The SIP protocol is an Application Layer protocol designed to be
independent of the underlying Transport Layer; it can run on
Transmission Control Protocol (TCP), User Datagram Protocol
(UDP), or Stream Control Transmission Protocol (SCTP). It is a
text-based protocol, incorporating many elements of the
Hypertext Transfer Protocol (HTTP) and the Simple Mail Transfer
Protocol (SMTP).  SIP protocol can be used for creating,
modifying and terminating two-party (unicast) or multiparty
(multicast) sessions. Sessions may consist of one or several
media streams.  Other SIP applications include video
conferencing, streaming multimedia distribution, instant
messaging, presence information, file transfer and online games.
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