VOIP plus NAT

[jeff.yau]

System (1): 3640 with T1 interface, IOS 12.2(7),

System (2): Other Brand VOIP Gateway with E&M interface.

Connection: (1)--Checkpoint NG--Internet--Checkpoint NG--(2)

Description: We use checkpoint firealls to process NAT for both system which have private address only. Now I can make phone connection but only get one way voice. In the firewall's log, it shows all traffic are passed completely. I am not sure whether this case is realted to NAT or not. But similar case wroks without NAT process.Please help!

Any comment will be appreciated.

[travis-dennis_2]

You may have already tried this but can you ping the IP phone from the other side? One way voice is sometimes the result of a routing issue. The packets can get to the phone on the other side but don't know how to get back.

Also try this:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a008009484b.shtml

[jeff.yau]

Sorry, the system (2) should be using FXO module.

I can do ping tests successfully from the VOIP gateways.

Moreover, I want to understand that is there any difference between E&M and FXO module when I want to perform a NAT VOIP call?