Real-time text media handling in multi-party conferences

Document Type Replaced Internet-Draft (individual)
Last updated 2020-03-03
Replaces draft-hellstrom-text-conference
Replaced by draft-hellstrom-avtcore-multi-party-rtt-solutions
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This memo specifies methods for Real-Time Text (RTT) media handling in multi-party calls. The main RTT transport is to carry Real-Time text by the RTP protocol in a time-sampled mode according to RFC 4103 RFC 4103 [RFC4103] . The mechanisms enable the receiving application to present the received real-time text medium 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 one is provided. The main solution for 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 untouched by the bridge are also discussed. Brief information is also provided for multi-party RTT in the WebRTC environment.


Gunnar Hellstrom (

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