Michael Gilfix Online

Work's been keeping me very busy lately. So, I plan on writing about a commonly asked question around the new converged HTTP/SIP capabilities in WebSphere Application server (WAS) V6.1. So first, what is a converged service? A converged service is an application that spans communication over multiple protocols to provide higher level function. In the case of the HTTP & SIP protocols, a converged service joins together session information from both protocols, allowing interactions over one protocol to influence communication over the other (subjects to the constraints of the protocol). WAS provides a Servlet programming model for both HTTP & SIP. Unification of those protocols is achieved though a converged web container solution, whereby sessions for both protocols may live in a single parent "application session" instance under the covers -the application session concept being first introduced as a SIPApplicationSession concept in the JSR116 SIP Servlet programming model.

The basic benefit to converged services? For SIP enabled applications, HTTP provides an ideal control protocol for communication with SIP signaling logic, which may participate in many different sessions, and may be constantly sending and receiving signaling messages asynchronously out the back-end. However, SIP also supports the notion of a basic request and response exchange, so what makes HTTP so ideal? First, you don't have to deal with the unreliability in SIP in a situation where decisive action is needed. But then enter Web Services. Central to Web Services is the notion of a Web Service Definition Language (WSDL) document that describes the structure of the request being issued. While you can always stuff a bunch of XML into an HTTP or SIP request to communicate with the application, WSDL provides the formal structure to allow you to communicate that interface to others. This approach also provides a path to interoperability with other programming stacks.