After many hours of reading on voip technology I have some questions.

Right now I have a VOIPO ATA Adapter sitting inside a DMZ behind my router. I assigned it an internal private static ip address and I set my router to forward all UDP packets from 5000-65000 to it.

First, why is this a requirement? (Please note without this forwarding my calls wouldn't work properly) My softphone software running on my PC inside my network requires no such port forwarding, why does the voip ATA box require this? Second if I wanted to add another VOIP ATA box, then this would seem to be a problem since I have UDP packets forwarded to a specific adapter.

In my readings, I read about STUN servers and these looked to be an alternative to port forwarding. Is this correct?

Thanks