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Versions: (draft-holmberg-avtcore-5761-update) 00 01 02 03 04 05 06 RFC 8035

Network Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 5761 (if approved)                             October 13, 2016
Intended status: Standards Track
Expires: April 16, 2017


         RTP/RTCP Multiplexing SDP Offer/Answer Clarifications
                 draft-ietf-avtcore-5761-update-06.txt

Abstract

   This document updates RFC 5761 by clarifying the SDP offer/answer
   negotiation of RTP and RTCP multiplexing.  It makes it clear that an
   answerer can only include an "a=rtcp-mux" attribute in an SDP answer
   if the associated SDP offer contained the attribute.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 16, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Update to RFC 5761  . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Update to section 5.1.1 . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   RFC 5761 [RFC5761] specifies how to multiplex RTP data packets and
   RTP Control Protocol (RTCP) packets on a single UDP port, and how to
   negotiate usage of such multiplexing using the SDP offer/answer
   mechanism [RFC3264], using an "a=rtcp-mux" attribute.  However, the
   text is unclear on whether an answerer is allowed to include the
   attribute in an answer even if the associated offer did not contain
   an attribute.

   This document updates RFC 5761 [RFC5761] by clarifying that an
   answerer can only include an "a=rtcp-mux" attribute in an answer if
   the associated offer contained the attribute.  It also clarifies that
   the negotiation of RTP and RTCP multiplexing is for usage in both
   directions.

2.  Conventions

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





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3.  Update to RFC 5761

   This section updates section 5.1.1 of RFC 5761 by clarifying that an
   answerer can only include an "a=rtcp-mux" attribute in an answer if
   the associated offer contained the attribute, and by clarifying that
   the negotiation of RTP and RTCP multiplexing is for usage in both
   directions.

3.1.  Update to section 5.1.1

   In this section references to Sections 4 and 8 are to sections in
   [RFC5761].


 OLD TEXT:

  When the Session Description Protocol (SDP) [8] is used to negotiate
  RTP sessions following the offer/answer model [9], the "a=rtcp-mux"
  attribute (see Section 8) indicates the desire to multiplex RTP and
  RTCP onto a single port.  The initial SDP offer MUST include this
  attribute at the media level to request multiplexing of RTP and RTCP
  on a single port.  For example:

      v=0
      o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e
      s=-
      c=IN IP6 2001:DB8::211:24ff:fea3:7a2e
      t=1153134164 1153137764
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      a=rtcp-mux

  This offer denotes a unicast voice-over-IP session using the RTP/AVP
  profile with iLBC coding.  The answerer is requested to send both RTP
  and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e.

  If the answerer wishes to multiplex RTP and RTCP onto a single port,
  it MUST include a media-level "a=rtcp-mux" attribute in the answer.
  The RTP payload types used in the answer MUST conform to the rules in
  Section 4.

  If the answer does not contain an "a=rtcp-mux" attribute, the offerer
  MUST NOT multiplex RTP and RTCP packets on a single port.  Instead,
  it should send and receive RTCP on a port allocated according to the
  usual port-selection rules (either the port pair, or a signalled port
  if the "a=rtcp:" attribute [10] is also included).  This will occur
  when talking to a peer that does not understand the "a=rtcp-mux"
  attribute.



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  When SDP is used in a declarative manner, the presence of an "a=rtcp-
  mux" attribute signals that the sender will multiplex RTP and RTCP on
  the same port.  The receiver MUST be prepared to receive RTCP packets
  on the RTP port, and any resource reservation needs to be made
  including the RTCP bandwidth.


 NEW TEXT:

  When the Session Description Protocol (SDP) [8] is used to negotiate
  RTP sessions following the offer/answer model [9], the "a=rtcp-mux"
  attribute (see Section 8) indicates the desire to multiplex RTP and
  RTCP onto a single port, and the usage is always negotiated for both
  directions.

  If the offerer wishes to multiplex RTP and RTCP onto a single port,
  the initial SDP offer MUST include the attribute at the media level to
  request multiplexing of RTP and RTCP on a single port. For example:

      v=0
      o=csp 1153134164 1153134164 IN IP6 2001:DB8::211:24ff:fea3:7a2e
      s=-
      c=IN IP6 2001:DB8::211:24ff:fea3:7a2e
      t=1153134164 1153137764
      m=audio 49170 RTP/AVP 97
      a=rtpmap:97 iLBC/8000
      a=rtcp-mux

  This offer denotes a unicast voice-over-IP session using the RTP/AVP
  profile with iLBC coding.  The answerer is requested to send both RTP
  and RTCP to port 49170 on IPv6 address 2001:DB8::211:24ff:fea3:7a2e.

  If the offer contains the "a=rtcp-mux" attribute, and if the answerer
  wishes to multiplex RTP and RTCP onto a single port, it MUST include a
  media-level "a=rtcp-mux" attribute in the answer. The RTP payload
  types used in the answer MUST conform to the rules in Section 4. If
  the offer does not contain the "a=rtcp-mux" attribute the answerer
  MUST NOT include an "a=rtcp-mux" attribute in the answer, and the
  answerer MUST NOT multiplex RTP and RTCP packets on a single port.

  If the answer contains an "a=rtcp-mux" attribute, the offerer and
  answerer MUST multiplex RTP and RTCP packets on a single port.

  If the answer does not contain an "a=rtcp-mux" attribute, the offerer
  and answerer MUST NOT multiplex RTP and RTCP packets on a single port.
  Instead, they should send and receive RTCP on a port allocated
  according to the usual port-selection rules (either the port pair, or
  a signalled port if the "a=rtcp:" attribute [10] is also included).



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  This will occur when talking to a peer that does not understand the
  "a=rtcp-mux" attribute.

  When SDP is used in a declarative manner, the presence of an "a=rtcp-
  mux" attribute signals that the sender will multiplex RTP and RTCP on
  the same port.  The receiver MUST be prepared to receive RTCP packets
  on the RTP port, and any resource reservation needs to be made
  including the RTCP bandwidth.


4.  Security Considerations

   The security considerations for RTP and RTCP multiplexing are
   described in RFC 5761.  This specification does not impact those
   security considerations.

5.  IANA Considerations

   IANA is requested to add a reference to this document for the add-
   field (media level only) registration "rtcp-mux" in Session
   Description Protocol (SDP) Parameters registry.

6.  Acknowledgements

   Thanks to Colin Perkins, Magnus Westerlund, Paul Kyzivat, Roni Even
   for providing comments on the document.  Thomas Belling provided
   useful input in the discussions that took place in 3GPP and resulted
   in the submission of the document.  Elwyn Davies performed the Gen-
   ART review.  Rick Casarez performed the Ops-Dir review.  Alissa
   Cooper and Spencer Dawkins provided IESG review comments.

7.  Change Log

   [RFC EDITOR NOTE: Please remove this section when publishing]

   Change from -05

   o  Changes based on IESG- and Gen-Art reviews:

   o  - Change of document title.

   o  - Editorial fix.

   Change from -04

   o  Change of document title.

   Change from -03



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   o  Addition to IANA Considerations.

   Change from -02

   o  Editorial change based on Gen-ART review of Elwyn Davis
      (https://www.ietf.org/mail-archive/web/gen-art/current/
      msg13713.html).

   Change from -01

   o  pre-RFC5378 disclaimer added.

   Change from -00

   o  Editorial changes based on WGLC comments from Roni Even.

8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port", RFC 5761,
              DOI 10.17487/RFC5761, April 2010,
              <http://www.rfc-editor.org/info/rfc5761>.

Author's Address

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com









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