Hi Gunnar,
I believe we had this discussion before - And I still find no justification to sending Text (which inherently must be lossless and is extreme low bit-rate) using RTP. Nothing stops us from opening an TCP channel using OLC/CLC procedures and sending text over it. I agree - when lip-sync is required, TCP delay (on average 1/3 for text chat type apps) may miss out a little, but I don't believe that to be such a big issue.
The main problem I see is that using RTP on average text typist means that IP/UDP/RTP/Text packets are going to be sent every 2-3 characters, and even with redundancy, packetloss can still occur which is unacceptable.
- gur
The document "RTP Payload for Text Conversation" is submitted to IETF-draft as agreed in the avt wg in the IETF Oslo meeting. Comments are welcome to the author at gunnar.hellstrom@omnitor.se or to the rem-conf@es.net mail list.
This RTP payload is used by H.323 Annex G Text conversation and text SET
ABSTRACT
This memo describes how to carry text conversation session contents in RTP packets. Text conversation session contents is specified in ITU-T Recommendation T.140 [1].
Text conversation is used alone or in connection to other conversational facilities such as video and voice, to form multimedia conversation services.
This RTP payload description contains an optional possibility to include redundant text from already transmitted packets in order to reduce the risk of text loss caused by packet loss. The redundancy coding follows RFC 2198.
Gunnar Hellstr
öm ______________________________________ Gunnar Hellström LM Ericsson Sweden
Tel +46 708 204 288 or +46 556 002 03 Fax +46 8 556 002 06 Video +46 8 556 002 05 Txt (All kinds) +46 8 556 002 05 E-mail gunnar.hellstrom@omnitor.se WWW: http://www.omnitor.se