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Plugging the Communications Time Drain: Page 8 of 19

Unity 4. Cisco Systems, (800) 553-6387, (408)526-4000. www.cisco.com

Sean Doherty is a technology editor and lawyer based at our Syracuse University Real-World Labs®. A former project manager and IT engineer at Syracuse University, he helped develop centrally supported applications and storage systems. Write to him at [email protected].

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Why focus on unified-messaging vendors that support the Session Initiation Protocol? SIP is a call-processing protocol designed to set up, modify and tear down sessions. Sessions can be point-to-point telephone calls or multimedia conferences. SIP is not dependent on a single conference-control protocol, like H.323 is, and does not dictate a method to transport the session traffic. It can operate over TCP or UDP, where multiple SIP transactions can be carried out in a single TCP connection or UDP datagram.

But it's more than just an efficient signaling protocol. SIP can boost support for mobile professionals. If a remote user registers his or her location with a SIP server, a UM application can direct SIP messages to the user's location, be it a remote office or a cell phone.

It is also a compelling protocol for enterprise networks. SIP can operate as a stateful or a stateless protocol. As a stateless implementation, it can scale to large networks where servers do not have to maintain state information on calls once a session is initiated. It integrates well into enterprises that leverage Web-browser interfaces because it uses HTTP formats to describe messages. And the message description is not limited to HTTP but can be transmitted in a number of ways. For example, it could be described in MIME or XML. Because it is based in HTTP, SIP can also support Java and JPEG and provide a rich multimedia experience.