ZyXEL Communications P-2812HNU-51c User Manual page 192

Chapter 9 Voice
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.
Client device A sends a call invitation for C to the SIP redirect server (B).
1
The SIP redirect server sends the invitation back to A with C's IP address (or
2
domain name).
Client device A then sends the call invitation to client device C.
3
Figure 87 SIP Redirect Server
SIP Register Server
A SIP register server maintains a database of SIP identity-to-IP address (or
domain name) mapping. The register server checks your user name and password
when you register.
RTP
When you make a VoIP call using SIP, the RTP (Real time Transport Protocol) is
used to handle voice data transfer. See RFC 1889 for details on RTP.
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P-2812HNU-51c User's Guide