ZyXEL Communications vmg8924-b10a User Manual page 253

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 domain name).
2
Client device A then sends the call invitation to client device C.
3
Figure 153 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.
Pulse Code Modulation
Pulse Code Modulation (PCM) measures analog signal amplitudes at regular time intervals and
converts them into bits.
VMG8924-B10A User's Guide
Chapter 21 Voice
253