ZyXEL Communications NBG410W3G - Manual (Page 294)

Chapter 18 ALG Screen
NBG410W3G Series User’s Guide
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18.1.3 ALG and Multiple WAN
When the ZyXEL Device has two WAN interfaces and uses the second highest priority WAN
interfaces as a back up, traffic cannot pass through when the primary WAN connection fails.
The ZyXEL Device does not automatically change the connection to the secondary WAN
interfaces.
If the primary WAN connection fails, the client needs to re-initialize the connection through
the secondary WAN interfaces to have the connection go through the secondary WAN
interfaces.
18.2 FTP
File Transfer Protocol (FTP) is an Internet file transfer service that operates on the Internet and
over TCP/IP networks. A system running the FTP server accepts commands from a system
running an FTP client. The service allows users to send commands to the server for uploading
and downloading files. The FTP ALG allows TCP packets with a port 21 destination to pass
through. If the FTP server is located on the LAN, you must also configure NAT port
forwarding and firewall rules if you want to allow access to the server from the WAN.
18.3 H.323
H.323 is a standard teleconferencing protocol suite that provides audio, data and video
conferencing. It allows for real-time point-to-point and multipoint communication between
client computers over a packet-based network that does not provide a guaranteed quality of
service. NetMeeting uses H.323.
18.4 RTP
When you make a VoIP call using H.323 or SIP, the RTP (Real time Transport Protocol) is
used to handle voice data transfer. See RFC 1889 for details on RTP.
18.4.1 H.323 ALG Details
• The H.323 ALG supports peer-to-peer H.323 calls.
• The H.323 ALG handles H.323 calls that go through NAT or that the ZyXEL Device
routes. You can also make other H.323 calls that do not go through NAT or routing.
Examples would be calls between LAN IP addresses that are on the same subnet.
• The H.323 ALG allows calls to go out through NAT. For example, you could make a call
from a private IP address on the LAN to a peer device on the WAN.
• You must configure the firewall and port forwarding to allow incoming (peer-to-peer)
calls from the WAN to a private IP address on the LAN or DMZ. The following example
shows H.323 signaling (1) and audio (2) sessions between H.323 devices A and B.