T.38 is an ITU standard for sending FAX accross IP networks in a real-time mode.
FAX messages are sent as UDP or TCP/IP packets.

• The IETF RFC RFC 3362 implements a media type called image/t38 for T.38 faxes.

From RFC 3362:

• Commetrex runs a free interoperability test lab and keeps a list of tested equipment. Commetrex T.38 Interop Lab
• Brooktrout White paper: http://www.brooktrout.com/whitepapers/pdf/fax_over_ip.pdf (link no longer works as Brooktrout became part of Cantata Technology, which is now itself part of Dialogic). The document can be found at www.viatechnology.es/Documents/Productos/fax_over_ip.pdf

T.38 with Asterisk

Built in support for T.38

Asterisk 1.6 support G.711 and T.38 FAX origination and termination. T.38 gateway features are still in development.

Initial work

From version 1.4, Asterisk supports T.38 negotiation for SIP users, and the related passthrough of UDPTL T.38 data. This allows many T.38 nodes to communicate through an Asterisk box. Asterisk 1.4 does not, however, understand the T.38 protocol. It cannot terminate T.38 calls, or act as a T.38 PSTN gateway without external support - i.e. by passing the T.38 data to something which can perform those functions.

T.38 with Asterisk and Attractel (commercial solution)

A full fledged t.30 and t.38 stack for asterisk (both passthrough, termination and gateway) is available from Attractel
As the software is not under GPL, this can be used together with other non GPL parts of asterisk, such as g729 or iLBC.
The software comes with ITU t.30 modems : v.21, v27ter, v29, v17 and includes standalone FAX transmit and receive programs for use in fax2email and email2fax gateways.

T.38 with CallWeaver (supported)

Callweaver has rapidly maturing support for T.38 passthrough, T.38 gateway and T.38 termination. Passthrough simply means forwarding T.38 between two other T.38 entities. Gateway operation provides interworking between the PSTN and the T.38 world. Termination makes Callweaver act as a T.38 FAX machine. Callweaver can also act as a traditional PSTN type FAX machine.

Many T38 implementations are quirky, and work is ongoing to extend the number of T.38 platforms which interoperate smoothly with Callweaver. At present it has been successfully used with products from Cisco, Patton, Quintum and many others.

For further information, see the Callweaver home page at www.callweaver.org

T.38 with Commetrex (supported)

Commetrex' TerminatingT38 is a combination of its ITU T.38 fax and T.30 ITU fax protocol engines, a package that gives the developer of a network-service platform or an enterprise fax server the technology necessary to terminate T.38 fax (IP network) real-time fax transmissions just as one would real-time faxes from the PSTN using analog modems. When combined with Commetrex’ stand-alone T.38 fax, a developer can now implement both terminating and standard fax-gateway functions on the same platform, combining the functions of the service platform and the gateway.

TerminatingT38 is available as licensed source code for incorporation into proprietary systems. TerminatingT38 makes no assumptions regarding the connection setup, such as H.323 or SIP, nor does it assume a particular API for the application software. Interestingly, one of the legacy fax terminals (e.g. a fax machine)
can be removed from a fax system and Commetrex’ TerminatingT38 substituted so that the fax terminates in the service platform rather than a fax terminal. Commetrex has developed a version of its PowerRelay T.38 fax gateway product that, rather than relaying the fax to the PSTN, terminates it in TerminatingT38’s server-based T.30 protocol engine.

Commetrex has more than 75 T.38 FoIP customers and has completed a multi-year development effort that produced BladeWare, an IMS-ready software-only media server featuring TerminatingT38. Commetrex is enhancing the BladeWare IMS Media Resource Function by introducing voice capabilities, including BladeWare VXML Interpreter (CE), a
VoiceXML-based Media Resource Function Controller. Commetrex' list of technology partners and licensees is a who's who of telecom industry leaders, including Agere, Iperia, Genband, Castelle, Lucent, Sonus, OpenWave, Nortel, Broadsoft, Siemens, ShoreTel, Avaya, Empirix, LogicaCMG, and Movius.

For additional information, visit the Commetrex home page at www.commetrex.com

T.38 with Fax Voip and Fax Boom

FaxVoip Software ' http://www.t38faxvoip.com develops solutions for the transmission of a fax via the Internet Telephony (FOIP). The main emphasis has been placed on the transfer t38 fax using SIP.
Fax Voip application works with t38 faxes via standart COM port interface. You can send and receive T38 faxes via SIP networks with your standart fax program (like Microsoft Fax) to work with Fax Voip COM ports or virtual modems. Fax Voip is also a fully-functional system for sending faxes via e-mail (Mail -> Fax) and for receiving faxes to e-mail (Fax -> Mail).
As for Fax Boom program, it is a completed SIP fax application. Fax Boom does not require independent fax program for its work. Fax Boom has support for t38 fax and for fax over G711 codec, so it is possible to send and receive faxes via sip-networks without t38 support for faxes (for example, Betamax). Mail -> Fax and Fax->Mail features also supported.
Please, visit the Fax Voip home page at ' http://www.t38faxvoip.com

T.38 with Gridborg HMP Server (supported)

Gridborg HMP Server supports T.38 fax origination, fax termination and fax pass through. All of these options are available for both H.323 and SIP protocols. Gridborg HMP Server stores received documents in a multitude of formats and also enables sending of fax documents saved in TIFF and other formats.

Gridborg HMP Server has been successfully used with VoIP gatways from many vendors like Cisco, Planet, Patton, Sipura, and many others.

T.38 with T38modem

What is T38modem www.openh323.org?

• It is not a modem.
• From a FAX application's view point (e.g. HylaFAX) T38modem looks like a class 1 FAX modem pool.
• From an IP network view point it's a H.323 endpoint with T.38 FAX support. Recent versions also support SIP.
• From your view point it's a gateway between a fax application and an IP network.

See also

• Asterisk T.38
• Asterisk T.38 Bounty
• Uniqall Gridborg HMP Server
• T38modem
• FAX
• FAX over IP
• T.37
• Asterisk fax
• Steve Underwood Faxing over IP networks Article - excellent explanation of issues
• AudioCodes explains fax relay methods in detail
• quintum VoIP gateways T.38 ready
• Patton VoIP gateways T.38 ready
• Traffic analysis of two T.38 devices (link now working at Dialogic website)
• Axacore FaxAgent T.38 Fax Server
• Voismart Fax Server T.38 and softmodem integrated into IP PBX