ftp.cc.uoc.gr
rfc3262
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 315, EID 4600, EID 4601, EID 4602, EID 4603, EID 4604
Network Working Group                                       J. Rosenberg
Request for Comments: 3262                                   dynamicsoft
Category: Standards Track                                 H. Schulzrinne
                                                             Columbia U.
                                                               June 2002


                 Reliability of Provisional Responses
               in 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 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document specifies an extension to the Session Initiation
   Protocol (SIP) providing reliable provisional response messages.
   This extension uses the option tag 100rel and defines the Provisional
   Response ACKnowledgement (PRACK) method.

Table of Contents

   1     Introduction ........................................    2
   2     Terminology .........................................    3
   3     UAS Behavior ........................................    3
   4     UAC Behavior ........................................    6
   5     The Offer/Answer Model and PRACK ....................    9
   6     Definition of the PRACK Method ......................   10
   7     Header Field Definitions ............................   10
   7.1   RSeq ................................................   10
   7.2   RAck ................................................   11
   8     IANA Considerations .................................   11
   8.1   IANA Registration of the 100rel Option Tag ..........   11
   8.2   IANA Registration of RSeq and RAck Headers ..........   12
   9     Security Considerations .............................   12
   10    Collected BNF .......................................   12
   11    Acknowledgements ....................................   12
   12    Normative References ................................   13
   13    Informative References ..............................   13

   14    Authors' Addresses ..................................   13
   15.   Full Copyright Statement.............................   14

1 Introduction

   The Session Initiation Protocol (SIP) (RFC 3261 [1]) is a request-
   response protocol for initiating and managing communications
   sessions.  SIP defines two types of responses, provisional and final.
   Final responses convey the result of the request processing, and are
   sent reliably.  Provisional responses provide information on the
   progress of the request processing, but are not sent reliably in RFC
   3261.

   It was later observed that reliability was important in several
   cases, including interoperability scenarios with the PSTN.
   Therefore, an optional capability was needed to support reliable
   transmission of provisional responses.  That capability is provided
   in this specification.

   The reliability mechanism works by mirroring the current reliability
   mechanisms for 2xx final responses to INVITE.  Those requests are
   transmitted periodically by the Transaction User (TU) until a
   separate transaction, ACK, is received that indicates reception of
   the 2xx by the UAC.  The reliability for the 2xx responses to INVITE
   and ACK messages are end-to-end.  In order to achieve reliability for
   provisional responses, we do nearly the same thing.  Reliable
   provisional responses are retransmitted by the TU with an exponential
   backoff.  Those retransmissions cease when a PRACK message is
   received.  The PRACK request plays the same role as ACK, but for
   provisional responses.  There is an important difference, however.
   PRACK is a normal SIP message, like BYE.  As such, its own
   reliability is ensured hop-by-hop through each stateful proxy.  Also
   like BYE, but unlike ACK, PRACK has its own response.  If this were
   not the case, the PRACK message could not traverse proxy servers
   compliant to RFC 2543 [4].

   Each provisional response is given a sequence number, carried in the
   RSeq header field in the response.  The PRACK messages contain an
   RAck header field, which indicates the sequence number of the
   provisional response that is being acknowledged.  The acknowledgments
   are not cumulative, and the specifications recommend a single
   outstanding provisional response at a time, for purposes of
   congestion control.

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 [2] and
   indicate requirement levels for compliant SIP implementations.

3 UAS Behavior

   A UAS MAY send any non-100 provisional response to INVITE reliably,
   so long as the initial INVITE request (the request whose provisional
   response is being sent reliably) contained a Supported header field
   with the option tag 100rel.  While this specification does not allow
   reliable provisional responses for any method but INVITE, extensions
   that define new methods that can establish dialogs may make use of
   the mechanism.

   The UAS MUST send any non-100 provisional response reliably if the
   initial request contained a Require header field with the option tag
   100rel.  If the UAS is unwilling to do so, it MUST reject the initial
   request with a 420 (Bad Extension) and include an Unsupported header
   field containing the option tag 100rel.

   A UAS MUST NOT attempt to send a 100 (Trying) response reliably.
   Only provisional responses numbered 101 to 199 may be sent reliably.
   If the request did not include either a Supported or Require header
   field indicating this feature, the UAS MUST NOT send the provisional
   response reliably.

      100 (Trying) responses are hop-by-hop only.  For this reason, the
      reliability mechanisms described here, which are end-to-end,
      cannot be used.

   An element that can act as a proxy can also send reliable provisional
   responses.  In this case, it acts as a UAS for purposes of that
   transaction.  However, it MUST NOT attempt to do so for any request
   that contains a tag in the To field.  That is, a proxy cannot
   generate reliable provisional responses to requests sent within the
   context of a dialog.  Of course, unlike a UAS, when the proxy element
   receives a PRACK that does not match any outstanding reliable
   provisional response, the PRACK MUST be proxied.

   There are several reasons why a UAS might want to send a reliable
   provisional response.  One reason is if the INVITE transaction will
   take some time to generate a final response.  As discussed in Section
   13.3.1.1 of RFC 3261, the UAS will need to send periodic provisional
   responses to request an "extension" of the transaction at proxies.
   The requirement is that a proxy receive them every three minutes, but

   the UAS needs to send them more frequently (once a minute is
   recommended) because of the possibility of packet loss.  As a more
   efficient alternative, the UAS can send the response reliably, in
   which case the UAS SHOULD send provisional responses once every two
   and a half minutes.  Use of reliable provisional responses for
   extending transactions is RECOMMENDED.

   The rest of this discussion assumes that the initial request
   contained a Supported or Require header field listing 100rel, and
   that there is a provisional response to be sent reliably.

   The provisional response to be sent reliably is constructed by the 
UAS core according to the procedures of Section 8.2.6 of RFC 3261.
In addition, it MUST contain a Require header field containing the
option tag 100rel, and MUST include an RSeq header field.  The
value of the header field for the first reliable provisional 
response in a transaction MUST be between 1 and 2**31 - 1.  It is
RECOMMENDED that it be chosen uniformly in this range. The RSeq 
numbering space is within a single transaction. This means that
the RSeq value of a provisional response within a fork of a request
is independent of the RSeq value of a provisional response within 
any other fork of that request, or for the responses for any other
request. It thus may be higher, lower, or the same as any other such
RSeq value.
EID 4600 (Verified) is as follows:

Section: 3

Original Text:

The provisional response to be sent reliably is constructed by the
UAS core according to the procedures of Section 8.2.6 of RFC 3261.
In addition, it MUST contain a Require header field containing the
option tag 100rel, and MUST include an RSeq header field.  The value
of the header field for the first reliable provisional response in a
transaction MUST be between 1 and 2**31 - 1.  It is RECOMMENDED that
it be chosen uniformly in this range.  The RSeq numbering space is
within a single transaction.  This means that provisional responses
for different requests MAY use the same values for the RSeq number.

Corrected Text:

The provisional response to be sent reliably is constructed by the
UAS core according to the procedures of Section 8.2.6 of RFC 3261.
In addition, it MUST contain a Require header field containing the
option tag 100rel, and MUST include an RSeq header field.  The
value of the header field for the first reliable provisional 
response in a transaction MUST be between 1 and 2**31 - 1.  It is
RECOMMENDED that it be chosen uniformly in this range. The RSeq 
numbering space is within a single transaction. This means that
the RSeq value of a provisional response within a fork of a request
is independent of the RSeq value of a provisional response within 
any other fork of that request, or for the responses for any other
request. It thus may be higher, lower, or the same as any other such
RSeq value.
Notes:
None
The reliable provisional response MAY contain a body. The usage of session descriptions is described in Section 5. The reliable provisional response is passed to the transaction layer periodically with an interval that starts at T1 seconds and doubles for each retransmission (T1 is defined in Section 17 of RFC 3261). Once passed to the server transaction, it is added to an internal list of unacknowledged reliable provisional responses. The transaction layer will forward each retransmission passed from the UAS core. This differs from retransmissions of 2xx responses, whose intervals cap at T2 seconds. This is because retransmissions of ACK are triggered on receipt of a 2xx, but retransmissions of PRACK take place independently of reception of 1xx. Retransmissions of the reliable provisional response cease when a matching PRACK is received by the UA core. PRACK is like any other request within a dialog, and the UAS core processes it according to the procedures of Sections 8.2 and 12.2.2 of RFC 3261. A matching PRACK is defined as one within the same dialog as the response, and whose method, CSeq-num, and response-num in the RAck header field match, respectively, the method from the CSeq, the sequence number from the CSeq, and the sequence number from the RSeq of the reliable provisional response. If a PRACK request is received by the UA core that does not match any unacknowledged reliable provisional response, the UAS MUST respond to the PRACK with a 481 response. If the PRACK does match an unacknowledged reliable provisional response, it MUST be responded to with a 2xx response. The UAS can be certain at this point that the provisional response has been received in order. It SHOULD cease retransmissions of the reliable provisional response, and MUST remove it from the list of unacknowledged provisional responses. If a reliable provisional response is retransmitted for 64*T1 seconds without reception of a corresponding PRACK, the UAS SHOULD reject the original request with a 5xx response. If the PRACK contained a session description, it is processed as described in Section 5 of this document. If the PRACK instead contained any other type of body, the body is treated in the same way that body in an ACK would be treated. After the first reliable provisional response for a request has been acknowledged, the UAS MAY send additional reliable provisional responses. The UAS MUST NOT send a second reliable provisional response until the first is acknowledged. After the first, it is RECOMMENDED that the UAS not send an additional reliable provisional response until the previous is acknowledged. The first reliable provisional response receives special treatment because it conveys the initial sequence number. If additional reliable provisional responses were sent before the first was acknowledged, the UAS could not be certain these were received in order. The value of the RSeq in each subsequent reliable provisional response for the same request MUST be greater by exactly one. RSeq numbers MUST NOT wrap around. Because the initial one is chosen to be less than 2**31 - 1, but the maximum is 2**32 - 1, there can be up to 2**31 reliable provisional responses per request, which is more than sufficient. The UAS MAY send a final response to the initial request before having received PRACKs for all unacknowledged reliable provisional responses, unless the final response is 2xx and any of the unacknowledged reliable provisional responses contained a session description. In that case, it MUST NOT send a final response until those provisional responses are acknowledged. If the UAS does send a final response when reliable responses are still unacknowledged, it SHOULD NOT continue to retransmit the unacknowledged reliable provisional responses, but it MUST be prepared to process PRACK requests for those outstanding responses. A UAS MUST NOT send new reliable provisional responses (as opposed to retransmissions of unacknowledged ones) after sending a final response to a request. 4 UAC Behavior When the UAC creates a new request, it can insist on reliable delivery of provisional responses for that request. To do that, it inserts a Require header field with the option tag 100rel into the request. A Require header with the value 100rel MUST NOT be present in any requests excepting INVITE, although extensions to SIP may allow its usage with other request methods. Header field where PRACK ___________________________________ Accept R o Accept 2xx - Accept 415 c Accept-Encoding R o Accept-Encoding 2xx - Accept-Encoding 415 c Accept-Language R o Accept-Language 2xx - Accept-Language 415 c Alert-Info R - Alert-Info 180 - Allow R o Allow 2xx o Allow r o Allow 405 m Authentication-Info 2xx o Authorization R o Call-ID c m Call-Info - Contact R - Contact 1xx - Contact 2xx - Contact 3xx o Contact 485 o Content-Disposition o Content-Encoding o Content-Language o Content-Length t Content-Type * CSeq c m Date o Error-Info 300-699 o Expires - From c m In-Reply-To R - Max-Forwards R m Min-Expires 423 - MIME-Version o Organization - Table 1: Summary of header fields, A--O Header field where PRACK __________________________________________ Priority R - Proxy-Authenticate 407 m Proxy-Authenticate 401 o Proxy-Authorization R o Proxy-Require R o Record-Route R o Record-Route 2xx,18x o Reply-To - Require c Retry-After 404,413,480,486 o 500,503 o 600,603 o Route R c Server r o Subject R - Supported R o Supported 2xx o Timestamp o To c m Unsupported 420 m User-Agent o Via c m Warning r o WWW-Authenticate 401 m Table 2: Summary of header fields, P--Z If the UAC does not wish to insist on usage of reliable provisional responses, but merely indicate that it supports them if the UAS needs to send one, a Supported header MUST be included in the request with the option tag 100rel. The UAC SHOULD include this in all INVITE requests. If a provisional response is received for an initial request, and that response contains a Require header field containing the option tag 100rel, the response was sent by the UAS reliably. If the response is a 100 (Trying) (as opposed to 101 to 199), this option tag MUST be ignored, and the procedures below MUST NOT be used.
EID 4601 (Verified) is as follows:

Section: 4

Original Text:

If a provisional response is received for an initial request, and
that response contains a Require header field containing the option
tag 100rel, the response is to be sent reliably.  If the response is
a 100 (Trying) (as opposed to 101 to 199), this option tag MUST be
ignored, and the procedures below MUST NOT be used.

Corrected Text:

If a provisional response is received for an initial request, and
that response contains a Require header field containing the option
tag 100rel, the response was sent by the UAS reliably.  If the
response is a 100 (Trying) (as opposed to 101 to 199), this option
tag MUST be ignored, and the procedures below MUST NOT be used.
Notes:
None
The provisional response MUST establish a dialog if one is not yet created. Assuming the response was transmitted reliably by the UAS, the UAC MUST create a new request with method PRACK. This request is sent within the dialog associated with the provisional response (indeed, the provisional response may have created the dialog). PRACK requests MAY contain bodies, which are interpreted according to their type and disposition.
EID 4602 (Verified) is as follows:

Section: 4

Original Text:

Assuming the response is to be transmitted reliably, the UAC MUST
create a new request with method PRACK.  This request is sent within
the dialog associated with the provisional response (indeed, the
provisional response may have created the dialog).  PRACK requests
MAY contain bodies, which are interpreted according to their type and
disposition.

Corrected Text:

Assuming the response was transmitted reliably by the UAS, the UAC
MUST create a new request with method PRACK.  This request is sent
within the dialog associated with the provisional response (indeed,
the provisional response may have created the dialog). PRACK 
requests MAY contain bodies, which are interpreted according to
their type and disposition.
Notes:
None
Note that the PRACK is like any other non-INVITE request within a dialog. In particular, a UAC SHOULD NOT retransmit the PRACK request when it receives a retransmission of the provisional response being acknowledged, although doing so does not create a protocol error. Once a reliable provisional response is received, retransmissions of that response MUST be discarded. A response is a retransmission when its dialog ID, CSeq, and RSeq match the original response. The UAC MUST maintain, independently for each dialog ID, a sequence number that indicates the most recently received in-order reliable provisional response for the initial request. This sequence number MUST be maintained until a final response is received for the initial request. Its value MUST, for each dialog (or early dialog), be initialized to the RSeq header field in the first reliable provisional response associated with the dialog received for the initial request.
EID 4603 (Verified) is as follows:

Section: 4

Original Text:

Once a reliable provisional response is received, retransmissions of
that response MUST be discarded.  A response is a retransmission when
its dialog ID, CSeq, and RSeq match the original response.  The UAC
MUST maintain a sequence number that indicates the most recently
received in-order reliable provisional response for the initial
request.  This sequence number MUST be maintained until a final
response is received for the initial request.  Its value MUST be
initialized to the RSeq header field in the first reliable
provisional response received for the initial request.

Corrected Text:

Once a reliable provisional response is received, retransmissions of
that response MUST be discarded.  A response is a retransmission 
when its dialog ID, CSeq, and RSeq match the original response. The
UAC MUST maintain, independently for each dialog ID, a sequence
number that indicates the most recently received in-order reliable
provisional response for the initial request.  This sequence number
MUST be maintained until a final response is received for the
initial request. Its value MUST, for each dialog (or early dialog),
be initialized to the RSeq header field in the first reliable
provisional response associated with the dialog received for the
initial request.
Notes:
Verifier edit: I removed two commas around "associated with the dialog" from the last sentence of the corrected text.
Subsequent reliable provisional responses for the same initial request are guaranteed to have been generated by the UAS in the order of their RSeq values and must be acknowledged in that order. As a result, if the UAC receives another reliable provisional response to the same request, and its RSeq value is one higher than the value of the previously received RSeq value in the dialog (or early dialog), then the new RSeq value is saved and the response is handled as described above. If the RSeq value is not one higher than the value of the sequence number, that response MUST NOT be acknowledged with a PRACK, and MUST NOT be processed further by the UAC. An implementation MAY discard the response, or MAY cache the response to be processed (and acknowledged) after receiving the missing responses.
EID 4604 (Verified) is as follows:

Section: 4

Original Text:

Handling of subsequent reliable provisional responses for the same
initial request follows the same rules as above, with the following
difference: reliable provisional responses are guaranteed to be in
order.  As a result, if the UAC receives another reliable provisional
response to the same request, and its RSeq value is not one higher
than the value of the sequence number, that response MUST NOT be
acknowledged with a PRACK, and MUST NOT be processed further by the
UAC.  An implementation MAY discard the response, or MAY cache the
response in the hopes of receiving the missing responses.

Corrected Text:

Subsequent reliable provisional responses for the same initial
request are guaranteed  to have been generated by the UAS in the
order of their RSeq values and must be acknowledged in that order.
As a result, if the UAC receives another reliable provisional
response to the same request, and its RSeq value is one higher than
the value of the previously received RSeq value in the dialog (or 
early dialog), then the new RSeq value is saved and the response is
handled as described above. If the RSeq value is not one higher than
the value of the sequence number, that response MUST NOT be
acknowledged with a PRACK, and MUST NOT be processed further by the
UAC. An implementation MAY discard the response, or MAY cache the
response to be processed (and acknowledged) after receiving the
missing responses.
Notes:
None
The UAC MAY acknowledge reliable provisional responses received after the final response or MAY discard them. 5 The Offer/Answer Model and PRACK RFC 3261 describes guidelines for the sets of messages in which offers and answers [3] can appear. Based on those guidelines, this extension provides additional opportunities for offer/answer exchanges. If the INVITE contained an offer, the UAS MAY generate an answer in a reliable provisional response (assuming these are supported by the UAC). That results in the establishment of the session before completion of the call. Similarly, if a reliable provisional response is the first reliable message sent back to the UAC, and the INVITE did not contain an offer, one MUST appear in that reliable provisional response. If the UAC receives a reliable provisional response with an offer (this would occur if the UAC sent an INVITE without an offer, in which case the first reliable provisional response will contain the offer), it MUST generate an answer in the PRACK. If the UAC receives a reliable provisional response with an answer, it MAY generate an additional offer in the PRACK. If the UAS receives a PRACK with an offer, it MUST place the answer in the 2xx to the PRACK. Once an answer has been sent or received, the UA SHOULD establish the session based on the parameters of the offer and answer, even if the original INVITE itself has not been responded to. If the UAS had placed a session description in any reliable provisional response that is unacknowledged when the INVITE is accepted, the UAS MUST delay sending the 2xx until the provisional response is acknowledged. Otherwise, the reliability of the 1xx cannot be guaranteed, and reliability is needed for proper operation of the offer/answer exchange. All user agents that support this extension MUST support all offer/answer exchanges that are possible based on the rules in Section 13.2 of RFC 3261, based on the existence of INVITE and PRACK as requests, and 2xx and reliable 1xx as non-failure reliable responses. 6 Definition of the PRACK Method This specification defines a new SIP method, PRACK. The semantics of this method are described above. Tables 1 and 2 extend Tables 2 and 3 from RFC 3261 for this new method. 7 Header Field Definitions This specification defines two new header fields, RAck and RSeq. Table 3 extends Tables 2 and 3 from RFC 3261 for these headers. 7.1 RSeq The RSeq header is used in provisional responses in order to transmit them reliably. It contains a single numeric value from 1 to 2**32 - 1. For details on its usage, see Section 3. Example: RSeq: 988789 Header field where proxy ACK BYE CAN INV OPT REG PRA ______________________________________________________ RAck R - - - - - - m RSeq 1xx - - - o - - - Table 3: RAck and RSeq Header Fields 7.2 RAck The RAck header is sent in a PRACK request to support reliability of provisional responses. It contains two numbers and a method tag. The first number is the value from the RSeq header in the provisional response that is being acknowledged. The next number, and the method, are copied from the CSeq in the response that is being acknowledged. The method name in the RAck header is case sensitive. Example: RAck: 776656 1 INVITE 8 IANA Considerations This document registers a new option tag and two new headers, based on the IANA registration process of RFC 3261. 8.1 IANA Registration of the 100rel Option Tag This specification registers a single option tag, 100rel. The required information for this registration, as specified in RFC 3261, is: Name: 100rel Description: This option tag is for reliability of provisional responses. When present in a Supported header, it indicates that the UA can send or receive reliable provisional responses. When present in a Require header in a request, it indicates that the UAS MUST send all provisional responses reliably. When present in a Require header in a reliable provisional response, it indicates that the response is to be sent reliably. 8.2 IANA Registration of RSeq and RAck Headers The following is the registration for the RSeq header: RFC Number: RFC3262 Header Name: RSeq Compact Form: none The following is the registration for the RAck header: RFC Number: RFC3262 Header Name: RAck Compact Form: none 9 Security Considerations The PRACK request can be injected by attackers to force retransmissions of reliable provisional responses to cease. As these responses can convey important information, PRACK messages SHOULD be authenticated as any other request. Authentication procedures are specified in RFC 3261. 10 Collected BNF The BNF for the RAck and RSeq headers and the PRACK method are defined here. PRACKm = %x50.52.41.43.4B ; PRACK in caps Method = INVITEm / ACKm / OPTIONSm / BYEm / CANCELm / REGISTERm / PRACKm / extension-method RAck = "RAck" HCOLON response-num LWS CSeq-num LWS Method response-num = 1*DIGIT CSeq-num = 1*DIGIT RSeq = "RSeq" HCOLON response-num 11 Acknowledgements The authors would like to thank Jo Hornsby, Jonathan Lennox, Rohan Mahy, Allison Mankin, Adam Roach, and Tim Schroeder for the comments on this document. 12 Normative References [1] 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. [2] Bradner, S., "Key Words for Use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with SDP", RFC 3264, June 2002. 13 Informative References [4] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg, "SIP: Session Initiation Protocol", RFC 2543, March 1999. 14 Authors' Addresses Jonathan Rosenberg dynamicsoft 72 Eagle Rock Avenue First Floor East Hanover, NJ 07936 EMail: jdrosen@dynamicsoft.com Henning Schulzrinne Columbia University M/S 0401 1214 Amsterdam Ave. New York, NY 10027-7003 EMail: schulzrinne@cs.columbia.edu 15. Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.
EID 315 (Verified) is as follows:

Section: None

Original Text:

None

Corrected Text:

None
Notes:
This document obsoletes RFC 2543.