ZyXEL Communications FMG3024-D10A User Manual

Chapter 18 VoIP

FMG3024-D10A / FMG3025-D10A Series User’s Guide

SIP Redirect 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. 

When you make a VoIP call using SIP, the RTP (Real time Transport Protocol) is used to handle voice 
data transfer. See RFC 3550 for details on RTP.

Pulse Code Modulation (PCM) measures analog signal amplitudes at regular time intervals and 
converts them into bits.

The following figure displays the basic steps in the setup and tear down of a SIP call. A calls B. 

SIP Call Progression

1. INVITE

2. Ringing

3. OK

4. ACK 

5.Dialogue (voice traffic)

6. BYE

7. OK