ZyXEL Communications P-2812HNU-51c User Manual page 191

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 85 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.
The client device (A in the figure) sends a call invitation to the SIP proxy server
1
(B).
The SIP proxy server forwards the call invitation to C.
2
Figure 86 SIP Proxy Server
SIP Redirect Server
A SIP redirect server accepts SIP requests, translates the destination address to
an IP address and sends the translated IP address back to the device that sent the
request. Then the client device that originally sent the request can send requests
P-2812HNU-51c User's Guide
Chapter 9 Voice
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