User`s guide

Chapter 11 The Service Configuration Screens

User’s Guide

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11.4.2 SIP Client Server

SIP is a client-server protocol. A SIP client is an application program or device that sends SIP

requests. A SIP server responds to the SIP requests.

When you use SIP to make a VoIP call, it originates at a client and terminates at a server. A

SIP client could be a computer or a SIP phone. One device can act as both a SIP client and a

SIP server.

11.4.3 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 66 SIP User Agent

11.4.4 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 67 SIP Proxy Server