SIP Communications For Dummies, Avaya Custom Edition
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Based on Existing Internet
Standards
Although SIP may seem new, it’s actually based on many
protocols that are widely used today across the Internet
and in many enterprise applications. The IETF community
took Internet standards as a model, and used a text-based
request/response model at the heart of the SIP protocol.
If you use Web browsers (and who doesn’t?), then you
already depend on a protocol very similar to SIP, called HTTP
(HyperText Transport Protocol) — yep, that bit before a stan-
dard Web address that you usually take for granted. SIP is
modeled after HTTP, and in fact uses much of HTTP’s syntax
and semantics. Both are text-encoded protocols, which means
that they are easy to read and debug. This readability pro-
motes integration across a decentralized architecture (such
as the Internet) and interoperability across a distributed net-
work. In effect, SIP is to converged communications what
HTTP is to information exchange for the World Wide Web
(WWW) — it makes the communications infrastructure
transparent to end-users and enables ready access to many
modes of communication. Just as pointing your browser to
an HTTP site enables you to play video, download pictures,
or upload files, SIP too has been designed to support multi-
media communications.
SIP goes beyond HTTP by embedding in communications the
intelligence to sense the media capabilities of the end device
as well as the availability of a user to communicate.
Getting Down to One Address
for Everything
One key feature of SIP is its ability to use an end-user’s address
of record (AOR) as a single unifying public address for all
communications. So, in the world of SIP-enhanced communi-
cations, a user’s AOR becomes her single address that links
the user to all of the communication devices or services that
she uses. For example, user Eileen Dover’s AOR would look like
SIP:eileendover@company.com. Using this AOR, a caller
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