Fax over IP - FoIP

Fax over IP can be done in many ways, either realtime or store-and-forward

Realtime

• Transmission of a fax audio stream over a VoIP protocol, like SIP, IAX, H.323. This requires an uncompressed 64 kbit codec to have any chance of working, resulting in the need of around 80 kbit bandwidth. For a number of reasons it may or may not work even then.
• Fax over IP with a special protocol designed for this application. The key standardised protocol for this is T.38.

Store and forward

• A FAX, from a FAX machine, is decoded and stored by a FoIP gateway. It is then sent, using SMTP or a similar transport, to another FoIP gateway where it may be sent out to a destination FAX machine. The key standardised protocol for this is T.37.

Start here

• Steve Underwood Faxing over IP networks Article - excellent explanation of issues related to realtime FoIP

See also

• Asterisk fax and Asterisk T.38
• T.37: The ITU protocol for store-and-forward FAX over IP
• T.38: The ITU protocol for realtime FAX over IP
• International engineering consortium online tutorial
• Business.com: Fax over IP directory
• VOIP FAX Hardware