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Faxing technologies predate internet, even TV and phone lines – faxing has been around and has changed significantly over the years. Here's a brief run on how fax machines work looking at the technical side of things. For more general information about fax machines, check out our Fax Machines from Start to Finish guide.

How Fax Machines Communicate

Definition of faxing shows us that we need the ability to create an exact copy of a document using electronic scanning and telecommunication lines to transmit the scanned data to a remote location where it can be printed.

Early models of fax machines had a very binary type of connection, they were using one tone if there was image on a certain part of the page, and another tone if there was. This would result in a “pixely” printing with white and black dots being lined up on a page to form a fax copy. Today's fax machines are much closer in what they can do to a regular scanner and printer, with very high dot density that allows for sharp and clear copies to be transmitted, and the speed of transfer is barely a limiting factor at all.

Fax Machine Connection – Step by Step

You can familiarize yourself with steps fax machines go through to communicate with each other:

  • Step 1 – Handshake

    The sending fax machine dials the number of the receiver as if it were a phone line and waits for the receiver to pick up (the receivers are usually set to automatically pick up after 2-3 rings). As soon as the connection is established, the sender and receiver start exchanging series of information in the form of series of beeps – the sound that you may have heard if you ever dialed a fax number by mistake. The info being exchanged here is called the Handshake – the machines agree on the protocols used for sending and receiving data, test the quality of connection and get ready to send/receive the message. Once all of this info is exchanged, they start the transfer of data.

  • Step 2 – Data Transmission

    After a successful handshake the machines should have selected one of the common protocols for sending the information (they pick the fastest common protocol) and the transfer of data begins.

  • Step 3 – Confirmation of the End of Transmission

    When the transmitter sends the signal that all of the data has been sent, it does not automatically disconnect – it waits for the return signal from the receiver that is the confirmation code, letting the sending machine know that the transfer was completed successfully, only then is the line disconnected.

Modern Fax Machines

Modern fax machines have many different protocols available for sending and receiving data this way, but some even allow sending of a fax message directly to an e-mail, or saving the received document directly to the PC as a PDF document without printing – they are much closer to multipurpose machines, with a scanner, a printer and a fax modem being bundled into one frame, than a dedicated fax machine just for sending and receiving faxes.

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