Real-time text solutions for multi-party sessions
draft-hellstrom-avtcore-multi-party-rtt-solutions-03
Internet Engineering Task Force G. Hellstrom
Internet-Draft Gunnar Hellstrom Accessible Communication
Intended status: Informational 8 August 2020
Expires: 9 February 2021
Real-time text solutions for multi-party sessions
draft-hellstrom-avtcore-multi-party-rtt-solutions-03
Abstract
This document specifies methods for Real-Time Text (RTT) media
handling in multi-party calls. The main discussed transport is to
carry Real-Time text by the RTP protocol in a time-sampled mode
according to RFC 4103. 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 9 February 2021 [Page 1]
Internet-Draft Real-time text multi-party solutions August 2020
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This Internet-Draft will expire on 9 February 2021.
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document authors. All rights reserved.
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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
3.1. General requirements . . . . . . . . . . . . . . . . . . 6
3.2. Performance requirements . . . . . . . . . . . . . . . . 7
4. RTP based solutions . . . . . . . . . . . . . . . . . . . . . 8
4.1. Coordination of text RTP streams . . . . . . . . . . . . 8
4.1.1. RTP-based solutions with a central mixer . . . . . . 8
4.1.1.1. RTP Mixer using default RFC 4103 methods . . . . 8
4.1.1.2. RTP Mixer using the default method but decreased
transmission interval . . . . . . . . . . . . . . . 9
4.1.1.3. RTP Mixer with frequent transmission and indicating
sources in CSRC-list . . . . . . . . . . . . . . . 10
4.1.1.4. RTP Mixer using timestamp to identify
redundancy . . . . . . . . . . . . . . . . . . . . 11
4.1.1.5. RTP Mixer with multiple primary data in each packet
and individual sequence numbers . . . . . . . . . . 12
4.1.1.6. RTP Mixer with multiple primary data in each
packet . . . . . . . . . . . . . . . . . . . . . . 13
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