Because a SIP URI supports both numeric (phone numbers)
and alphanumeric (Internet-style addresses) formatted con-
tact addressing, the public switched telephone network (PSTN)
and the Internet can be seamlessly linked together. With SIP,
users can potentially contact any user, whether they are on
the PSTN or on the Internet.
Enabling Voice, Video, and IM,
Oh My!
In keeping with the IETF philosophy of defining simple proto-
cols with powerful functionality, SIP follows a peer-to-peer
architecture containing a small set of different methods
(types of messages). At the same time, SIP is also very modu-
lar and extensible, enabling you to integrate SIP into your
existing legacy communications environment. As a result, SIP
can interoperate with many traditional telephony protocols
and scenarios, as well as with emerging communications serv-
ices. These properties make SIP an ideal protocol for any
company implementing a standards-based converged com-
munications network.
SIP is not designed simply to replace the PSTN. Rather, SIP
goes well beyond traditional telephony by facilitating any
type of peer-to-peer communication session, instant messag-
ing, video gaming, conferencing, and collaboration.
SIP is also not designed to be a one-stop shop for protocol
needs. You essentially use SIP to set up and tear down media
sessions (for example, IM, text, voice, or video communica-
tion sessions). SIP combines with other network protocols as
well as application-layer technologies to provide complete
end-to-end functionality. One such protocol is the Session
Description Protocol (SDP), which carries within it informa-
tion about the session that you’re setting up (namely, the
type of media, the codec to use, and the protocol for actually
transporting the media).
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