5
Configuring VoIP
An application-layer gateway provides basic proxy features for voice and video over IP traffic. Serving as an ALG proxy, the 6400-S provides Network Address Translation (NAT) services for the protected softswitch, gatekeeper or other media devices. It maps multiple devices on the subscriber interface (public) to a single IP address on the provider interface (private). The ALG must first recognize and register a public network based device before it presents traffic from the IP telephone, video endpoint or data device through its provider port.
The 6400-S contains an MGCP, SIP, and H.323 call-control proxy ALG. VoIP phones, video endponts and client adapters have to be configured to point to the 6400-S as the call-control server, proxy, gatekeeper or gateway (depending on protocol). The 6400-S then forward this traffic onto the actual call-control server or gatekeeper.
For corporate customers with high-end routers and firewalls, the 6400-S can be configured as a VoIP Application Layer Gateway only. This allows all of the normal data traffic to continue to be handled by the existing network devices, and only voice or traffic to be handled by the 6400-S. For this configuration, the 6400-S Subscriber Ethernet port is connected to the internet. The 6400-S Provider Ethernet port is connected to a port on the local Ethernet switch.