RFC 9071

RTP-Mixer Formatting of Multiparty Real-Time Text, July 2021

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RFC 4103
G. Hellström
avtcore (wit)

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DOI:  https://doi.org/10.17487/RFC9071

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This document provides enhancements of real-time text (as specified in RFC 4103) suitable for mixing in a centralized conference model, enabling source identification and rapidly interleaved transmission of text from different sources. The intended use is for real-time text mixers and participant endpoints capable of providing an efficient presentation or other treatment of a multiparty real-time text session. The specified mechanism builds on the standard use of the Contributing Source (CSRC) list in the Real-time Transport Protocol (RTP) packet for source identification. The method makes use of the same "text/t140" and "text/red" formats as for two-party sessions.

Solutions using multiple RTP streams in the same RTP session are briefly mentioned, as they could have some benefits over the RTP-mixer model. The RTP-mixer model was selected to be used for the fully specified solution in this document because it can be applied to a wide range of existing RTP implementations.

A capability exchange is specified so that it can be verified that a mixer and a participant can handle the multiparty-coded real-time text stream using the RTP-mixer method. The capability is indicated by the use of a Session Description Protocol (SDP) (RFC 8866) media attribute, "rtt-mixer".

This document updates RFC 4103 ("RTP Payload for Text Conversation").

A specification for how a mixer can format text for the case when the endpoint is not multiparty aware is also provided.

For the definition of Status, see RFC 2026.

For the definition of Stream, see RFC 8729.

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