What equipment is necessary for a fax machine to transfer data over a phone line?

A fax machine requires a modem to transfer data over a phone line. The modem acts as a crucial component that converts digital data from the fax machine into analog signals that can be transmitted over traditional telephone lines. When a document is sent via fax, the modem encodes the data, allowing it to be sent as sound waves along the phone line. Upon receiving the analog signal at the destination fax machine, another modem decodes the signal back into digital data, which can then be printed out.

While a router is essential for network communications, it does not play a role in the direct operation of traditional fax machines that rely on phone lines. Similarly, a scanner, while useful for digitizing documents for faxing, does not facilitate the transmission of data over phone lines. Lastly, a printer is necessary for outputting the received fax, but it is not involved in the data transfer process itself. Thus, the modem is the key piece of equipment needed for a fax machine to effectively transmit and receive faxed documents over phone lines.