Figure 14 SIP User Agent
5.2.3.2 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.
1The client device (A in the figure) sends a call invitation to the SIP proxy server (B).
2The SIP proxy server forwards the call invitation to C.
Figure 15 SIP Proxy Server
5.2.3.3 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 to the IP address that it received back from the redirect server. Redirect servers do not initiate SIP requests.
In the following example, you want to use client device A to call someone who is using client device C.
1Client device A sends a call invitation for C to the SIP redirect server (B).
2The SIP redirect server sends the invitation back to A with C’s IP address (or domain name).
3Client device A then sends the call invitation to client device C.
Chapter 5 Introduction to VoIP | 47 |