In this chapter we have looked at transport (end-to-end) protocols. To some extent, the term is meaningless for multimedia, and especially for multiple participant multimedia systems, in the normal protocol layering sense. The ``ends'' of a flow in a multimedia service are the sampling devices, and so the protocol system must reach right into the depths of the application at source and sink. Ideally, it must be possible to fill in (and extract) fields from the transport protocol header, from control status registers in media devices, if we wish to minimise delays, and provide the best possible stream synchronisation.
For some supporting applications, such as whiteboards, some slightly more conventional protocol is required for reliability. yet we can see that the notion of reliability is a slippery one when it comes to group and human communication.