I have a SPA9000 with 1 analog phone on fxs 1 using Callcentric and I get one way audio on inbound calls. Pretty much at wits end and I'm a newb at voice boxes. When I call out, it seems okay. When someone calls in, they can hear me, but I can't hear anything.
Last Nerve :)
The reason it worked after you enabled the SIP ALG (SIP Application Layer Gateway) is because your router is doing NAT. This is the most effective way (other than STUN or TURN) to mitigate NAT Traversal. Bottom line is when a call leaves your network it gets translated to a public ip and a random port but is aimed at a particular port on the destination ip address. When the reply gets back to the origin, the ports no longer match so the 9000 does not understand where to send the data it recieved. If you attached your SPA9000 directly to the internet without the router, you would get 2 way audio also because there would not be NAT to traverse. If you want more information on the SIP ALG, try this:
Congrats on your triumph over VoIP and NAT!
This sounds like an rtp port issue. You need to open ports 16384 - 16482 (UDP) on your router. You did not mention whether or not you were using digital phones and if they were experiencing the same issues. If they are and you open the ports listed above, and that does not work, then open ports 10000 - 20000 (UDP) on your firewall. The basic issue is that when you initiate a call from behind the firewall, it has a session open to that ip address on a corresponding port. However when a call is initiated from outside the network then there is not an open session and the router/firewall does not know to accept traffic on those ports. Hope this helps.