Fax over IP (FoIP)

Fax over IP (Internet Protocol), or FoIP, allows users to fax documents over the Internet instead of using a standard fax machine. Many VoIP services provide this feature, so it may seem a logical progression for businesses and individuals to utilize FoIP when VoIP also is used in a specific environment. The consolidation of separate voice, fax and other data resources offers the opportunity for savings and has become a popular choice for many network managers who seek to utilize excess broadband capacity for transmissions over traditional communication.

How It Works

FoIP enables standard fax machines to work with packet networks by extracting the fax image from an analog signal and carrying it as digital data over a packet network. Historically, two methods have been used for sending FoIP networks: the real-time methods (T.38) and the store-and forward method (T.37). The primary difference in the two approaches lies in the delivery and method of receipt confirmation.

T.38 is the fax transmission protocol selected for H.323. Fax data in its original form is digital, but it is modulated and converted to analog for transmission over the PSTN. This analog form uses 64 kbps of bandwidth in both directions. FoIP IWF (interworking function) reverses this analog conversion by transmitting digital data over a packet network and then reconverting the digital data to analog for the receiving fax machine. This conversion process actually reduces the overall bandwidth required to send a fax, because the digital form is more efficient and the fax transmission is half-duplex (meaning only one direction is used at any given time). The peak rate for a fax transmission is 14.4 kbps in one direction. As a side note, fax machines still retain some advantages over the FoIP protocols, particularly in the transmission of sensitive material. Sarbanes-Oxley and HIPAA mandates require that sensitive materials cannot be sent encrypted over the Internet. And, in some countries, digital signatures are not recognized by law whereas traditional faxed contracts with signature copies are accepted. Therefore, traditional fax machines may retain a place in the office for many years.

What You'll Need

To communicate effectively using FoIP, a fax server provided by a FoIP service provider would be employed. Look for the number of users and licenses offered by any given provider, and research any answers that would address the effects of delay through the network, a solution that minimizes the jitter effect, and features that resolve lost-packet compensation. Also seek a provider that would provide compatible software or hardware that would work with any existing VoIP networks. The IWF must support analog interfaces that directly interface to fax machines at the branches and to a PBX at the central site. The IWF must emulate the functions of a PBX for the fax machines.

Types Offered

Fax machines in common use today implement the ITU recommendations T.30 and T.4 protocols. The T.30 protocol describes the formatting of non-page data, such as messages that are used for capabilities negotiation. The T.4 protocol describes formatting of page image data. T.30 and T.4 have evolved substantially over time and they currently attempt to describe the behavior of an evolving set of fax machines. The timing related to the message interaction and phases of the call is critical and is one of the major causes of problems in the transmission of FoIP networks.