How a Fax Machine Works – From Start to Finish

The ability to send an image over a wire predates Alexander Graham Bell’s invention of the telephone. Today’s fax machines work in very much the same way as those earlier inventions.

History of Faxing

Faxing started as a way of sending an image across a distance. Initially being transmitted across a wire to pieces of chemically impregnated paper, telegraph lines were used in the first true example of a fax transmission.

Through the years, fax developed to be the best way to send a document across distances, and today is still one of the most reliable and quickest ways of sending a document and receiving a confirmation that it had been received.

For more on the history of Faxing, see our page dedicate to the history of fax.

The Basic Method of Faxing

All fax machines and fax transmissions revolve around the same basic concept – they scan a document, transfer the image of that document over to a signal, then send that signal to another fax machine that decodes the signal and prints the document back out.

Early fax machines simply worked on two tones – one for there being an image on a certain point on the page, and one for not being an image on a certain point on a page. This would result in either a black dot or white dot being transmitted over to the other machine.

Just like a computer screen or LCD display is made up of many tiny dots to put a picture together, a fax records that information to send it back in much the same way.

Today’s fax machines are much close to a scanner hardwired into a printer than they are the models from 10-20 years ago. Digital technology has made for a much more accurate picture as well as faster and compressible transmissions.

A Fax Transmission Example

A fax transmission works in a number of steps – the fax machines handshake, transmit their message, and the send confirmation.

Step 1 – the Handshake

The handshake is the first part of a fax communication.

When a fax is being sent, the sending machine waits for the line to pick up and then starts sending a series of beeps.

These beeps signify that the machine is requesting to send a fax. The sending fax machine is essentially saying “Hey! I’m a fax machine! I’m looking for another fax machine! Is there one there?”

If the machine on the other end is also a fax, that fax will answer the beep with its own signal. At this point the receiving fax machine is saying “Hey you’re a fax? Guess What? I’m a fax too!” And both machines now know that they’ve each made a friend.

Once both machines have acknowledge each other, they send information back and forth about them (just like two people getting to know each other). This information is along the lines of whether they are analog or digital faxes, as well as what compression formats they speak.

Once the two fax machines understand what the other is capable of, they decide on a format to send with, and then start their transmission.

Step 2 – Transmission of Messages

After the handshake has occurred, the sending fax will send the message through to the receiving fax.

As both machines know that they speak the same language, they’re able to send the messages through in a format that they know the other machine knows.

Step 3 – Confirmation of Message Reception

Once the message has been sent, the final step is the confirmation of the message being received. The receiving fax machine will send a confirmation notice, that the sending fax machine can now print out.