Stun; Outbound Proxy; Voice Coding; Figure 36 Stun - ZyXEL Communications VoIP Station Gateway P-2302R Series User Manual

7.7 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
details on STUN.
The following figure shows how STUN works.
1 The Prestige (A) sends SIP packets to the STUN server (B).
2 The STUN server (B) 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 (C).

Figure 36 STUN

7.8 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).

7.9 Voice Coding

A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital
signals back into voice signals. The Prestige supports the following codecs.
Chapter 7 Introduction to VoIP
Section 7.3.2.4 on page
P-2302R Series User's Guide
98) or firewalls. See RFC 3489 for
100