Hi Anees...
I got some ATA 186 and VG202 and never can send fax between them through ip network when use codec g.729, i need to use PSTN.
Try to send the fax using PSTN
FAX Machine (A) ---> ATA(A) ---> CUCM ---> PSTN GATEWAY--> CUCM --> ATA(B) --> FAX Machine (B)
if works try without PSTN
FAX Machine (A) ---> ATA(A) ---> CUCM ---> ATA(B) --> FAX Machine (B)
regards!