Assume the following topology:
A -----> S -------> B
A B2BUA is a UA. It originates and/or terminates calls. If S is a B2BUA, when it receives an incoming call (from A), it acts as the termination point for signaling of that call. It probably then originates another call with the intent of reaching the first caller's intended target (B). The two calls have different callids, different Via headers, different Route headers, etc. Nevertheless, S can operate in such a way that A thinks it has a call with B, and where offers and answers are exchanged between A and B (with S acting as relay), and media is exchanged directly between A and B (without S acting as a relay.) If it so desires, S can later alter the (virtual) call from A to B, by initiating an UPDATE or reINVITE, or BYE. It can thus cause the call to be retargeted, say to A->S->C.
If S is a call stateful proxy, then S simply proxies the messages from A to B and visa versa. It can add headers to them - notably a Record-Route header so that it ends up in the Route headers and so stays in the signaling path for a call. It can see the subsequent signaling that goes on within a call, and can alter those messaages. But it can't initiate new signaling within a call. For instance it cannot send a BYE to kill a call. Nor can it initiate a reINVITE or UPDATE to test if the call is still functional.
Paul
Desai Sunil Kumar wrote:
Can some body please point out the difference between B2Bua & SIP statefull proxy.
Reg Sunil Desai
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