RTP Control Protocol (RTCP) Port for Source-Specific Multicast (SSM) Sessions
RFC 6128

Internet Engineering Task Force (IETF)                          A. Begen
Request for Comments: 6128                                         Cisco
Updates: 5760                                              February 2011
Category: Standards Track
ISSN: 2070-1721

                  RTP Control Protocol (RTCP) Port for
                Source-Specific Multicast (SSM) Sessions

Abstract

   The Session Description Protocol (SDP) has an attribute that allows
   RTP applications to specify an address and a port associated with the
   RTP Control Protocol (RTCP) traffic.  In RTP-based source-specific
   multicast (SSM) sessions, the same attribute is used to designate the
   address and the RTCP port of the Feedback Target in the SDP
   description.  However, the RTCP port associated with the SSM session
   itself cannot be specified by the same attribute to avoid ambiguity,
   and thus, is required to be derived from the "m=" line of the media
   description.  Deriving the RTCP port from the "m=" line imposes an
   unnecessary restriction.  This document removes this restriction by
   introducing a new SDP attribute.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6128.

Begen                        Standards Track                    [Page 1]
RFC 6128            RTCP Port for Multicast Sessions       February 2011

Copyright Notice

   Copyright (c) 2011 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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   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. The 'multicast-rtcp' Attribute ..................................3
   3. SDP Example .....................................................3
   4. Security Considerations .........................................4
   5. IANA Considerations .............................................4
      5.1. Registration of SDP Attributes .............................5
   6. Acknowledgments .................................................5
   7. References ......................................................5
      7.1. Normative References .......................................5
      7.2. Informative References .....................................5

1.  Introduction

   The Session Description Protocol (SDP) [RFC4566] has an attribute
   that allows RTP applications [RFC3550] to specify an address and a
   port associated with the RTP Control Protocol (RTCP) traffic
   [RFC3605].  This attribute is called 'rtcp'.

   Now consider a network where one or more media senders send RTP
   packets to a distribution source, which then multicasts these RTP
   packets to multicast receivers using a source-specific multicast
   (SSM) arrangement [RFC5760].  The distribution source also multicasts
   the forward RTCP traffic (i.e., RTCP sender reports and receiver
   reports or their summaries) to the receivers in the same SSM session.

   In RTP-based SSM sessions, the 'rtcp' attribute is used to designate
   the address and the RTCP port of the Feedback Target in the SDP
   description [RFC5760].  However, the RTCP port associated with the
   SSM session itself cannot be specified by the same attribute since it
   could potentially cause ambiguity.  Thus, the multicast RTCP port is
   required to be derived from the "m=" line of the media description

Begen                        Standards Track                    [Page 2]
RFC 6128            RTCP Port for Multicast Sessions       February 2011

   (see Section 10.2 of [RFC5760]) by following the +1 rule (see Section
   11 of [RFC3550]).  However, [RFC3550] lifted the requirement for the
   +1 rule since it imposed an unnecessary restriction on RTCP port