A Session Initiation Protocol (SIP) application instance may consist of multiple protocol interactions. Each of these protocol interactions may be satisfied by a protocol library, that exposes its own Java API. As with SIP servlets or SIP Plain Old Java Objects (POJOs) acting as protocol listeners for SIP, these other protocol libraries can expose their own protocol listeners. For example, a Diameter library may expose a POJO that listens in on Diameter messages. Those messages may belong to a protocol session maintained by the Diameter protocol library. A SIP application archive, thus, may contain these protocol listeners as well. Furthermore, those protocol listeners can send SIP messages, while SIP POJOs might send other protocol messages as well.

For a detailed example of integrating with the Diameter protocol, see "Working with Diameter Applications Using CDI and POJOs" in Converged Application Server Diameter Application Development Guide.