User manual

4200 User Manual Edgewater Networks, Inc.

Version 2.2 20

VoIP Configuration

The 4200 provides a VoIP application layer gateway (ALG) for the SIP, MGCP, H.323

and SCCP protocols. The ALG proxies the connection between the VoIP softswitch or

IP PBX and voice devices such as IP phones, IADs or softphones. By acting as a

proxy the 4200 is able to provide several important functions for IP based voice:

 Provide NAT/PAT services for voice traffic. NAT/PAT for VoIP enables you to

use a single public IP address on the WAN interface of the 4200 to represent

multiple private IP addresses assigned to voice 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 devices.

 Provide security services for voice traffic.

o NAT/PAT services hide enterprise LAN topology from hackers.

o The ALG acts as a “voice 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 call.

 Automatically re-register voice devices with the softswitch subsequent to a

WAN IP address change. The WAN IP address can change when using WAN

DHCP and/or PPPoE. This is a typical combination for ADSL and cable modem

links.

 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 device may be changed.

Configure the VoIP ALG

In order to configure the VoIP ALG the 4200 must be told where to reach the

signaling servers and TFTP server on behalf of the voice devices.

A. Select VoIP ALG.

B. If you are using MGCP enter the MGCP

Server IP Address.

C. If you are using SIP enter the SIP

Server IP Address and SIP server

port. The SIP server port is the port

used by the SIP registrar. The default

value is port 5060.

D. If you are using SCCP enter the SCCP

Call Manager IP address.

E. Enter the TFTP Server Address. This

address is used to identify the TFTP

server that contains the images used by

IP phones at boot up. The 4200

performs a TFTP server relay function.