Once you have understood the advantages of sending fax messages over and IP network or the Internet instead of the traditional phone line, you will want to know how you can achieve that. There are 3 ways you can send fax over an IP network, and which one you choose will depend on your actual situation and facilities, and the nature of your activities. The 3 ways are:
- Using a fax gateway, through the T.38 protocol;
- Using the fax-to-email method, through the T.37 protocol; and
- Sending the fax over a VoIP channel.
One important thing to note in IP Faxing is that fax messages are not sent to and from phone lines as traditionally, and hence do not require phone numbers, but are sent to and from IP addresses. Let’s see how you can fax over IP in the three ways.
Using a fax gateway, through the T.38 protocol
This is also called real-time faxing, i.e. the fax messages are sent and received at once, without having to wait and stored. It works, on the outside, like traditional faxing. Computers can be used to send faxes this way, but more often (as this method is mostly used in corporate environments) IP fax machines are used. What is important is the presence of fax gateways or fax servers, that have the necessary mechanisms (including protocol algorithms) to handle faxing, and which make the bridge between the IP network and the PSTN line.
Using the scan-to-email T.37 protocol
T.37 is another protocol that controls fax transmission over IP, but unlike T.38, it works offline, meaning it stores fax messages, which are then delivered time after they are sent. This implies that the fax messages can be saved on servers and retrieved at will, or saved as email attachments.
Using this method, the fax message is scanned producing a TIFF binary image file, which can then be compressed using a standard compressing algorithm like JBIG, for example. The fax is sent to a destination email address as email attachment. The receiver of the fax will get the message when he/she checks mail, which is might not be immediately. To receive the fax, a standard email client (e.g. Outlook, Thunderbird etc.) can be used, or an Internet fax machine, one that is designed to work on IP networks and treat with IP Faxing protocols. The Internet fax machine will have the necessary decompression algorithms and standards to have the fax message printed. The email client will send the file to a conventional printer, and the algorithms and fax-handling modules must be present on the computer. This comes with fax software or add-ons.
Sending fax over a VoIP channel, using the G.711 protocol
This is maybe the simplest method, which simply involves sending a fax message using a machine connected to a VoIP network (which may be your residential or business VoIP line). This method has seen many problems, namely with the compression of the fax messages. Finally, it is better if the fax is not compressed, and this is achieved by the G.711 codec. You can have this with fax software available, and use it over your VoIP line.
For the average user, knowing all of the above is not primordial for being able to use IP faxing and benefit from it, as there are services that offer faxing service over the Internet against a monthly fee. They have the necessary servers, software and algorithms; you only pay and get the service. Here is a list of some of those services.