Converged Application Server supports the Diameter base protocol. It supports the IMS Sh interface provider on engines, which then act as Diameter Sh client nodes. SIP Servlets deployed on the engines can use the profile service API to initiate requests for user profile data, or to subscribe to and receive notification of profile data changes. The Sh interface is also used to communicate between multiple IP Multimedia Subsystem (IMS) Application Servers.

One or more server instances may be also be configured as Diameter relay agents, which route Diameter messages from the client nodes to a configured Home Subscriber Server (HSS) in the network, but do not modify the messages. Oracle recommends configuring one or more servers to act as relay agents in a domain. The relays simplify the configuration of Diameter client nodes, and reduce the number of network connections to the HSS. Using at least two relays ensures that a route can be established to an HSS even if one relay agent fails.

The relay agents included in Converged Application Server perform only stateless proxying of Diameter messages; messages are not cached or otherwise processed before delivery to the HSS.

Note that relay agent servers do not function as engines: they should not host applications, store call state data, maintain SIP timers, or even use SIP protocol network resources (sip or sips network channels).

In summary, Converged Application Server supports the following Diameter functions:

• Diameter Sh interface client node (for querying a Home Subscriber Service)
• Diameter Rf interface client node (for offline charging)
• Diameter Ro interface client node (for online charging)
• Diameter relay node
• HSS simulator node (suitable for testing and development only, not for production deployment)

Converged Application Server also provides a simple HSS simulator that you can use for testing Sh client applications. You can configure a Converged Application Server instance to function as an HSS simulator by deploying the appropriate application.

For information on developing Diameter applications for Converged Application Server, see the Converged Application Server Diameter Application Development Guide.