User's Manual

4 Overview

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Overview

The SIP Application Module is a service execution engine that provides

the following functionality:

• core signaling functionality enabling communication among SIP

clients

• SIP proxy server

• Back-to-Back User Agent

• SIP Registration

• CPL interpretation

• Location server

• optional Presence subscription and notification (For more

information on the Presence feature, see the MCP SIP Presence

Basics document.)

The SIP Application Module handles SIP sessions and applications and

provides the core services that enable communication between SIP

clients. The SIP Application Module is housed on the SIP Application

Server.

Functional description

The SIP Application Module includes the following components:

• Back-to-Back User Agent (BBUA)/Proxy Server

Although the BBUA and Proxy Server are basically two different

logical entities within the same physical server, they both act as

clients and servers. The SIP Application Module decides on a

call-by-call basis whether to process the request as a pure Proxy or

BBUA.

The Proxy Server processes SIP requests and responses, rewrites

headers, modifies request-URIs (Universal Resource Indicator),

performs location look-up, and forwards requests to SIP clients or

other servers in the network.

The SIP Application Module provides a fully session-stated proxy; in

other words, the SIP Application Module maintains a call state for

the entire session.

The BBUA extends the proxy function to perform advanced

functions such as

— originating new calls

— tearing down existing calls

— modifying messages