RTP-mixer formatting of multi-party Real-time text
draft-ietf-avtcore-multi-party-rtt-mix-06

Document Type Active Internet-Draft (avtcore WG)
Last updated 2020-06-11
Replaces draft-hellstrom-avtcore-multi-party-rtt-source
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AVTCore                                                     G. Hellstrom
Internet-Draft                 Gunnar Hellstrom Accessible Communication
Updates: RFC 4102, RFC 4103 (if approved)                   11 June 2020
Intended status: Standards Track                                        
Expires: 13 December 2020

           RTP-mixer formatting of multi-party Real-time text
               draft-ietf-avtcore-multi-party-rtt-mix-06

Abstract

   Real-time text mixers for multi-party sessions need to identify the
   source of each transmitted group of text so that the text can be
   presented by endpoints in suitable grouping with other text from the
   same source.

   Regional regulatory requirements specify provision of real-time text
   in multi-party calls.  RFC 4103 mixer implementations can use
   traditional RTP functions for source identification, but the mixer
   source switching performance is limited when using the default
   transmission with redundancy.

   An enhancement for RFC 4103 real-time text mixing is provided in this
   document, suitable for a centralized conference model that enables
   source identification and efficient source switching.  The intended
   use is for real-time text mixers and multi-party-aware participant
   endpoints.  The mechanism builds on use of the CSRC list in the RTP
   packet and an extended packet format "text/rex".

   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 the media subtype "text/rex".

   The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103]

   A brief description about how a mixer can format text for the case
   when the endpoint is not multi-party aware is also provided.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

Hellstrom               Expires 13 December 2020                [Page 1]
Internet-Draft    RTP-mixer format for multi-party RTT         June 2020

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 13 December 2020.

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
   Provisions Relating to IETF Documents (https://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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Selected solution and considered alternative  . . . . . .   5
     1.2.  Nomenclature  . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Intended application  . . . . . . . . . . . . . . . . . .   6
   2.  Use of fields in the RTP packets  . . . . . . . . . . . . . .   6
   3.  Actions at transmission by a mixer  . . . . . . . . . . . . .   9
     3.1.  Initial BOM transmission  . . . . . . . . . . . . . . . .   9
     3.2.  Keep-alive  . . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  Transmission interval . . . . . . . . . . . . . . . . . .  10
     3.4.  Do not send received text to the originating source . . .  10
     3.5.  Clean incoming text . . . . . . . . . . . . . . . . . . .  10
     3.6.  Redundancy  . . . . . . . . . . . . . . . . . . . . . . .  10
     3.7.  Text placement in packets . . . . . . . . . . . . . . . .  10
     3.8.  Maximum number of sources per packet  . . . . . . . . . .  11
     3.9.  Empty T140blocks  . . . . . . . . . . . . . . . . . . . .  11
     3.10. Creation of the redundancy  . . . . . . . . . . . . . . .  11
     3.11. Timer offset fields . . . . . . . . . . . . . . . . . . .  12
     3.12. Other RTP header fields . . . . . . . . . . . . . . . . .  12
     3.13. Pause in transmission . . . . . . . . . . . . . . . . . .  12
   4.  Actions at reception  . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Multi-party vs two-party use  . . . . . . . . . . . . . .  12
     4.2.  Level of redundancy . . . . . . . . . . . . . . . . . . .  13
     4.3.  Extracting text and handling recovery and loss  . . . . .  13
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