In my experiemce there are always issues with T.38 and ATA 187 devices and VG's.
This is when ywe have this setup PSTN----PRI-ISDN------GW------SW----CUCM
Could also be FXO doesnt matter still have issues.
NOTE This dicussion relates to this architecture PSTN----PRI-ISDN------GW------SW----CUCM
I find T.38 to be very incosistant and unreliable when there is POTS and ATA 187 and also VG224,
Ive even tried T.38 fallback none with modem passthough under global config and found that doesnt work well (consistantly) and we get failures.
What I have also tried and found is if we have T.38 configured with ulaw and fallback none
then modem passthrough under Voice Service VoIP - the calls dont connect always either.
What I have found to be seemless and work
creating dedicated dial-peer for the actuall faxes and doing fax/modem passthough on these with G711ulaw as codec.
Given CUCM only allows setting of ulaw - there is no point sending alaw or setting in voice class or dial-peer point to CUCM at it or the Cisco IP to analogue gatereways dont transmit or take a setting for alaw?
In summary Id ask
- Is it preferebale to only use T.38 when both call legs are IP ?
- Note I have tested "PSTN----PRI-ISDN------GW------SW----CUCM" when the other end is a IP brooktrout stack and T.38 seem ok no problems
- All the Cisco docs I remember seeing relating to T.38 show VoIP legs and no POTS leg
Thanks
