Real-time text media handling in multi-party conferences
Omnitor
This memo specifies methods for Real-Time Text (RTT) media handling in multi-party calls. The main solution is to carry Real-Time text by the RTP protocol in a time-sampled mode according to RFC 4103. 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 session. Identification for the streams are provided through the RTCP messages. This mechanism enables the receiving application to present the received real-time text medium 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. Two 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. Brief information is also provided for multi-party RTT in the WebRTC environment. EDITOR NOTE: A number of alternatives are specified for discussion. A decision is needed which alternatives are preferred and then how the preferred alternatives shall be emphasized.