Chapter 10 The Service Configuration Screens
User’s Guide
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6After talking, A hangs up and sends a BYE request.
7B replies with an OK response confirming receipt of the BYE request and the call is
terminated.
10.4.2 SIP Client ServerSIP 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.
10.4.3 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 49 SIP User Agent
10.4.4 SIP Proxy ServerA 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.
1The client device (A in the figure) sends a call invitation to the SIP proxy server
(B).