Figure 86 Sip Redirect Server - ZyXEL Communications V300 Series User Manual

Chapter 10 SIP Account Setup
Client device A then sends the call invitation to client device C.
3

Figure 86 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.
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.
The V300 must register its public IP address with a SIP register server. If there is
a NAT router between the V300 and the SIP register server, the V300 probably has
a private IP address. The V300 lists its IP address in the SIP message that it sends
to the SIP register server. NAT does not translate this IP address in the SIP
message. The SIP register server gets the V300's IP address from inside the SIP
message and maps it to your SIP identity. If the V300 has a private IP address
listed in the SIP message, the SIP server cannot map it to your SIP identity.
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V300 Series User's Guide