Sip User Agent; Sip Proxy Server; Figure 27 Sip User Agent; Figure 28 Sip Proxy Server - ZyXEL Communications VoIP Station Gateway P-2302R Series User Manual

7.2.3.1 SIP User Agent

A SIP user agent can make and receive VoIP telephone calls. This means that SIP can be used
for peer-to-peer communications even though it is a client-server protocol. In the following
figure, either A or B can act as a SIP user agent client to initiate a call. A and B can also both
act as a SIP user agent to receive the call.

Figure 27 SIP User Agent

7.2.3.2 SIP Proxy Server

A SIP proxy server receives requests from clients and forwards them to another server.
In the following example, you want to use client device A to call someone who is using client
device C.
1 The client device (A in the figure) sends a call invitation to the SIP proxy server (B).
2 The SIP proxy server forwards the call invitation to C.

Figure 28 SIP Proxy Server

Chapter 7 Introduction to VoIP
P-2302R Series User's Guide
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