Switching to VoIP

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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placing a media proxy on the DMZ, while others suggest avoiding the Internet alto-

gether as preferable to using STUN. But this advice is overblown. STUN works

great—when it’s there.

STUN is defined by RFC 3489. A free, open source implementation of the client and

server is available from http://www.vovida.org/applications/downloads/stun. Vovida

also operates two public STUN servers that you can use in small-scale applications

and for your own STUN client development. Try configuring the X-Lite softphone to

use Vovida’s STUN servers, either 128.107.250.38 or 128.107.250.39, to place SIP

phone calls through a NAT firewall.

VPN Allows Coexistence with NAT

There’s another solution that can help you avoid VoIP-through-NAT, if you are the

proprietor of both the VoIP server and the endpoints it supports. Virtual private net-

works allow VPN clients on the Internet to use the same IP network address as the

VPN server. Therefore, if a VPN server and a VoIP server are on the same LAN, VPN

clients connecting to that VoIP server from the Internet needn’t be concerned with

NAT. Of course, you have the normal headaches of a VPN, such as latency and the

lack of QoS. But if your VPN is good enough, it saves you from the NAT problem.

Peer-by-Peer Codec Selection

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