How Voice Over IP Fax Works
Other People Are Reading
-
Overview
-
Voice over Internet Protocol (VoIP) is a communication technology that enables the transmission of voice calls over the Internet. The traditional and common telephone call is made through a public switched telephone network (PSTN). VoIP uses Internet Protocol networks but still connects to PSTN allowing for features similar to the traditional phone service. One such feature is sending and receiving a fax. Sending a fax over an IP network is also known as Fax over Internet Protocol (FoIP).
Operation
-
Whereas the old way of sending a fax would simply require a fax machine and a telephone line, FoIP makes use of a gateway. A gateway is a device that functions as the intersection point between the PSTN and IP network. It enables voice or fax calls to be carried as compressed packets of information over a phone line. In FoIP, the document is fed into the fax machine and is processed by the gateway. This is where the facsimile is digitally compressed and converted to packets of information. The facsimile then moves through the phone line and is printed out on the recipient's fax machine. The process is two way as long as the recipient also makes use of a VoIP capable system.
-
Problem
-
VoIP systems are optimized for voice which means that they can efficiently convert the analog signal of a human voice into a digital signal and carry it over an IP network. Data in an IP network is transmitted as packets of information. Networks are not constantly 100 percent error free, and some packets may be lost or arrive out of sequence. Through the built-in packet-management techniques of a VoIP gateway and the ability of human hearing to synthesize audio data, these packets of information turn out to sound like fluid conversation. Since fax data are sent and received by modems which are nothing at all like the human ear and brain, missing packets can actually disrupt, slow down or cause garbled images to come out of the recipient's fax machine.
Solution
-
To bypass this inefficiency in processing fax data, a new protocol was designed that in effect made the IP network invisible to the fax machines in either end of the transmission. This solution is called the T.38 standard. For a fax transmission to proceed smoothly and in real time, the devices interconnected in a VoIP system must be compliant to this new standard. This means that their software is capable of executing certain functions that will overcome the inability of fax machines to cope with network errors. One such function is known as spoofing. A T.38 compliant gateway executes spoofing by correcting errors in a network's timing. It also handles delayed or missing packets through a buffer-management technique that specifically administers fax data.
Examples of spoofing would be padding garbled images on the facsimile or retransmitting lost messages. The result is that the fax machines on either end of the session do not 'feel' the discontinuous transmission that is inherent in VoIP networks. Although this new standard allows even old fax machines to do FoIP, an additional solution is to upgrade fax machines to be able to handle digital formats. These new types of fax machines have the advantage of significantly reducing the transmission time.
-
