Technologies used for FoIP
Here's a list of the most commonly used technologies in FoIP networks (along with a short
explanation)
T.38 - is an ITU standard for sending and receiving faxes through IP networks in real-time
mode. Fax messages are split and sent as UDP or TCP/IP packets. A virtual fax is emulated to
compensate the delay between packet transmission.
T.37 - is an ITU standard for sending FAX accross IP networks in a store and forward mode.
FAX messages are sent as MIME encoded email messages using SMTP. This is the most widely used standard
by Fax (To/From) Email providers.
Fax Server - Software based fax server that receives a fax through an email address or a
virtual printer and stores it locally to forward it to a fax number using a fax-modem like
device.
Fax Gateway - Hardware based fax forwarder that receives faxes and forwards them using either
T.37 or T.38 to the destination fax number.
G.711 u-law - Voice codec used for experimental faxing. It transfers voice over IP networks
uncompressed, so it's the only codec suitable for fax sending through IP networks. The results are
unpredictable, sometimes you get a full fax transfered without a problem, but other times it just
starts the fax handshake and hangs.
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