The T.38 fax relay standard

A brief overview

Fax, also known as facsimile, involves the transmission of scanned material via electronic signals through a telephone system. Once this information has been transmitted, the device receiving the information (typically a fax machine) will convert the electronic signals into an image. The use of fax machines to transmit images and information has declined over recent years due to the emergence of internet based technologies such as email, however, there are many industries that still rely on faxes to transmit information such as financial records and signed contracts.

As technologies have advanced over the past 10 years, we have seen the use of IP network switching and Voice over Internet Protocol (VoIP) networks increase significantly. As this IP technology has progressed, and the use of this technology has increased, so have the requirements for better transmission standards for organisations that still use faxes. This is due to the fact that old analogue fax machines work very poorly on networks such as this, and can have significant problems when trying to transmit data.

IP networks rely heavily on codecs to compress data before it is transmitted over the network, and then uncompress the data when it arrives on the other side. This is done to maximise and optimise the amount of data that can be transmitted over the bandwidth that is available to the network is question. The downside to this is that analogue faxes have been found to transmit poorly due to packet loss, delay and jitter that can be associated with some IP networks. Therefore, it became apparent very quickly that a new transmission standard needed to be developed in order to compensate for these issues when transmitting faxes.

In 1998, the T.38 fax relay standard was devised in order to overcome the shortcomings associated with sending analogue faxes over IP networks. T.38 is now an Internet Telecommunications Union (ITU) recommendation for transmission of fax over IP (Internet Protocol) in real time. Other fax standards, such as T.30 can still be used in conjunctions with T.38 when transmitting faxes. For example, you may have a T.30 fax machine that sends a fax that would hit a fax server, which converts the fax to T.38 and transmits the fax over an IP network. Once the fax has been transmitted over the IP network, the fax typically hits another fax server that converts the fax back to the T.30 standard and passes the fax onto the receiving fax machine.

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