Presenting Presence Services
SIP introduces a new model for communications through its
support of presence. Presence enables you to locate a user
and determine his willingness and ability to participate in a
session, even before you initiate communications. This infor-
mation, reflected across multiple devices such as IP phones,
cell phones, and instant messaging clients, makes communi-
cation simple and efficient by helping you to reach the right
person at the right time, on the right device.
Presence and preference features enabled by SIP are dis-
cussed in more detail in Part 3.
Celebrating User-Centric
Communications
Communications today are device-centric. Every device has
its own phone number, address, or alias. The more devices
you use, the more addresses others need to remember in
order to reach you. And without presence, as described in
the previous section, communication becomes a guessing
game when trying to connect with people, wherever they
may be and whatever they’re doing.
Part 1: The Case for SIP
7
A brief history of SIP
SIP traces its origins to the mid 1990s
in the Internet’s experimental multicast
backbone, or “Mbone.” This network
was used to facilitate the distribution of
streaming multimedia content includ-
ing seminars, broadcasts of space
shuttle launches, and IETF meetings.
The original draft of the SIP specifica-
tion was published in the IETF in 1996,
and eventually standardized in 1999.
Today, the most up-to-date core SIP
specification can be found in RFC
(Request for Comment) 3261.
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