I have set up a lab where a fax call flows like this:
FAXA->FXS-2651VoiceGW(adventerprisek9_ivs-mz.124-19)->7206VXR IPIPGW(advipservicesk9_li-mz.124-15.T5)-> (gatekeeper) -> 5400HPX->PSTN->FAXB
The problem is that when I want to send a fax using this scenario the T.38 fails and fall back to pass through... sometimes. T.38 is always failing. No T30 messages are been exchanged and i get a no answer message. The IPIPGW is configured as flow-through.
Doing several tests and configuration changes I saw that configuring it as flow-around T.38 is working just fine. The codec that i' m using is g729r8 all the way.
I then changed 7206VXR with a 3845 IPIPGW with same configuration and IOS FEATURE set(without changing something else just the IPIPGW chassis) and T.38 is working fine on every test i did.
The terminating GWs are AS5400HPX and XMs . I use c5400-js-mz.123-19.bin for HPXs and c5400-js-mz.124-11.T3.bin for XMs like always. These GWs are connected to the PSTN via SS7 so no changes there. This nework is in production anyway for the last years.
The lab was made for test reasons so I can implement 7206vxr IPIPGWs in the future as network grows.
Can you please advice if there is any known issue with this problem?
Any help will be very much appreciated.