The fact that fax machines can not work while connected to the VoIP lines is very well known, but that doesn't mean that there were no attempts to give fax machines and modems the ability to transfer data over standard IP networks in real time.
One of the results of International Telecommunication Union in that regard is development of T.38 standard, created to give fax machines ability to use the internet to transfer faxes.

The biggest problem in developing this method of fax communication is the fact that fax machines were using modems for transferring clear voice data, and the levels of compression that IP lines use are just too much for them to handle. This resulted resulting in failed transfers of data, or, at best, in random lines and dots on the receiver's end.

Which are T.38 biggest advantages?

What T.38 standard allows is that IP friendly fax machines send multiple sets of each packet containing data, and gives these faxes the ability to assemble the final fax message by comparing all of the packets of data, taking into the account only the packets that arrived completely.
This increases the amount of data passing through the IP network, but reduces the errors during transfer. This recommendation for fax transfer standards takes into the account spoofing of data and buffering, which increased the demand for raw processing power on the side of the both sender and receiver devices.
Reduction of raw data being transferred and the ability to use some of the modern existing networks is more than worth the offset, and many of the current models of fax machines have the T.38 standards capabilities.

Matt Gerchow

Matt Gerchow is an author, marketer, inventor, husband, father and yoga enthusiast. He enjoys travel to distant lands , fine wine, time with his family and dinner with friends.