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The Future of Fax without the PSTN

Fax is one big reason why some users don’t want the PSTN to be shut down. This 1980’s era technology survives against the odds. Brick sized cellphones, dial-up modems, 8” floppy disks—all are similar aged and all are extinct. Curiously fax survives—but is it time for that too to go extinct? Should we find better ways of transmitting printed material or must we keep fax on life support?

By Peter Aggus

Peter, as an engineer & technology management consultant, has developed innovative & cost-effective solutions for clients in many industries.

History of Fax

Facsimile as we know it today dates to 1964 when Xerox introduced what they called ‘Long Distance Xerography‘. Our current machines operate on ITU standard G3, which was introduced in 1980. Fax rapidly replaced telex as a way of transmitting printed messages. In turn, e-mail has replaced most fax use, yet some uses persist for many reasons, most of which are spurious.

Positives

Back in the ‘80s it was an attractive selling point to be able to drop a sheet of paper into a fax machine and push the speed-dial button for a pre-set destination—knowing that a near perfect copy of the paper would print out at the remote site. Answerback codes provided legal proof that a document had been sent and received. Entire business structures evolved based on that simple concept, with the largest being the medical community.

Negatives

Most fax machines basically convert the image into pixels by scanning. The pixel values are transmitted to the remote machine using a 1980’s era device called a modem. It is assumed that a high quality 4kHz analog path exists over the phone network link.

VoIP technology introduces two errors that make new technology PSTN- replacement paths less than perfect. VoIP packets are delayed in transit by a variable amount thanks to the way IP packets are passed through routers in the network. This results in ‘jitter’, where some packets arrive out of order. If the analog termination devices cannot compensate for this, the fax modems will suffer errors and the received fax will be distorted. Also the digital bandwidth in the PSTN is 64kbit/s, while VoIP usually works at around an eighth of that—again introducing more distortions.

What Actually Happens

Internally the fax starts with analog brightness values of the pixels. They are converted to digital and compressed to remove redundant white space. The digital information is then converted back to analog by the G3 modem to be sent over a nominal 4kHz audio phone line to the far end, where a similar modem converts it back to analog pixel brightness for printing.

Add in the fact that the ‘nominal 4kHz audio phone line’ is usually converted back to digital for transmission between telco central offices and it becomes clear why ‘old school fax’ often suffers problems even using what should be simple PSTN lines.

What Can You Do?

You need to face the fact that the days of PSTN dial-up fax are numbered.

Analog IP adapters can be made to largely compensate for VoIP issues— but why spend money doing that (they are not cheap).

Ideally your services need to evolve into a networked data solution that avoids intermediate paper. If you have a paper source document, scan the document to a file, send the file, and print it (or not) remotely. If not, just send it.

For most applications, a basic PDF document image is acceptable. Legally, the lack of a fax ‘handshake’ can be a problem—but even lawyers are now happy to use digitally signed PDF files.

If you’d like to explore these ideas further or comment on this article, reach me at .

This article was published in the February 2023 edition of The TMC Advisor
- ISSN 2369-663X Volume:10 Issue:2

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