ZyXEL Communications PRESTIGE 2000W V2, User Manual

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P-2000W_V2 User’s Guide
Chapter 12 User Web Configurator Screens 89
12.12.3 STUN
STUN (Simple Traversal of User Datagram Protocol (UDP) through Network Address
Translators) allows the Prestige to find the presence and types of NAT routers and/or firewalls
between it and the public Internet. STUN also allows the Prestige to find the public IP address
that NAT assigned, so the Prestige can embed it in the SIP data stream. STUN does not work
with symmetric NAT routers (see
Section 12.11.2.4 on page 87 ) or firewalls. See RFC 3489
for details on STUN.
The following figure shows how STUN works.
1 The Prestige (A) sends SIP packets to the STUN server.
2 The STUN server finds the public IP address and port number that the NAT router used
on the Prestige’s SIP packets and sends them to the Prestige.
3 The Prestige uses the public IP address and port number in the SIP packets that it sends to
the SIP server.
Figure 26 STUN
12.12.4 Outbound Proxy
Your VoIP service provider may host a SIP outbound proxy server to handle all of the
Prestige’s VoIP traffic. This allows the Prestige to work with any type of NAT router and
eliminates the need for STUN or a SIP ALG. Turn off a SIP ALG on a NAT router in front of
the Prestige to keep it from retranslating the IP address (since this is already handled by the
outbound proxy server).
12.13 NAT Traversal Configuration
Click NAT TRVSL to open the following screen where you can configure your Prestige to
operate through a NAT router that is not SIP-friendly.
The following screen displays the IP address and port number of an outbound proxy server the
Prestige uses to connect to the outbound proxy server.