Indicating source of multi-party Real-time text
draft-hellstrom-avtcore-multi-party-rtt-source-01

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Document Type Active Internet-Draft (individual)
Author Gunnar Hellstrom 
Last updated 2020-02-29
Replaced by draft-ietf-avtcore-multi-party-rtt-mix
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Network Working Group                                       G. Hellstrom
Internet-Draft                                                   Omnitor
Updates: RFC 4102, RFC 4103 (if                        February 29, 2020
         approved)
Intended status: Standards Track
Expires: September 1, 2020

            Indicating source of multi-party Real-time text
           draft-hellstrom-avtcore-multi-party-rtt-source-01

Abstract

   Real-time text mixers need to identify the source of each transmitted
   text chunk so that it can be presented in suitable grouping with
   other text from the same source.  An enhancement for RFC 4103 real-
   time text is provided, suitable for a centralized conference model
   that enables source identification, for use by text mixers and
   conference-enabled participants.  The mechanism builds on use of the
   CSRC list in the RTP packet.  A capability exchange is specified so
   that it can be verified that a participant can handle the multi-party
   coded real-time text stream.  The capability is indicated by an sdp
   media attribute "rtt-mix".

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 1, 2020.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

Hellstrom               Expires September 1, 2020               [Page 1]
Internet-Draft     Indicate source of multi-party RTT      February 2020

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Nomenclature  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Intended application  . . . . . . . . . . . . . . . . . . . .   3
   4.  Use of fields in the RTP packets  . . . . . . . . . . . . . .   3
   5.  Actions at transmission by a mixer  . . . . . . . . . . . . .   4
   6.  Actions at reception  . . . . . . . . . . . . . . . . . . . .   5
   7.  RTCP considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Chained operation . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Use with SIP centralized conferencing framework . . . . . . .   6
   10. Usage without redundancy  . . . . . . . . . . . . . . . . . .   7
   11. SDP Capability negotiation  . . . . . . . . . . . . . . . . .   7
   12. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   13. Performance considerations  . . . . . . . . . . . . . . . . .   9
   14. Presentation level considerations . . . . . . . . . . . . . .  10
   15. Congestion considerations . . . . . . . . . . . . . . . . . .  10
   16. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   17. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   18. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   19. Change history  . . . . . . . . . . . . . . . . . . . . . . .  11
     19.1.  Changes from version -00 to -01  . . . . . . . . . . . .  11
   20. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     20.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     20.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   RFC 4103[RFC4103] specifies use of RFC 3550 RTP[RFC3550] for
   transmission of real-time text (RTT) and the "text/t140" format.  It
   also specifies a redundancy format "text/red" for increased
   robustness.  RFC 4102 [RFC4102] registers the "text/red" format.  The
   redundancy scheme enables efficient transmission of redundant text in
   packets together with new text.  However the redundant header format
   has no source indicators for the redundant transmissions.  An
   assumption has had to be made that the redundant parts in a packet
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