Text media handling in RTP based real-time conferences
A.L.M.Van Wijk, Gunnar Hellström · 2011
This memo specifies methods for text media handling in multi-party calls, where the text is carried by the RTP protocol. Real-time text is carried in a time-sampled mode according to RFC 4103. Centralized multi-party handling of real-time text is achieved through a media control unit coordinating multiple RTP text streams into one RTP session, identifying each stream with its own SSRC. 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, while the transport mechanisms should be suitable for any IP based call control environment using RTP transport. An alternative method using a single RTP stream and source identification inline in the text stream is also described.