A SIMPLE Presence Solution
One of the key SIP extensions defined by the IETF is SIP for
Instant Messaging and Presence Leveraging Extensions (or
even more simply, SIMPLE). SIMPLE defines functions for
presence and instant messaging.
In an advanced communications network, users can specify
their communications preferences and availability. This feature
is known as presence — an intelligent “network overlay” that
makes it easy for a calling party to reach an available and
willing-to-be-called party. Presence streamlines the communica-
tion process by enabling users to inform others of their status,
their availability, and how they can be contacted before a com-
munication session even begins. Many devices can provide
presence information, and it becomes extremely powerful
when integrated across all of the user’s communication
devices such as IP phones, cell phones, softphones, PDAs,
and wireless/Bluetooth appliances. As Part 5 explains, realiza-
tion of such a vision requires not only open interoperability,
but also well-built ecosystems that promote cooperation
between many industry players, standards, and protocols.
Presence is not limited to a single user; it can also apply to
a group of users (for example, Finance Group) or a device
(for example, Phone Status = “Off-hook” or “On-hook”).
Even more exciting, both users and applications can access
presence information, providing the opportunity to create
next-generation converged communication applications.
For example, your network can deliver new capabilities such
as polite calling (calls that are less disruptive for the party
being called) as when, based on information from her calendar
application, calls to an executive can automatically be routed
to an assistant if the executive is scheduled to be in a meeting.
Components in a SIP Network
When you are ready to enhance your communications with
SIP, it’s important to understand the building blocks that you
will need to form the foundation of your new SIP-enhanced
enterprise.
Part 2: SIP at a Glance
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