods are listed below and their usage and semantics are
   defined in Section 3 of this document.

   +----------------+--------------------------------------------------+
   | Method         | Description                                      |
   +----------------+--------------------------------------------------+
   | PUBLISH        | Used to publish an iCalendar object to one or    |
   |                | more "Calendar Users".  There is no              |
   |                | interactivity between the publisher and any      |
   |                | other "Calendar User".  An example might include |
   |                | a baseball team publishing its schedule to the   |
   |                | public.                                          |
   |                |                                                  |
   | REQUEST        | Used to schedule an iCalendar object with other  |
   |                | "Calendar Users".  Requests are interactive in   |
   |                | that they require the receiver to respond using  |
   |                | the reply methods.  Meeting requests, busy-time  |
   |                | requests, and the assignment of tasks to other   |
   |                | "Calendar Users" are all examples.  Requests are |
   |                | also used by the Organizer to update the status  |
   |                | of an iCalendar object.                          |
   |                |                                                  |
   | REPLY          | A reply is used in response to a request to      |
   |                | convey Attendee status to the Organizer.         |
   |                | Replies are commonly used to respond to meeting  |
   |                | and task requests.                               |
   |                |                                                  |
   | ADD            | Add one or more new instances to an existing     |
   |                | recurring iCalendar object.                      |
   |                |                                                  |
   | CANCEL         | Cancel one or more instances of an existing      |
   |                | iCalendar object.                                |
   |                |                                                  |
   | REFRESH        | Used by an Attendee to request the latest        |
   |                | version of an iCalendar object.                  |
   |                |                                                  |
   | COUNTER        | Used by an Attendee to negotiate a change in an  |
   |                | iCalendar object.  Examples include the request  |
   |                | to change a proposed event time or change the    |
   |                | due date for a task.                             |
   |                |                                                  |
   | DECLINECOUNTER | Used by the Organizer to decline the proposed    |
   |                | counter proposal.                                |
   +----------------+--------------------------------------------------+

   Group scheduling in iTIP is accomplished using the set of "request"
   and "response" methods described above.  The following table shows
   the methods broken down by who can send them.

   +------------+------------------------------------------------------+
   | Originator | Methods                                              |
   +------------+------------------------------------------------------+
   | Organizer  | PUBLISH, REQUEST, ADD, CANCEL, DECLINECOUNTER        |
   |            |                                                      |
   | Attendee   | REPLY, REFRESH, COUNTER, REQUEST (only when          |
   |            | delegating)                                          |
   +------------+------------------------------------------------------+

   Note that for some calendar component types, the allowable methods
   are a subset of the above set.  In addition, apart from "VTIMEZONE"
   iCalendar components, only one component type is allowed in a single
   iTIP message.

2.  Interoperability Models

   There are two distinct protocols relevant to interoperability: an
   "application protocol" and a "transport protocol".  The application
   protocol defines the content of the iCalendar objects sent between
   sender and receiver to accomplish the scheduling transactions listed
   above.  The transport protocol defines how the iCalendar objects are
   sent between the sender and receiver.  This document focuses on the
   application protocol.  Binding documents such as [iMIP] focus on the
   transport protocol.

   The connection between sender and receiver in the diagram below
   refers to the application protocol.  The iCalendar objects passed
   from the sender to the receiver are presented in Section 3,
   "Application Protocol Elements".

           +----------+                +----------+
           |          |      iTIP      |          |
           |  Sender  |<-------------->| Receiver |
           |          |                |          |
           +----------+                +----------+

   There are several variations of this diagram in which the sender and
   receiver take on various roles of a "Calendar User Agent" (CUA) or a
   "Calendar Service" (CS).

   The architecture of iTIP is depicted in the diagram below.  An
   application written to this specification may work with bindings for
   the store-and-forward transport, the real-time transport, or both.
   Also note that iTIP could be bound to other transports.

      +--------------------------------------------------------+
      |                     iTIP Protocol                      |
      +--------------------------------------------------------+
      |                       Transport                        |
      +  -  -  -  -  -  +  -  -  -  -  -  -  +  -  -  -  -  -  +
      | Real-Time       | Store-and-Forward  | Others          |
      +-----------------+--------------------+-----------------+

2.1.  Application Protocol

   In the iTIP model, an iCalendar object is created and managed by an
   "Organizer".  The "Organizer" interacts with other CUs by sending one
   or more of the iTIP messages listed above.  "Attendees" use the
   "REPLY" method to communicate their status.  "Attendees" do not make
   direct changes to the master iCalendar object.  They can, however,
   use the "COUNTER" method to suggest changes to the "Organizer".  In
   any case, the "Organizer" has complete control over the master
   iCalendar object.

2.1.1.  Scheduling State

   There are two distinct states relevant to iCalendar objects used in
   scheduling: the overall state of the iCalendar object and the state
   associated with an "Attendee" in that iCalendar object.

   The state of an iCalendar object is defined by the "STATUS" property
   and is controlled by the "Organizer."  There is no default value for
   the "STATUS" property.  The "Organizer" sets the "STATUS" property to
   the appropriate value for each iCalendar object.

   The state of a particular "Attendee" relative to an iCalendar object
   used for scheduling is defined by the "PARTSTAT" parameter in the
   "ATTENDEE" property for each "Attendee".  When an "Organizer" issues
   the initial iCalendar object, "Attendee" status is typically unknown.
   The "Organizer" specifies this by setting the "PARTSTAT" parameter to
   "NEEDS-ACTION".  Each "Attendee" modifies their "ATTENDEE" property
   "PARTSTAT" parameter to an appropriate value as part of a "REPLY"
   message sent back to the "Organizer".

2.1.2.  Delegation

   Delegation is defined as the process by which an "Attendee" grants
   another CU (or several CUs) the right to attend on their behalf.  The
   "Organizer" is made aware of this change because the delegating
   "Attendee" informs the "Organizer".  These steps are detailed in the
   "REQUEST" method sections for the appropriate components.

2.1.3.  Acting on Behalf of Other Calendar Users

   In many organizations, one user will act on behalf of another to
   organize and/or respond to meeting requests. iTIP provides two
   mechanisms that support these activities.

   First, the "Organizer" is treated as a special entity, separate from
   "Attendees".  All responses from "Attendees" flow to the "Organizer",
   making it easy to separate a "Calendar User" organizing a meeting
   from "Calendar Users" attending the meeting.  Additionally, iCalendar
   provides descriptive roles for each "Attendee".  For instance, a role
   of "chair" may be ascribed to one or more "Attendees".  The "chair"
   and the "Organizer" may or may not be the same "Calendar User".  This
   maps well to scenarios where an assistant may manage meeting
   logistics for another individual who chairs a meeting.

   Second, a "SENT-BY" parameter may be specified in either the
   "Organizer" or "Attendee" properties.  When specified, the "SENT-BY"
   parameter indicates that the responding CU acted on behalf of the
   specified "Attendee" or "Organizer".

2.1.4.  Component Revisions

   The "SEQUENCE" property is used by the "Organizer" to indicate
   revisions to the calendar component.  When the "Organizer" makes
   changes to one of the following properties, the sequence number MUST
   be incremented:

   o  "DTSTART"

   o  "DTEND"

   o  "DURATION"

   o  "DUE"

   o  "RRULE"

   o  "RDATE"

   o  "EXDATE"

   o  "STATUS"

   In addition, changes made by the "Organizer" to other properties MAY
   also require the sequence number to be incremented.  The "Organizer"
   CUA MUST increment the sequence number whenever it makes changes to
   properties in the calendar component that the "Organizer" deems will

   jeopardize the validity of the participation status of the
   "Attendees".  For example, changing the location of a meeting from
   one location to another distant location could effectively impact the
   participation status of the "Attendees".

   Depending on the "METHOD", the "SEQUENCE" property MUST follow these
   rules in the context of iTIP:

   o  For the "PUBLISH" and "REQUEST" methods, the "SEQUENCE" property
      value is incremented according to the rules stated above.

   o  The "SEQUENCE" property value MUST be incremented each time the
      "Organizer" uses the "ADD" or "CANCEL" methods.

   o  The "SEQUENCE" property value MUST NOT be incremented when using
      "REPLY", "REFRESH", "COUNTER", "DECLINECOUNTER", or when sending a
      delegation "REQUEST".

   In some circumstances, the "Organizer" may not have received
   responses to the final revision sent out.  In this situation, the
   "Organizer" may wish to send an update "REQUEST" and set "RSVP=TRUE"
   for all "Attendees" so that current responses can be collected.

   The value of the "SEQUENCE" property contained in a response from an
   "Attendee" may not always match the "Organizer's" revision.
   Implementations may choose to have the CUA indicate to the CU that
   the response is to an iCalendar object that has been revised, and
   allow the CU to decide whether or not to accept the response.

   Whilst a change in sequence number is indicative of a significant
   change to a previously scheduled item, "Attendee" CUAs SHOULD NOT
   rely solely on a change in sequence number as a means of detecting a
   significant change.  Instead, CUAs SHOULD compare the old and new
   versions of the calendar components, determine the exact nature of
   the changes, and make decisions -- possibly based on "Calendar User"
   preferences -- as to whether the user needs to be explicitly informed
   of the change.

2.1.5.  Message Sequencing

   CUAs that handle the iTIP application protocol must often correlate a
   component in a calendar store with a component received in the iTIP
   message.  For example, an event may be updated with a later revision
   of the same event.  To accomplish this, a CUA must correlate the
   version of the event already in its calendar store with the version
   sent in the iTIP message.  In addition to this correlation, there are
   several factors that can cause iTIP messages to arrive in an
   unexpected order.  That is, an "Organizer" could receive a reply to

   an earlier revision of a component after receiving a reply to a later
   revision.

   To maximize interoperability and to handle messages that arrive in an
   unexpected order, use the following rules:

   1.  The primary key for referencing a particular iCalendar component
       is the "UID" property value.  To reference an instance of a
       recurring component, the primary key is composed of the "UID" and
       the "RECURRENCE-ID" properties.

   2.  The secondary key for referencing a component is the "SEQUENCE"
       property value.  For components where the "UID" and
       "RECURRENCE-ID" property values are the same, the component with
       the highest numeric value for the "SEQUENCE" property obsoletes
       all other revisions of the component with lower values.

   3.  "Attendees" send "REPLY" messages to the "Organizer".  For
       replies where the "UID" and "RECURRENCE-ID" property values are
       the same, the value of the "SEQUENCE" property indicates the
       revision of the component to which the "Attendee" is replying.
       The reply with the highest numeric value for the "SEQUENCE"
       property obsoletes all other replies with lower values.

   4.  In situations where the "UID", "RECURRENCE-ID", and "SEQUENCE"
       property values match, the "DTSTAMP" property is used as the tie-
       breaker.  The component with the latest "DTSTAMP" overrides all
       others.  Similarly, for "Attendee" responses where the "UID",
       "RECURRENCE-ID", and "SEQUENCE" property values match, the
       response with the latest "DTSTAMP" overrides all others.

   Hence, CUAs will need to persist the following component properties
   in order to correctly process iTIP messages: "UID", "RECURRENCE-ID",
   "SEQUENCE", and "DTSTAMP".  Furthermore, for each "ATTENDEE" property
   of a component, "Organizer" CUAs will need to persist the "SEQUENCE"
   and "DTSTAMP" property values associated with the "Attendee's" last
   response, so that any earlier responses from an "Attendee" that are
   received out of order (e.g., due to a delay in the transport) can be
   correctly discarded.

3.  Application Protocol Elements

   iTIP messages are "text/calendar" MIME entities that contain
   calendaring and scheduling information.  The particular type of
   iCalendar message is referred to as the "method type".  Each method
   type is identified by a "METHOD" property specified as part of the
   "text/calendar" content type.  The table below shows various

   combinations of calendar components and the method types that this
   specification supports.

        +----------------+--------+-------+----------+-----------+
        |                | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
        +----------------+--------+-------+----------+-----------+
        | PUBLISH        | Yes    | Yes   | Yes      | Yes       |
        | REQUEST        | Yes    | Yes   | No       | Yes       |
        | REFRESH        | Yes    | Yes   | No       | No        |
        | CANCEL         | Yes    | Yes   | Yes      | No        |
        | ADD            | Yes    | Yes   | Yes      | No        |
        | REPLY          | Yes    | Yes   | No       | Yes       |
        | COUNTER        | Yes    | Yes   | No       | No        |
        | DECLINECOUNTER | Yes    | Yes   | No       | No        |
        +----------------+--------+-------+----------+-----------+

   Each method type is defined in terms of its associated components and
   properties.  Some components and properties are required, some are
   optional, and others are excluded.  The restrictions are expressed in
   this document using a simple "restriction table".  The first column
   indicates the name of a component or property.  Properties of the
   iCalendar object are not indented.  Properties of a component are
   indented.  The second column (the "Presence" column) indicates
   whether or not a component or property should be present and, if
   present, how many times it can occur.  The third column contains
   comments for further clarification.

   The presence column uses the following values to assert whether a
   property is required or optional, and the number of times it may
   appear in the iCalendar object.

   +----------------+--------------------------------------------------+
   | Presence Value | Description                                      |
   +----------------+--------------------------------------------------+
   | 1              | One instance MUST be present.                    |
   | 1+             | At least one instance MUST be present.           |
   | 0              | Instances of this property MUST NOT be present.  |
   | 0+             | Multiple instances MAY be present.               |
   | 0 or 1         | Up to 1 instance of this property MAY be         |
   |                | present.                                         |
   +----------------+--------------------------------------------------+

   The tables also call out "IANA-PROPERTY", "X-PROPERTY", "IANA-
   COMPONENT", and "X-COMPONENT" to show where registered and
   experimental property and component extensions can appear.  The
   tables do not lay out the restrictions of property parameters.  Those
   restrictions are defined in [RFC5545].

3.1.  Common Component Restriction Tables

3.1.1.  VCALENDAR

   The restriction table below applies to properties of the iCalendar
   object.  That is, the properties at the outermost scope.

          +-----------------------------------------------------+
          | Constraints for Properties in a VCALENDAR Component |
          +-----------------------------------------------------+

          +--------------------+----------+--------------------+
          | Component/Property | Presence | Comment            |
          +--------------------+----------+--------------------+
          | CALSCALE           | 0 or 1   |                    |
          | PRODID             | 1        |                    |
          | VERSION            | 1        | Value MUST be 2.0. |
          | IANA-PROPERTY      | 0+       |                    |
          | X-PROPERTY         | 0+       |                    |
          +--------------------+----------+--------------------+

3.1.2.  VTIMEZONE

   "VTIMEZONE" components may be referred to by other components via a
   "TZID" parameter on a "DATETIME" value type.  The property
   restrictions in the table below apply to any "VTIMEZONE" component in
   an iTIP message.

                 +--------------------------------------+
                 | Constraints for VTIMEZONE Components |
                 +--------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to timezone.               |
      |   DAYLIGHT         | 0+       | MUST be one or more of either     | 
   |                    |          | STANDARD or DAYLIGHT.             |
   |     COMMENT        | 0+       |                                   |
   |     DTSTART        | 1        | MUST be local time format.        |
   |     RDATE          | 0+       | If present, RRULE MUST NOT be     |
   |                    |          | present                           |
   |     RRULE          | 0 or 1   | If present, RDATE MUST NOT be     |
   |                    |          | present                           |
   |     TZNAME         | 0+       |                                   |
EID 3932 (Verified) is as follows:

Section: 3.1.2

Original Text:

   |   DAYLIGHT         | 0+       | MUST be one or more of either     |
   |                    |          | STANDARD or DAYLIGHT.             |
   |     COMMENT        | 0+       |                                   |
   |     DTSTART        | 1        | MUST be local time format.        |
   |     RDATE          | 0+       |                                   |
   |     RRULE          | 0 or 1   |                                   |
   |     TZNAME         | 0+       |                                   |

Corrected Text:

   |   DAYLIGHT         | 0+       | MUST be one or more of either     |
   |                    |          | STANDARD or DAYLIGHT.             |
   |     COMMENT        | 0+       |                                   |
   |     DTSTART        | 1        | MUST be local time format.        |
   |     RDATE          | 0+       | If present, RRULE MUST NOT be     |
   |                    |          | present                           |
   |     RRULE          | 0 or 1   | If present, RDATE MUST NOT be     |
   |                    |          | present                           |
   |     TZNAME         | 0+       |                                   |
Notes:
The corrected text appeared in RFC 2446, however I couldn't find the reasoning as to why it was omitted in RFC 5546.

The correct comments also appear a few lines below, under "STANDARD".
| TZOFFSETFROM | 1 | | | TZOFFSETTO | 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | LAST-MODIFIED | 0 or 1 | | | STANDARD | 0+ | MUST be one or more of either | | | | STANDARD or DAYLIGHT. | | COMMENT | 0+ | | | DTSTART | 1 | MUST be local time format. | | RDATE | 0+ | If present, RRULE MUST NOT be | | | | present. | | RRULE | 0 or 1 | If present, RDATE MUST NOT be | | | | present. | | TZNAME | 0+ | | | TZOFFSETFROM | 1 | | | TZOFFSETTO | 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | TZID | 1 | | | TZURL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | +--------------------+----------+-----------------------------------+ 3.1.3. VALARM The property restrictions in the table below apply to any "VALARM" component in an iTIP message. +-----------------------------------+ | Constraints for VALARM Components | +-----------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | VALARM | 0+ | | | ACTION | 1 | | | ATTACH | 0+ | | | ATTENDEE | 0+ | | | DESCRIPTION | 0 or 1 | | | DURATION | 0 or 1 | If present, REPEAT MUST be | | | | present. | | REPEAT | 0 or 1 | If present, DURATION MUST be | | | | present. | | SUMMARY | 0 or 1 | | | TRIGGER | 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | +--------------------+----------+-----------------------------------+ 3.2. Methods for VEVENT Calendar Components This section defines the property set restrictions for the method types that are applicable to the "VEVENT" calendar component. Each method is defined using a table that clarifies the property constraints that define the particular method. The following summarizes the methods that are defined for the "VEVENT" calendar component. +----------------+--------------------------------------------------+ | Method | Description | +----------------+--------------------------------------------------+ | PUBLISH | Post notification of an event. Used primarily | | | as a method of advertising the existence of an | | | event. | | | | | REQUEST | Make a request for an event. This is an | | | explicit invitation to one or more Attendees. | | | Event requests are also used to update or change | | | an existing event. Clients that cannot handle | | | REQUEST MAY degrade the event to view it as a | | | PUBLISH. | | | | | REPLY | Reply to an event request. Clients may set | | | their status (PARTSTAT) to ACCEPTED, DECLINED, | | | TENTATIVE, or DELEGATED. | | | | | ADD | Add one or more instances to an existing event. | | | | | CANCEL | Cancel one or more instances of an existing | | | event. | | | | | REFRESH | A request is sent to an Organizer by an Attendee | | | asking for the latest version of an event to be | | | resent to the requester. | | | | | COUNTER | Counter a REQUEST with an alternative proposal. | | | Sent by an Attendee to the Organizer. | | | | | DECLINECOUNTER | Decline a counter proposal. Sent to an Attendee | | | by the Organizer. | +----------------+--------------------------------------------------+ 3.2.1. PUBLISH The "PUBLISH" method in a "VEVENT" calendar component is an unsolicited posting of an iCalendar object. Any CU may add published components to their calendar. The "Organizer" MUST be present in a published iCalendar component. "Attendees" MUST NOT be present. Its expected usage is for encapsulating an arbitrary event as an iCalendar object. The "Organizer" may subsequently update (with another "PUBLISH" method), add instances to (with an "ADD" method), or cancel (with a "CANCEL" method) a previously published "VEVENT" calendar component. This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------+ | Constraints for a METHOD:PUBLISH of a VEVENT | +----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST equal PUBLISH. | | | | | | VEVENT | 1+ | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | SUMMARY | 1 | Can be null. | | UID | 1 | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | SEQUENCE | 0 or 1 | MUST be present if value is | | | | greater than 0; MAY be present if | | | | 0. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0 or 1 | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | TENTATIVE/CONFIRMED/CANCELLED. | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTENDEE | 0 | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0+ | | | | | | | VFREEBUSY | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTODO | 0 | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | +--------------------+----------+-----------------------------------+ 3.2.2. REQUEST The "REQUEST" method in a "VEVENT" component provides the following scheduling functions: o Invite "Attendees" to an event. o Reschedule an existing event. o Response to a "REFRESH" request. o Update the details of an existing event, without rescheduling it. o Update the status of "Attendees" of an existing event, without rescheduling it. o Reconfirm an existing event, without rescheduling it. o Forward a "VEVENT" to another uninvited CU. o For an existing "VEVENT" calendar component, delegate the role of "Attendee" to another CU. o For an existing "VEVENT" calendar component, change the role of "Organizer" to another CU. The "Organizer" originates the "REQUEST". The recipients of the "REQUEST" method are the CUs invited to the event, the "Attendees". "Attendees" use the "REPLY" method to convey attendance status to the "Organizer". The "UID" and "SEQUENCE" properties are used to distinguish the various uses of the "REQUEST" method. If the "UID" property value in the "REQUEST" is not found on the recipient's calendar, then the "REQUEST" is for a new "VEVENT" calendar component. If the "UID" property value is found on the recipient's calendar, then the "REQUEST" is for a rescheduling, an update, or a reconfirmation of the "VEVENT" calendar component. For the "REQUEST" method, multiple "VEVENT" components in a single iCalendar object are only permitted for components with the same "UID" property. That is, a series of recurring events may have instance-specific information. In this case, multiple "VEVENT" components are needed to express the entire series. This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------+ | Constraints for a METHOD:REQUEST of a VEVENT | +----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REQUEST. | | | | | | VEVENT | 1+ | All components MUST have the same | | | | UID. | | ATTENDEE | 1+ | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 0 or 1 | MUST be present if value is | | | | greater than 0; MAY be present if | | | | 0. | | SUMMARY | 1 | Can be null. | | UID | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | REQUEST-STATUS | 0 | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | TENTATIVE/CONFIRMED. | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VFREEBUSY | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.2.2.1. Rescheduling an Event The "REQUEST" method may be used to reschedule an event. A rescheduled event involves a change to the existing event in terms of its time or recurrence intervals and possibly the location or description. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar but that the "SEQUENCE" (or "DTSTAMP") property value in the "REQUEST" method is greater than the value for the existing event, then the "REQUEST" method describes a rescheduling of the event. 3.2.2.2. Updating or Reconfirmation of an Event The "REQUEST" method may be used to update or reconfirm an event. An update to an existing event does not involve changes to the time or recurrence intervals, and might not involve a change to the location or description for the event. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar and that the "SEQUENCE" property value in the "REQUEST" is the same as the value for the existing event, then the "REQUEST" method describes an update of the event details, but not a rescheduling of the event. The update "REQUEST" method is the appropriate response to a "REFRESH" method sent from an "Attendee" to the "Organizer" of an event. The "Organizer" of an event may also send unsolicited "REQUEST" methods. The unsolicited "REQUEST" methods may be used to update the details of the event without rescheduling it, to update the "PARTSTAT" parameter of "Attendees", or to reconfirm the event. 3.2.2.3. Delegating an Event to Another CU Some calendar and scheduling systems allow "Attendees" to delegate their presence at an event to another "Calendar User". iTIP supports this concept using the following workflow. Any "Attendee" may delegate their right to participate in a calendar "VEVENT" to another CU. The implication is that the delegate participates in lieu of the original "Attendee", NOT in addition to the "Attendee". The delegator MUST notify the "Organizer" of this action using the steps outlined below. Implementations may support or restrict delegation as they see fit. For instance, some implementations may restrict a delegate from delegating a "REQUEST" to another CU. The "Delegator" of an event forwards the existing "REQUEST" to the "Delegate". The "REQUEST" method MUST include an "ATTENDEE" property with the calendar address of the "Delegate". The "Delegator" MUST also send a "REPLY" method to the "Organizer" with the "Delegator's" "ATTENDEE" property "PARTSTAT" parameter value set to "DELEGATED". In addition, the "DELEGATED-TO" parameter MUST be included with the calendar address of the "Delegate". Also, a new "ATTENDEE" property for the "Delegate" MUST be included and must specify the calendar user address set in the "DELEGATED-TO" parameter, as above. In response to the request, the "Delegate" MUST send a "REPLY" method to the "Organizer", and optionally to the "Delegator". The "REPLY" method SHOULD include the "ATTENDEE" property with the "DELEGATED- FROM" parameter value of the "Delegator's" calendar address. The "Delegator" may continue to receive updates to the event even though they will not be attending. This is accomplished by the "Delegator" setting their "role" attribute to "NON-PARTICIPANT" in the "REPLY" to the "Organizer". 3.2.2.4. Changing the Organizer The situation may arise where the "Organizer" of a "VEVENT" is no longer able to perform the "Organizer" role and abdicates without passing on the "Organizer" role to someone else. When this occurs, the "Attendees" of the "VEVENT" may use out-of-band mechanisms to communicate the situation and agree upon a new "Organizer". The new "Organizer" should then send out a new "REQUEST" with a modified version of the "VEVENT" in which the "SEQUENCE" number has been incremented and the "ORGANIZER" property has been changed to the new "Organizer". 3.2.2.5. Sending on Behalf of the Organizer There are a number of scenarios that support the need for a "Calendar User" to act on behalf of the "Organizer" without explicit role changing. This might be the case if the CU designated as "Organizer" is sick or unable to perform duties associated with that function. In these cases, iTIP supports the notion of one CU acting on behalf of another. Using the "SENT-BY" parameter, a "Calendar User" could send an updated "VEVENT" "REQUEST". In the case where one CU sends on behalf of another CU, the "Attendee" responses are still directed back towards the CU designated as "Organizer". 3.2.2.6. Forwarding to an Uninvited CU An "Attendee" invited to a "VEVENT" calendar component may send the "VEVENT" calendar component to another new CU not previously associated with the "VEVENT" calendar component. The current "Attendee" invited to the "VEVENT" calendar component does this by forwarding the original "REQUEST" method to the new CU. The new CU can send a "REPLY" to the "Organizer" of the "VEVENT" calendar component. The reply contains an "ATTENDEE" property for the new CU. The "Organizer" ultimately decides whether or not the new CU becomes part of the event and is not obligated to do anything with a "REPLY" from a new (uninvited) CU. If the "Organizer" does not want the new CU to be part of the event, the new "ATTENDEE" property is not added to the "VEVENT" calendar component. The "Organizer" MAY send the CU a "CANCEL" message to indicate that they will not be added to the event. If the "Organizer" decides to add the new CU, the new "ATTENDEE" property is added to the "VEVENT" calendar component. Furthermore, the "Organizer" is free to change any "ATTENDEE" property parameter from the values supplied by the new CU to something the "Organizer" considers appropriate. The "Organizer" SHOULD send the new CU a "REQUEST" message to inform them that they have been added. When forwarding a "REQUEST" to another CU, the forwarding "Attendee" MUST NOT make changes to the original message. 3.2.2.7. Updating Attendee Status The "Organizer" of an event may also request updated status from one or more "Attendees". The "Organizer" sends a "REQUEST" method to the "Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The "SEQUENCE" property for the event is not changed from its previous value. A recipient will determine that the only change in the "REQUEST" is that their "RSVP" property parameter indicates a request for updated status. The recipient SHOULD respond with a "REPLY" method indicating their current status with respect to the "REQUEST". 3.2.3. REPLY The "REPLY" method in a "VEVENT" calendar component is used to respond (e.g., accept or decline) to a "REQUEST" or to reply to a delegation "REQUEST". When used to provide a delegation response, the "Delegator" SHOULD include the calendar address of the "Delegate" on the "DELEGATED-TO" property parameter of the "Delegator's" "ATTENDEE" property. The "Delegate" SHOULD include the calendar address of the "Delegator" on the "DELEGATED-FROM" property parameter of the "Delegate's" "ATTENDEE" property. The "REPLY" method is also used when processing of a "REQUEST" fails. Depending on the value of the "REQUEST-STATUS" property, no scheduling action may have been performed. The "Organizer" of an event may receive the "REPLY" method from a CU not in the original "REQUEST". For example, a "REPLY" may be received from a "Delegate" to an event. In addition, the "REPLY" method may be received from an unknown CU (a "Party Crasher"). This uninvited "Attendee" may be accepted, or the "Organizer" may cancel the event for the uninvited "Attendee" by sending a "CANCEL" method to the uninvited "Attendee". An "Attendee" MAY include a message to the "Organizer" using the "COMMENT" property. For example, if the user indicates tentative acceptance and wants to let the "Organizer" know why, the reason can be expressed in the "COMMENT" property value. The "Organizer" may also receive a "REPLY" from one CU on behalf of another. Like the scenario enumerated above for the "Organizer", "Attendees" may have another CU respond on their behalf. This is done using the "SENT-BY" parameter. The optional properties listed in the table below (those listed as "0+" or "0 or 1") MUST NOT be changed from those of the original request. If property changes are desired, the "COUNTER" message must be used. This method type is an iCalendar object that conforms to the following property constraints: +--------------------------------------------+ | Constraints for a METHOD:REPLY of a VEVENT | +--------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REPLY. | | | | | | VEVENT | 1+ | All components MUST have the same | | | | UID. | | ATTENDEE | 1 | MUST be the address of the | | | | Attendee replying. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | UID | 1 | MUST be the UID of the original | | | | REQUEST. | | SEQUENCE | 0 or 1 | If non-zero, MUST be the sequence | | | | number of the original REQUEST. | | | | MAY be present if 0. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DTSTART | 0 or 1 | | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | REQUEST-STATUS | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | | | SUMMARY | 0 or 1 | | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0 or 1 | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VFREEBUSY | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.2.4. ADD The "ADD" method allows the "Organizer" to add one or more new instances to an existing "VEVENT" using a single iTIP message without having to send the entire "VEVENT" with all the existing instance data, as it would have to do if the "REQUEST" method were used. The "UID" must be that of the existing event. If the "UID" property value in the "ADD" is not found on the recipient's calendar, then the recipient SHOULD send a "REFRESH" to the "Organizer" in order to be updated with the latest version of the "VEVENT". If an "Attendee" implementation does not support the "ADD" method, it should respond with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH". When handling an "ADD" message, the "Attendee" treats each component in the "ADD" message as if it were referenced via an "RDATE" in the main component. This method type is an iCalendar object that conforms to the following property constraints: +------------------------------------------+ | Constraints for a METHOD:ADD of a VEVENT | +------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be ADD. | | | | | | VEVENT | 1 | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | MUST be greater than 0. | | SUMMARY | 1 | Can be null. | | UID | 1 | MUST match that of the original | | | | event. | | ATTACH | 0+ | | | ATTENDEE | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | STATUS | 0 or 1 | MAY be one of | | | | TENTATIVE/CONFIRMED. | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | EXDATE | 0 | | | RECURRENCE-ID | 0 | | | REQUEST-STATUS | 0 | | | RDATE | 0 | | | RRULE | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VFREEBUSY | 0 | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | +--------------------+----------+-----------------------------------+ 3.2.5. CANCEL The "CANCEL" method in a "VEVENT" calendar component is used to send a cancellation notice of an existing event request to the affected "Attendees". The message is sent by the "Organizer" of the event. For a recurring event, either the whole event or instances of an event may be cancelled. To cancel the complete range of a recurring event, the "UID" property value for the event MUST be specified and a "RECURRENCE-ID" MUST NOT be specified in the "CANCEL" method. In order to cancel an individual instance of the event, the "RECURRENCE-ID" property value for the event MUST be specified in the "CANCEL" method. There are two options for canceling a sequence of instances of a recurring "VEVENT" calendar component: a. The "RECURRENCE-ID" property for an instance in the sequence MUST be specified with the "RANGE" property parameter value of "THISANDFUTURE" to indicate cancellation of the specified "VEVENT" calendar component and all instances after. b. Individual recurrence instances may be cancelled by specifying multiple "VEVENT" components each with a "RECURRENCE-ID" property corresponding to one of the instances to be cancelled. The "Organizer" MUST send a "CANCEL" message to each "Attendee" affected by the cancellation. This can be done using a single "CANCEL" message for all "Attendees" or by using multiple messages with different subsets of the affected "Attendees" in each. When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be incremented as described in Section 2.1.4. This method type is an iCalendar object that conforms to the following property constraints: +---------------------------------------------+ | Constraints for a METHOD:CANCEL of a VEVENT | +---------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be CANCEL. | | | | | | VEVENT | 1+ | All must have the same UID. | | ATTENDEE | 0+ | MUST include some or all | | | | Attendees being removed from the | | | | event. MUST include some or all | | | | Attendees if the entire event is | | | | cancelled. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | | | UID | 1 | MUST be the UID of the original | | | | REQUEST. | | COMMENT | 0+ | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DTSTART | 0 or 1 | | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MUST be set to CANCELLED to | | | | cancel the entire event. If | | | | uninviting specific Attendees, | | | | then MUST NOT be included. | | SUMMARY | 0 or 1 | | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.2.6. REFRESH The "REFRESH" method in a "VEVENT" calendar component is used by "Attendees" of an existing event to request an updated description from the event "Organizer". The "REFRESH" method must specify the "UID" property of the event to update. A recurrence instance of an event may be requested by specifying the "RECURRENCE-ID" property corresponding to the associated event. The "Organizer" responds with the latest description and version of the event. This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------+ | Constraints for a METHOD:REFRESH of a VEVENT | +----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REFRESH. | | | | | | VEVENT | 1 | | | ATTENDEE | 1 | MUST be the address of requester. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | UID | 1 | MUST be the UID associated with | | | | original REQUEST. | | COMMENT | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTACH | 0 | | | CATEGORIES | 0 | | | CLASS | 0 | | | CONTACT | 0 | | | CREATED | 0 | | | DESCRIPTION | 0 | | | DTEND | 0 | | | DTSTART | 0 | | | DURATION | 0 | | | EXDATE | 0 | | | GEO | 0 | | | LAST-MODIFIED | 0 | | | LOCATION | 0 | | | PRIORITY | 0 | | | RDATE | 0 | | | RELATED-TO | 0 | | | REQUEST-STATUS | 0 | | | RESOURCES | 0 | | | RRULE | 0 | | | SEQUENCE | 0 | | | STATUS | 0 | | | SUMMARY | 0 | | | TRANSP | 0 | | | URL | 0 | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0+ | | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.2.7. COUNTER The "COUNTER" method for a "VEVENT" calendar component is used by an "Attendee" of an existing event to submit to the "Organizer" a counter proposal to the event. The "Attendee" sends this message to the "Organizer" of the event. The counter proposal is an iCalendar object consisting of a "VEVENT" calendar component that provides the complete description of the alternate event. The "Organizer" rejects the counter proposal by sending the "Attendee" a "DECLINECOUNTER" method. The "Organizer" accepts the counter proposal by rescheduling the event as described in Section 3.2.2.1, "Rescheduling an Event". The "Organizer's" CUA SHOULD send a "REQUEST" message to all "Attendees" affected by any change triggered by an accepted "COUNTER". This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------+ | Constraints for a METHOD:COUNTER of a VEVENT | +----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be COUNTER. | | | | | | VEVENT | 1 | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | MUST be the Organizer of the | | | | original event. | | SEQUENCE | 1 | MUST echo the original SEQUENCE | | | | number. MUST be present if | | | | non-zero. MAY be present if | | | | zero. | | SUMMARY | 1 | Can be null. | | UID | 1 | MUST be the UID associated with | | | | the REQUEST being countered. | | ATTACH | 0+ | | | ATTENDEE | 0+ | Can also be used to propose other | | | | Attendees. | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | REQUEST-STATUS | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | Value must be one of | | | | CONFIRMED/TENATIVE/CANCELLED. | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.2.8. DECLINECOUNTER The "DECLINECOUNTER" method in a "VEVENT" calendar component is used by the "Organizer" of an event to reject a counter proposal submitted by an "Attendee". The "Organizer" must send the "DECLINECOUNTER" message to the "Attendee" that sent the "COUNTER" method to the "Organizer". This method type is an iCalendar object that conforms to the following property constraints: +-----------------------------------------------------+ | Constraints for a METHOD:DECLINECOUNTER of a VEVENT | +-----------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be DECLINECOUNTER. | | | | | | VEVENT | 1+ | All components MUST have the same | | | | UID. | | ATTENDEE | 1+ | MUST for all Attendees. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | MUST echo the original SEQUENCE | | | | number. | | UID | 1 | MUST echo original UID. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTSTART | 0 or 1 | | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DTEND MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | REQUEST-STATUS | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | TENTATIVE/CONFIRMED. | | SUMMARY | 0 or 1 | Can be null. | | TRANSP | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VALARM | 0 | | | VFREEBUSY | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.3. Methods for VFREEBUSY Components This section defines the property set for the methods that are applicable to the "VFREEBUSY" calendar component. Each of the methods is defined using a restriction table. This document only addresses the transfer of busy time information. Applications desiring free time information MUST infer this from available busy time information. The "FREEBUSY" property value MAY include a list of values, separated by the COMMA character (US-ASCII decimal 44). Alternately, multiple busy time periods MAY be specified with multiple instances of the "FREEBUSY" property. Both forms MUST be supported by implementations conforming to this document. Duplicate busy time periods SHOULD NOT be specified in an iCalendar object. However, two different busy time periods MAY overlap. "FREEBUSY" properties SHOULD be sorted such that their values are in ascending order, based on the start time and then the end time, with the earliest periods first. For example, today's busy time information should appear after yesterday's busy time information. And the busy time for this half-hour should appear after the busy time for earlier today. Busy time periods can also span a day boundary. The following summarizes the methods that are defined for the "VFREEBUSY" calendar component. +---------+-------------------------------------+ | Method | Description | +---------+-------------------------------------+ | PUBLISH | Publish unsolicited busy time data. | | | | | REQUEST | Request busy time data. | | | | | REPLY | Reply to a busy time request. | +---------+-------------------------------------+ 3.3.1. PUBLISH The "PUBLISH" method in a "VFREEBUSY" calendar component is used to publish busy time data. The method may be sent from one CU to any other. The purpose of the method is to provide a way to send unsolicited busy time data. That is, the busy time data is not being sent as a "REPLY" to the receipt of a "REQUEST" method. The "ORGANIZER" property MUST be specified in the busy time information. The value is the CU address of the originator of the busy time information. The busy time information within the iCalendar object MAY be grouped into more than one "VFREEBUSY" calendar component. This capability allows busy time periods to be grouped according to some common periodicity, such as a calendar week, month, or year. In this case, each "VFREEBUSY" calendar component MUST include the "ORGANIZER", "DTSTART", and "DTEND" properties in order to specify the source of the busy time information and the date and time interval over which the busy time information covers. This method type is an iCalendar object that conforms to the following property constraints: +-------------------------------------------------+ | Constraints for a METHOD:PUBLISH of a VFREEBUSY | +-------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be PUBLISH. | | | | | | VFREEBUSY | 1+ | | | DTSTAMP | 1 | | | DTSTART | 1 | DateTime values must be in UTC. | | DTEND | 1 | DateTime values must be in UTC. | | FREEBUSY | 0+ | MUST be BUSYTIME. Multiple | | | | instances are allowed. Multiple | | | | instances SHOULD be sorted in | | | | ascending order. | | ORGANIZER | 1 | MUST contain the address of | | | | originator of busy time data. | | UID | 1 | | | COMMENT | 0+ | | | CONTACT | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | URL | 0 or 1 | Specifies busy time URL. | | ATTENDEE | 0 | | | DURATION | 0 | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0 | | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTIMEZONE | 0 | | +--------------------+----------+-----------------------------------+ 3.3.2. REQUEST The "REQUEST" method in a "VFREEBUSY" calendar component is used to ask a "Calendar User" for their busy time information. The request may be for a busy time information bounded by a specific date and time interval. This message only permits requests for busy time information. The message is sent from a "Calendar User" requesting the busy time information of one or more intended recipients. If the originator of the "REQUEST" method is not authorized to make a busy time request on the recipient's calendar system, then an exception message SHOULD be returned in a "REPLY" method, but no busy time data need be returned. This method type is an iCalendar object that conforms to the following property constraints: +-------------------------------------------------+ | Constraints for a METHOD:REQUEST of a VFREEBUSY | +-------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REQUEST. | | | | | | VFREEBUSY | 1 | | | ATTENDEE | 1+ | Contains the calendar user | | | | addresses of the "Calendar Users" | | | | whose freebusy is being | | | | requested. | | DTEND | 1 | DateTime values must be in UTC. | | DTSTAMP | 1 | | | DTSTART | 1 | DateTime values must be in UTC. | | ORGANIZER | 1 | MUST be the request originator's | | | | address. | | UID | 1 | | | COMMENT | 0+ | | | CONTACT | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | FREEBUSY | 0 | | | DURATION | 0 | | | REQUEST-STATUS | 0 | | | URL | 0 | | | | | | | VALARM | 0 | | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTIMEZONE | 0 | | +--------------------+----------+-----------------------------------+ 3.3.3. REPLY The "REPLY" method in a "VFREEBUSY" calendar component is used to respond to a busy time request. The method is sent by the recipient of a busy time request to the originator of the request. The "REPLY" method may also be used to respond to an unsuccessful "REQUEST" method. Depending on the "REQUEST-STATUS" value, no busy time information may be returned. This method type is an iCalendar object that conforms to the following property constraints: +-----------------------------------------------+ | Constraints for a METHOD:REPLY of a VFREEBUSY | +-----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REPLY. | | | | | | VFREEBUSY | 1 | | | ATTENDEE | 1 | MUST be the address of the | | | | Attendee replying. | | DTSTAMP | 1 | | | DTEND | 1 | DateTime values must be in UTC. | | DTSTART | 1 | DateTime values must be in UTC. | | FREEBUSY | 0+ | MUST be BUSYTIME. Multiple | | | | instances are allowed. Multiple | | | | instances SHOULD be sorted in | | | | ascending order. | | ORGANIZER | 1 | MUST be the request originator's | | | | address. | | UID | 1 | MUST be the UID of the original | | | | REQUEST. | | COMMENT | 0+ | | | CONTACT | 0 or 1 | | | REQUEST-STATUS | 0+ | | | URL | 0 or 1 | Specifies busy time URL. | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | DURATION | 0 | | | SEQUENCE | 0 | | | | | | | VALARM | 0 | | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VTODO | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VTIMEZONE | 0 | | +--------------------+----------+-----------------------------------+ 3.4. Methods for VTODO Components This section defines the property set for the methods that are applicable to the "VTODO" calendar component. Each of the methods is defined using a restriction table that specifies the property constraints that define the particular method. The following summarizes the methods that are defined for the "VTODO" calendar component. +----------------+--------------------------------------------------+ | Method | Description | +----------------+--------------------------------------------------+ | PUBLISH | Post notification of a VTODO. Used primarily as | | | a method of advertising the existence of a | | | VTODO. | | | | | REQUEST | Assign a VTODO. This is an explicit assignment | | | to one or more Calendar Users. The REQUEST | | | method is also used to update or change an | | | existing VTODO. Clients that cannot handle | | | REQUEST MAY degrade the method to treat it as a | | | PUBLISH. | | | | | REPLY | Reply to a VTODO request. Attendees MAY set | | | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE, | | | DELEGATED, IN-PROCESS, and COMPLETED. |
EID 2331 (Verified) is as follows:

Section: 3.4.

Original Text:

   | REPLY          | Reply to a VTODO request.  Attendees MAY set     |
   |                | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE,       |
   |                | DELEGATED, PARTIAL, and COMPLETED.               |
 

Corrected Text:

   | REPLY          | Reply to a VTODO request.  Attendees MAY set     |
   |                | PARTSTAT to ACCEPTED, DECLINED, TENTATIVE,       |
   |                | DELEGATED, IN-PROCESS, and COMPLETED.            |
Notes:
The PARTSTAT value for VTODO component that is in progress is IN-PROCESS, not PARTIAL, per RFC 5545.
| | | | ADD | Add one or more instances to an existing to-do. | | | | | CANCEL | Cancel one or more instances of an existing | | | to-do. | | | | | REFRESH | A request sent to a VTODO Organizer asking for | | | the latest version of a VTODO. | | | | | COUNTER | Counter a REQUEST with an alternative proposal. | | | | | DECLINECOUNTER | Decline a counter proposal by an Attendee. | +----------------+--------------------------------------------------+ 3.4.1. PUBLISH The "PUBLISH" method in a "VTODO" calendar component has no associated response. It is simply a posting of an iCalendar object that may be added to a calendar. It MUST have an "Organizer". It MUST NOT have "Attendees". Its expected usage is for encapsulating an arbitrary "VTODO" calendar component as an iCalendar object. The "Organizer" MAY subsequently update (with another "PUBLISH" method), add instances to (with an "ADD" method), or cancel (with a "CANCEL" method) a previously published "VTODO" calendar component. This method type is an iCalendar object that conforms to the following property constraints: +---------------------------------------------+ | Constraints for a METHOD:PUBLISH of a VTODO | +---------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be PUBLISH. | | | | | | VTODO | 1+ | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | PRIORITY | 1 | | | SEQUENCE | 0 or 1 | MUST be present if value is | | | | greater than 0; MAY be present if | | | | 0. | | SUMMARY | 1 | Can be null. | | UID | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | COMPLETED/NEEDS-ACTION/ | | | | IN-PROCESS/CANCELLED. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTENDEE | 0 | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VFREEBUSY | 0 | | | | | | | VEVENT | 0 | | | | | | | VJOURNAL | 0 | | +--------------------+----------+-----------------------------------+ 3.4.2. REQUEST The "REQUEST" method in a "VTODO" calendar component provides the following scheduling functions: o Assign a to-do to one or more "Calendar Users". o Reschedule an existing to-do. o Update the details of an existing to-do, without rescheduling it. o Update the completion status of "Attendees" of an existing to-do, without rescheduling it. o Reconfirm an existing to-do, without rescheduling it. o Delegate/reassign an existing to-do to another "Calendar User". The assigned "Calendar Users" are identified in the "VTODO" calendar component by individual "ATTENDEE;ROLE=REQ-PARTICIPANT" property value sequences. Typically, the originator of a "REQUEST" is the "Organizer" of the to-do, and the recipient of a "REQUEST" is the "Calendar User" assigned the to-do. The "Attendee" uses the "REPLY" method to convey their acceptance and completion status to the "Organizer" of the "REQUEST". The "UID", "SEQUENCE", and "DTSTAMP" properties are used to distinguish the various uses of the "REQUEST" method. If the "UID" property value in the "REQUEST" is not found on the recipient's calendar, then the "REQUEST" is for a new to-do. If the "UID" property value is found on the recipient's calendar, then the "REQUEST" is a rescheduling, an update, or a reconfirmation of the "VTODO" calendar object. If the "Organizer" of the "REQUEST" method is not authorized to make a to-do request on the "Attendee's" calendar system, then an exception is returned in the "REQUEST-STATUS" property of a subsequent "REPLY" method, but no scheduling action is performed. For the "REQUEST" method, multiple "VTODO" components in a single iCalendar object are only permitted for components with the same "UID" property. That is, a series of recurring events may have instance-specific information. In this case, multiple "VTODO" components are needed to express the entire series. This method type is an iCalendar object that conforms to the following property constraints: +---------------------------------------------+ | Constraints for a METHOD:REQUEST of a VTODO | +---------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REQUEST. | | | | | | VTODO | 1+ | All components must have the same | | | | UID. | | ATTENDEE | 1+ | | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | PRIORITY | 1 | | | SEQUENCE | 0 or 1 | MUST be present if value is | | | | greater than 0; MAY be present if | | | | 0. | | SUMMARY | 1 | Can be null. | | UID | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | COMPLETED/NEEDS-ACTION/ | | | | IN-PROCESS. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | | | | | | VJOURNAL | 0 | | +--------------------+----------+-----------------------------------+ 3.4.2.1. REQUEST for Rescheduling a VTODO The "REQUEST" method may be used to reschedule a "VTODO" calendar component. Rescheduling a "VTODO" calendar component involves a change to the existing "VTODO" calendar component in terms of its start or due time, recurrence intervals, and possibly the description. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar but that the "SEQUENCE" property value in the "REQUEST" is greater than the value for the existing "VTODO", then the "REQUEST" method describes a rescheduling of the "VTODO" calendar component. 3.4.2.2. REQUEST for Update or Reconfirmation of a VTODO The "REQUEST" method may be used to update or reconfirm a "VTODO" calendar component. Reconfirmation is merely an update of "Attendee" completion status or overall "VTODO" calendar component status. An update to an existing "VTODO" calendar component does not involve changes to the start or due time, recurrence intervals, or (generally) the description for the "VTODO" calendar component. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar and that the "SEQUENCE" property value in the "REQUEST" is the same as the value for the existing event, then the "REQUEST" method describes an update of the "VTODO" calendar component details, but not a rescheduling of the "VTODO" calendar component. The update "REQUEST" is the appropriate response to a "REFRESH" method sent from an "Attendee" to the "Organizer" of a "VTODO" calendar component. Unsolicited "REQUEST" methods MAY be sent by the "Organizer" of a "VTODO" calendar component. The unsolicited "REQUEST" methods are used to update the details of the "VTODO" (without rescheduling it or updating the completion status of "Attendees") or the "VTODO" calendar component itself (i.e., reconfirm the "VTODO"). 3.4.2.3. REQUEST for Delegating a VTODO The "REQUEST" method is also used to delegate or reassign ownership of a "VTODO" calendar component to another "Calendar User". For example, it may be used to delegate an "Attendee's" role (i.e., "chair" or "participant") for a "VTODO" calendar component. The "REQUEST" method is sent by one of the "Attendees" of an existing "VTODO" calendar component to some other individual. For the purposes of this description, the "Attendee" delegating the "VTODO" calendar component is referred to as the "Delegator". The "Attendee" receiving the delegation request is referred to as the "Delegate". The "Delegator" of a "VTODO" calendar component MUST forward the existing "REQUEST" method for a "VTODO" calendar component to the "Delegate". The "VTODO" calendar component description MUST include the "Delegator's" up-to-date "VTODO" calendar component definition. The "REQUEST" method MUST also include an "ATTENDEE" property with the calendar address of the "Delegate". The "Delegator" MUST also send a "REPLY" method back to the "Organizer" with the "Delegator's" "Attendee" property "PARTSTAT" parameter value set to "DELEGATED". In addition, the "DELEGATED-TO" parameter MUST be included with the calendar address of the "Delegate". A response to the delegation "REQUEST" is sent from the "Delegate" to the "Organizer", and optionally to the "Delegator". The "REPLY" method from the "Delegate" SHOULD include the "ATTENDEE" property with their calendar address and the "DELEGATED-FROM" parameter with the value of the "Delegator's" calendar address. The delegation "REQUEST" method MUST assign a value for the "RSVP" property parameter associated with the "Delegator's" "Attendee" property to that of the "Delegate's" "ATTENDEE" property. For example, if the "Delegator's" "ATTENDEE" property specifies "RSVP=TRUE", then the "Delegate's" "ATTENDEE" property MUST specify "RSVP=TRUE". 3.4.2.4. REQUEST Forwarded to an Uninvited Calendar User An "Attendee" assigned a "VTODO" calendar component may send the "VTODO" calendar component to another new CU not previously associated with the "VTODO" calendar component. The current "Attendee" assigned the "VTODO" calendar component does this by forwarding the original "REQUEST" method to the new CU. The new CU can send a "REPLY" to the "Organizer" of the "VTODO" calendar component. The reply contains an "ATTENDEE" property for the new CU. The "Organizer" ultimately decides whether or not the new CU becomes part of the to-do and is not obligated to do anything with a "REPLY" from a new (uninvited) CU. If the "Organizer" does not want the new CU to be part of the to-do, the new "ATTENDEE" property is not added to the "VTODO" calendar component. The "Organizer" MAY send the CU a "CANCEL" message to indicate that they will not be added to the to- do. If the "Organizer" decides to add the new CU, the new "ATTENDEE" property is added to the "VTODO" calendar component. Furthermore, the "Organizer" is free to change any "ATTENDEE" property parameter from the values supplied by the new CU to something the "Organizer" considers appropriate. The "Organizer" SHOULD send the new "Attendee" a "REQUEST" message to inform them that they have been added. When forwarding a "REQUEST" to another CU, the forwarding "Attendee" MUST NOT make changes to the original message. 3.4.2.5. REQUEST Updated Attendee Status An "Organizer" of a "VTODO" may request an updated status from one or more "Attendees". The "Organizer" sends a "REQUEST" method to the "Attendee" with the "ATTENDEE;RSVP=TRUE" property sequence. The "SEQUENCE" property for the "VTODO" is not changed from its previous value. A recipient determines that the only change in the "REQUEST" is that their "RSVP" property parameter indicates a request for an updated status. The recipient SHOULD respond with a "REPLY" method indicating their current status with respect to the "REQUEST". 3.4.3. REPLY The "REPLY" method in a "VTODO" calendar component is used to respond (e.g., accept or decline) to a request or to reply to a delegation request. It is also used by an "Attendee" to update their completion status. When used to provide a delegation response, the "Delegator" MUST include the calendar address of the "Delegate" in the "DELEGATED-TO" parameter of the "Delegator's" "ATTENDEE" property. The "Delegate" MUST include the calendar address of the "Delegator" on the "DELEGATED-FROM" parameter of the "Delegate's" "ATTENDEE" property. The "REPLY" method MAY also be used to respond to an unsuccessful "VTODO" calendar component "REQUEST" method. Depending on the "REQUEST-STATUS" value, no scheduling action may have been performed. The "Organizer" of a "VTODO" calendar component MAY receive a "REPLY" method from a "Calendar User" not in the original "REQUEST". For example, a "REPLY" method MAY be received from a "Delegate" of a "VTODO" calendar component. In addition, the "REPLY" method MAY be received from an unknown "Calendar User" who has been forwarded the "REQUEST" by an original "Attendee" of the "VTODO" calendar component. This uninvited "Attendee" MAY be accepted or the "Organizer" MAY cancel the "VTODO" calendar component for the uninvited "Attendee" by sending them a "CANCEL" method. This method type is an iCalendar object that conforms to the following property constraints: +-------------------------------------------+ | Constraints for a METHOD:REPLY of a VTODO | +-------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REPLY. | | | | | | VTODO | 1+ | All components MUST have the same | | | | UID. | | ATTENDEE | 1 | MUST be the address of the | | | | Attendee replying. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | REQUEST-STATUS | 0+ | | | UID | 1 | MUST be the UID of the original | | | | REQUEST. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTSTART | 0 or 1 | | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | SEQUENCE | 0 or 1 | MUST be the sequence number of | | | | the original REQUEST if greater | | | | than 0. MAY be present if 0. | | STATUS | 0 or 1 | | | SUMMARY | 0 or 1 | Can be null. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0 or 1 | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.4.4. ADD The "ADD" method allows the "Organizer" to add one or more new instances to an existing "VTODO" using a single iTIP message without having to send the entire "VTODO" with all the existing instance data, as it would have to do if the "REQUEST" method were used. The "UID" must be that of the existing to-do. If the "UID" property value in the "ADD" is not found on the recipient's calendar, then the recipient SHOULD send a "REFRESH" to the "Organizer" in order to be updated with the latest version of the "VTODO". If an "Attendee" implementation does not support the "ADD" method, it should respond with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH". When handling an "ADD" message, the "Attendee" treats each component in the "ADD" message as if it were referenced via an "RDATE" in the main component. The "SEQUENCE" property value is incremented since the sequence of to-dos has changed. This method type is an iCalendar object that conforms to the following property constraints: +-----------------------------------------+ | Constraints for a METHOD:ADD of a VTODO | +-----------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be ADD. | | | | | | VTODO | 1 | | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | PRIORITY | 1 | | | SEQUENCE | 1 | MUST be greater than 0. | | SUMMARY | 1 | Can be null. | | UID | 1 | MUST match that of the original | | | | to-do. | | ATTACH | 0+ | | | ATTENDEE | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTSTART | 0 or 1 | | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | STATUS | 0 or 1 | MAY be one of | | | | COMPLETED/NEEDS-ACTION/ | | | | IN-PROCESS. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | EXDATE | 0 | | | RECURRENCE-ID | 0 | | | REQUEST-STATUS | 0 | | | RDATE | 0 | | | RRULE | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VJOURNAL | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.4.5. CANCEL The "CANCEL" method in a "VTODO" calendar component is used to send a cancellation notice of an existing "VTODO" calendar request to the affected "Attendees". The message is sent by the "Organizer" of a "VTODO" calendar component to the "Attendees" of the "VTODO" calendar component. For a recurring "VTODO" calendar component, either the whole "VTODO" calendar component or instances of a "VTODO" calendar component may be cancelled. To cancel the complete range of a recurring "VTODO" calendar component, the "UID" property value for the "VTODO" calendar component MUST be specified and a "RECURRENCE- ID" MUST NOT be specified in the "CANCEL" method. In order to cancel an individual instance of a recurring "VTODO" calendar component, the "RECURRENCE-ID" property value for the "VTODO" calendar component MUST be specified in the "CANCEL" method. There are two options for canceling a sequence of instances of a recurring "VTODO" calendar component: a. The "RECURRENCE-ID" property for an instance in the sequence MUST be specified with the "RANGE" property parameter value of "THISANDFUTURE" to indicate cancellation of the specified "VTODO" calendar component and all instances after. b. Individual recurrence instances may be cancelled by specifying multiple "VTODO" components each with a "RECURRENCE-ID" property corresponding to one of the instances to be cancelled. The "Organizer" MUST send a "CANCEL" message to each "Attendee" affected by the cancellation. This can be done by using either a single "CANCEL" message for all "Attendees" or multiple messages with different subsets of the affected "Attendees" in each. When a "VTODO" is cancelled, the "SEQUENCE" property value MUST be incremented as described in Section 2.1.4. This method type is an iCalendar object that conforms to the following property constraints: +--------------------------------------------+ | Constraints for a METHOD:CANCEL of a VTODO | +--------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be CANCEL. | | | | | | VTODO | 1+ | | | ATTENDEE | 0+ | MUST include some or all | | | | Attendees being removed from the | | | | to-do. MUST include some or all | | | | Attendees if the entire to-do is | | | | cancelled. | | UID | 1 | MUST echo original UID. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTSTART | 0 or 1 | | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | PRIORITY | 0 or 1 | | | STATUS | 0 or 1 | MUST be set to CANCELLED to | | | | cancel the entire VTODO. If | | | | removing specific Attendees, then | | | | MUST NOT be included. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0 or 1 | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.4.6. REFRESH
EID 2097 (Verified) is as follows:

Section: 3.4.6

Original Text:

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   |                    |          |                                   |
   | ...                |          |                                   |
   |                    |          |                                   |
   |   ORGANIZER        | 0        |                                   |

Corrected Text:

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   |                    |          |                                   |
   | ...                |          |                                   |
   |                    |          |                                   |
   |   ORGANIZER        | 1        |                                   |
Notes:
The "ORGANIZER" property should be REQUIRED in "VTODO" calendar components with the "REFRESH" method.
The "REFRESH" method in a "VTODO" calendar component is used by "Attendees" of an existing "VTODO" calendar component to request an updated description from the "Organizer" of the "VTODO" calendar component. The "Organizer" of the "VTODO" calendar component MAY use this method to request an updated status from the "Attendees". The "REFRESH" method MUST specify the "UID" property corresponding to the "VTODO" calendar component needing update. A refresh of a recurrence instance of a "VTODO" calendar component may be requested by specifying the "RECURRENCE-ID" property corresponding to the associated "VTODO" calendar component. The "Organizer" responds with the latest description and rendition of the "VTODO" calendar component. In most cases, this will be a "REQUEST" unless the "VTODO" has been cancelled, in which case the "Organizer" MUST send a "CANCEL". This method is intended to facilitate machine processing of requests for updates to a "VTODO" calendar component. This method type is an iCalendar object that conforms to the following property constraints: +---------------------------------------------+ | Constraints for a METHOD:REFRESH of a VTODO | +---------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be REFRESH. | | | | | | VTODO | 1 | | | ATTENDEE | 1 | | | DTSTAMP | 1 | | | UID | 1 | MUST echo original UID. | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTACH | 0 | | | CATEGORIES | 0 | | | CLASS | 0 | | | COMMENT | 0 | | | COMPLETED | 0 | | | CONTACT | 0 | | | CREATED | 0 | | | DESCRIPTION | 0 | | | DTSTART | 0 | | | DUE | 0 | | | DURATION | 0 | | | EXDATE | 0 | | | GEO | 0 | | | LAST-MODIFIED | 0 | | | LOCATION | 0 | | | ORGANIZER | 0 | | | PERCENT-COMPLETE | 0 | | | PRIORITY | 0 | | | RDATE | 0 | | | RELATED-TO | 0 | | | REQUEST-STATUS | 0 | | | RESOURCES | 0 | | | RRULE | 0 | | | SEQUENCE | 0 | | | STATUS | 0 | | | URL | 0 | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0+ | | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.4.7. COUNTER The "COUNTER" method in a "VTODO" calendar component is used by an "Attendee" of an existing "VTODO" calendar component to submit to the "Organizer" a counter proposal for the "VTODO" calendar component. The counter proposal is an iCalendar object consisting of a "VTODO" calendar component that provides the complete description of the alternate "VTODO" calendar component. The "Organizer" rejects the counter proposal by sending the "Attendee" a "DECLINECOUNTER" method. The "Organizer" accepts the counter proposal by rescheduling the to-do as described in Section 3.4.2.1, "REQUEST for Rescheduling a To-Do". The "Organizer's" CUA SHOULD send a "REQUEST" message to all "Attendees" affected by any change triggered by an accepted "COUNTER". This method type is an iCalendar object that conforms to the following property constraints: +---------------------------------------------+ | Constraints for a METHOD:COUNTER of a VTODO | +---------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be COUNTER. | | | | | | VTODO | 1 | | | ATTENDEE | 1+ | | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | PRIORITY | 1 | | | SUMMARY | 1 | Can be null. | | UID | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTSTART | 0 or 1 | | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | REQUEST-STATUS | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | SEQUENCE | 0 or 1 | MUST echo the original SEQUENCE | | | | number. MUST be present if | | | | non-zero. MAY be present if | | | | zero. | | STATUS | 0 or 1 | MAY be one of | | | | COMPLETED/NEEDS-ACTION/ | | | | IN-PROCESS/CANCELLED. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0 or 1 | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.4.8. DECLINECOUNTER The "DECLINECOUNTER" method in a "VTODO" calendar component is used by an "Organizer" of the "VTODO" calendar component to reject a counter proposal offered by one of the "Attendees". The "Organizer" sends the message to the "Attendee" that sent the "COUNTER" method to the "Organizer". This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------------+ | Constraints for a METHOD:DECLINECOUNTER of a VTODO | +----------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be DECLINECOUNTER. | | | | | | VTODO | 1 | | | ATTENDEE | 1+ | MUST for all ATTENDEEs. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | MUST echo the original SEQUENCE | | | | number. | | UID | 1 | MUST echo original UID. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | COMPLETED | 0 or 1 | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTSTART | 0 or 1 | | | DUE | 0 or 1 | If present, DURATION MUST NOT be | | | | present. | | DURATION | 0 or 1 | If present, DUE MUST NOT be | | | | present. | | EXDATE | 0+ | | | GEO | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | LOCATION | 0 or 1 | | | PERCENT-COMPLETE | 0 or 1 | | | PRIORITY | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | REQUEST-STATUS | 0+ | | | RESOURCES | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be one of | | | | COMPLETED/NEEDS-ACTION/ | | | | IN-PROCESS. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | +--------------------+----------+-----------------------------------+ 3.5. Methods for VJOURNAL Components This section defines the property set for the methods that are applicable to the "VJOURNAL" calendar component. The following summarizes the methods that are defined for the "VJOURNAL" calendar component. +---------+---------------------------------------------------------+ | Method | Description | +---------+---------------------------------------------------------+ | PUBLISH | Post a journal entry. Used primarily as a method of | | | advertising the existence of a journal entry. | | | | | ADD | Add one or more instances to an existing journal entry. | | | | | CANCEL | Cancel one or more instances of an existing journal | | | entry. | +---------+---------------------------------------------------------+ 3.5.1. PUBLISH The "PUBLISH" method in a "VJOURNAL" calendar component has no associated response. It is simply a posting of an iCalendar object that may be added to a calendar. It MUST have an "Organizer". It MUST NOT have "Attendees". The expected usage is for encapsulating an arbitrary journal entry as an iCalendar object. The "Organizer" MAY subsequently update (with another "PUBLISH" method) or cancel (with a "CANCEL" method) a previously published journal entry. This method type is an iCalendar object that conforms to the following property constraints: +------------------------------------------------+ | Constraints for a METHOD:PUBLISH of a VJOURNAL | +------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be PUBLISH. | | | | | | VJOURNAL | 1+ | | | DESCRIPTION | 1 | Can be null. | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | UID | 1 | | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | EXDATE | 0+ | | | LAST-MODIFIED | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RRULE | 0 or 1 | | | SEQUENCE | 0 or 1 | MUST be present if non-zero. MAY | | | | be present if zero. | | STATUS | 0 or 1 | MAY be one of | | | | DRAFT/FINAL/CANCELLED. | | SUMMARY | 0 or 1 | Can be null. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTENDEE | 0 | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.5.2. ADD The "ADD" method allows the "Organizer" to add one or more new instances to an existing "VJOURNAL" using a single iTIP message without having to send the entire "VJOURNAL" with all the existing instance data, as it would have to do if the "REQUEST" method were used. The "UID" must be that of the existing journal entry. If the "UID" property value in the "ADD" is not found on the recipient's calendar, then the recipient MAY treat the "ADD" as a "PUBLISH". When handling an "ADD" message, the "Attendee" treats each component in the "ADD" message as if it were referenced via an "RDATE" in the main component. There is no response to the "Organizer". This method type is an iCalendar object that conforms to the following property constraints: +--------------------------------------------+ | Constraints for a METHOD:ADD of a VJOURNAL | +--------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be ADD. | | | | | | VJOURNAL | 1 | | | DESCRIPTION | 1 | Can be null. | | DTSTAMP | 1 | | | DTSTART | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | MUST be greater than 0. | | UID | 1 | MUST match that of the original | | | | journal. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | LAST-MODIFIED | 0 or 1 | | | RELATED-TO | 0+ | | | STATUS | 0 or 1 | MAY be one of | | | | DRAFT/FINAL/CANCELLED. | | SUMMARY | 0 or 1 | Can be null. | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | ATTENDEE | 0 | | | EXDATE | 0 | | | RECURRENCE-ID | 0 | | | REQUEST-STATUS | 0 | | | RDATE | 0 | | | RRULE | 0 | | | | | | | VALARM | 0+ | | | | | | | VTIMEZONE | 0 or 1 | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.5.3. CANCEL The "CANCEL" method in a "VJOURNAL" calendar component is used to send a cancellation notice of an existing journal entry. The message is sent by the "Organizer" of a journal entry. For a recurring journal entry, either the whole journal entry or instances of a journal entry may be cancelled. To cancel the complete range of a recurring journal entry, the "UID" property value for the journal entry MUST be specified and a "RECURRENCE-ID" property MUST NOT be specified in the "CANCEL" method. In order to cancel an individual instance of the journal entry, the "RECURRENCE-ID" property value for the journal entry MUST be specified in the "CANCEL" method. There are two options for canceling a sequence of instances of a recurring "VJOURNAL" calendar component: a. The "RECURRENCE-ID" property for an instance in the sequence MUST be specified with the "RANGE" property parameter value of "THISANDFUTURE" to indicate cancellation of the specified "VJOURNAL" calendar component and all instances after. b. Individual recurrence instances may be cancelled by specifying multiple "VJOURNAL" components each with a "RECURRENCE-ID" property corresponding to one of the instances to be cancelled. When a "VJOURNAL" is cancelled, the "SEQUENCE" property value MUST be incremented as described in Section 2.1.4. This method type is an iCalendar object that conforms to the following property constraints: +-----------------------------------------------+ | Constraints for a METHOD:CANCEL of a VJOURNAL | +-----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be CANCEL. | | | | | | VJOURNAL | 1+ | All MUST have the same UID. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | | | UID | 1 | MUST be the UID of the original | | | | REQUEST. | | ATTACH | 0+ | | | ATTENDEE | 0 | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | | | DTSTART | 0 or 1 | | | EXDATE | 0+ | | | LAST-MODIFIED | 0 or 1 | | | RDATE | 0+ | | | RECURRENCE-ID | 0 or 1 | Only if referring to an instance | | | | of a recurring calendar | | | | component. Otherwise, it MUST | | | | NOT be present. | | RELATED-TO | 0+ | | | RRULE | 0 or 1 | | | STATUS | 0 or 1 | MAY be present; MUST be CANCELLED | | | | if present. | | SUMMARY | 0 or 1 | | | URL | 0 or 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | | REQUEST-STATUS | 0 | | | | | | | VALARM | 0 | | | | | | | VTIMEZONE | 0+ | MUST be present if any date/time | | | | refers to a timezone. | | | | | | IANA-COMPONENT | 0+ | | | X-COMPONENT | 0+ | | | | | | | VEVENT | 0 | | | | | | | VFREEBUSY | 0 | | | | | | | VTODO | 0 | | +--------------------+----------+-----------------------------------+ 3.6. Status Replies The "REQUEST-STATUS" property is used to convey status information about a "REPLY", "COUNTER", or "DECLINECOUNTER" iTIP message. The codes listed in the table below SHOULD be used. If the "REQUEST- STATUS" property is not present in one of these iTIP messages, then a status code of "2.0" (success) MUST be assumed. This specification adds a new IANA registry for "REQUEST-STATUS" property values, as defined in Section 7, which includes a new registration template for defining the specific components of the "REQUEST-STATUS" property value. Additional codes MAY be used, provided the process described in Section 8.2.1 of [RFC5545] is used to register them. This specification allows for multiple "REQUEST-STATUS" properties to be returned in iCalendar components in the appropriate iTIP messages. When multiple "REQUEST-STATUS" properties are present, the following restrictions apply: 1. Within any one component, the "top-level" numeric value of the "short return status code" MUST be the same for all "REQUEST- STATUS" properties, i.e., there cannot be a mixture of, e.g., 2.xx and 5.xx codes within a single component. 2. Across all components in the iTIP message, the following applies: A. If any one component would have a 5.xx code, then either all components MUST have a code in that range or "REQUEST-STATUS" MUST NOT be present in the other components if a 5.xx code is not appropriate for those components. B. Otherwise, if any one component would have a 3.xx code, then either all components MUST have a code in that range or "REQUEST-STATUS" MUST NOT be present in the other components if a 3.xx code is not appropriate for those components. C. 2.xx and 4.xx codes can be used in different components, provided that each component follows the restriction in (1) above. The following "REQUEST-STATUS" codes are defined (any "Offending Data" MAY be specified in the "REQUEST-STATUS" value as the extdata field): 3.6.1. Status Code 2.0 Status Code: 2.0 Status Description: Success. Status Exception Data: None. Description: iTIP operation succeeded. 3.6.2. Status Code 2.1 Status Code: 2.1 Status Description: Success, but fallback taken on one or more property values. Status Exception Data: Property name and value MAY be specified. Description: iTIP operation succeeded with fallback on one or more property values. 3.6.3. Status Code 2.2 Status Code: 2.2 Status Description: Success; invalid property ignored. Status Exception Data: Property name MAY be specified. Description: iTIP operation succeeded but a property was ignored. 3.6.4. Status Code 2.3 Status Code: 2.3 Status Description: Success; invalid property parameter ignored. Status Exception Data: Property parameter name and value MAY be specified. Description: iTIP operation succeeded but a property parameter was ignored because it was invalid. 3.6.5. Status Code 2.4 Status Code: 2.4 Status Description: Success; unknown, non-standard property ignored. Status Exception Data: Non-standard property name MAY be specified. Description: iTIP operation succeeded but a property parameter was ignored because it was unknown. 3.6.6. Status Code 2.5 Status Code: 2.5 Status Description: Success; unknown, non-standard property value ignored. Status Exception Data: Property and non-standard value MAY be specified. Description: iTIP operation succeeded but a property was ignored because its value was unknown. 3.6.7. Status Code 2.6 Status Code: 2.6 Status Description: Success; invalid calendar component ignored. Status Exception Data: Calendar component sentinel (e.g., BEGIN: ALARM) MAY be specified. Description: iTIP operation succeeded but a component was ignored because it was invalid. 3.6.8. Status Code 2.7 Status Code: 2.7 Status Description: Success; request forwarded to Calendar User. Status Exception Data: Original and forwarded calendar user addresses MAY be specified. Description: iTIP operation succeeded, and the request was forwarded to another Calendar User. 3.6.9. Status Code 2.8 Status Code: 2.8 Status Description: Success; repeating event ignored. Scheduled as a single component. Status Exception Data: RRULE or RDATE property name and value MAY be specified. Description: iTIP operation succeeded but a repeating event was truncated to a single instance. 3.6.10. Status Code 2.9 Status Code: 2.9 Status Description: Success; truncated end date time to date boundary. Status Exception Data: DTEND property value MAY be specified. Description: iTIP operation succeeded but the end time was truncated to a date boundary. 3.6.11. Status Code 2.10 Status Code: 2.10 Status Description: Success; repeating VTODO ignored. Scheduled as a single VTODO. Status Exception Data: RRULE or RDATE property name and value MAY be specified. Description: iTIP operation succeeded but a repeating to-do was truncated to a single instance. 3.6.12. Status Code 2.11 Status Code: 2.11 Status Description: Success; unbounded RRULE clipped at some finite number of instances. Status Exception Data: RRULE property name and value MAY be specified. Number of instances MAY also be specified. Description: iTIP operation succeeded but an unbounded repeating object was clipped to a finite number of instances. 3.6.13. Status Code 3.0 Status Code: 3.0 Status Description: Invalid property name. Status Exception Data: Property name MAY be specified. Description: iTIP operation failed because of an invalid property name. 3.6.14. Status Code 3.1 Status Code: 3.1 Status Description: Invalid property value. Status Exception Data: Property name and value MAY be specified. Description: iTIP operation failed because of an invalid property value. 3.6.15. Status Code 3.2 Status Code: 3.2 Status Description: Invalid property parameter. Status Exception Data: Property parameter name and value MAY be specified. Description: iTIP operation failed because of an invalid property parameter. 3.6.16. Status Code 3.3 Status Code: 3.3 Status Description: Invalid property parameter value. Status Exception Data: Property parameter name and value MAY be specified. Description: iTIP operation failed because of an invalid property parameter value. 3.6.17. Status Code 3.4 Status Code: 3.4 Status Description: Invalid calendar component sequence. Status Exception Data: Calendar component sentinel MAY be specified (e.g., BEGIN:VTIMEZONE). Description: iTIP operation failed because of an invalid component. 3.6.18. Status Code 3.5 Status Code: 3.5 Status Description: Invalid date or time. Status Exception Data: Date/time value(s) MAY be specified. Description: iTIP operation failed because of an invalid date or time property. 3.6.19. Status Code 3.6 Status Code: 3.6 Status Description: Invalid rule. Status Exception Data: RRULE property value MAY be specified. Description: iTIP operation failed because of an invalid rule property. 3.6.20. Status Code 3.7 Status Code: 3.7 Status Description: Invalid Calendar User. Status Exception Data: ATTENDEE property value MAY be specified. Description: iTIP operation failed because of an invalid ATTENDEE property. 3.6.21. Status Code 3.8 Status Code: 3.8 Status Description: No authority. Status Exception Data: METHOD and ATTENDEE property values MAY be specified. Description: iTIP operation failed because an Attendee does not have suitable privileges for the operation. 3.6.22. Status Code 3.9 Status Code: 3.9 Status Description: Unsupported version. Status Exception Data: VERSION property name and value MAY be specified. Description: iTIP operation failed because the calendar data version is not supported. 3.6.23. Status Code 3.10 Status Code: 3.10 Status Description: Request entity too large. Status Exception Data: None. Description: iTIP operation failed because the calendar data was too large. 3.6.24. Status Code 3.11 Status Code: 3.11 Status Description: Required component or property missing. Status Exception Data: Component or property name MAY be specified. Description: iTIP operation failed because the calendar data did not contain a required property or component. 3.6.25. Status Code 3.12 Status Code: 3.12 Status Description: Unknown component or property found. Status Exception Data: Component or property name MAY be specified. Description: iTIP operation failed because the calendar data contained an unknown property or component. 3.6.26. Status Code 3.13 Status Code: 3.13 Status Description: Unsupported component or property found. Status Exception Data: Component or property name MAY be specified. Description: iTIP operation failed because the calendar data contained an unsupported property or component. 3.6.27. Status Code 3.14 Status Code: 3.14 Status Description: Unsupported capability. Status Exception Data: METHOD or action MAY be specified. Description: iTIP operation failed because the operation is not supported. 3.6.28. Status Code 4.0 Status Code: 4.0 Status Description: Event conflict. Date/time is busy. Status Exception Data: DTSTART and DTEND property names and values MAY be specified. Description: iTIP operation failed because the event overlaps the date and time of another event. 3.6.29. Status Code 5.0 Status Code: 5.0 Status Description: Request not supported. Status Exception Data: METHOD property value MAY be specified. Description: iTIP operation failed because the operation is not supported. 3.6.30. Status Code 5.1 Status Code: 5.1 Status Description: Service unavailable. Status Exception Data: ATTENDEE property value MAY be specified. Description: iTIP operation failed because scheduling is not active. 3.6.31. Status Code 5.2 Status Code: 5.2 Status Description: Invalid calendar service. Status Exception Data: ATTENDEE property value MAY be specified. Description: iTIP operation failed because there is no scheduling capability. 3.6.32. Status Code 5.3 Status Code: 5.3 Status Description: No scheduling support for user. Status Exception Data: ATTENDEE property value MAY be specified. Description: iTIP operation failed because scheduling is not enabled for an Attendee. 3.7. Implementation Considerations 3.7.1. Working With Recurrence Instances iCalendar includes a recurrence grammar to represent recurring events. The benefit of such a grammar is the ability to represent a number of events in a single object. However, while this simplifies creation of a recurring event, meeting instances still need to be referenced. For instance, an "Attendee" may decline the third instance of a recurring Friday event. Similarly, the "Organizer" may change the time or location to a single instance of the recurring event. Since implementations may elect to store recurring events as either a single event object or a collection of discrete, related event objects, the protocol is designed so that each recurring instance may be both referenced and versioned. Hence, implementations that choose to maintain per-instance properties (such as "ATTENDEE" property "PARTSTAT" parameter) may do so. However, the protocol does not require per-instance recognition unless the instance itself must be renegotiated. The scenarios for recurrence instance referencing are listed below. For purposes of simplification, a change to an event refers to a "trigger property." That is, a property that has a substantive effect on the meeting itself, such as start time, location, due date (for "VTODO" calendar components), and possibly description. "Organizer"-initiated actions: o deletes or changes a single instance of a recurring event o makes changes that affect all future instances o makes changes that affect all previous instances o deletes or modifies a previously changed instance "Attendee"-initiated actions: o changes status for a particular recurrence instance o sends a "COUNTER" for a particular recurrence instance An instance of a recurring event is assigned a unique identification, "RECURRENCE-ID" property, when that instance is renegotiated. Negotiation may be necessary when a substantive change to the event or to-do has been made (such as changing the start time, end time, due date, or location). The "Organizer" can identify a specific recurrence instance using the "RECURRENCE-ID" property. The property value is equal to the date/time of the instance. If the "Organizer" wishes to change the "DTSTART", the original, unmodified "DTSTART" value of the instance is used as the value "RECURRENCE-ID" property, and the new "DTSTART" and "DTEND" values reflect the change. 3.7.2. Attendee Property Considerations The "ORGANIZER" property is required on published events, to-dos, and journal entries for two reasons. First, only the "Organizer" is allowed to update and redistribute an event or to-do component. It follows that the "ORGANIZER" property MUST be present in the event, to-do, or journal entry component so that the CUA has a basis for authorizing an update. Second, it is prudent to provide a point of contact for anyone who receives a published component, in case of problems. Email addresses that correspond to groups of "Calendar Users" could be specified as a mailto: URI [RFC2368] calendar user address. Sending email to such an address results in email being sent to multiple recipients. Such an address may be used as the value of an "ATTENDEE" property. Thus, it is possible that the recipient of a "REQUEST" does not appear explicitly in the list. It is recommended that the general approach to finding a "Calendar User" in an "Attendee" list be as follows: 1. Search for the "Calendar User" in the "Attendee" list where "CUTYPE=INDIVIDUAL" 2. Failing (1), look for "Attendees" where "CUTYPE=GROUP" or "CUTYPE=UNKNOWN". The CUA then determines if the "Calendar User" is a member of one of these groups. If so, the "REPLY" method sent to the "Organizer" MUST contain a new "ATTENDEE" property in which: * the "TYPE" property parameter is set to INDIVIDUAL * the "MEMBER" property parameter is set to the name of the group 3. Failing (2), the CUA MAY ignore or accept the request as the "Calendar User" wishes. 3.7.3. Extension Tokens To make iCalendar objects extensible, new component, property, or property parameters can be used. Two types of extensions are defined by [RFC5545]: IANA-registered tokens ("iana-token") and experimental use tokens ("x-name"). A client SHOULD save "iana-token's" and MAY use them in replies. A client MAY save "x-name's" and MAY use them in replies. When delegating or forwarding messages to other CUs, a client SHOULD include "iana-token's" and "x-names's". 4. Examples 4.1. Published Event Examples In the calendaring and scheduling context, publication refers to the one-way transfer of event information. Consumers of published events simply incorporate the event into a calendar. No reply is expected. Individual "A" publishes an event. Individual "B" reads the event and incorporates it into their calendar. Events are published in several ways, including embedding the event as an object in a web page, emailing the event to a distribution list, or posting the event to a newsgroup. The table below illustrates the sequence of events between the publisher and the consumers of a published event. +----------------+-----------------------+--------------------------+ | Action | Organizer | Receiver | +----------------+-----------------------+--------------------------+ | Publish an | "A" sends or posts a | "B" reads a published | | event | PUBLISH message. | event. | | | | | | Publish an | "A" sends or posts a | "B" reads the updated | | updated event | PUBLISH message. | event. | | | | | | Cancel a | "A" sends or posts a | "B" reads the canceled | | published | CANCEL message. | event publication. | | event | | | +----------------+-----------------------+--------------------------+ 4.1.1. A Minimal Published Event The iCalendar object below describes a single event that begins on July 1, 1997 at 20:00 UTC. This event contains the minimum set of properties for a "PUBLISH" for a "VEVENT" calendar component. BEGIN:VCALENDAR METHOD:PUBLISH PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com DTSTART:19970701T200000Z DTSTAMP:19970611T190000Z SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES UID:0981234-1234234-23@example.com END:VEVENT END:VCALENDAR 4.1.2. Changing a Published Event The iCalendar object below describes an update to the event described in Section 4.1.1; the time has been changed, an end time has been added, and the sequence number has been adjusted. BEGIN:VCALENDAR METHOD:PUBLISH VERSION:2.0 PRODID:-//Example/ExampleCalendarClient//EN BEGIN:VEVENT ORGANIZER:mailto:a@example.com DTSTAMP:19970612T190000Z DTSTART:19970701T210000Z DTEND:19970701T230000Z SEQUENCE:1 UID:0981234-1234234-23@example.com SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES END:VEVENT END:VCALENDAR The "UID" property is used by the client to identify the event. The "SEQUENCE" property indicates that this is a change to the event. The event with a matching "UID" and sequence number 0 is superseded by this event. The "SEQUENCE" property provides a reliable way to distinguish different versions of the same event. Each time an event is published, its sequence number is incremented. If a client receives an event with a sequence number 5 and finds it has the same event with sequence number 2, the event SHOULD be updated. However, if the client received an event with sequence number 2 and finds it already has sequence number 5 of the same event, the event MUST NOT be updated. 4.1.3. Canceling a Published Event The iCalendar object below cancels the event described in Section 4.1.1. This cancels the event with "SEQUENCE" property of 0, 1, and 2. BEGIN:VCALENDAR METHOD:CANCEL VERSION:2.0 PRODID:-//Example/ExampleCalendarClient//EN BEGIN:VEVENT ORGANIZER:mailto:a@example.com COMMENT:DUKES forfeit the game SEQUENCE:2 UID:0981234-1234234-23@example.com DTSTAMP:19970613T190000Z END:VEVENT END:VCALENDAR 4.1.4. A Rich Published Event This example describes the same event as in Section 4.1.1, but in much greater detail. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:PUBLISH SCALE:GREGORIAN VERSION:2.0 BEGIN:VTIMEZONE TZID:America-Chicago TZURL:http://example.com/tz/America-Chicago BEGIN:STANDARD DTSTART:19671029T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:CST END:STANDARD BEGIN:DAYLIGHT DTSTART:19870405T020000 RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:CDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTACH:http://www.example.com/ CATEGORIES:SPORTS EVENT,ENTERTAINMENT CLASS:PRIVATE DESCRIPTION:MIDWAY STADIUM\n Big time game. MUST see.\n Expected duration:2 hours\n DTEND;TZID=America-Chicago:19970701T180000 DTSTART;TZID=America-Chicago:19970702T160000 DTSTAMP:19970614T190000Z STATUS:CONFIRMED LOCATION;VALUE=URI:http://stadium.example.com/ PRIORITY:2 RESOURCES:SCOREBOARD SEQUENCE:3 SUMMARY:ST. PAUL SAINTS -VS- DULUTH-SUPERIOR DUKES UID:0981234-1234234-23@example.com RELATED-TO:0981234-1234234-14@example.com BEGIN:VALARM TRIGGER:-PT2H ACTION:DISPLAY DESCRIPTION:You should be leaving for the game now. END:VALARM BEGIN:VALARM TRIGGER:-PT30M ACTION:AUDIO END:VALARM END:VEVENT END:VCALENDAR The "RELATED-TO" field contains the "UID" property of a related calendar event. The "SEQUENCE" property 3 indicates that this event supersedes versions 0, 1, and 2. 4.1.5. Anniversaries or Events Attached to Entire Days This example demonstrates the use of the "VALUE" parameter to tie a "VEVENT" to a day rather than a specific time. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:PUBLISH VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com DTSTAMP:19970614T190000Z UID:0981234-1234234-23@example.com DTSTART;VALUE=DATE:19970714 RRULE:FREQ=YEARLY;INTERVAL=1 SUMMARY: Bastille Day END:VEVENT END:VCALENDAR 4.2. Group Event Examples Group events are distinguished from published events in that they have "Attendees" and there is interaction between the "Attendees" and the "Organizer" with respect to the event. Individual "A" requests a meeting between individuals "A", "B", "C", and "D". Individual "B" confirms attendance to the meeting. Individual "C" declines attendance. Individual "D" tentatively confirms attendance. The following table illustrates the message flow between these individuals. "A", the CU scheduling the meeting, is referenced as the "Organizer". +--------------+-----------------------+----------------------------+ | Action | "Organizer" | Attendee | +--------------+-----------------------+----------------------------+ | Initiate a | "A" sends a REQUEST | | | meeting | message to "B", "C", | | | request | and "D". | | | | | | | Accept the | | "B" sends a REPLY message | | meeting | | to "A" with its ATTENDEE | | request | | PARTSTAT parameter set to | | | | ACCEPTED. | | | | | | Decline the | | "C" sends a REPLY message | | meeting | | to "A" with its ATTENDEE | | request | | PARTSTAT parameter set to | | | | DECLINED. | | | | | | Tentatively | | "D" sends a REPLY message | | accept the | | to "A" with its ATTENDEE | | meeting | | PARTSTAT parameter set to | | request | | TENTATIVE. | | | | | | Confirm | "A" sends a REQUEST | | | meeting | message to "B" and | | | status with | "D" with updated | | | Attendees | information. | | +--------------+-----------------------+----------------------------+ 4.2.1. A Group Event Request A sample meeting request is sent from "A" to "B", "C", and "D". "E" is also sent a copy of the request but is not expected to attend and need not reply. "E" illustrates how CUAs might implement an "FYI"- type feature. Note the use of the "ROLE" parameter. The default value for the "ROLE" parameter is "REQ-PARTICIPANT" and it need not be enumerated. In this case, we are using the value "NON- PARTICIPANT" to indicate "E" is a non-attending CU. The parameter is not needed on other "Attendees" since "PARTICIPANT" is the default value. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED;CN=A:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=B:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=C:mailto:c@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=Hal:mailto:d@example.com ATTENDEE;RSVP=FALSE;CUTYPE=ROOM:conf_big@example.com ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:mailto:e@example.com DTSTAMP:19970611T190000Z DTSTART:19970701T200000Z DTEND:19970701T2100000Z SUMMARY:Conference UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.2.2. Reply to a Group Event Request "Attendee" "B" accepts the meeting. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VEVENT ATTENDEE;PARTSTAT=ACCEPTED:mailto:b@example.com ORGANIZER:mailto:a@example.com UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 REQUEST-STATUS:2.0;Success DTSTAMP:19970612T190000Z END:VEVENT END:VCALENDAR "B" could have declined the meeting or indicated tentative acceptance by setting the "ATTENDEE" "PARTSTAT" parameter to "DECLINED" or "TENTATIVE", respectively. Also, "REQUEST-STATUS" is not required in successful transactions. 4.2.3. Update an Event The event is moved to a different time. The combination of the "UID" property (unchanged) and the "SEQUENCE" (bumped to 1) properties indicate the update. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL;CN=Hal:mailto:d@example.com ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE; CUTYPE=ROOM:mailto:conf@example.com ATTENDEE;ROLE=NON-PARTICIPANT;RSVP=FALSE:mailto:e@example.com DTSTART:19970701T180000Z DTEND:19970701T190000Z SUMMARY:Phone Conference UID:calsrv.example.com-873970198738777@example.com SEQUENCE:1 DTSTAMP:19970613T190000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.2.4. Countering an Event Proposal "A" sends a "REQUEST" to "B" and "C". "B" makes a counter proposal to "A" to change the time and location. "A" sends the following "REQUEST": BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com DTSTART:19970701T190000Z DTEND:19970701T200000Z SUMMARY:Discuss the Merits of the election results LOCATION:Green Conference Room UID:calsrv.example.com-873970198738777a@example.com SEQUENCE:0 DTSTAMP:19970611T190000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR "B" sends "COUNTER" to "A", requesting changes to time and place. "B" uses the "COMMENT" property to communicate a rationale for the change. Note that the "SEQUENCE" property is not incremented on a "COUNTER". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:COUNTER VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com DTSTART:19970701T160000Z DTEND:19970701T170000Z DTSTAMP:19970612T190000Z SUMMARY:Discuss the Merits of the election results LOCATION:Blue Conference Room COMMENT:This time works much better and I think the big conference room is too big UID:calsrv.example.com-873970198738777a@example.com SEQUENCE:0 END:VEVENT END:VCALENDAR "A" accepts the changes from "B". To accept a counter proposal, the "Organizer" sends a new event "REQUEST" with an incremented sequence number. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:c@example.com DTSTAMP:19970613T190000Z DTSTART:19970701T160000Z DTEND:19970701T170000Z SUMMARY:Discuss the Merits of the election results - changed to meet B's schedule LOCATION:Blue Conference Room UID:calsrv.example.com-873970198738777@example.com SEQUENCE:1 STATUS:CONFIRMED END:VEVENT END:VCALENDAR Instead, "A" rejects "B's" counter proposal. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:DECLINECOUNTER VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com COMMENT:Sorry, I cannot change this meeting time UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 DTSTAMP:19970614T190000Z END:VEVENT END:VCALENDAR 4.2.5. Delegating an Event When delegating an event request to another "Calendar User", the "Delegator" must both update the "Organizer" with a "REPLY" and send a request to the "Delegate". There is currently no protocol limitation to delegation depth. It is possible for the original delegate to delegate the meeting to someone else, and so on. When a request is delegated from one CUA to another, there are a number of responsibilities required of the "Delegator". The "Delegator" MUST: o Send a "REPLY" to the "Organizer" with the following updates: A. The "Delegator's" "ATTENDEE" property "PARTSTAT" parameter is set to "DELEGATED" and the "DELEGATED-TO" parameter is set to the address of the "Delegate". B. Add an additional "ATTENDEE" property for the "Delegate" with the "DELEGATED-FROM" property parameter set to the "Delegator". C. Indicate whether they want to continue to receive updates when the "Organizer" sends out updated versions of the event. Setting the "RSVP" property parameter to "TRUE" will cause the updates to be sent; setting it to "FALSE" causes no further updates to be sent. Note that in either case, if the "Delegate" declines the invitation, the "Delegator" will be notified. o The "Delegator" MUST also send a copy of the original "REQUEST" method to the "Delegate", with changes (A) and (B), as detailed above applied. If the "Delegate" declines the meeting, the "Organizer" MUST send an update "REQUEST" to the "Delegator" so that the "Delegator" may elect to delegate the "REQUEST" to another CUA. +----------------+-----------------+--------------------------------+ | Action | "Organizer" | Attendee | +----------------+-----------------+--------------------------------+ | Initiate a | "A" sends a | | | meeting | REQUEST message | | | request | to "B" and "C". | | | | | | | Delegate: "C" | | "C" sends a REPLY to "A" with | | delegates to | | the ATTENDEE PARTSTAT | | "E" | | parameter set to DELEGATED and | | | | with a new ATTENDEE property | | | | for "E". "E's" ATTENDEE | | | | DELEGATED-FROM parameter is | | | | set to "C". "C's" ATTENDEE | | | | DELEGATED-TO parameter is set | | | | to "E". "C" sends REQUEST | | | | message to "E" with the | | | | original meeting request | | | | information. The PARTSTAT | | | | property parameter for "C" is | | | | set to DELEGATED and the | | | | DELEGATED-TO parameter is set | | | | to the address of "E". An | | | | ATTENDEE property is added for | | | | "E" and the DELEGATED-FROM | | | | parameter is set to the | | | | address of "C". | | | | | | Confirm | | "E" sends REPLY message to | | meeting | | "A", and optionally to "C", | | attendance | | with its PARTSTAT property | | | | parameter set to ACCEPTED. | | | | | | Optional: | "A" sends | | | Redistribute | REQUEST message | | | meeting to | to "B", "C", | | | Attendees | and "E". | | +----------------+-----------------+--------------------------------+ "C" responds to the "Organizer". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=DELEGATED;DELEGATED- TO="mailto:e@example.com":mailto:c@example.com UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 REQUEST-STATUS:2.0;Success DTSTAMP:19970611T190000Z END:VEVENT END:VCALENDAR "Attendee" "C" delegates presence at the meeting to "E". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=DELEGATED;DELEGATED- TO="mailto:e@example.com":mailto:c@example.com ATTENDEE;RSVP=TRUE; DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com DTSTART:19970701T180000Z DTEND:19970701T200000Z SUMMARY:Phone Conference UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 STATUS:CONFIRMED DTSTAMP:19970611T190000Z END:VEVENT END:VCALENDAR 4.2.6. Delegate Accepts the Meeting To accept a delegated meeting, the delegate, "E", sends the following message to "A" and "C". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=ACCEPTED;DELEGATED- FROM="mailto:c@example.com":mailto:e@example.com ATTENDEE;PARTSTAT=DELEGATED; DELEGATED-TO="mailto:e@example.com":mailto:c@example.com UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 REQUEST-STATUS:2.0;Success DTSTAMP:19970614T190000Z END:VEVENT END:VCALENDAR 4.2.7. Delegate Declines the Meeting In this example, the "Delegate" declines the meeting request and sets the "ATTENDEE" property "PARTSTAT" parameter to "DECLINED". The "Organizer" SHOULD resend the "REQUEST" to "C" with the "PARTSTAT" parameter of the "Delegate" set to "DECLINED". This lets the "Delegator" know that the "Delegate" has declined and provides an opportunity to the "Delegator" to either accept the request or delegate it to another CU. "E" responds to "A" and "C". Note the use of the "COMMENT" property "E" uses to indicate why the delegation was declined. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=DELEGATED; DELEGATED-TO="mailto:e@example.com":mailto:c@example.com ATTENDEE;PARTSTAT=DECLINED; DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com COMMENT:Sorry, I will be out of town at that time. UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 REQUEST-STATUS:2.0;Success DTSTAMP:19970614T190000Z END:VEVENT END:VCALENDAR "A" resends the "REQUEST" method to "C". "A" may also wish to express the fact that the item was delegated in the "COMMENT" property. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=DECLINED; DELEGATED-FROM="mailto:c@example.com":mailto:e@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 SUMMARY:Phone Conference DTSTART:19970701T180000Z DTEND:19970701T200000Z DTSTAMP:19970614T200000Z COMMENT:DELEGATE (ATTENDEE mailto:e@example.com) DECLINED YOUR INVITATION END:VEVENT END:VCALENDAR 4.2.8. Forwarding an Event Request The protocol does not prevent an "Attendee" from "forwarding" a "VEVENT" calendar component to other "Calendar Users". Forwarding differs from delegation in that the forwarded "Calendar User" (often referred to as a "Party Crasher") does not replace the forwarding "Calendar User". Implementations are not required to add the "Party Crasher" to the "Attendee" list, and hence there is no guarantee that a "Party Crasher" will receive additional updates to the event. The forwarding "Calendar User" SHOULD NOT add the "Party Crasher" to the "Attendee" list. The "Organizer" MAY add the forwarded "Calendar User" to the "Attendee" list. 4.2.9. Cancel a Group Event Individual "A" requests a meeting between individuals "A", "B", "C", and "D". Individual "B" declines attendance to the meeting. Individual "A" decides to cancel the meeting. The following table illustrates the sequence of messages that would be exchanged between these individuals. Messages related to a previously canceled event ("SEQUENCE" property value is less than the "SEQUENCE" property value of the "CANCEL" message) MUST be ignored. +-------------+---------------------+-------------------------------+ | Action | Organizer | Attendee | +-------------+---------------------+-------------------------------+ | Initiate a | "A" sends a REQUEST | | | meeting | message to "B", | | | request | "C", and "D". | | | | | | | Decline the | | "B" sends a REPLY message to | | meeting | | "A" with its PARTSTAT | | request | | parameter set to DECLINED. | | | | | | Cancel the | "A" sends a CANCEL | | | meeting | message to "B", | | | | "C", and "D". | | +-------------+---------------------+-------------------------------+ This example shows how "A" cancels the event. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:CANCEL VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;CUTYPE=INDIVIDUAL;mailto:a@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com COMMENT:Mr. B cannot attend. It's raining. Lets cancel. UID:calsrv.example.com-873970198738777@example.com SEQUENCE:1 STATUS:CANCELLED DTSTAMP:19970613T190000Z END:VEVENT END:VCALENDAR 4.2.10. Removing Attendees "A" wants to remove "B" from a meeting. This is done by sending a "CANCEL" to "B" and removing "B" from the "Attendee" list in the master copy of the event. +--------------------+-----------------------------------+----------+ | Action | Organizer | Attendee | +--------------------+-----------------------------------+----------+ | Remove "B" as an | "A" sends a CANCEL message to | | | Attendee | "B". | | | | | | | Update the master | "A" optionally sends the updated | | | copy of the event | event to the remaining Attendees. | | +--------------------+-----------------------------------+----------+ The original meeting includes "A", "B", "C", and "D". The example below shows the "CANCEL" that "A" sends to "B". Note that in the example below, the "STATUS" property is omitted. This is used when the meeting itself is cancelled and not when the intent is to remove an "Attendee" from the event. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:CANCEL VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE:mailto:b@example.com COMMENT:You're off the hook for this meeting UID:calsrv.example.com-873970198738777@example.com DTSTAMP:19970613T193000Z SEQUENCE:1 END:VEVENT END:VCALENDAR The updated master copy of the event is shown below. The "Organizer" MAY resend the updated event to the remaining "Attendees". Note that "B" has been removed. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com ATTENDEE;CUTYPE=ROOM:mailto:cr_big@example.com ATTENDEE;ROLE=NON-PARTICIPANT; RSVP=FALSE:mailto:e@example.com DTSTAMP:19970611T190000Z DTSTART:19970701T200000Z DTEND:19970701T203000Z SUMMARY:Phone Conference UID:calsrv.example.com-873970198738777@example.com SEQUENCE:2 STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.2.11. Replacing the Organizer The scenario for this example begins with "A" as the "Organizer" for a recurring meeting with "B", "C", and "D". "A" receives a new job offer in another country and drops out of touch. "A" left no forwarding address or way to be reached. Using out-of-band communication, the other "Attendees" eventually learn what has happened and reach an agreement that "B" should become the new "Organizer" for the meeting. To do this, "B" sends out a new version of the event and the other "Attendees" agree to accept "B" as the new "Organizer". "B" also removes "A" from the event. When the "Organizer" is replaced, the "SEQUENCE" property value MUST be incremented. This is the message "B" sends to "C" and "D". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:b@example.com ATTENDEE;ROLE=CHAIR;STATUS=ACCEPTED:mailto:b@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:c@example.com ATTENDEE;CUTYPE=INDIVIDUAL:mailto:d@example.com DTSTAMP:19970611T190000Z DTSTART:19970701T200000Z DTEND:19970701T203000Z RRULE:FREQ=WEEKLY SUMMARY:Phone Conference UID:123456@example.com SEQUENCE:1 STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.3. Busy Time Examples Busy time objects can be used in several ways. First, a CU may request busy time from another CU for a specific range of time. That request can be answered with a busy time "REPLY". Additionally, a CU may simply publish their busy time for a given interval and point other CUs to the published location. The following examples outline both scenarios. 4.3.1. Publish Busy Time Individual "A" publishes busy time for one week. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 METHOD:PUBLISH BEGIN:VFREEBUSY DTSTAMP:19980101T124100Z ORGANIZER:mailto:a@example.com DTSTART:19980101T124200Z DTEND:19980108T124200Z FREEBUSY:19980101T180000Z/19980101T190000Z FREEBUSY:19980103T020000Z/19980103T050000Z FREEBUSY:19980107T020000Z/19980107T050000Z FREEBUSY:19980113T000000Z/19980113T010000Z FREEBUSY:19980115T190000Z/19980115T200000Z FREEBUSY:19980115T220000Z/19980115T230000Z FREEBUSY:19980116T013000Z/19980116T043000Z END:VFREEBUSY END:VCALENDAR 4.3.2. Request Busy Time Individual "A" requests busy time from individuals "B" and "C". Individuals "B" and "C" reply with busy time data to individual "A". The following table illustrates the sequence of messages that would be exchanged between these individuals. +---------------------+--------------------+------------------------+ | Action | Organizer | Attendee | +---------------------+--------------------+------------------------+ | Initiate a busy | "A" sends REQUEST | | | time request | message to "B" and | | | | "C". | | | | | | | Reply to the BUSY | | "B" sends a REPLY | | request with BUSY | | message to "A" with | | time data | | busy time data. | +---------------------+--------------------+------------------------+ "A" sends a "REQUEST" to "B" and "C" for busy time. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VFREEBUSY ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com DTSTAMP:19970613T190000Z DTSTART:19970701T080000Z DTEND:19970701T200000 UID:calsrv.example.com-873970198738777@example.com END:VFREEBUSY END:VCALENDAR 4.3.3. Reply to a Busy Time Request "B" sends a "REPLY" method type of a "VFREEBUSY" calendar component to "A". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VFREEBUSY ORGANIZER:mailto:a@example.com ATTENDEE:mailto:b@example.com DTSTART:19970701T080000Z DTEND:19970701T200000Z UID:calsrv.example.com-873970198738777@example.com FREEBUSY:19970701T090000Z/PT1H,19970701T140000Z/PT30M DTSTAMP:19970613T190030Z END:VFREEBUSY END:VCALENDAR "B" is busy from 09:00 to 10:00 and from 14:00 to 14:30. 4.4. Recurring Event and Time Zone Examples 4.4.1. A Recurring Event Spanning Time Zones This event describes a weekly phone conference. The "Attendees" are each in a different time zone. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTIMEZONE TZID:America-SanJose TZURL:http://example.com/tz/America-SanJose BEGIN:STANDARD DTSTART:19671029T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZOFFSETFROM:-0700 TZOFFSETTO:-0800 TZNAME:PST END:STANDARD BEGIN:DAYLIGHT DTSTART:19870405T020000 RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4 TZOFFSETFROM:-0800 TZOFFSETTO:-0700 TZNAME:PDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED; CUTYPE=INDIVIDUAL:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:b@example.fr ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:c@example.jp DTSTAMP:19970613T190030Z DTSTART;TZID=America-SanJose:19970701T140000 DTEND;TZID=America-SanJose:19970701T150000 RRULE:FREQ=WEEKLY;COUNT=20;WKST=SU;BYDAY=TU RDATE;TZID=America-SanJose:19970910T140000 EXDATE;TZID=America-SanJose:19970909T140000 EXDATE;TZID=America-SanJose:19971028T140000 SUMMARY:Weekly Phone Conference UID:calsrv.example.com-873970198738777@example.com SEQUENCE:0 STATUS:CONFIRMED END:VEVENT END:VCALENDAR The first component of this iCalendar object is the time zone component. The "DTSTART" date coincides with the first instance of the "RRULE" property. The recurring meeting is defined in a particular time zone, presumably that of the originator. The client for each "Attendee" has the responsibility of determining the recurrence time in the "Attendee's" time zone. The repeating event starts on Tuesday, July 1, 1997 at 2:00pm PDT (UTC-7). "Attendee" B@example.fr is in France, where the local time on this date is 9 hours ahead of PDT, or 23:00 CEST (UTC+2). "Attendee" C@example.jp is in Japan, where local time is 16 hours ahead of PDT, or Wednesday, July 2 at 06:00 JST (UTC+9). The event repeats weekly on Tuesdays (in PST/PDT). The "RRULE" property results in 20 instances. The last instance falls on Tuesday, November 11, 1997 2:00pm PST. The "RDATE" property adds another instance: WED, 10-SEP-1997 2:00 PM PDT. There are also two exception dates to the recurrence rule. The first one is: o TUE, 09-SEP-1997 14:00 PDT (UTC-7) o TUE, 09-SEP-1997 23:00 CEST (UTC+2) o WED, 10-SEP-1997 06:00 JST (UTC+9) and the second is: o TUE, 28-OCT-1997 14:00 PST (UTC-8) o TUE, 28-OCT-1997 23:00 CET (UTC+1) o WED, 29-OCT-1997 07:00 JST (UTC+9) 4.4.2. Modify a Recurring Instance In this example, the "Organizer" issues a recurring meeting. Later, the "Organizer" changes an instance of the event by changing the "DTSTART" property. Note the use of "RECURRENCE-ID" property and "SEQUENCE" property in the second request. Original Request: BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com SEQUENCE:0 RRULE:FREQ=MONTHLY;BYMONTHDAY=1;UNTIL=19980901T210000Z ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com ATTENDEE:mailto:d@example.com DESCRIPTION:IETF-C&S Conference Call CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970601T210000Z DTEND:19970601T220000Z LOCATION:Conference Call DTSTAMP:19970526T083000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR The event request below is to change the time of a specific instance. This changes the July 1st instance to July 3rd. BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com RECURRENCE-ID:19970701T210000Z SEQUENCE:1 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com ATTENDEE:mailto:d@example.com DESCRIPTION:IETF-C&S Conference Call CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970703T210000Z DTEND:19970703T220000Z LOCATION:Conference Call DTSTAMP:19970626T093000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.4.3. Cancel an Instance In this example, the "Organizer" of a recurring event deletes the August 1st instance. BEGIN:VCALENDAR METHOD:CANCEL PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com ATTENDEE:mailto:d@example.com RECURRENCE-ID:19970801T210000Z SEQUENCE:2 STATUS:CANCELLED DTSTAMP:19970721T093000Z END:VEVENT END:VCALENDAR 4.4.4. Cancel a Recurring Event In this example, the "Organizer" wishes to cancel the entire recurring event and any exceptions. BEGIN:VCALENDAR METHOD:CANCEL PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com ATTENDEE:mailto:d@example.com DTSTAMP:19970721T103000Z STATUS:CANCELLED SEQUENCE:3 END:VEVENT END:VCALENDAR 4.4.5. Change All Future Instances This example changes the meeting location from a conference call to Seattle, starting September 1 and extending to all future instances. BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com RECURRENCE-ID;THISANDFUTURE:19970901T210000Z SEQUENCE:3 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com ATTENDEE;RSVP=TRUE:mailto:d@example.com DESCRIPTION:IETF-C&S Discussion CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970901T210000Z DTEND:19970901T220000Z LOCATION:Building 32, Microsoft, Seattle, WA DTSTAMP:19970526T083000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.4.6. Add a New Instance to a Recurring Event This example adds a one-time additional instance to the recurring event. "Organizer" adds a second July meeting on the 15th. BEGIN:VCALENDAR METHOD:ADD PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:4 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com ATTENDEE;RSVP=TRUE:mailto:d@example.com DESCRIPTION:IETF-C&S Conference Call CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970715T210000Z DTEND:19970715T220000Z LOCATION:Conference Call DTSTAMP:19970629T093000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.4.7. Add a New Series of Instances to a Recurring Event The scenario for this example involves an ongoing meeting, originally set up to occur every Tuesday. The "Organizer" later decides that the meetings need to be on Tuesdays and Thursdays. The original event: BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:0 RRULE:WKST=SU;BYDAY=TU;FREQ=WEEKLY ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980303T210000Z DTEND:19980303T220000Z LOCATION:The White Room DTSTAMP:19980301T093000Z STATUS:CONFIRMED END:VEVENT END:VCALENDAR The entire event can be rescheduled using a "REQUEST". This is done by using the "UID" of the event to reschedule and including the modified "RRULE". Note that since this is an entire rescheduling of the event, any instance-specific information will be lost, unless explicitly included with the update "REQUEST". BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:7 RRULE:WKST=SU;BYDAY=TU,TH;FREQ=WEEKLY ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980303T210000Z DTEND:19980303T220000Z DTSTAMP:19980303T193000Z LOCATION:The White Room STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.4.8. Refreshing a Recurring Event The next series of examples illustrate how an "Organizer" would respond to a "REFRESH" submitted by an "Attendee" after a series of instance-specific modifications. To convey all instance-specific changes, the "Organizer" must provide the latest event description and the relevant instances. The first three examples show the history, including the initial "VEVENT" request and subsequent instance changes, and finally the "REFRESH". Original Request: BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:0 RDATE:19980304T180000Z RDATE:19980311T180000Z RDATE:19980318T180000Z ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980304T180000Z DTEND:19980304T200000Z DTSTAMP:19980303T193000Z LOCATION:Conference Room A STATUS:CONFIRMED END:VEVENT END:VCALENDAR Organizer changes 2nd instance location and time: BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:1 RECURRENCE-ID:19980311T180000Z ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980311T160000Z DTEND:19980311T180000Z DTSTAMP:19980306T193000Z LOCATION:The Small conference room STATUS:CONFIRMED END:VEVENT END:VCALENDAR Organizer adds a 4th instance of the meeting using the "ADD" method. BEGIN:VCALENDAR METHOD:ADD PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:2 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980315T180000Z DTEND:19980315T200000Z DTSTAMP:19980307T193000Z LOCATION:Conference Room A STATUS:CONFIRMED END:VEVENT END:VCALENDAR If "B" requests a "REFRESH", "A" responds with the following to capture all instance-specific data. In this case, both the initial request and an additional "VEVENT" that specifies the instance- specific data are included. Because these are both of the same type (they are both "VEVENTS"), they can be conveyed in the same iCalendar object. BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:123456789@example.com SEQUENCE:2 RDATE:19980304T180000Z RDATE:19980311T160000Z RDATE:19980315T180000Z ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980304T180000Z DTEND:19980304T200000Z DTSTAMP:19980303T193000Z LOCATION:Conference Room A STATUS:CONFIRMED END:VEVENT BEGIN:VEVENT SEQUENCE:2 UID:123456789@example.com RECURRENCE-ID:19980311T160000Z ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com SUMMARY:Review Accounts DTSTART:19980311T160000Z DTEND:19980304T180000Z DTSTAMP:19980306T193000Z LOCATION:The Small conference room STATUS:CONFIRMED END:VEVENT END:VCALENDAR 4.4.9. Counter an Instance of a Recurring Event In this example, one of the "Attendees" counters the "DTSTART" property of the proposed second July meeting. BEGIN:VCALENDAR METHOD:COUNTER PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com RECURRENCE-ID:19970715T210000Z SEQUENCE:4 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;RSVP=TRUE:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com ATTENDEE;RSVP=TRUE:mailto:d@example.com DESCRIPTION:IETF-C&S Conference Call CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970715T220000Z DTEND:19970715T230000Z LOCATION:Conference Call COMMENT:May we bump this by an hour? I have a conflict DTSTAMP:19970629T094000Z END:VEVENT END:VCALENDAR 4.4.10. Error Reply to a Request The following example illustrates a scenario where a meeting is proposed containing an unsupported property and a bad property. Original Request: BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:guid-1@example.com SEQUENCE:0 RRULE:FREQ=MONTHLY;BYMONTHDAY=1 ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com ATTENDEE;RSVP=TRUE:mailto:d@example.com DESCRIPTION:IETF-C&S Conference Call CLASS:PUBLIC SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970601T210000Z DTEND:19970601T220000Z DTSTAMP:19970602T094000Z LOCATION:Conference Call STATUS:CONFIRMED FOO:BAR END:VEVENT END:VCALENDAR "B" responds to indicate that "RRULE" is not supported and that an unrecognized property was encountered. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE:mailto:b@example.com REQUEST-STATUS:3.0;Invalid Property Name;FOO UID:guid-1@example.com SEQUENCE:0 DTSTAMP:19970603T094000Z END:VEVENT END:VCALENDAR 4.5. Group To-Do Examples Individual "A" creates a group task in which individuals "A", "B", "C", and "D" will participate. Individual "B" confirms acceptance of the task. Individual "C" declines the task. Individual "D" tentatively accepts the task. The following table illustrates the sequence of messages that would be exchanged between these individuals. Individual "A" then issues a "REQUEST" method to obtain the status of the to-do from each participant. The response indicates the individual "Attendee's" completion status. The table below illustrates the message flow. +--------------+------------------------+---------------------------+ | Action | Organizer | Attendee | +--------------+------------------------+---------------------------+ | Initiate a | "A" sends a REQUEST | | | to-do | message to "B", "C", | | | request | and "D". | | | | | | | Accept the | | "B" sends a REPLY message | | to-do | | to "A" with its PARTSTAT | | request | | parameter set to | | | | ACCEPTED. | | | | | | Decline the | | "C" sends a REPLY message | | to-do | | to "A" with its PARTSTAT | | request | | parameter set to | | | | DECLINED. | | | | | | Tentatively | | "D" sends a REPLY message | | accept the | | to "A" with its PARTSTAT | | to-do | | parameter set to | | request | | TENTATIVE. | | | | | | Check | "A" sends a REQUEST | | | Attendee | message to "B" and "D" | | | completion | with current | | | status | information. | | | | | | | Attendee | | "B" sends a REPLY message | | indicates | | indicating percent | | percent | | complete. | | complete | | | | | | | | Attendee | | "D" sends a REPLY message | | indicates | | indicating completion. | | completion | | | +--------------+------------------------+---------------------------+ 4.5.1. A VTODO Request A sample "REQUEST" for a "VTODO" calendar component that "A" sends to "B", "C", and "D". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR:mailto:a@example.com ATTENDEE;RSVP=TRUE:mailto:b@example.com ATTENDEE;RSVP=TRUE:mailto:c@example.com ATTENDEE;RSVP=TRUE:mailto:d@example.com DTSTART:19970701T170000Z DUE:19970722T170000Z PRIORITY:1 SUMMARY:Create the requirements document UID:calsrv.example.com-873970198738777-00@example.com SEQUENCE:0 DTSTAMP:19970717T200000Z STATUS:NEEDS-ACTION END:VTODO END:VCALENDAR 4.5.2. A VTODO Reply "B" accepts the to-do. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=ACCEPTED:mailto:b@example.com UID:calsrv.example.com-873970198738777-00@example.com COMMENT:I'll send you my input by email SEQUENCE:0 DTSTAMP:19970717T203000Z REQUEST-STATUS:2.0;Success END:VTODO END:VCALENDAR "B" could have declined the "VTODO" or indicated tentative acceptance by setting the "PARTSTAT" property parameter sequence to "DECLINED" or "TENTATIVE", respectively. 4.5.3. A VTODO Request for Updated Status "A" requests status from all "Attendees". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:d@example.com UID:calsrv.example.com-873970198738777-00@example.com SUMMARY:Create the requirements document PRIORITY:1 SEQUENCE:0 STATUS:IN-PROCESS DTSTART:19970701T170000Z DTSTAMP:19970717T230000Z END:VTODO END:VCALENDAR 4.5.4. A Reply: Percent-Complete A reply indicating the task being worked on and that "B" is 75% complete with "B's" part of the assignment. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=IN-PROCESS:mailto:b@example.com PERCENT-COMPLETE:75 UID:calsrv.example.com-873970198738777-00@example.com DTSTAMP:19970717T233000Z SEQUENCE:0 END:VTODO END:VCALENDAR 4.5.5. A Reply: Completed A reply indicating that "D" completed "D's" part of the assignment. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=COMPLETED:mailto:d@example.com UID:calsrv.example.com-873970198738777-00@example.com DTSTAMP:19970717T233000Z SEQUENCE:0 END:VTODO END:VCALENDAR 4.5.6. An Updated VTODO Request "Organizer" "A" resends the "VTODO" calendar component. "A" sets the overall completion for the to-do at 40%. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE;PARTSTAT=ACCEPTED;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;PARTSTAT=COMPLETED;CUTYPE=INDIVIDUAL:mailto:d@example.com DTSTART:19970701T170000Z DUE:19970722T170000Z PRIORITY:1 SUMMARY:Create the requirements document UID:calsrv.example.com-873970198738777-00@example.com SEQUENCE:1 DTSTAMP:19970718T100000Z STATUS:IN-PROCESS PERCENT-COMPLETE:40 END:VTODO END:VCALENDAR 4.5.7. Recurring VTODOs The following examples relate to recurring "VTODO" calendar components. 4.5.7.1. Request for a Recurring VTODO In this example, "A" sends a recurring "VTODO" calendar component to "B" and "D". BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REQUEST VERSION:2.0 BEGIN:VTODO ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR:mailto:a@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:b@example.com ATTENDEE;RSVP=TRUE;CUTYPE=INDIVIDUAL:mailto:d@example.com RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR DTSTART:19980101T100000Z DUE:19980103T100000Z SUMMARY:Send Status Reports to Area Managers UID:calsrv.example.com-873970198738777-00@example.com SEQUENCE:0 DTSTAMP:19970717T200000Z STATUS:NEEDS-ACTION PRIORITY:1 END:VTODO END:VCALENDAR 4.5.7.2. Replying to an Instance of a Recurring VTODO In this example, "B" updates "A" on a single instance of the "VTODO" calendar component. BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REPLY VERSION:2.0 BEGIN:VTODO ATTENDEE;PARTSTAT=IN-PROCESS:mailto:b@example.com PERCENT-COMPLETE:75 UID:calsrv.example.com-873970198738777-00@example.com DTSTAMP:19970717T233000Z RECURRENCE-ID:19980101T170000Z SEQUENCE:1 END:VTODO END:VCALENDAR 4.6. Journal Examples The iCalendar object below describes a single journal entry for October 2, 1997. The "RELATED-TO" property references the phone conference event for which minutes were taken. BEGIN:VCALENDAR METHOD:PUBLISH PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VJOURNAL DTSTART:19971002T200000Z DTSTAMP:19970717T233100Z ORGANIZER:mailto:a@example.com SUMMARY:Phone conference minutes DESCRIPTION:The editors meeting was held on October 1, 1997. Details are in the attached document. UID:0981234-1234234-2410@example.com RELATED-TO:0981234-1234234-2402-35@example.com ATTACH:ftp://ftp.example.com/pub/ed/minutes100197.txt END:VJOURNAL END:VCALENDAR 4.7. Other Examples 4.7.1. Event Refresh Refresh the event with a "UID" property value of "guid-1-12345@example.com": BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REFRESH VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com ATTENDEE:mailto:c@example.com ATTENDEE:mailto:d@example.com UID:guid-1-12345@example.com DTSTAMP:19970603T094000 END:VEVENT END:VCALENDAR 4.7.2. Bad RECURRENCE-ID Component instances are identified by the combination of "UID", "RECURRENCE-ID", and "SEQUENCE". When an "Organizer" sends an iTIP message to an "Attendee", there are three cases in which an instance cannot be found. They are: 1. The component with the referenced "UID" and "RECURRENCE-ID" has been found but the "SEQUENCE" number in the calendar store does not match that of the iTIP message. 2. The component with the referenced "UID" has been found, the "SEQUENCE" numbers match, but the "RECURRENCE-ID" cannot be found. 3. The "UID" and "SEQUENCE" numbers are found but the CUA does not support recurrences. In case (1), two things can happen. If the "SEQUENCE" number of the "Attendee's" instance is larger than that in the "Organizer's" message, then the "Attendee" is receiving an out-of-sequence message and MUST ignore it. If the "SEQUENCE" number of the "Attendee's" instance is smaller, then the "Organizer" is sending out a newer version of the component and the "Attendee's" version needs to be updated. Since one or more updates have been missed, the "Attendee" SHOULD send a "REFRESH" message to the "Organizer" to get an updated version of the event. In case (2), something has gone wrong. Both the "Organizer" and the "Attendee" should have the same instances, but the "Attendee" does not have the referenced instance. In this case, the "Attendee" SHOULD send a "REFRESH" to the "Organizer" to get an updated version of the event. In case (3), the limitations of the "Attendee's" CUA makes it impossible to match an instance other than the single instance scheduled. In this case, the "Attendee" need not send a "REFRESH" to the "Organizer". The example below shows a sequence in which an "Attendee" sends a "REFRESH" to the "Organizer". +-------------------------+--------------------+--------------------+ | Action | Organizer | Attendee | +-------------------------+--------------------+--------------------+ | Update an instance | "A" sends REQUEST | | | request | message to "B". | | | | | | | Attendee requests | | "B" sends a | | refresh because | | REFRESH message to | | RECURRENCE-ID was not | | "A". | | found | | | | | | | | Refresh the entire | "A" sends the | | | event | latest copy of the | | | | event to "B" | | | | | | | Attendee handles the | | "B" updates to the | | request and updates the | | latest copy of the | | instance | | meeting. | +-------------------------+--------------------+--------------------+ Request from "A": BEGIN:VCALENDAR METHOD:REQUEST PRODID:-//Example/ExampleCalendarClient//EN VERSION:2.0 BEGIN:VEVENT UID:example-12345@example.com SEQUENCE:3 RRULE:FREQ=WEEKLY RDATE;VALUE=PERIOD:19970819T210000Z/199700819T220000Z ORGANIZER:mailto:a@example.com ATTENDEE;ROLE=CHAIR;PARTSTAT=ACCEPTED:mailto:a@example.com ATTENDEE:mailto:b@example.com DESCRIPTION:IETF-C&S Conference Call SUMMARY:IETF Calendaring Working Group Meeting DTSTART:19970801T210000Z DTEND:19970801T220000Z RECURRENCE-ID:19970809T210000Z DTSTAMP:19970726T083000 STATUS:CONFIRMED END:VEVENT END:VCALENDAR "B" has the event with "UID" property "example-12345@example.com", but "B's" "SEQUENCE" property value is "1" and the event does not have an instance at the specified recurrence time. This means that "B" has missed at least one update and needs a new copy of the event. "B" requests the latest copy of the event with the following refresh message: BEGIN:VCALENDAR PRODID:-//Example/ExampleCalendarClient//EN METHOD:REFRESH VERSION:2.0 BEGIN:VEVENT ORGANIZER:mailto:a@example.com ATTENDEE:mailto:b@example.com UID:example-12345@example.com DTSTAMP:19970603T094000 END:VEVENT END:VCALENDAR 5. Application Protocol Fallbacks 5.1. Partial Implementation Applications that support this specification are not required to support the entire protocol. The following describes how methods and properties SHOULD "fallback" in applications that do not support the complete protocol. If a method or property is not addressed in this section, it may be ignored. 5.1.1. Event-Related Fallbacks +----------------+--------------------------------------------------+ | Method | Fallback | +----------------+--------------------------------------------------+ | PUBLISH | Required | | REQUEST | PUBLISH | | REPLY | Required | | ADD | Required if recurrences supported; otherwise, | | | reply with a REQUEST-STATUS "2.8; Success, | | | repeating event ignored. Scheduled as a single | | | component", and schedule as a single component. | | CANCEL | Required | | REFRESH | Required | | COUNTER | Reply with "Not Supported". | | DECLINECOUNTER | Required if COUNTER is implemented for VEVENTs; | | | otherwise, reply with "Not Supported". | +----------------+--------------------------------------------------+ +-----------------+-------------------------------------------------+ | iCalendar | Fallback | | Property | | +-----------------+-------------------------------------------------+ | CALSCALE | Ignore - assume GREGORIAN. | | PRODID | Ignore | | METHOD | Required as described in the Method list above. | | VERSION | Ignore | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | Event-Related | Fallback | | Components | | +-----------------+-------------------------------------------------+ | VALARM | Reply with "Not Supported". | | VTIMEZONE | Required if any DateTime value refers to a time | | | zone. | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | Component | Fallback | | Property | | +-----------------+-------------------------------------------------+ | ATTACH | Ignore | | ATTENDEE | Required if METHOD is REQUEST; otherwise, | | | ignore. | | CATEGORIES | Ignore | | CLASS | Ignore | | COMMENT | Ignore | | COMPLETED | Ignore | | CONTACT | Ignore | | CREATED | Ignore | | DESCRIPTION | Ignore | | DURATION | Required | | DTSTAMP | Required | | DTSTART | Required | | DTEND | Required | | EXDATE | Ignore | | GEO | Ignore | | LAST-MODIFIED | Ignore | | LOCATION | Required | | ORGANIZER | Required if METHOD is REQUEST; otherwise, | | | ignore. | | PRIORITY | Ignore | | RELATED-TO | Ignore | | RDATE | Ignore | | RRULE | Ignore - assume the first instance occurs on | | | the DTSTART property. If implemented, | | | VTIMEZONE MUST also be implemented. | | RECURRENCE-ID | Required if RRULE is implemented; otherwise, | | | ignore. | | REQUEST-STATUS | Required | | RESOURCES | Ignore | | SEQUENCE | Required | | STATUS | Ignore | | SUMMARY | Ignore | | TRANSP | Required if FREEBUSY is implemented; otherwise, | | | ignore. | | URL | Ignore | | UID | Required | | X- | Ignore | +-----------------+-------------------------------------------------+ 5.1.2. Free/Busy-Related Fallbacks +---------+---------------------------------------------------------+ | Method | Fallback | +---------+---------------------------------------------------------+ | PUBLISH | Required if freebusy lookups are supported; otherwise, | | | reply with a REQUEST-STATUS "3.14; Unsupported | | | capability". | | REQUEST | Required if freebusy lookups are supported; otherwise, | | | reply with a REQUEST-STATUS "3.14; Unsupported | | | capability". | | REPLY | Required if freebusy lookups are supported; otherwise, | | | reply with a REQUEST-STATUS "3.14; Unsupported | | | capability". | +---------+---------------------------------------------------------+ +-----------------+-------------------------------------------------+ | iCalendar | Fallback | | Property | | +-----------------+-------------------------------------------------+ | CALSCALE | Ignore - assume GREGORIAN. | | PRODID | Ignore | | METHOD | Required as described in the Method list above. | | VERSION | Ignore | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | Component | Fallback | | Property | | +-----------------+-------------------------------------------------+ | ATTENDEE | Required if METHOD is REQUEST; otherwise, | | | ignore. | | COMMENT | Ignore | | CONTACT | Ignore | | DTEND | Required | | DTSTAMP | Required | | DTSTART | Required | | DURATION | Ignore | | FREEBUSY | Required | | ORGANIZER | Required if METHOD is REQUEST; otherwise, | | | ignore. | | REQUEST-STATUS | Ignore | | UID | Required | | URL | Ignore | | X- | Ignore | +-----------------+-------------------------------------------------+ 5.1.3. To-Do-Related Fallbacks +----------------+--------------------------------------------------+ | Method | Fallback | +----------------+--------------------------------------------------+ | PUBLISH | Required | | REQUEST | PUBLISH | | REPLY | Required | | ADD | Required if recurrences supported; otherwise, | | | reply with a REQUEST-STATUS "2.8; Success, | | | repeating event ignored. Scheduled as a single | | | component", and schedule as a single component. | | CANCEL | Required | | REFRESH | Required | | COUNTER | Reply with "Not Supported". | | DECLINECOUNTER | Required if COUNTER for VTODOs is implemented; | | | otherwise, reply with "Not Supported". | +----------------+--------------------------------------------------+ +-----------------+-------------------------------------------------+ | iCalendar | Fallback | | Property | | +-----------------+-------------------------------------------------+ | CALSCALE | Ignore - assume GREGORIAN. | | PRODID | Ignore | | METHOD | Required as described in the Method list above. | | VERSION | Ignore | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | To-Do-Related | Fallback | | Components | | +-----------------+-------------------------------------------------+ | VALARM | Reply with "Not Supported". | | VTIMEZONE | Required if any DateTime value refers to a time | | | zone. | +-----------------+-------------------------------------------------+ +------------------+------------------------------------------------+ | Component | Fallback | | Property | | +------------------+------------------------------------------------+ | ATTACH | Ignore | | ATTENDEE | Required if METHOD is REQUEST; otherwise, | | | ignore. | | CATEGORIES | Ignore | | CLASS | Ignore | | COMMENT | Ignore | | COMPLETED | Required | | CONTACT | Ignore | | CREATED | Ignore | | DESCRIPTION | Required if METHOD is REQUEST; otherwise, | | | ignore. | | DUE | Required | | DURATION | Required | | DTSTAMP | Required | | DTSTART | Required | | EXDATE | Ignore - reply with "Not Supported". | | LAST-MODIFIED | Ignore | | LOCATION | Ignore | | ORGANIZER | Required if METHOD is REQUEST; otherwise, | | | ignore. | | PERCENT-COMPLETE | Ignore | | PRIORITY | Required | | RECURRENCE-ID | Required if RRULE is implemented; otherwise, | | | ignore. | | RELATED-TO | Ignore | | REQUEST-STATUS | Ignore | | RDATE | Ignore | | RRULE | Ignore - assume the first instance occurs on | | | the DTSTART property. If implemented, | | | VTIMEZONE MUST also be implemented. | | RESOURCES | Ignore | | SEQUENCE | Required | | STATUS | Required | | SUMMARY | Ignore | | URL | Ignore | | UID | Required | | X- | Ignore | +------------------+------------------------------------------------+ 5.1.4. Journal-Related Fallbacks +---------+---------------------------------------------------------+ | Method | Fallback | +---------+---------------------------------------------------------+ | PUBLISH | Implementations MAY ignore the METHOD type. The | | | REQUEST-STATUS "3.14; Unsupported capability" MUST be | | | returned. | | ADD | Implementations MAY ignore the METHOD type. The | | | REQUEST-STATUS "3.14; Unsupported capability" MUST be | | | returned. | | CANCEL | Implementations MAY ignore the METHOD type. The | | | REQUEST-STATUS "3.14; Unsupported capability" MUST be | | | returned. | +---------+---------------------------------------------------------+ +-----------------+-------------------------------------------------+ | iCalendar | Fallback | | Property | | +-----------------+-------------------------------------------------+ | CALSCALE | Ignore - assume GREGORIAN. | | PRODID | Ignore | | METHOD | Required as described in the Method list above. | | VERSION | Ignore | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | Journal-Related | Fallback | | Components | | +-----------------+-------------------------------------------------+ | VTIMEZONE | Required if any DateTime value refers to a time | | | zone. | +-----------------+-------------------------------------------------+ +-----------------+-------------------------------------------------+ | Component | Fallback | | Property | | +-----------------+-------------------------------------------------+ | ATTACH | Ignore | | ATTENDEE | Ignore | | CATEGORIES | Ignore | | CLASS | Ignore | | COMMENT | Ignore | | CONTACT | Ignore | | CREATED | Ignore | | DESCRIPTION | Ignore | | DTSTAMP | Required | | DTSTART | Required | | EXDATE | Ignore | | LAST-MODIFIED | Ignore | | ORGANIZER | Ignore | | RECURRENCE-ID | Required if RRULE is implemented; otherwise, | | | ignore. | | RELATED-TO | Ignore | | RDATE | Ignore | | RRULE | Ignore - assume the first instance occurs on | | | the DTSTART property. If implemented, | | | VTIMEZONE MUST also be implemented. | | SEQUENCE | Required | | STATUS | Ignore | | SUMMARY | Required | | URL | Ignore | | UID | Required | | X- | Ignore | +-----------------+-------------------------------------------------+ 5.2. Latency Issues With a store-and-forward transport, it is possible for events to arrive out of sequence. That is, a "CANCEL" method may be received prior to receiving the associated "REQUEST" for the calendar component. This section discusses a few of these scenarios. 5.2.1. Cancellation of an Unknown Calendar Component When a "CANCEL" method is received before the original "REQUEST" method, the calendar will be unable to correlate the "UID" property of the cancellation with an existing calendar component. It is suggested that messages that cannot be correlated and that also contain non-zero sequence numbers be held and not discarded. Implementations MAY age them out if no other messages arrive with the same "UID" property value and a lower sequence number. 5.2.2. Unexpected Reply from an Unknown Delegate When an "Attendee" delegates an item to another CU, they MUST send a "REPLY" method to the "Organizer" using the "ATTENDEE" properties to indicate that the request was delegated and to whom. Hence, it is possible for an "Organizer" to receive a "REPLY" from a CU not listed as one of the original "Attendees". The resolution is left to the implementation, but it is expected that the calendaring software will either accept the reply or hold it until the related "REPLY" method is received from the "Delegator". If the version of the "REPLY" method is out of date, the "Organizer" SHOULD treat the message as a "REFRESH" message and update the "Delegate" with the correct version, provided that delegation to that delegate is acceptable. 5.3. Sequence Number Under some conditions, a CUA may receive requests and replies with the same "SEQUENCE" property value. The "DTSTAMP" property is utilized as a tie-breaker when two items with the same "SEQUENCE" property value are evaluated. 6. Security Considerations iTIP is an abstract transport protocol that will be bound to a real- time transport, a store-and-forward transport, and perhaps other transports. The transport protocol will be responsible for providing facilities for authentication and encryption using standard Internet mechanisms that are mutually understood between the sender and receiver. 6.1. Security Threats 6.1.1. Spoofing the Organizer In iTIP, the "Organizer" (or someone working on the "Organizer's" behalf) is the only person authorized to make changes to an existing "VEVENT", "VTODO", or "VJOURNAL" calendar component and republish it or redistribute updates to the "Attendees". An iCalendar object that maliciously changes or cancels an existing "VEVENT", "VTODO", or "VJOURNAL" calendar component may be constructed by someone other than the "Organizer" and republished or sent to the "Attendees". 6.1.2. Spoofing the Attendee In iTIP, an "Attendee" of a "VEVENT" or "VTODO" calendar component (or someone working on the "Attendee's" behalf) is the only person authorized to update any parameter associated with their "ATTENDEE" property and send it to the "Organizer". An iCalendar object that maliciously changes the "ATTENDEE" parameters may be constructed by someone other than the real "Attendee" and sent to the "Organizer". 6.1.3. Unauthorized Replacement of the Organizer There will be circumstances when "Attendees" of an event or to-do decide, using out-of-band mechanisms, that the "Organizer" must be replaced. When the new "Organizer" sends out the updated "VEVENT" or "VTODO", the "Attendee's" CUA will detect that the "Organizer" has been changed, but it has no way of knowing whether or not the change was mutually agreed upon. 6.1.4. Eavesdropping and Data Integrity The iCalendar object is constructed with human-readable clear text. Any information contained in an iCalendar object may be read and/or changed by unauthorized persons while the object is in transit. 6.1.5. Flooding a Calendar Implementations could provide a means to automatically incorporate "REQUEST" methods into a calendar. This presents the opportunity for a calendar to be flooded with requests, which effectively blocks all the calendar's free time. 6.1.6. Unauthorized REFRESH Requests It is possible for an "Organizer" to receive a "REFRESH" request from someone who is not an "Attendee" of an event or to-do. Only "Attendees" of an event or to-do are authorized to receive replies to "REFRESH" requests. Replying to such requests to anyone who is not an "Attendee" may be a security problem. 6.2. Recommendations For an application where the information is sensitive or critical and the network is subject to a high probability of attack, iTIP transactions SHOULD be encrypted and authenticated. This helps mitigate the threats of spoofing, eavesdropping, and malicious changes in transit. 6.2.1. Securing iTIP transactions iTIP transport bindings MUST provide a mechanism to enable authentication of the sender's identity as well as privacy and integrity of the data being transmitted. This allows the receiver of a signed iCalendar object to verify the identity of the sender. This sender may then be correlated to an "ATTENDEE" property in the iCalendar object. If the correlation is made and the sender is authorized to make the requested change or update, then the operation may proceed. It also allows the message to be encrypted to prevent unauthorized reading of the message contents in transit. iTIP transport binding documents describe this process in detail. 6.2.2. Implementation Controls The threat of unauthorized replacement of the "Organizer" SHOULD be mitigated by a calendar system that uses this protocol by providing controls or alerts that make "Calendar Users" aware of such "Organizer" changes and allowing them to decide whether or not the request should be honored. The threat of flooding a calendar SHOULD be mitigated by a calendar system that uses this protocol by providing controls that may be used to limit the acceptable sources for iTIP transactions, and perhaps the size of messages and volume of traffic, by source. The threat of unauthorized "REFRESH" requests SHOULD be mitigated by a calendar system that uses this protocol by providing controls or alerts that allow "Calendar Users" to decide whether or not the request should be honored. An implementation MAY decide to maintain, for audit or historical purposes, "Calendar Users" who were part of an "Attendee" list and who were subsequently uninvited. Similar controls or alerts should be provided when a "REFRESH" request is received from these "Calendar Users" as well. 6.2.3. Access Controls and Filtering In many environments, there could be restrictions on who is allowed to schedule with whom and who the allowed delegates are for particular "Calendar Users". iTIP transport bindings SHOULD provide mechanisms for implementing access controls or filtering to ensure iTIP transactions only take place between authorized "Calendar Users". That would include preventing one "Calendar User" from scheduling with another or one "Calendar User" delegating to another. 6.3. Privacy Issues The "Organizer" might want to keep "Attendees" from knowing which other "Attendees" are participating in an event or to-do. The "Organizer" has the choice of sending single iTIP messages with a full list of "Attendees" or sending iTIP messages to each "Attendee" with only that "Attendee" listed. 7. IANA Considerations 7.1. Registration Template for REQUEST-STATUS Values This specification updates [RFC5545] by adding a "REQUEST-STATUS" value registry to the iCalendar Elements registry. A "REQUEST-STATUS" value is defined by completing the following template. Status Code: Hierarchical, numeric return status code, following the rules defined in Section 3.8.8.3 of [RFC5545]. Status Description: Textual status description. A short but clear description of the error. Status Exception Data: Textual exception data. A short but clear description of what might appear in this field. Description: Describe the underlying cause for this status code value. 7.2. Additions to iCalendar METHOD Registry This document defines the following values for the iCalendar "METHOD" property, using the values template from Section 8.2.6 of [RFC5545]. These should be added to the Methods Registry defined in Section 8.3.12 of [RFC5545]: 7.2.1. METHOD:PUBLISH Value: PUBLISH Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.2. METHOD:REQUEST Value: REQUEST Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.3. METHOD:REPLY Value: REPLY Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.4. METHOD:ADD Value: ADD Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.5. METHOD:CANCEL Value: CANCEL Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.6. METHOD:REFRESH Value: REFRESH Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.7. METHOD:COUNTER Value: COUNTER Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.2.8. METHOD:DECLINECOUNTER Value: DECLINECOUNTER Purpose: Standard iTIP "METHOD" value. Conformance: Only used with the "METHOD" property. Examples: See this RFC. 7.3. REQUEST-STATUS Value Registry New "REQUEST-STATUS" values can be registered using the process described in Section 8.2.1 of [RFC5545]. The following table is to be used to initialize the "REQUEST-STATUS" value registry. +-------------+---------+--------------------------+ | Status Code | Status | Reference | +-------------+---------+--------------------------+ | 2.0 | Current | RFC 5546, Section 3.6.1 | | 2.1 | Current | RFC 5546, Section 3.6.2 | | 2.2 | Current | RFC 5546, Section 3.6.3 | | 2.3 | Current | RFC 5546, Section 3.6.4 | | 2.4 | Current | RFC 5546, Section 3.6.5 | | 2.5 | Current | RFC 5546, Section 3.6.6 | | 2.6 | Current | RFC 5546, Section 3.6.7 | | 2.7 | Current | RFC 5546, Section 3.6.8 | | 2.8 | Current | RFC 5546, Section 3.6.9 | | 2.9 | Current | RFC 5546, Section 3.6.10 | | 2.10 | Current | RFC 5546, Section 3.6.11 | | 2.11 | Current | RFC 5546, Section 3.6.12 | | 3.0 | Current | RFC 5546, Section 3.6.13 | | 3.1 | Current | RFC 5546, Section 3.6.14 | | 3.2 | Current | RFC 5546, Section 3.6.15 | | 3.3 | Current | RFC 5546, Section 3.6.16 | | 3.4 | Current | RFC 5546, Section 3.6.17 | | 3.5 | Current | RFC 5546, Section 3.6.18 | | 3.6 | Current | RFC 5546, Section 3.6.19 | | 3.7 | Current | RFC 5546, Section 3.6.20 | | 3.8 | Current | RFC 5546, Section 3.6.21 | | 3.9 | Current | RFC 5546, Section 3.6.22 | | 3.10 | Current | RFC 5546, Section 3.6.23 | | 3.11 | Current | RFC 5546, Section 3.6.24 | | 3.12 | Current | RFC 5546, Section 3.6.25 | | 3.13 | Current | RFC 5546, Section 3.6.26 | | 3.14 | Current | RFC 5546, Section 3.6.27 | | 4.0 | Current | RFC 5546, Section 3.6.28 | | 5.0 | Current | RFC 5546, Section 3.6.29 | | 5.1 | Current | RFC 5546, Section 3.6.30 | | 5.2 | Current | RFC 5546, Section 3.6.31 | | 5.3 | Current | RFC 5546, Section 3.6.32 | +-------------+---------+--------------------------+ 8. Acknowledgments This is an update to the original iTIP document authored by S. Silverberg, S. Mansour, F. Dawson, and R. Hopson. This revision is the product of the Calsify IETF Working Group, and several participants have made important contributions to this specification, including Oliver Block, Bernard Desruisseaux, Mike Douglass, Tim Hare, Ciny Joy, Bruce Kahn, Reinhold Kainhofer, Eliot Lear, Jonathan Lennox, Andy Mabbett, Aki Niemi, John W. Noerenberg II, Robert Ransdell, and Caleb Richardson. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2368] Hoffman, P., Masinter, L., and J. Zawinski, "The mailto URL scheme", RFC 2368, July 1998. [RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009. 9.2. Informative References [iMIP] Melnikov, A., Ed., "iCalendar Message-Based Interoperability Protocol (iMIP)", Work in Progress, October 2009. Appendix A. Differences from RFC 2446 A.1. Changed Restrictions This specification now defines an allowed combination of "REQUEST- STATUS" codes when multiple iCalendar components are included in an iTIP message. This specification now restricts "RECURRENCE-ID" to only a single occurrence in any one iCalendar component in an iTIP message, as required by [RFC5545]. Changed the "RECURRENCE-ID" entry in the component restriction table to "0 or 1" from "0+", to fall in line with [RFC5545]. Changed the "FREEBUSY" entry in the "VFREEBUSY", "PUBLISH", and "REPLY" restriction tables to "0+" from "1+", to fall in line with [RFC5545]. Changed the "FREEBUSY" description in the "VFREEBUSY" and "REPLY" restriction tables to indicate that different "FBTYPE" ranges MUST NOT overlap. Changed the "TZNAME" entry in the "VTIMEZONE" restriction table to "0+" from "0 or 1", to fall in line with [RFC5545]. Changed the "COMMENT" entry in the component restriction tables to "0+" from "0 or 1", to fall in line with [RFC5545]. Added the "ATTENDEE" entry in the "VALARM" restriction table to match the email alarm type in [RFC5545]. Changed the "CATEGORIES" entry in the component restriction tables to "0+" from "0 or 1", to fall in line with [RFC5545]. Changed the "RESOURCES" entry in the component restriction tables to "0+" from "0 or 1", to fall in line with [RFC5545]. Changed the "CONTACT" entry in the "VFREEBUSY" restriction table to "0 or 1" from "0+", to fall in line with [RFC5545]. Changed the "UID" entry in the "VFREEBUSY" and "PUBLISH" restriction tables to "1" from "0", to fall in line with [RFC5545]. Added the "COMPLETED" entry in the "VTODO" restriction tables to fall in line with [RFC5545]. Added the "REQUEST-STATUS" entry in the "VJOURNAL" restriction tables to fall in line with [RFC5545]. A.2. Deprecated Features The "EXRULE" property was removed in [RFC5545] and references to that have been removed in this document too. The "PROCEDURE" value for the "ACTION" property was removed in [RFC5545] and references to that have been removed in this document too. The "THISANDPRIOR" option for the "RANGE" parameter was removed in [RFC5545] and references to that have been removed in this document too. Author's Address Cyrus Daboo (editor) Apple Inc. 1 Infinite Loop Cupertino, CA 95014 USA EMail: cyrus@daboo.name URI: http://www.apple.com/