Zyxel V301-T1 [103/240] Sip client server

Zyxel V301-T1 [103/240] Sip client server
Chapter 10 SIP Account Setup
V300 Series User’s Guide
103
2 B sends a response indicating that the telephone is ringing.
3 B sends an OK response after the call is answered.
4 A then sends an ACK message to acknowledge that B has answered the call.
5 Now A and B exchange voice media (talk).
6 After talking, A hangs up and sends a BYE request.
7 B replies with an OK response confirming receipt of the BYE request and the call is
terminated.
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.
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 84 SIP User Agent
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).

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