Duplication Grouping Semantics in the Session Description Protocol
RFC 7104

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Internet Engineering Task Force (IETF)                          A. Begen
Request for Comments: 7104                                         Cisco
Category: Standards Track                                         Y. Cai
ISSN: 2070-1721                                                Microsoft
                                                                   H. Ou
                                                                   Cisco
                                                            January 2014

   Duplication Grouping Semantics in the Session Description Protocol

Abstract

   Packet loss is undesirable for real-time multimedia sessions, but it
   can occur due to congestion or other unplanned network outages.  This
   is especially true for IP multicast networks, where packet loss
   patterns can vary greatly between receivers.  One technique that can
   be used to recover from packet loss without incurring unbounded delay
   for all the receivers is to duplicate the packets and send them in
   separate redundant streams.  This document defines the semantics for
   grouping redundant streams in the Session Description Protocol (SDP).
   The semantics defined in this document are to be used with the SDP
   Grouping Framework.  Grouping semantics at the Synchronization Source
   (SSRC) level are also defined in this document for RTP streams using
   SSRC multiplexing.

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/rfc7104.

Begen, et al.                Standards Track                    [Page 1]
RFC 7104          Duplication Grouping Semantics in SDP     January 2014

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Requirements Notation ...........................................3
   3. Duplication Grouping ............................................3
      3.1. "DUP" Grouping Semantics ...................................3
      3.2. Duplication Grouping for SSRC-Multiplexed RTP Streams ......3
      3.3. SDP Offer/Answer Model Considerations ......................4
   4. SDP Examples ....................................................5
      4.1. Separate Source Addresses ..................................5
      4.2. Separate Destination Addresses .............................6
      4.3. Temporal Redundancy ........................................7
   5. Security Considerations .........................................7
   6. IANA Considerations .............................................8
   7. Acknowledgments .................................................8
   8. References ......................................................8
      8.1. Normative References .......................................8
      8.2. Informative References .....................................9

Begen, et al.                Standards Track                    [Page 2]
RFC 7104          Duplication Grouping Semantics in SDP     January 2014

1.  Introduction

   The Real-time Transport Protocol (RTP) [RFC3550] is widely used today
   for delivering IPTV traffic and other real-time multimedia sessions.
   Many of these applications support very large numbers of receivers
   and rely on intra-domain UDP/IP multicast for efficient distribution
   of traffic within the network.

   While this combination has proved successful, there does exist a
   weakness.  As [RFC2354] noted, packet loss is not avoidable, even in
   a carefully managed network.  This loss might be due to congestion;
   it might also be a result of an unplanned outage caused by a flapping
   link, a link or interface failure, a software bug, or a maintenance
   person accidentally cutting the wrong fiber.  Since UDP/IP flows do
   not provide any means for detecting loss and retransmitting packets,