ZyXEL Communications NBG410W3G - Manual (Page 295)

Chapter 18 ALG Screen
NBG410W3G Series User’s Guide
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Figure 182 H.323 ALG Example
• With multiple WAN IP addresses on the ZyXEL Device, you can configure different
firewall and port forwarding rules to allow incoming calls from each WAN IP address to
go to a specific IP address on the LAN or DMZ.
For example, you configure firewall and port forwarding rules to allow LAN IP address A
to receive calls through public WAN IP address 1. You configure different firewall and
port forwarding rules to allow LAN IP address B to receive calls through public WAN IP
address 2.
Figure 183 H.323 with Multiple WAN IP Addresses
• The H.323 ALG operates on TCP packets with a port 1720 destination.
• The ZyXEL Device allows H.323 audio connections.
18.5 SIP
The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol that
handles the setting up, altering and tearing down of voice and multimedia sessions over the
Internet. SIP is used in VoIP (Voice over IP), the sending of voice signals over the Internet
Protocol.
SIP signaling is separate from the media for which it handles sessions. The media that is
exchanged during the session can use a different path from that of the signaling. SIP handles
telephone calls and can interface with traditional circuit-switched telephone networks.
18.5.1 STUN
STUN (Simple Traversal of User Datagram Protocol (UDP) through Network Address
Translators) allows the VoIP device to find the presence and types of NAT routers and/or
firewalls between it and the public Internet. STUN also allows the VoIP device to find the
public IP address that NAT assigned, so the VoIP device can embed it in the SIP data stream.
See RFC 3489 for details on STUN. You do not need to use STUN for devices behind the
ZyXEL Device if you enable the SIP ALG.
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