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Forward-Shifted RTP Redundancy Payload Support
RFC 6354

Internet Engineering Task Force (IETF)                            Q. Xie
Request for Comments: 6354                                   August 2011
Updates: 2198, 4102
Category: Standards Track
ISSN: 2070-1721

             Forward-Shifted RTP Redundancy Payload Support

Abstract

   This document defines a simple enhancement to support RTP sessions
   with forward-shifted redundant encodings, i.e., redundant data sent
   before the corresponding primary data.  Forward-shifted redundancy
   can be used to conceal losses of a large number of consecutive media
   frames (e.g., consecutive loss of seconds or even tens of seconds of
   media).

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/rfc6354.

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
   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.

Xie                          Standards Track                    [Page 1]
RFC 6354             Forward-Shifted RTP Redundancy          August 2011

   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
      1.1. Sending Redundant Data Inband vs. Out-of-Band ..............3
   2. Conventions .....................................................4
   3. Allowing Forward-Shifted Redundant Data .........................4
   4. Registration of Media Type "fwdred" .............................5
   5. Mapping Media Type Parameters into SDP ..........................7
   6. Usage in Offer/Answer ...........................................7
   7. IANA Considerations .............................................7
   8. Security Considerations .........................................8
   9. Normative References ............................................8
   Appendix A. Anti-Shadow Loss Concealment Using
               Forward-Shifted Redundancy .............................9
      A.1. Sender-Side Operations .....................................9
      A.2. Receiver-Side Operations ..................................11
         A.2.1. Normal-Mode Operation ................................11
         A.2.2. Anti-Shadow-Mode Operation ...........................12

1.  Introduction

   This document defines a simple enhancement to RFC 2198 [RFC2198] to
   support RTP sessions with forward-shifted redundant encodings, i.e.,
   redundant data sent before the corresponding primary data.

   Forward-shifted redundancy can be used to conceal losses of a large
   number of consecutive media frames (e.g., consecutive loss of seconds
   of media).  Such capability is highly desirable, especially in
   wireless mobile communication environments where the radio signal to
   a mobile wireless media receiver can be temporarily blocked by tall
   buildings, mountains, tunnels, etc.  In other words, the receiver
   enters into a shadow of the radio coverage.  No new data will be
   received when the receiver is in a shadow.

Xie                          Standards Track                    [Page 2]

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