There are two families of protocol for setting up multimedia sessions: the IETF family of protocols, and the ITU family of protocols. There is some overlap between these two families, and some re-use of IETF protocols in the ITU family. The reason for the overlap is that the different standards groups started work from different points, and slowly expanded their area of applicability so that now there are two ways to do some things. In the long run, the market will no doubt decide which protocol is chosen for a particular task, but for now the picture is a little confusing.
In the IETF arena, work started in the area of loosely coupled large scale multicast multimedia conferences.
In the ITU arena, work started with ISDN-based circuit-switched video conferencing, and was expanded to extend ISDN conferencing over packet-switched LANs within companies.
At the time, wide-area internet telephony seemed a long way off because while multicast offered great advantages for large conferences, the internet was a poor environment to provide high quality calls that compete with the traditional telephone system.
In practice it seems that the latent demand for convergence of data and telephony networks was larger than either group foresaw, and rapidly both sets of protocols started to be applied to internet telephony and small wide-area video-conferences, and hence although they were not designed as competitors, that is the situation we find ourselves in today.
In this chapter we shall discuss the IETF family of protocols, including the Session Description Protocol (SDP), the Session Announcement Protocol (SAP) and the Session Initiation Protocol (SIP). In chapter we will discuss the ITU's H323 family of protocols. In some environments we envisage that hybrids will be widely used, for example, using SIP to initiate an H.323 conference. However, at the time of writing it is not yet clear exactly what form such hybrids will take.