No voice on other end of call

[sr98user]

The main reason is there are different kinds of NAT

http://en.wikipedia.org/wiki/Network...ss_translation

Firewall and SIP ALG (SIP packet re-write) implementation differ for each router. That might cause problems on some routers.

Since VOIPo doesn't proxy the audio stream and traffic goes directly to the upstream carrier, the routers need to allow traffic from upstream carriers. Some routers don't do that.

[stevech]

Since VOIPo doesn't proxy the audio stream and traffic goes directly to the upstream carrier, the routers need to allow traffic from upstream carriers. Some routers don't do that.

Tutorial for me...
Is it the case that the VoIP bearer traffic (audio) is a stream of UDP (RTSP) packets from the ATA through the router to the carrier's host - and the return is a likewise stream of UDP packets. And some routers figure out that the return stream mates with the outbound stream and forwards to the correct private LAN IP address? This is somehow done by remembering the port and remote host in the router for outbound, then when packets come back from that same host, they go to the LAN IP that is doing the outbound? Or something like that? Is there an IETF/RFC for this scheme that one could confirm before buying a router (to see if they claim to do so)?

I've owned several Linksys routers and this Cradlepoint MBR900 and none have needed explicit port forwarding for VoIP, perhaps due to the above.

(end of lesson 1)

[voipinit]

My Linksys router will break VOIP if I forward the ports for VOIP traffic, it shouldn't but typical crappy firmware from Linksys. Fortunately, placing the ATA in DMZ allows it to function correctly but does require STUN setup on the ATA and UPnP enabled on the router. It's a WRT54GX2 in case you are wondering.