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SIP Constructs Applied To the Contact Center

In order to understand some of the differences between the various SIP-based contact center solutions being offered by vendors, it will be useful to understand a little more about SIP components, and what function they serve when applied to the contact center.

* SIP User Agents: These are the SIP endpoints, which in the contact center would be desk phones or softphones for agents. For noncontact center enterprise experts, mobile smart phones might be the SIP user agent, and in some scenarios, such as a bank branch, the agent could be a video kiosk. The term SIP user agents can also be applied to resources used by the contact center, such as recorded announcements or recording applications.

* SIP Back to Back User Agent (logical rather than physical): This refers to the bridging of two independent SIP sessions by an intelligent application. SIP sessions terminating on the incoming user agent are passed to the intelligent application which determines what to do with the session, based on business rules or logic. In the contact center context, a skillsbased routing application would be an example of a B2BUA.

* SIP Proxy/Redirect Server: The proxy server is an intermediate device that receives SIP requests from a client and then forwards the requests on the client's behalf. A SIP proxy redirect server provides the client with information about the next hop that a message should take, and then drops out of the session completely. A SIP proxy server can initiate sessions with the necessary applications to perform call routing and information lookups that once required a CTI (computer-telephony integration) server.

* SIP Registrar: SIP endpoints send "register" messages to identify their current location in the IP network to the SIP registrar, and the SIP registrar maintains the users' whereabouts. Registrar servers are often co-located with a redirect or proxy server. This may be a PBXrelated function, as is true with Avaya's Session Enablement Services, or may be found wholly within the contact center application, as is true in the case of the Genesys SIP Server.

* SIP Presence Server: A SIP presence server accepts SIP PUBLISH sessions from users who announce their current state (Busy, Away from Desk, On the Phone). A SIP-based contact center agent should be able to take advantage of SIP presence to determine the status of enterprise subject matter experts, and then connect with them.

This originally appeared in the March 2007 issue of Business Communications Review.