To STUN or not to STUN

STUN, Simple Traversal of UDP through NATs , is a protocol used to work around the problems caused by router/firewall for VOIP applications. It is also known as Session Traversal Utilities for NAT.

The basic problem of a router/firewall for VOIP traffic is that a computer’s IP address inside NAT cannot be seen from outside. So in order for other application to send audio strean to a VOIP application inside a router, it must know the outside IP address used by the router. And in order to discover the outside IP address, a STUN client sends a request to a STUN server outside the router/firewall. Since the request has to pass through the router, it will carry the outside IP address in the request. The STUN server simply returns the outside IP address to the STUN client.

To setup Voicent software, if your computer has to pass through a router in order to reach your VOIP service, then you must specify a STUN server. If your computer and the VOIP service or PBX system are on the same local area network (LAN), then DO NOT specify a STUN server (if you do, the audio will be sent ourside the router and you will not be able to hear anything).