And then we finally get to NGN signaling protocols: SIP and SDP. The picture below was extracted from RFC 3261 and gives a fairly good example of a SIP dialog between two users, Alice and Bob.
The entities involved in the call setup are called User Agents (UA). UAs which request services are called User Agent Clients (UAC), and those which fulfill requests are called User Agent Servers (UAS). Although the basic operating mode is end-to-end, the model supports the use of intermediate ...
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