Network address translation

VoIP does not work well with networks that use Network Address Translation (NAT) because most NAT implementations do not support H.323 protocols. The destination IP address is encapsulated in more than one header: the Q.931, H.225, and IP headers. NAT changes only the address in the IP header resulting in a mismatch that prohibits the control of calls. Avaya does suggest implementing a firewall to guard against intruders, but the firewall should not provide NAT functions for VoIP packets, unless it is Q.931 friendly like the Lucent 201 Brick.