Considerations for Deploying the Rapid Acquisition of Multicast RTP Sessions (RAMS) Method
RFC 6659

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Internet Engineering Task Force (IETF)                          A. Begen
Request for Comments: 6659                                         Cisco
Category: Informational                                        July 2012
ISSN: 2070-1721

         Considerations for Deploying the Rapid Acquisition of
                  Multicast RTP Sessions (RAMS) Method

Abstract

   The Rapid Acquisition of Multicast RTP Sessions (RAMS) solution is a
   method based on RTP and the RTP Control Protocol (RTCP) that enables
   an RTP receiver to rapidly acquire and start consuming the RTP
   multicast data.  Upon a request from the RTP receiver, an auxiliary
   unicast RTP retransmission session is set up between a retransmission
   server and the RTP receiver, over which the reference information
   about the new multicast stream the RTP receiver is about to join is
   transmitted at an accelerated rate.  This often precedes, but may
   also accompany, the multicast stream itself.  When there is only one
   multicast stream to be acquired, the RAMS solution works in a
   straightforward manner.  However, when there are two or more
   multicast streams to be acquired from the same or different multicast
   RTP sessions, care should be taken to configure each RAMS session
   appropriately.  This document provides example scenarios and
   discusses how the RAMS solution could be used in such scenarios.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see 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/rfc6659.

Begen                         Informational                     [Page 1]
RFC 6659                   RAMS Considerations                 July 2012

Copyright Notice

   Copyright (c) 2012 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Background ......................................................3
   3. Example Scenarios ...............................................4
      3.1. Scenario #1: Two Multicast Groups ..........................4
      3.2. Scenario #2: One Multicast Group ...........................5
      3.3. Scenario #3: SSRC Multiplexing .............................6
      3.4. Scenario #4: Payload-Type Multiplexing .....................6
   4. Feedback Target and SSRC Signaling Issues .......................7
   5. FEC during RAMS and Bandwidth Issues ............................7
      5.1. Scenario #1 ................................................7
      5.2. Scenario #2 ................................................9
      5.3. Scenario #3 ...............................................10
   6. Security Considerations ........................................10
   7. Acknowledgments ................................................10
   8. References .....................................................11
      8.1. Normative References ......................................11
      8.2. Informative References ....................................11

1.  Introduction

   The Rapid Acquisition of Multicast RTP Sessions (RAMS) solution is a
   method based on RTP and the RTP Control Protocol (RTCP) that enables
   an RTP receiver to rapidly acquire and start consuming the RTP
   multicast data.  Through an auxiliary unicast RTP retransmission
   session [RFC4588], the RTP receiver receives reference information
   about the new multicast stream it is about to join.  This often
   precedes, but may also accompany, the multicast stream itself.  The
   RAMS solution is documented in detail in [RFC6285].

Begen                         Informational                     [Page 2]
RFC 6659                   RAMS Considerations                 July 2012

   The RAMS specification [RFC6285] has provisions for concurrently
   acquiring multiple streams inside a multicast RTP session.  However,