can reach Eileen’s multiple communication devices (known as
user agents or UAs to techno-types) without having to know
each of Eileen’s unique device addresses or phone numbers.
To complement the AOR, SIP provides a mechanism called the
Uniform Resource Identifier (URI) that establishes a common
addressing scheme for all of an individual’s user agents.
The format of a URI address follows the same basic format
as a Web or e-mail address: contact-address@domain.
By applying this style of addressing, SIP can map the unique
addresses of a user’s multiple devices and services to a com-
munication domain, and then link all the user agents to a
user’s single AOR for that domain. Following are some exam-
ples of how this URI might be applied:
ߜ A phone: sip:408-555-1212@company.com;user=
phone
ߜ A fax: sip: 408-555-1214@company.com;user=fax
ߜ An IM user: sip:eileendover@company.com
A user typically has just one SIP AOR, such as eileendover@
domain. Then, each of the user’s devices has its own URI,
such as sip:408-555-1214@company.com; user=fax.
Part 2: SIP at a Glance
15
SIP “business cards”
One nifty benefit of SIP is how easy it
makes the transition for end-users who
are still using traditional communica-
tions devices, like, um, telephones. For
example, imagine professors at a uni-
versity who want to make it easier for
their colleagues, including researchers
at other universities, to contact them.
To do so, they are replacing multiple
contact numbers on their business
cards with a single easy-to-remember
SIP address. The problem? The univer-
sity has started to deploy SIP, but most
of the professors are still using tradi-
tional (analog) phones, and a complete
update to SIP is still years away. As a
solution, Avaya Handle-Based Dialing
works with the university’s
Lightweight
Directory Access Protocol (LDAP)
directory server to reach any non-SIP
phones by translating the SIP AOR in
real time to a standard telephone
number. Now, the professors can
hand out their business cards and be
reached at their existing phone through
one simple address, such as: SIP:
CoolestProf@oncampus.edu.
(Part 3 explains how you can also still
dial this number on a traditional
phone.)
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