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David Sims - TMCnet CRM Alert Columnist[February 21, 2005]

Conference Primer: SIP

By David Sims, TMCnet CRM Alert Columnist


Thursday at ITEXPO a lot of time will be given over to Session Initiation Protocol (SIP). What should you know about it?

What Is It? Session Initiation Protocol enables service convergence between different access technologies. It makes IP-based person-to-person services possible.


So? It’s a signaling protocol for Internet conferencing, telephony, presence, events notification, and instant messaging. Real-time person-to-person communications are fast becoming a critical communications tool for enterprises of all sizes, and with the standardization of SIP as the Internet protocol for applications such as VoIP, instant messaging, presence, and increasingly video, businesses are eager to adapt their existing hardware to accept SIP quickly, cost-effectively and securely.

What’s the Short of It? You need SIP to support address resolution, name mapping, and call redirection. You also need it to:

  • Determine the media capabilities of the target end point. SIP determines the "lowest level" of common services between the end points. Conferences are established using only the media capabilities that can be supported by all end points.
  • Determine the availability of the target end point. If a call cannot be completed because the target end point is unavailable, SIP determines whether the called party is already on the phone or did not answer in the allotted number of rings. It then returns a message indicating why the target end point was unavailable.
  • Establish a session between the originating and target end point. If the call can be completed, SIP establishes a session between the end points. SIP also supports mid-call changes, such as the addition of another end point to the conference or the changing of a media characteristic or codec.
  • Handle the transfer and termination of calls. SIP supports the transfer of calls from one end point to another. During a call transfer, SIP simply establishes a session between the transferee and a new end point (specified by the transferring party) and terminates the session between the transferee and the transferring party. At the end of a call, SIP terminates the sessions between all parties.

The Buzzwords?

  • Simplicity. The SIP stack is smaller than other VoIP protocols.
  • Scalability. The peer-to-peer architecture permits inexpensive scaling. When compared to other Voice over IP protocols, the hardware and software requirements for adding new users to SIP-based systems is greatly reduced.
  • Distributed Functionality. A decentralized intelligence permits more functionality within each component. Changes made to specific components have a minor impact on the rest of the system.

And I Care Because… It’s generally viewed as the protocol of choice for VoIP because it promises interoperability between vendors and an underlying foundation upon which new applications and services can be provided. Meaning, it presents providers with many new revenue opportunities.

Who Should I See? There’ll be a great SIP workshop at Miami 2005, Thursday and Friday in Brickell pretty much all day.


David Sims is contributing editor and CRM Alert columnist for TMCnet.


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