Real-time text solutions for multi-party sessions
draft-hellstrom-avtcore-multi-party-rtt-solutions-02

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Last updated 2020-06-19
Replaces draft-hellstrom-mmusic-multi-party-rtt
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Internet Engineering Task Force                             G. Hellstrom
Internet-Draft                 Gunnar Hellstrom Accessible Communication
Intended status: Informational                              19 June 2020
Expires: 21 December 2020

           Real-time text solutions for multi-party sessions
          draft-hellstrom-avtcore-multi-party-rtt-solutions-02

Abstract

   This document specifies methods for Real-Time Text (RTT) media
   handling in multi-party calls.  The main transport is to carry Real-
   Time text by the RTP protocol in a time-sampled mode according to RFC
   4103 [RFC4103].  The mechanisms enable the receiving application to
   present the received real-time text media separated per source, in
   different ways according to user preferences.  Some presentation
   related features are also described explaining suitable variations of
   transmission and presentation of text.

   Call control features are described for the SIP environment.  A
   number of alternative methods for providing the multi-party
   negotiation, transmission and presentation are discussed and a
   recommendation for the main ones is provided.  The main solution for
   SIP based centralized multi-party handling of real-time text is
   achieved through a media control unit coordinating multiple RTP text
   streams into one RTP stream.

   Alternative methods using a single RTP stream and source
   identification inline in the text stream are also described, one of
   them being provided as a lower functionality fallback method for
   endpoints with no multi-party awareness for RTT.

   Bridging methods where the text stream is carried without the
   contents being dealt with in detail by the bridge are also discussed.

   Brief information is also provided for multi-party RTT in the WebRTC
   environment.

   The intention is to provide background for decisions, specification
   and implementation of selected methods.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

Hellstrom               Expires 21 December 2020                [Page 1]
Internet-Draft    Real-time text multi-party solutions         June 2020

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Copyright Notice

   Copyright (c) 2020 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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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Centralized conference model  . . . . . . . . . . . . . . . .   5
   3.  Requirements on multi-party RTT . . . . . . . . . . . . . . .   6
   4.  RTP based solutions . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Coordination of text RTP streams  . . . . . . . . . . . .   7
       4.1.1.  RTP-based solutions with a central mixer  . . . . . .   7
         4.1.1.1.  RTP Mixer using default RFC 4103 methods  . . . .   7
         4.1.1.2.  RTP Mixer using the default method but decreased
                 transmission interval . . . . . . . . . . . . . . .   8
         4.1.1.3.  RTP Mixer with frequent transmission and indicating
                 sources in CSRC-list  . . . . . . . . . . . . . . .   9
         4.1.1.4.  RTP Mixer using timestamp to identify
                 redundancy  . . . . . . . . . . . . . . . . . . . .  10
         4.1.1.5.  RTP Mixer with multiple primary data in each packet
                 and individual sequence numbers . . . . . . . . . .  11
         4.1.1.6.  RTP Mixer with multiple primary data in each
                 packet  . . . . . . . . . . . . . . . . . . . . . .  12
         4.1.1.7.  RTP Mixer with RFC 5109 FEC and RFC 2198 redundancy
                 in the packets  . . . . . . . . . . . . . . . . . .  13

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