IPComms transports T.38 through our network by allowing the T.38 UDPTL data to pass through to a T.38 PSTN gateway or other T.38 SIP device. Upon detecting a fax tone, our network will send a re-INVITE to attempt to switch to T.38. If the re-INVITE fails, another re-INVITE will be sent to attempt to switch to G.711 ulaw (if not already ulaw).