-- Off-ramp -- Still within T.37, an off-ramp gateway receives TIFF digital fax from the Internet and delivers it to local analog fax functions in fax machines or PCs with fax software. Again, there are commercial services that perform this function. As with on-ramps, this gateway may also have analog capability.

-- T.38: Real-Time Fax in Packets? -- Conventional fax machines that transmit using the T.30 protocol learn from T.30 messages if the transmission is considered complete by the receiver. Knowing that the message has been received can be important when, for example, you are negotiating a contract with marked-up documents. Note that a T.30 fax should give an error message if it has a paper jam or another nonprotocol problem, but this doesn't always happen.

T.38 gets around the delivery-confirmation problem but gives up some of the flexibility of store-and-forward. A typical system takes traditional T.30 fax from the PSTN, routes it over an IP network, connects in real-time to a T.38 gateway and then converts it back to a T.30 fax session at or near the destination fax machine.

T.38 can experience the equivalent of a busy signal if an Internet connection cannot be made. Some T.38 gateways also have backup G3 analog interfaces.

Applications