i have a ccme behind an ios nat router and when i make calls to the incoming sip trunk the phones ring but when i answer there is no audio and the cell phone im using to caal the sip trunk keeps ringing like i didnt even answer. i can make outgoing calls fine but something is getting blocked coming in. could this be a nat traversal issue, i have implemented the ip inspect sip etc..
We should be able to support the IOS NAT ALG. There were a few posts about this yesterday. This feature was added in 12.2(8)T.
Compare the SIP message you see on the outside of your NAT router with 'debug ccsip messages'. Check the SDP for the IP address.
To be honest - this problem sounds like more of a firewall problem than pure NAT. Since you have one-way calling abilities, you have problems. On your outgoing dial peer, try adding 'session tranport tcp', or if it's already TCP, try UDP. Sometimes this helps figure out the firewall problem.