Figure 136 Sip Redirect Server - ZyXEL Communications V501-T1 User Manual

Chapter 11 SIP Account Setup
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.
1 Client device A sends a call invitation for C to the SIP redirect server (B).
2 The SIP redirect server sends the invitation back to A with C's IP address (or domain
name).
3 Client device A then sends the call invitation to client device C.

Figure 136 SIP Redirect Server

SIP Register Server
A SIP register server (also known as a registrar 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.
NAT and SIP
NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a
host in a packet, for example, the source address of an outgoing packet, used within one
network to a different IP address known within another network.
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