ZyXEL Communications Corporation V630 Manuel D’Utilisation
Chapter 14 SIP Account Setup
V630 User’s Guide
133
14.1.6.1 STUN
STUN (Simple Traversal of User Datagram Protocol (UDP) through Network Address
Translators) allows the V630 to find the presence and types of NAT routers and/or firewalls
between it and the public Internet. STUN also allows the V630 to find the public IP address
that NAT assigned, so the V630 can embed it in the SIP data stream. STUN does not work
with symmetric NAT routers or firewalls. See RFC 3489 for details on STUN.
Translators) allows the V630 to find the presence and types of NAT routers and/or firewalls
between it and the public Internet. STUN also allows the V630 to find the public IP address
that NAT assigned, so the V630 can embed it in the SIP data stream. STUN does not work
with symmetric NAT routers or firewalls. See RFC 3489 for details on STUN.
The following figure shows how STUN works.
1 The V630 (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
2 The STUN server (B) finds the public IP address and port number that the NAT router
used on the V630’s SIP packets and sends them to the V630.
3 The V630 uses the public IP address and port number in the SIP packets that it sends to
the SIP server (C).
Figure 137 STUN
14.1.6.2 Outbound Proxy
Your VoIP service provider may host a SIP outbound proxy server to handle all of the V630’s
VoIP traffic. This allows the V630 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 V630 to
keep it from retranslating the IP address (since this is already handled by the outbound proxy
server).
VoIP traffic. This allows the V630 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 V630 to
keep it from retranslating the IP address (since this is already handled by the outbound proxy
server).
14.1.7 Voice Coding
A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital
signals back into voice signals. The V630 supports the following codecs.
signals back into voice signals. The V630 supports the following codecs.
• G.711 is a Pulse Code Modulation (PCM) waveform codec. PCM measures analog signal
amplitudes at regular time intervals (sampling) and converts them into digital bits
(quantization). Quantization “reads” the analog signal and then “writes” it to the nearest
digital value. For this reason, a digital sample is usually slightly different from its analog
original (this difference is known as “quantization noise”).
(quantization). Quantization “reads” the analog signal and then “writes” it to the nearest
digital value. For this reason, a digital sample is usually slightly different from its analog
original (this difference is known as “quantization noise”).
• G.726 is an ADPCM waveform codec that uses a lower bit rate than standard PCM
conversion. G.726 operates at 16, 24, 32 or 40 kbps.