RTP-mixer formatting of multi-party Real-time text
draft-ietf-avtcore-multi-party-rtt-mix-07
AVTCore G. Hellstrom
Internet-Draft Gunnar Hellstrom Accessible Communication
Updates: RFC 4102, RFC 4103 (if approved) 12 July 2020
Intended status: Standards Track
Expires: 13 January 2021
RTP-mixer formatting of multi-party Real-time text
draft-ietf-avtcore-multi-party-rtt-mix-07
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.
Enhancements for RFC 4103 real-time text mixing is provided in this
document, suitable for a centralized conference model that enables
source identification and source switching. The intended use is for
real-time text mixers and multi-party-aware participant endpoints.
Two mechanisms are provided. The mechanisms builds on use of the
CSRC list in the RTP packet for source identification. One method
makes use of the same "text/red" format as for two-party sessions,
while the other makes use of an extended packet format "text/rex" for
more efficient transmission.
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 for one method is by use of a media attribute a=rtt-
mix-rtp-mixer. The other method 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.
Hellstrom Expires 13 January 2021 [Page 1]
Internet-Draft RTP-mixer format for multi-party RTT July 2020
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This Internet-Draft will expire on 13 January 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Selected solution and considered alternative . . . . . . 5
1.2. Nomenclature . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Intended application . . . . . . . . . . . . . . . . . . 7
2. Specified solutions . . . . . . . . . . . . . . . . . . . . . 7
2.1. Negotiated use of the RFC 4103 format for multi-party in a
single RTP stream . . . . . . . . . . . . . . . . . . . . 7
2.2. Use of an extended packet format "text/rex" with text from
multiple sources . . . . . . . . . . . . . . . . . . . . 17
2.3. Mixing for multi-party unaware endpoints . . . . . . . . 35
3. Presentation level considerations . . . . . . . . . . . . . . 36
3.1. Presentation by multi-party aware endpoints . . . . . . . 36
3.2. Multi-party mixing for multi-party unaware endpoints . . 38
4. Gateway Considerations . . . . . . . . . . . . . . . . . . . 44
4.1. Gateway considerations with Textphones (e.g. TTYs). . . 44
4.2. Gateway considerations with WebRTC. . . . . . . . . . . . 45
5. Updates to RFC 4102 and RFC 4103 . . . . . . . . . . . . . . 45
6. Congestion considerations . . . . . . . . . . . . . . . . . . 46
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46
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