We have the following scheme:
PRI---GWoutside(FAX1 with FXS)---SW3750--(fiber)---SW3750---GWinside-(FXS)-FAX2
The FAX1 can send and receive fax to/from PSTN perfectly, but FAX2 fails randomly, so I think the problem is in IP path. It usually can send fax to PSTN, but the reception fails very often. I have seen show voice call summary, and it negotiates codec g729r8. After a while it change the codec to cisco (it uses cisco fax relay by default). When the reception fails I can't see cisco codec because it disconnects before that. What is the best way to do this implementation? I think the CCM is not necessary involucred.