Real-time text solutions for multi-party sessions
draft-hellstrom-avtcore-multi-party-rtt-solutions-02
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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This Internet-Draft will expire on 21 December 2020.
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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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