245We will present in this chapter conferencing services based on SIP. Though the
interest in SIP is at present mostly because of telephony and other IP communi-
cation services, it is useful to remember that SIP has been developed initially in
the IETF MMUSIC Working Group for large-scale multimedia conferencing
over the Internet within the Internet Multimedia Conferencing Architecture [1].
Introduction
Present commercial conferencing products and services are mainly of three
types:
■■ PSTN-based telephone conferences, which are the most widely used.
■■ Various video conferencing products, such as based on the ITU H.3xx
series of recommendations that support voice, video, and also document
sharing, using the T.120 standard. Contrary to voice conferencing, most
video and data conferencing products are not fully interoperable, though
they may be advertised as being in compliance with the previous stan-
dards. This is because of the large number of options permitted in ITU
conferencing standards and the fact that various products may support
different sets of options, besides some proprietary enhancements.