When connecting a SIP subscriber fax adapter on STMI2 or STMI4 boards, DMC must be deactivated for the device or T.38 transmission is not possible (the reason is classic STMIs have no internal media relay function and cannot negotiate T.38 on two separate streams). If DMC is important for the customer on those devices, the codec must be set to G.711 and T.38 switched off.

T.38 fax streams are not supported for SPE.

T.38 configuration/usage requires end-to-end DMC between OpenScape 4000 gateways (minimized IP hops) because of timing requirements according to T.38 standard. In case of multiple IP hops the fax transmission could fail with some fax machines - see Section 2.2.1, “Delay problems in scenario with 2 and more IP-hops and certain fax machines”.

T.38 can be used right from the beginning of a transmission, that is, with initial SIP invite.