Polycom V2IU 4350 - Manual (Page 74)

User Manual V 2 IU 4350 Converged Network Appliance
3 - 56
VoIP Configuration
The 4350 provides a VoIP application layer gateway (ALG) for the SIP, MGCP,
and H.323 protocols. The ALG proxies the connection between the VoIP
softswitch, IP PBX or gatekeeper and voice and video devices such as IP
phones, IADs or softphones. By acting as a proxy the 4350 is able to provide
several important functions for IP based voice and video:
• Provide NAT/PAT services for voice and video traffic. NAT/PAT for
VoIP enables you to use a single public IP address on the WAN interface
of the 4350 to represent multiple private IP addresses assigned to voice or
video devices on the LAN. The NAT function maps both IP address and
IP port number between the public and private addresses so that all
signaling and VoIP media packets are translated. A single public IP
address can support up to 253 voice and video devices.
• Provide security services for voice and video traffic.
— NAT/PAT services hide enterprise LAN topology from hackers.
— The ALG acts as a “voice and video aware” firewall and ensures only
authenticated voice traffic enters the enterprise LAN. This is
accomplished by the dynamic provisioning of signaling and media
ports for authenticated voice devices. The implementation is stateful
and open ports are closed automatically when no longer required to
support the voice or video call.
• Enable mobility in the enterprise LAN for voice devices. This is useful, for
example, when using WiFi or moving office locations. In these instances
the IP address of the voice and video device may be changed.