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- Serve as rendezvous point at which callees are globally reachable
- Perform routing function, i.e., determine to which hop (UA/proxy/redirect) signaling should be relayed
- Allow the routing function to be programmable.
- Arbitrary logic may be built on top of the protocol user’s signaling preferences
AAA firewall control
- Forking: Several destinations may be tried for a request sequentially or in parallel.

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Posted by nareshkumar

Proxy server—This server can perform call routing, authentication, authorization, address resolution, and loop detection. A UA sends its call setup messages through a proxy server. The proxy server can forward the messages if it knows where the called party is located, or it can query other servers to find that information. It then forwards the request to the next hop. When it receives a response to the request, it forwards that to the client UA. After the call is set up, the proxy server can elect to stay in the signaling path so that it also sees call change or termination messages, or it can withdraw from the path and let the UAs communicate directly. Cisco has a SIP proxy server product.

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Posted by sagitraz