SIP User Agent

A SIP User Agent is a fundamental component in the SIP protocol architecture, acting as the client-side application that initiates and terminates real-time communication sessions over IP networks. It plays a dual role, functioning both as a User Agent Client (UAC), which sends SIP requests, and a User Agent Server (UAS), which responds to SIP requests. This dual functionality enables the SIP User Agent to handle a wide range of communications, including voice, video calls, and instant messaging, by managing the setup, modification, and teardown of sessions. 

Functionality: 

Session Initiation and Termination: The SIP User Agent initiates session setup requests and handles incoming requests to start communication sessions. It is also responsible for closing sessions, either by sending or responding to termination requests.