ftp.cc.uoc.gr
rfc4235
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 158, EID 771, EID 774, EID 781, EID 788
Network Working Group                                       J. Rosenberg
Request for Comments: 4235                                 Cisco Systems
Category: Standards Track                                 H. Schulzrinne
                                                     Columbia University
                                                            R. Mahy, Ed.
                                                            SIP Edge LLC
                                                           November 2005


            An INVITE-Initiated Dialog Event Package for the
                   Session Initiation Protocol (SIP)

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 01) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines a dialog event package for the SIP Events
   architecture, along with a data format used in notifications for this
   package.  The dialog package allows users to subscribe to another
   user and to receive notification of the changes in state of INVITE-
   initiated dialog usages in which the subscribed-to user is involved.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Dialog Event Package ............................................4
      3.1. Event Package Name .........................................4
      3.2. Event Package Parameters ...................................4
      3.3. SUBSCRIBE Bodies ...........................................5
      3.4. Subscription Duration ......................................6
      3.5. NOTIFY Bodies ..............................................6
      3.6. Notifier Processing of SUBSCRIBE Requests ..................7
      3.7. Notifier Generation of NOTIFY Requests .....................8
           3.7.1. The Dialog State Machine ............................8
           3.7.2. Applying the State Machine .........................11

      3.8. Subscriber Processing of NOTIFY Requests ..................12
      3.9. Handling of Forked Requests ...............................12
      3.10. Rate of Notifications ....................................13
      3.11. State Agents .............................................13
   4. Dialog Information Format ......................................13
      4.1. Structure of Dialog Information ...........................13
           4.1.1. Dialog Element .....................................14
           4.1.2. State Element ......................................15
           4.1.3. Duration Element ...................................15
           4.1.4. Replaces Element ...................................15
           4.1.5. Referred-By Element ................................16
           4.1.6. Local and Remote Elements ..........................16
      4.2. Sample Notification Body ..................................17
      4.3. Constructing Coherent State ...............................18
      4.4. Schema ....................................................19
   5. Definition of New Media Feature Parameters .....................22
      5.1. The "sip.byeless" Parameter ...............................22
      5.2. The "sip.rendering" parameter .............................23
   6. Examples .......................................................24
      6.1. Basic Example .............................................24
      6.2. Emulating a Shared-Line Phone System ......................26
      6.3. Minimal Dialog Information with Privacy ...................31
   7. Security Considerations ........................................32
   8. IANA Considerations ............................................32
      8.1. application/dialog-info+xml MIME Registration .............33
      8.2. URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:dialog-info ........................34
      8.3. Schema Registration .......................................34
      8.4. Media Feature Parameter Registration ......................34
           8.4.1. sip.byeless ........................................35
           8.4.2. sip.rendering ......................................35
   9. Acknowledgements ...............................................36
   10. References ....................................................36
      10.1. Normative References .....................................36
      10.2. Informative References ...................................37

1.  Introduction

   The SIP Events framework [1] defines general mechanisms for
   subscription to, and notification of, events within SIP networks.  It
   introduces the notion of a package, which is a specific
   "instantiation" of the events mechanism for a well-defined set of
   events.  Packages have been defined for user presence [16], watcher
   information [17], and message waiting indicators [18], amongst
   others.  This document defines an event package for INVITE-initiated
   dialog usages.  Dialogs refer to the SIP relationship established
   between two SIP peers [2].  Dialogs can be created by many methods,
   although RFC 3261 defines only one: the INVITE method.  RFC 3265 [1]
   defines the SUBSCRIBE and NOTIFY methods, which also create new
   dialog usages.  However, using this package to model state for non-
   session dialog usages is out of the scope of this specification.

   A variety of applications are enabled through knowledge of INVITE
   dialog usage state.  Some examples include:

      Automatic Callback: In this basic Public Switched Telephone
         Network (PSTN) application, user A calls user B but User B is
         busy.  User A would like to get a callback when user B hangs
         up.  When B hangs up, user A's phone rings.  When A picks up,
         they hear ringing, while they are being connected to B.  To
         implement this with SIP, a mechanism is required for A to
         receive a notification when the dialogs at B are complete.

      Presence-Enabled Conferencing: In this application, user A wishes
         to set up a conference call with users B and C.  Rather than
         being scheduled, the call is created automatically when A, B
         and C are all available.  To do this, the server providing the
         application would like to know whether A, B, and C are
         "online", not idle, and not in a phone call.  Determining
         whether or not A, B, and C are in calls can be done in two
         ways.  In the first, the server acts as a call-stateful proxy
         for users A, B, and C, and therefore knows their call state.
         This won't always be possible, however, and it introduces
         scalability, reliability, and operational complexities.  In the
         second way, the server subscribes to the dialog state of those
         users and receives notifications as this state changes.  This
         enables the application to be provided in a distributed way;
         the server need not reside in the same domain as the users.

      IM Conference Alerts: In this application, a user can receive an
         Instant Message (IM) on their phone whenever someone joins a
         conference that the phone is involved in.  The IM alerts are
         generated by an application separate from the conference
         server.

   In general, the dialog package allows for construction of distributed
   applications, where the application requires information on dialog
   state but is not co-resident with the end user on which that state
   resides.

   This document also defines two new callee capability [10] feature
   parameters:

      o "sip.byeless", which indicates that a SIP user agent (UA) is not
         capable of terminating a session itself (for example, in some
         announcement or recording services, or in some call centers) in
         which the UA is no longer interested in participating; and

      o "sip.rendering", which positively describes whether the user
         agent is rendering any of the media it is receiving.  These
         feature parameters are useful in many of the same applications
         that motivated the dialog package, such as conferencing,
         presence, and the shared-line example described in Section 6.2.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [9] and
   indicate requirement levels for compliant implementations.

3.  Dialog Event Package

   This section provides the details for defining a SIP Events package,
   as specified in [1].

3.1.  Event Package Name

   The name of this event package is "dialog".  This package name is
   carried in the Event and Allow-Events header fields, as defined in
   [1].

3.2.  Event Package Parameters

   This package defines four Event Package parameters:  call-id, to-tag,
   from-tag, and include-session-description.  If a subscription to a
   specific dialog is requested, the first three of these parameters
   MUST be present, to identify the dialog that is being subscribed to.
   The to-tag is matched against the local tag, the from-tag is matched
   against the remote tag, and the call-id is matched against the
   Call-ID.  The include-session-description parameter indicates whether
   the subscriber would like to receive the session descriptions
   associated with the subscribed dialog usage or usages.

   It is also possible to subscribe to the set of dialogs created as a
   result of a single INVITE sent by a UAC (user agent client).  In that
   case, the call-id and to-tag MUST be present.  The to-tag is matched
   against the local tag and the call-id is matched against the Call-ID.

   The ABNF for these parameters is shown below.  It refers to many
   constructions from the ABNF of RFC3261, such as EQUAL, DQUOTE, and
   token.

   call-id     =  "call-id" EQUAL ( token / DQUOTE callid DQUOTE )
                    ;; NOTE: any DQUOTEs inside callid MUST be escaped!
   from-tag    =  "from-tag" EQUAL token
   to-tag      =  "to-tag" EQUAL token
   with-sessd  =  "include-session-description"

   If any call-ids contain embedded double-quotes, those double-quotes
   MUST be escaped using the backslash-quoting mechanism.  Note that the
   call-id parameter may need to be expressed as a quoted string.  This
   is because the ABNF for the callid production and the word
   production, which is used by callid (both from RFC 3261 [1]), allow
   some characters (such as "@", "[", and ":") that are not allowed
   within a token.

3.3.  SUBSCRIBE Bodies

   A SUBSCRIBE request for a dialog package MAY contain a body.  This
   body defines a filter to be applied to the subscription.  Filter
   documents are not specified in this document, and at the time of
   writing, they are expected to be the subject of future
   standardization activity.

   A SUBSCRIBE request for a dialog package MAY be sent without a body.
   This implies the default subscription filtering policy.  The default
   policy is:

   o  If the Event header field contained dialog identifiers, a
      notification is generated every time there is a change in the
      state of any matching dialogs for the user identified in the
      request URI of the SUBSCRIBE.

   o  If there were no dialog identifiers in the Event header field, a
      notification is generated every time there is any change in the
      state of any dialogs for the user identified in the request URI of
      the SUBSCRIBE with the following exceptions.  If the target
      (Contact) URI of a subscriber is equivalent to the remote target
      URI of a specific dialog, then the dialog element for that dialog
      is suppressed for that subscriber.  (The subscriber is already a
      party in the dialog directly, so these notifications are

      superfluous.)  If no dialogs remain after suppressing dialogs, the
      entire notification to that subscriber is suppressed and the
      version number in the dialog-info element is not incremented for
      that subscriber.  Implicit filtering for one subscriber does not
      affect notifications to other subscribers.

   o  Notifications do not normally contain full state; rather, they
      only indicate the state of the dialog(s) whose state has changed.
      The exceptions are a NOTIFY sent in response to a SUBSCRIBE, and a
      NOTIFY that contains no dialog elements.  These NOTIFYs contain
      the complete view of dialog state.

   o  The notifications contain the identities of the participants in
      the dialog, the target URIs, and the dialog identifiers.  Session
      descriptions are not included unless explicitly requested and
      explicitly authorized.

3.4.  Subscription Duration

   Dialog state changes fairly quickly.  Once established, a typical
   phone call lasts a few minutes (this is different for other session
   types, of course).  However, the interval between new calls is
   typically long.  Clients SHOULD specify an explicit duration.

   There are two distinct use cases for dialog state.  The first is when
   a subscriber is interested in the state of a specific dialog or
   dialogs (and they are authorized to find out just the state of those
   dialogs).  In that case, when the dialogs terminate, so too does the
   subscription.  In these cases, the value of the subscription duration
   is largely irrelevant; it SHOULD be longer than the typical duration
   of a dialog.  We recommend a default duration of two hours, which is
   likely to cover most dialogs.

   In another case, a subscriber is interested in the state of all
   dialogs for a specific user.  In these cases, a shorter interval
   makes more sense.  The default is one hour for these subscriptions.

3.5.  NOTIFY Bodies

   As described in RFC 3265 [1], the NOTIFY message will contain bodies
   that describe the state of the subscribed resource.  This body is in
   a format listed in the Accept header field of the SUBSCRIBE, or in a
   package-specific default format if the Accept header field was
   omitted from the SUBSCRIBE.

   In this event package, the body of the notification contains a dialog
   information document.  This document describes the state of one or
   more dialogs associated with the subscribed resource.  All

   subscribers and notifiers MUST support the "application/
   dialog-info+xml" data format described in Section 4.  The subscribe
   request MAY contain an Accept header field.  If no such header field
   is present, it has a default value of "application/dialog-info+xml".
   If the header field is present, it MUST include "application/
   dialog-info+xml", and it MAY include any other types capable of
   representing dialog state.

   Of course, the notifications generated by the server MUST be in one
   of the formats specified in the Accept header field in the SUBSCRIBE
   request.

3.6.  Notifier Processing of SUBSCRIBE Requests

   The dialog information for a user contains sensitive information.
   Therefore, all subscriptions SHOULD be authenticated and then
   authorized before approval.  All implementors of this package MUST
   support the digest authentication mechanism as a baseline.  The
   authorization policy is at the discretion of the administrator, as
   always.  However, a few recommendations can be made.

   It is RECOMMENDED that, if the policy of user B is that user A is
   allowed to call them, dialog subscriptions from user A be allowed.
   However, the information provided in the notifications does not
   contain any dialog identification information, merely an indication
   of whether the user is in at least one call.  Specifically, they
   should not be able to find out any more information than if they sent
   an INVITE.  (This concept of a "virtual" dialog is discussed more in
   Section 3.7.2, and an example of such a notification body is shown
   below).

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
                   version="0" state="full"
                   entity="sip:alice@example.com">
        <dialog id="as7d900as8">
          <state>confirmed</state>
        </dialog>
      </dialog-info>

   A user agent that registers with the address-of-record X SHOULD
   authorize subscriptions that come from any entity that can
   authenticate itself as X.  Complete information on the dialog state
   SHOULD be sent in this case.  This authorization behavior allows a
   group of devices representing a single user to become aware of each
   other's state.  This is useful for applications such as
   single-line-extension, also known as shared lines.

      Note that many implementations of "shared-lines" have a feature
      that allows details of calls on a shared address-of-record to be
      made private.  This is a completely reasonable authorization
      policy that could result in notifications that contain only the id
      attribute of the dialog element and the state element when
      shared-line privacy is requested, and notifications with more
      complete information when shared-line privacy is not requested.

3.7.  Notifier Generation of NOTIFY Requests

   Notifications are generated for the dialog package when an INVITE
   request is sent, when a new dialog comes into existence at a UA, or
   when the state or characteristics of an existing dialog changes.
   Therefore, a model of dialog state is needed in order to determine
   precisely when to send notifications, and what their content should
   be.  The SIP specification has a reasonably well defined lifecycle
   for dialogs.  However, it is not explicitly modelled.  This
   specification provides an explicit model of dialog state through a
   finite state machine.

   It is RECOMMENDED that NOTIFY requests only contain information on
   the dialogs whose state or participation information has changed.
   However, if a notifier receives a SUBSCRIBE request, the triggered
   NOTIFY SHOULD contain the state of all dialogs that the subscriber is
   authorized to see.

3.7.1.  The Dialog State Machine

   Modelling of dialog state is complicated by two factors.  The first
   is forking, which can cause a single INVITE to generate many dialogs
   at a UAC.  The second is the differing views of state at the UAC
   (user agent client) and UAS (usage agent server).  We have chosen to
   handle the first issue by extending the dialog finite state machine
   (FSM) to include the states between transmission of the INVITE and
   the creation of actual dialogs through receipt of 1xx and 2xx
   responses.  As a result, this specification supports the notion of
   dialog state for dialogs before they are fully instantiated.

   We have also chosen to use a single FSM for both UAC and UAS.

                +----------+            +----------+
                |          | 1xx-notag  |          |
                |          |----------->|          |
                |  Trying  |            |Proceeding|-----+
                |          |---+  +-----|          |     |
                |          |   |  |     |          |     |
                +----------+   |  |     +----------+     |
                     |   |     |  |          |           |
                     |   |     |  |          |           |
                     +<--C-----C--+          |1xx-tag    |
                     |   |     |             |           |
            cancelled|   |     |             V           |
             rejected|   |     |1xx-tag +----------+     |
                     |   |     +------->|          |     |2xx
                     |   |              |          |     |
                     +<--C--------------|  Early   |-----C---+ 1xx-tag
                     |   |   replaced   |          |     |   | w/new tag
                     |   |              |          |<----C---+ (new FSM
                     |   |              +----------+     |      instance
                     |   |   2xx             |           |      created)
                     |   +----------------+  |           |
                     |                    |  |2xx        |
                     |                    |  |           |
                     V                    V  V           |
                +----------+            +----------+     |
                |          |            |          |     |
                |          |            |          |     |
                |Terminated|<-----------| Confirmed|<----+
                |          |  error     |          |
                |          |  timeout   |          |
                +----------+  replaced  +----------+
                              local-bye   |      ^
                              remote-bye  |      |
                                          |      |
                                          +------+
                                           2xx w. new tag
                                            (new FSM instance
                                             created)

                               Figure 3

   The FSM for dialog state is shown in Figure 3.  The FSM is best
   understood by considering the UAC and UAS cases separately.

   The FSM is created in the Trying state when the UAC sends an INVITE
   request.  Upon receipt of a 1xx without a tag, the FSM transitions to
   the Proceeding state.  Note that there is no actual dialog yet, as
   defined by the SIP specification.  However, there is a "half-dialog",
   in the sense that two of the three components of the dialog ID (the
   call identifier and local tag) are known.  If a 1xx with a tag is
   received, the FSM transitions to the Early state.  The full dialog
   identifier is now defined.  Had a 2xx been received, the FSM would
   have transitioned to the Confirmed state.

   If, after transitioning to the Early or Confirmed states, the UAC
   receives another 1xx or 2xx respectively with a different tag,
   another instance of the FSM is created, initialized into the Early or
   Confirmed state, respectively.  The benefit of this approach is that
   there will be a single FSM representing the entire state of the
   invitation and resulting dialog when dealing in the common case of no
   forking.

   If the UAC sends a CANCEL and then subsequently receives a 487 to its
   INVITE transaction, all FSMs spawned from that INVITE transition to
   the Terminated state with the event "cancelled".  If the UAC receives
   a new invitation (with a Replaces [13] header) that replaces the
   current Early or Confirmed dialog, all INVITE transactions spawned
   from the replaced invitation transition to the Terminated state with
   the event "replaced".  If the INVITE transaction terminates with a
   non-2xx response for any other reason, all FSMs spawned from that
   INVITE transition to the Terminated state with the event "rejected".

   Once in the Confirmed state, the call is active.  It can transition
   to the Terminated state if the UAC sends a BYE or receives a BYE
   (corresponding to the "local-bye" and "remote-bye" events as
   appropriate), if a mid-dialog request generates a 481 or 408 response
   (corresponding to the "error" event), or a mid-dialog request
   generates no response (corresponding to the "timeout" event).

   From the perspective of the UAS, when an INVITE is received, the FSM
   is created in the Trying state.  If it sends a 1xx without a tag, the
   FSM transitions to the Proceeding state.  If a 1xx is sent with a
   tag, the FSM transitions to the Early state, and if a 2xx is sent, it
   transitions to the Confirmed state.  If the UAS receives a CANCEL
   request and then generates a 487 response to the INVITE (which can
   occur in the Proceeding and Early states), the FSM transitions to the
   Terminated state with the event "cancelled".  If the UAS generates
   any other non-2xx final response to the INVITE request, the FSM
   transitions to the Terminated state with the event "rejected".  If
   the UAS receives a new invitation (with a Replaces [13] header field)
   that replaces the current Confirmed dialog, the replaced invitation
   transitions to the Terminated state with the event "replaced".  Once

   in the Confirmed state, the other transitions to the Terminated state
   occur for the same reasons they do in the case of UAC.

      There should never be a transition from the Trying state to the
      Terminated state with the event "cancelled", since the SIP
      specification prohibits transmission of CANCEL until a provisional
      response is received.  However, this transition is defined in the
      FSM just to unify the transitions from Trying, Proceeding, and
      Early states to the Terminated state.

3.7.2.  Applying the State Machine

   The notifier MAY generate a NOTIFY request on any event transition of
   the FSM.  Whether it does or not is policy dependent.  However, some
   general guidelines are provided.

   When the subscriber is unauthenticated, or it is authenticated but
   represents a third party with no specific authorization policies, it
   is RECOMMENDED that subscriptions to an individual dialog or to a
   specific set of dialogs be forbidden.  Only subscriptions to all
   dialogs (i.e., there are no dialog identifiers in the Event header
   field) are permitted.  In that case, actual dialog states across all
   dialogs will not be reported.  Rather, a single "virtual" dialog FSM
   will be used, and event transitions on that FSM will be reported.

   If there is any dialog at the UA whose state is Confirmed, the
   virtual FSM is in the Confirmed state.  If there are no dialogs at
   the UA in the Confirmed state but there is at least one in the Early
   state, the virtual FSM is in the Early or Confirmed state.  If there
   are no dialogs in the Confirmed or Early states but there is at least
   one in the Proceeding state, the virtual FSM is in the Proceeding,
   Early, or Confirmed state.  If there are no dialogs in the Confirmed,
   Early, or Proceeding states but there is at least one in the Trying
   state, the virtual FSM is in the Trying, Proceeding, Early or
   Confirmed state.  The choice of state to use depends on whether the
   UA wishes to let unknown users know that their phone is ringing, as
   opposed to being in an active call.

   It is RECOMMENDED that, in the absence of any preference, Confirmed
   is used in all cases as shown in the example in Section 3.6.
   Furthermore, it is RECOMMENDED that the notifications of changes in
   the virtual FSM machine not convey any information except the state
   of the FSM and its event transitions - no dialog identifiers (which
   are ill-defined in this model in any case).  The use of this virtual
   FSM allows minimal information to be conveyed.  A subscriber cannot
   know how many calls are in progress, or with whom, just that there
   exists a call.  This is the same information they would receive if

   they simply sent an INVITE to the user instead; a 486 (Busy Here)
   response would indicate that they are on a call.

   When the subscriber is authenticated and has authenticated itself
   with the same address-of-record that the UA itself uses, if no
   explicit authorization policy is defined, it is RECOMMENDED that all
   state transitions on dialogs that have been subscribed to be
   reported, along with complete dialog IDs.  This means either all of
   the dialogs, if no dialog identifiers were present in the Event
   header field, or the specific set of dialogs identified by the Event
   header field parameters.

   The notifier SHOULD generate a NOTIFY request on any change in the
   characteristics associated with the dialog.  Since these include
   Contact URIs, Contact parameters, and session descriptions, receipt
   of re-INVITEs and UPDATE requests [3] that modify this information
   MAY trigger notifications.

3.8.  Subscriber Processing of NOTIFY Requests

   The SIP Events framework expects packages to specify how a subscriber
   processes NOTIFY requests in package-specific ways.  In particular, a
   package should specify how it uses the NOTIFY requests to construct a
   coherent view of the state of the subscribed resource.

   Typically, the NOTIFY for the dialog package will contain information
   about only those dialogs whose state has changed.  To construct a
   coherent view of the total state of all dialogs, a subscriber to the
   dialog package will need to combine NOTIFYs received over time.

   Notifications within this package can convey partial information;
   that is, they can indicate information about a subset of the state
   associated with the subscription.  This means that an explicit
   algorithm needs to be defined in order to construct coherent and
   consistent state.  The details of this mechanism are specific to the
   particular document type.  See Section 4.3 for information on
   constructing coherent information from an application/dialog-info+xml
   document.

3.9.  Handling of Forked Requests

   Since dialog state is distributed across the UA for a particular
   user, it is reasonable and useful for a SUBSCRIBE request for dialog
   state to fork and to reach multiple UAs.

   As a result, a forked SUBSCRIBE request for dialog state can install
   multiple subscriptions.  Subscribers to this package MUST be prepared

   to install subscription state for each NOTIFY generated as a result
   of a single SUBSCRIBE.

3.10.  Rate of Notifications

   For reasons of congestion control, it is important that the rate of
   notifications not be excessive.  It is RECOMMENDED that the server
   not generate notifications for a single subscriber faster than once
   every 1 second.

3.11.  State Agents

   Dialog state is ideally maintained in the user agents in which the
   dialog resides.  Therefore, the elements that maintain the dialog are
   the ones best suited to handle subscriptions to it.  However, in some
   cases, a network agent may also know the state of the dialogs held by
   a user.  Such state agents MAY be used with this package.

4.  Dialog Information Format

   Dialog information is an XML document [4] that MUST be well-formed
   and SHOULD be valid.  Dialog information documents MUST be based on
   XML 1.0 and MUST be encoded using UTF-8.  This specification makes
   use of XML namespaces for identifying dialog information documents
   and document fragments.  The namespace URI for elements defined by
   this specification is a URN [5], using the namespace identifier
   'ietf' defined by [6] and extended by [7].  This URN is:

      urn:ietf:params:xml:ns:dialog-info

   A dialog information document begins with the root element tag
   "dialog-info".

4.1.  Structure of Dialog Information

   A dialog information document starts with a dialog-info element.
   This element has three mandatory attributes:

   o  version: This attribute allows the recipient of dialog information
      documents to properly order them.  Versions start at 0, and
      increment by one for each new document sent to a subscriber.
      Versions are scoped within a subscription.  Versions MUST be
      representable using a non-negative 32 bit integer.

   o  state: This attribute indicates whether the document contains the
      full dialog information, or whether it contains only information
      on those dialogs that have changed since the previous document
      (partial).

   o  entity: This attribute contains a URI that identifies the user
      whose dialog information is reported in the remainder of the
      document.  This user is referred to as the "observed user".

   The dialog-info element has a series of zero or more dialog sub-
   elements.  Each of those represents a specific dialog.  An example:

            <?xml version="1.0"?> 
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
                   version="0" state="full"
                   entity="sip:alice@example.com">
      </dialog-info>
EID 158 (Verified) is as follows:

Section: 4.1

Original Text:

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
                   version="0" notify-state="full"
                   entity="sip:alice@example.com">
      </dialog-info>

Corrected Text:

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
                   version="0" state="full"
                   entity="sip:alice@example.com">
      </dialog-info>
Notes:
The proposed version of text is consistent with the rest of the document,
including the schema in section 4.4.
4.1.1. Dialog Element The dialog element reports information about a specific dialog or "half-dialog". It has a single mandatory attribute: id. The id attribute provides a single string that can be used as an identifier for this dialog or "half-dialog". This is a different identifier than the dialog ID defined in RFC 3261 [2], but related to it. For a caller, the id is created when an INVITE request is sent. When a 1xx response with a tag, or a 2xx response is received, the dialog is formally created. The id remains unchanged. However, if an additional 1xx or 2xx is received, resulting in the creation of another dialog (and resulting FSM), that dialog is allocated a new id. For a callee, the id is created when an INVITE outside of an existing dialog is received. When a 2xx or a 1xx with a tag is sent, creating the dialog, the id remains unchanged. The id MUST be unique amongst all current dialogs at a UA. There are a number of optional attributes that provide identification information about the dialog: o call-id: This attribute is a string that represents the call-id component of the dialog identifier. (Note that single and double quotes inside a call-id must be escaped using &quote; for " and &apos; for ' .) o local-tag: This attribute is a string that represents the local-tag component of the dialog identifier. o remote-tag: This attribute is a string that represents the remote-tag component of the dialog identifier. The remote tag attribute won't be present if there is only a "half-dialog", resulting from the generation of an INVITE for which no final responses or provisional responses with tags has been received. o direction: This attribute is either initiator or recipient, and indicates whether the observed user was the initiator of the dialog, or the recipient of the INVITE that created it. <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="0" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" direction="initiator"> ... </dialog> </dialog-info> The sub-elements of the dialog element provide additional information about the dialog. Some of these sub-elements provide more detail about the dialog itself, while the local and remote sub-elements describe characteristics of the participants involved in the dialog. The only mandatory sub-element is the state element. 4.1.2. State Element The "state" element indicates the state of the dialog. Its value is an enumerated type describing one of the states in the FSM above. It has an optional event attribute that can be used to indicate the event that caused any transition into the terminated state, and an optional code attribute that indicates the response code associated with any transition caused by a response to the original INVITE. <state event="rejected" code="486">terminated</state> 4.1.3. Duration Element The "duration" element contains the amount of time, in seconds, since the FSM was created. <duration>145</duration> 4.1.4. Replaces Element The "replaces" element is used to correlate a new dialog with one it replaced as a result of an invitation with a Replaces header field. This element is present in the replacement dialog only (the newer dialog) and contains attributes with the call-id, local-tag, and remote-tag of the replaced dialog. <replaces call-id="hg287s98s89" local-tag="6762h7" remote-tag="09278hsb"/> 4.1.5. Referred-By Element The "referred-by" element is used to correlate a new dialog with a REFER [12] request that triggered it. The element is present in a dialog that was triggered by a REFER request that contained a Referred-By [11] header field and contains the (optional) display name attribute and the Referred-By URI as its value. <referred-by display="Bob">sip:bob@example.com</referred-by> 4.1.6. Local and Remote Elements The "local" and "remote" elements are sub-elements of the dialog element that contain information about the local and remote participants, respectively. They both have a number of optional sub-elements that indicate the identity conveyed by the participant, the target URI, the feature-tags of the target, and the session-description of the participant. 4.1.6.1. Identity Element The "identity" element indicates a local or remote URI, as defined in [2] as appropriate. It has an optional attribute, display, that contains the display name from the appropriate URI. Note that multiple identities (for example a sip: URI and a tel: URI) could be included if they all correspond to the participant. To avoid repeating identity information in each request, the subscriber can assume that the identity URIs are the same as in previous notifications if no identity elements are present in the corresponding local or remote element. If any identity elements are present in the local or remote part of a notification, the new list of identity tags completely supersedes the old list in the corresponding part. <identity display="Anonymous"> sip:anonymous@anonymous.invalid</identity> 4.1.6.2. Target Element The "target" contains the local or remote target URI constructed by the user agent for this dialog, as defined in RFC 3261 [2] in a "uri" attribute. It can contain a list of Contact header parameters in param sub- elements (such as those defined in [10]). The param element contains two required attributes, pname and pval. Boolean parameters are represented by the explicit pval values, "true" and "false" (for example, when a feature parameter is explicitly negated). Parameters that have no value at all are represented by the explicit pval value "true". The param element itself has no contents. To avoid repeating Contact information in each request, the subscriber can assume that the target URI and parameters are the same as in previous notifications if no target element is present in the corresponding local or remote element. If a target element is present in the local or remote part of a notification, the new target tag and list of parameter tags completely supersedes the old target and parameter list in the corresponding part. Note that any quoting (including extra angle-bracket quoting used to quote string values in [10]) or backslash escaping MUST be removed before being placed in a pval attribute. Any remaining single quotes, double quotes, and ampersands MUST be properly XML escaped. <target uri="sip:alice@pc33.example.com"> <param pname="isfocus" pval="true"/> <param pname="class" pval="business"/> <param pname="description" pval="Alice's desk &amp; office"/> <param pname="sip.rendering" pval="no"/> </target> 4.1.6.3. Session Description Element The session-description element contains the session description used by the observed user for its end of the dialog. This element should generally NOT be included in the notifications, unless it was explicitly requested by the subscriber. It has a single attribute, "type", which indicates the MIME media type of the session description. To avoid repeating session description information in each request, the subscriber can assume that the session description is the same as in previous notifications if no session description element is present in the corresponding local or remote element. 4.2. Sample Notification Body <?xml version="1.0" encoding="UTF-8"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:ietf:params:xml:ns:dialog-info" version="1" state="full"> <dialog id="123456"> <state>confirmed</state> <duration>274</duration> <local> <identity display="Alice">sip:alice@example.com</identity> <target uri="sip:alice@pc33.example.com"> <param pname="isfocus" pval="true"/> <param pname="class" pval="personal"/> </target> </local> <remote> <identity display="Bob">sip:bob@example.org</identity> <target uri="sip:bobster@phone21.example.org"/> </remote> </dialog> </dialog-info> 4.3. Constructing Coherent State The dialog information subscriber maintains a table listing the dialogs, with a row for each dialog. Each row is indexed by an ID that is present in the "id" attribute of the "dialog" element. Each row contains the state of that dialog, as conveyed in the document. The table is also associated with a version number. The version number MUST be initialized with the value of the "version" attribute from the "dialog-info" element in the first document received. Each time a new document is received, the value of the local version number is compared to the "version" attribute in the new document. If the value in the new document is one higher than the local version number, the local version number is increased by one and the document is processed. If the value in the document is more than one higher than the local version number, the local version number is set to the value in the new document and the document is processed. If the document did not contain full state, the subscriber SHOULD generate a refresh request (SUBSCRIBE) to trigger a full state notification. If the value in the document is less than the local version, the document is discarded without processing. The processing of the dialog information document depends on whether it contains full or partial state. If it contains full state, indicated by the value of the "state" attribute in the "dialog-info" element, the contents of the table are flushed and then repopulated from the document. A new row in the table is created for each "dialog" element. If the document contains partial state, as indicated by the value of the "state" attribute in the "dialog-info" element, the document is used to update the table. For each "dialog" element in the document, the subscriber checks to see whether a row exists for that dialog. This check compares the ID in the "id" attribute of the "dialog" element with the ID associated with the row. If the dialog does not exist in the table, a row is added and its state is set to the information from that "dialog" element. If the dialog does exist, its state is updated to be the information from that "dialog" element. If a row is updated or created, such that its state is now terminated, that entry MAY be removed from the table at any time. 4.4. Schema The following is the schema for the application/dialog-info+xml type: <?xml version="1.0" encoding="UTF-8"?> <xs:schema targetNamespace="urn:ietf:params:xml:ns:dialog-info" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:tns="urn:ietf:params:xml:ns:dialog-info" elementFormDefault="qualified" attributeFormDefault="unqualified"> <!-- This import brings in the XML language attribute xml:lang--> <xs:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/03/xml.xsd"/> <xs:element name="dialog-info"> <xs:complexType> <xs:sequence> <xs:element ref="tns:dialog" minOccurs="0" maxOccurs="unbounded"/> <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> <xs:attribute name="version" type="xs:nonNegativeInteger" use="required"/> <xs:attribute name="state" use="required"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="full"/> <xs:enumeration value="partial"/> </xs:restriction> </xs:simpleType> </xs:attribute> <xs:attribute name="entity" type="xs:anyURI" use="required"/> </xs:complexType> </xs:element> <xs:element name="dialog"> <xs:complexType> <xs:sequence> <xs:element ref="tns:state" minOccurs="1" maxOccurs="1"/> <xs:element name="duration" type="xs:nonNegativeInteger" minOccurs="0" maxOccurs="1"/> <xs:element name="replaces" minOccurs="0" maxOccurs="1"> <xs:complexType> <xs:attribute name="call-id" type="xs:string" use="required"/> <xs:attribute name="local-tag" type="xs:string" use="required"/> <xs:attribute name="remote-tag" type="xs:string" use="required"/> </xs:complexType> </xs:element> <xs:element name="referred-by" type="tns:nameaddr" minOccurs="0" maxOccurs="1"/> <xs:element name="route-set" minOccurs="0" maxOccurs="1"> <xs:complexType> <xs:sequence> <xs:element name="hop" type="xs:string" minOccurs="1" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="local" type="tns:participant" minOccurs="0" maxOccurs="1"/> <xs:element name="remote" type="tns:participant" minOccurs="0" maxOccurs="1"/> <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> <xs:attribute name="id" type="xs:string" use="required"/> <xs:attribute name="call-id" type="xs:string" use="optional"/> <xs:attribute name="local-tag" type="xs:string" use="optional"/> <xs:attribute name="remote-tag" type="xs:string" use="optional"/> <xs:attribute name="direction" use="optional"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="initiator"/> <xs:enumeration value="recipient"/> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> <xs:complexType name="participant"> <xs:sequence> <xs:element name="identity" type="tns:nameaddr" minOccurs="0" maxOccurs="1"/> <xs:element name="target" minOccurs="0" maxOccurs="1"> <xs:complexType> <xs:sequence> <xs:element name="param" minOccurs="0" maxOccurs="unbounded"> <xs:complexType> <xs:attribute name="pname" type="xs:string" use="required"/> <xs:attribute name="pval" type="xs:string" use="required"/> </xs:complexType> </xs:element> </xs:sequence> <xs:attribute name="uri" type="xs:string" use="required"/> </xs:complexType> </xs:element> <xs:element name="session-description" type="tns:sessd" minOccurs="0" maxOccurs="1"/> <xs:element name="cseq" type="xs:nonNegativeInteger" minOccurs="0" maxOccurs="1"/> <xs:any namespace="##other" processContents="lax" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> <xs:complexType name="nameaddr"> <xs:simpleContent> <xs:extension base="xs:anyURI"> <xs:attribute name="display" type="xs:string"
EID 774 (Verified) is as follows:

Section: 4.4

Original Text:

<xs:attribute name="display-name" type="xs:string"

Corrected Text:

<xs:attribute name="display" type="xs:string"
Notes:
The proposed version of text is consistent with the rest of the document,
especially with all examples and has been implemented by several
manufacturers this way.

from pending
use="optional"/> </xs:extension> </xs:simpleContent> </xs:complexType> <xs:complexType name="sessd"> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute name="type" type="xs:string" use="required"/> </xs:extension> </xs:simpleContent> </xs:complexType> <xs:element name="state"> <xs:complexType> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute name="event" use="optional"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="cancelled"/> <xs:enumeration value="rejected"/> <xs:enumeration value="replaced"/> <xs:enumeration value="local-bye"/> <xs:enumeration value="remote-bye"/> <xs:enumeration value="error"/> <xs:enumeration value="timeout"/> </xs:restriction> </xs:simpleType> </xs:attribute> <xs:attribute name="code" use="optional"> <xs:simpleType> <xs:restriction base="xs:positiveInteger"> <xs:minInclusive value="100"/> <xs:maxInclusive value="699"/> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:extension> </xs:simpleContent> </xs:complexType> </xs:element> </xs:schema> 5. Definition of New Media Feature Parameters This section defines two new media feature parameters that are useful as input to user presence, in conferencing applications, and in applications like the shared-line example described in Section 6.2. These feature parameters are especially useful in combination with the dialog package, as they allow an authorized third party to become aware of these characteristics. 5.1. The "sip.byeless" Parameter The "sip.byeless" media feature parameter is a new boolean parameter, defined in this document, that provides a positive indication that the user agent setting the parameter is unable to terminate sessions on its own (for example, by sending a BYE request). For example, continuous announcement services and certain recording services are unable to determine when it would be desirable to terminate a session, and therefore they do not have the ability to terminate sessions at all. Also, many human call centers are configured so that they never terminate sessions. (This is to prevent call center agents from accidentally disconnecting the caller). (Note that per [10], this parameter name must be preceded by a "+" character when used in a SIP Contact header field.) Contact: <sip:recording-service@host.example.net> ;automaton;+sip.byeless 5.2. The "sip.rendering" Parameter The "sip.rendering" media feature parameter is a new string parameter, defined in this document, that can provide a positive indication whether the user agent setting the parameter is currently rendering any of the media it is receiving in the context of a specific session. It MUST only be used in a Contact header field in a dialog created using the INVITE request. This parameter has three legal values: "yes", "no", and "unknown". The value "yes" indicates positive knowledge that the user agent is rendering at least one of the streams of media that it is receiving. The value "no" indicates positive knowledge that the user agent is rendering none of the media that it is receiving. The value "unknown" indicates that the user agent does not know whether the media associated with the session is being rendered (which may be the case if the user agent is acting as a 3pcc (Third Party Call Control) [19] controller). The "sip.rendering" parameter is useful in applications such as shared appearances, conference status monitoring, or as an input to user presence. Contact: <sip:musak-onhold@host.example.net> ;automaton;+sip.rendering="no" 6. Examples 6.1. Basic Example For example, if a UAC sends an INVITE that looks, in part, like: INVITE sip:bob@example.com SIP/2.0 Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 Max-Forwards: 70 To: Bob <sip:bob@example.com> From: Alice <sip:alice@example.com>;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: <sip:alice@pc33.example.com> Content-Type: application/sdp Content-Length: 142 [SDP not shown] The XML document in a notification from Alice might look like: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="0" state="full" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" direction="initiator"> <state>trying</state> </dialog> </dialog-info> If the following 180 response is received: SIP/2.0 180 Ringing Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 To: Bob <sip:bob@example.com>;tag=456887766 From: Alice <sip:alice@example.com>;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: <sip:bob@host.example.com> The XML document in a notification might look like: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="1" state="full" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="456887766" direction="initiator"> <state>early</state> </dialog> </dialog-info> If it receives a second 180 with a different tag: SIP/2.0 180 Ringing Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bKnashds8 To: Bob <sip:bob@example.com>;tag=hh76a From: Alice <sip:alice@example.com>;tag=1928301774 Call-ID: a84b4c76e66710 CSeq: 314159 INVITE Contact: <sip:jack@host.example.com> This results in the creation of a second dialog: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="full" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="456887766" direction="initiator"> <state>early</state> </dialog> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="hh76a" direction="initiator"> <state>early</state> </dialog> </dialog-info> If a 200 OK response is received on the second dialog, the dialog moves to confirmed: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="3" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="hh76a" direction="initiator"> <state>confirmed</state> </dialog> </dialog-info> 32 seconds later, the other early dialog terminates because no 2xx response has been received for it. This implies that it was successfully cancelled, and therefore the following notification is sent: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="4" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="hh76a" direction="initiator"> <state event="cancelled">terminated</state> </dialog> </dialog-info> 6.2. Emulating a Shared-Line Phone System
EID 788 (Verified) is as follows:

Section: 6.2

Original Text:

          <state reason="cancelled">terminated</state>
 
          <state reason="replaced">terminated</state>
 
          <state reason="replaced">confirmed</state>
 
          <state reason="remote-bye">terminated</state>

Corrected Text:

          <state event="cancelled">terminated</state>
 
          <state event="replaced">terminated</state>
 
          <state event="replaced">confirmed</state>
 
          <state event="remote-bye">terminated</state>
Notes:
The "state" element does not have a "reason" attribute. It is called "event"
by definition in section 4.1.2. and the schema in 4.4.

from pending
The following example shows how a SIP telephone user agent can provide detailed state information and also emulate a shared-line telephone system (the phone "lies" about having a dialog while it is merely offhook). Idle: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="0" state="full" entity="sip:alice@example.com"> </dialog-info> Seized: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="1" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8"> <state>trying</state> </dialog> </dialog-info> Dialing: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" direction="initiator"> <state>trying</state> <local> <identity display="Alice Smith"> sip:alice@example.com </identity> <target uri="sip:alice@pc33.example.com"/> </local> <remote> <identity>sip:bob@example.net</identity> </remote> </dialog> </dialog-info> Ringing: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="3" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="07346y131" direction="initiator"> <state code="180">early</state> <remote> <target uri="sip:bobster@host2.example.net"/> </remote> </dialog> </dialog-info> Answered (by voicemail): <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="4" state="partial" entity="sip:alice@example.com"> <dialog id="as7d900as8" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="07346y131" direction="initiator"> <state reason="cancelled">terminated</state> </dialog> <dialog id="zxcvbnm3" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="8736347" direction="initiator"> <state code="200">confirmed</state> <remote> <target uri="sip:bob-is-not-here@vm.example.net"> <param pname="actor" pval="msg-taker"/> <param pname="automaton" pval="true"/> <param pname="+sip.byeless" pval="true"/> </target> </remote> </dialog> </dialog-info> Alice would rather talk to Bob's assistant (Cathy Jones) than to Bob's voicemail. She indicates this preference by pressing a key (perhaps "0" in North America or "9" in Europe). Bob's voicemail system then acts on this keypress by transferring [20] Alice's call to Cathy's AOR. <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="5" state="partial" entity="sip:alice@example.com"> <dialog id="zxcvbnm3" call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="8736347" direction="initiator"> <state reason="replaced">terminated</state> </dialog> <dialog id="sfhjsjk12" call-id="o34oii1" local-tag="8903j4" remote-tag="78cjkus" direction="recipient">
EID 771 (Verified) is as follows:

Section: 6.2

Original Text:

direction="receiver">

Corrected Text:

direction="recipient">
Notes:
Occurs on pages 28, 29 (2 times), and 30.

The proposed version of text is consistent with the rest of the document,
including the schema in section 4.4.

from pending
<state reason="replaced">confirmed</state> <replaces call-id="a84b4c76e66710" local-tag="1928301774" remote-tag="8736347"/> <referred-by> sip:bob-is-not-here@vm.example.net </referred-by> <local> <target uri="sip:alice@pc33.example.com"> <param pname="+sip.rendering" pval="yes"/> </target> </local>
EID 781 (Verified) is as follows:

Section: 6.2

Original Text:

          <local>
            <target uri="sip:alice@pc33.example.com"/>
              <param pname="+sip.rendering" pval="yes"/>
          </local>

Corrected Text:

           <local>
            <target uri="sip:alice@pc33.example.com">
              <param pname="+sip.rendering" pval="yes"/>
            </target>
          </local>
Notes:
The <param> element must be enclosed by the <target> element.

from pending
<remote> <identity display="Cathy Jones"> sip:cjones@example.net </identity> <target uri="sip:line3@host3.example.net"> <param pname="actor" pval="attendant"/> <param pname="automaton" pval="false"/> </target> </remote> </dialog> </dialog-info> Alice and Cathy talk, Cathy adds Alice to a local conference: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="6" state="partial" entity="sip:alice@example.com"> <dialog id="sfhjsjk12" call-id="o34oii1" local-tag="8903j4" remote-tag="78cjkus" direction="receiver"> <state>confirmed</state> <remote> <target uri="sip:confid-34579@host3.example.net"> <param pname="isfocus" pval="true"/> </target> </remote> </dialog> </dialog-info> Alice puts Cathy on hold: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="7" state="partial" entity="sip:alice@example.com"> <dialog id="sfhjsjk12" call-id="o34oii1" local-tag="8903j4" remote-tag="78cjkus" direction="receiver"> <state>confirmed</state> <local> <target uri="sip:alice@pc33.example.com"/> <param pname="+sip.rendering" pval="no"/> </target> </local> </dialog> </dialog-info> Cathy hangs up: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="8" state="partial" entity="sip:alice@example.com"> <dialog id="sfhjsjk12" call-id="o34oii1" local-tag="8903j4" remote-tag="78cjkus" direction="receiver"> <state reason="remote-bye">terminated</state> </dialog> <dialog id="08hjh1345"> <state>trying</state> </dialog> </dialog-info> Alice hangs up: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="9" state="full" entity="sip:alice@example.com"> </dialog-info> 6.3. Minimal Dialog Information with Privacy The following example shows the same user agent providing minimal information to maintain privacy for services like automatic callback. Onhook: <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="0" state="full" entity="sip:alice@example.com"> </dialog-info> Offhook: (implementation/policy choice for Alice to transition to this "state" when "seized", when Trying, when Proceeding, or when Confirmed.) <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="1" state="full" entity="sip:alice@example.com"> <dialog id="1"> <state>confirmed</state> </dialog> </dialog-info> Onhook: (implementation/policy choice for Alice to transition to this "state" when terminated, or when no longer "seized") <?xml version="1.0"?> <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info" version="2" state="full" entity="sip:alice@example.com"> </dialog-info> 7. Security Considerations Subscriptions to dialog state can reveal sensitive information. For this reason, Section 3.6 discusses authentication and authorization of subscriptions, and provides guidelines on sensible authorization policies. All implementations of this package MUST support the digest authentication mechanism. Since the data in notifications is sensitive as well, end-to-end SIP encryption mechanisms using S/MIME MAY be used to protect it. User agents that implement the dialog package SHOULD also implement SIP over TLS [15] and the sips: scheme. 8. IANA Considerations This document registers a new MIME type, application/dialog-info+xml; a new XML namespace; and two new media feature parameters in the SIP tree. 8.1. MIME Registration for application/dialog-info+xml Type MIME media type name: application MIME subtype name: dialog-info+xml Mandatory parameters: none Optional parameters: Same as charset parameter application/xml as specified in RFC 3023 [8]. Encoding considerations: Same as encoding considerations of application/xml as specified in RFC 3023 [8]. Security considerations: See Section 10 of RFC 3023 [8] and Section 7 of this specification. Interoperability considerations: none. Published specification: This document. Applications that use this media type: This document type has been used to support SIP applications such as call return and auto-conference. Additional Information: Magic Number: None File Extension: .xml Macintosh file type code: "TEXT" Personal and email address for further information: Jonathan Rosenberg, <jdrosen@jdrosen.net> Intended usage: COMMON Author/Change controller: The IETF. 8.2. URN Sub-Namespace Registration for urn:ietf:params:xml:ns:dialog-info This section registers a new XML namespace, per the guidelines in [7]. URI: The URI for this namespace is urn:ietf:params:xml:ns:dialog-info. Registrant Contact: The IESG, <iesg@ietf.org> XML: BEGIN <?xml version="1.0"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN" "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="content-type" content="text/html;charset=iso-8859-1"/> <title>Dialog Information Namespace</title> </head> <body> <h1>Namespace for Dialog Information</h1> <h2>urn:ietf:params:xml:ns:dialog-info</h2> <p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc4235.txt"> RFC4235</a>.</p> </body> </html> END 8.3. Schema Registration This specification registers a schema, per the guidelines in [7]. URI: urn:ietf:params:xml:schema:dialog-info Registrant Contact: The IESG, <iesg@ietf.org> XML: The XML can be found as the sole content of Section 4.4. 8.4. Media Feature Parameter Registration This section registers two new media feature tags, per the procedures defined in RFC 2506 [14]. The tags are placed into the sip tree, which is defined in [10]. 8.4.1. Media Feature Tag sip.byeless Media feature tag name sip.byeless ASN.1 Identifier 19 Summary of the media feature indicated by this tag: This feature tag is a boolean flag. When set it indicates that the device is incapable of terminating a session autonomously. Values appropriate for use with this feature tag: Boolean. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: This feature tag is most useful in a communications application for describing the capabilities of an application, such as an announcement service, recording service, conference, or call center. Examples of typical use: Call centers and media services. Related standards or documents: RFC 4235 Security Considerations: This media feature tag can be used in ways that affect application behaviors or may reveal private information. For example, a conferencing or other application may decide to terminate a call prematurely if this media feature tag is set. Therefore, if an attacker can modify the values of this tag, they may be able to affect the behavior of applications. As a result of this, applications that utilize this media feature tag SHOULD provide a means for ensuring its integrity. Similarly, this feature tag should only be trusted as valid when it comes from the user or user agent described by the tag. As a result, protocols for conveying this feature tag SHOULD provide a mechanism for guaranteeing authenticity. 8.4.2. Media Feature Tag sip.rendering Media feature tag name: sip.rendering ASN.1 Identifier: 20 Summary of the media feature indicated by this tag: This feature tag contains one of three string values indicating if the device is rendering any media from the current session ("yes"), none of the media from the current session ("no"), or if this status is not known to the device ("unknown"). Values appropriate for use with this feature tag: String. The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms: This feature tag is most useful in a communications application, for describing the state of a device (such as a phone or PDA) during a multimedia session. Examples of typical use: Conferencing, telephone shared-line emulation, and presence applications. Related standards or documents: RFC 4235 Security Considerations: This media feature tag can be used in ways that affect application behaviors or may reveal private information. For example, a conferencing or other application may decide to terminate a call prematurely if this media feature tag is set to "no". Therefore, if an attacker can modify the values of this tag, they may be able to affect the behavior of applications. As a result of this, applications that utilize this media feature tag SHOULD provide a means for ensuring its integrity. Similarly, this feature tag should only be trusted as valid when it comes from the user or user agent described by the tag. As a result, protocols for conveying this feature tag SHOULD provide a mechanism for guaranteeing authenticity. 9. Acknowledgements The authors would like to thank Sean Olson for his comments. 10. References 10.1. Normative References [1] Roach, A.B., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [3] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE Method", RFC 3311, October 2002. [4] Paoli, J., Sperberg-McQueen, C., Bray, T., and E. Maler, "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C FirstEdition REC-xml-20001006, October 2000. [5] Moats, R., "URN Syntax", RFC 2141, May 1997. [6] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, August 1999. [7] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [8] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001. [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [10] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [11] Sparks, R., "The Session Initiation Protocol (SIP) Referred-By Mechanism", RFC 3892, September 2004. [12] Sparks, R., "The Session Initiation Protocol (SIP) Refer Method", RFC 3515, April 2003. [13] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation Protocol (SIP) "Replaces" Header", RFC 3891, September 2004. [14] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag Registration Procedure", BCP 31, RFC 2506, March 1999. [15] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. 10.2. Informative References [16] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [17] Rosenberg, J., "A Watcher Information Event Template-Package for the Session Initiation Protocol (SIP)", RFC 3857, August 2004. [18] Mahy, R., "A Message Summary and Message Waiting Indication Event Package for the Session Initiation Protocol (SIP)", RFC 3842, August 2004. [19] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [20] Sparks, R., "Session Initiation Protocol Call Control - Transfer", Work in Progress, July 2005. Authors' Addresses Jonathan Rosenberg Cisco Systems 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 EMail: jdrosen@cisco.com URI: http://www.jdrosen.net Henning Schulzrinne Columbia University M/S 0401 1214 Amsterdam Ave. New York, NY 10027 US EMail: schulzrinne@cs.columbia.edu URI: http://www.cs.columbia.edu/~hgs Rohan Mahy (editor) SIP Edge LLC EMail: rohan@ekabal.com Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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