Fax machines relied on telephone lines for years, but that's no longer necessary. FoIP -- Fax over IP -- technology lets businesses transmit faxes along computer cables, sending them over the Internet or through the corporate local-area network. Some fax machines are Internet-capable, but even non-Internet fax machines can transmit if you add the right equipment.
Fax machines use analog transmission to send images along phone lines. To use the Internet instead, the data must be digitized. One method is to connect the fax machine to a "fax gateway," which is a device that converts the message for Internet transmission and converts faxes you receive back into analog for printing out. Both sender and receiver need to have FoIP equipment to make a transmission work.
If you want to buy FoIP technology for your business, most FoIP equipment uses the T37 standard. T37 FoIP sends faxes across the Internet as encoded email messages; the gateway device stores the fax, digitizes it and then forwards it to the recipient machine. One drawback is that your fax capabilities are limited to those of the fax gateway; if your fax can send and receive in color but the gateway only handles black and white, black and white is all you get. T37 also lags behind the speed of a phone-line fax machine.
The T38 protocol allows for faster transmissions without the lag of a T37. Far fewer devices support T38. Fax machines that connect directly to the Internet use the T38 protocol. Some manufacturers use the term "Internet capable" very loosely, so when shopping for a FoIP fax machine ask for specifics. In many cases it only means the machine is compatible with T38 equipment, not that it can access the Internet without a gateway.
When you send faxes over a network cable instead of a phone line, there's a greater chance of interference. Jitters, lag time or other problems in transmission may scramble the data, preventing you from transmitting or receiving an accurate copy. Having a T38 gateway or fax machine on both ends of the transmission reduces the risk. If only a little bit of data gets scrambled a T38 will only lose a little bit of the image, whereas a T37 might mangle the entire message.
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