T.38 is an ITU standard for sending FAX across 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:

ITU-T Recommendation T.38 T.38 describes the technical features necessary to transfer facsimile documents in real-time between two standard Group 3 facsimile terminals over the Internet or other networks using IP protocols. The Recommendation allows the use of either TCP or UDP depending on the service environment.

ITU-T Recommendation T.38 T.38 Annex D describes system level requirements and procedures for internet aware facsimile implementations and internet aware facsimile gateways conforming to ITU-T T.38 to establish calls with other ITU-T T.38 implementations using the procedures defined in IETF RFC 2543 SIP-99 and IETF RFC 2327 SDP.

Note that ITU-T T.38 Recommendation T.38 (04/02) T.38 is an aggregation of the original ITU-T Recommendation T.38 (06/98)T.38-98 and all of the subsequent Amendments and Corrigendum including T.38D-00. While T.38 and T.38D-00 describe SIP procedures per SIP-99, the procedures can also be applied to the revised Session Initiation Protocol specification SIP.

The Importance of T.30 ECM Error Correction Mode (ECM) in T.38 Deployments

One of the most important features of the traditional facsimile standard (T.30) is ECM error correction. The inventors of fax recognized that the audio quality of PSTN phone lines could not be trusted to be 100% error free - it was not uncommon to hear static, or the occasional pop or crackle on some fax calls. ECM error correction allows the sending and receiving terminals to compare notes at the end of each page, and selectively retransmit any data that was not received the first time around. This retransmission process is continued until the received page is certified error free, and the transmission of the next page begins.

Remarkably, many T.38 implementations, including those of top tier carriers such as Level3, XO, Verizon etc have explicitly disabled ECM error correction. This problem is discussed in detail here. Don't make this mistake! Be sure to enable ECM and insist your provider or PBX vendor do the same!

Want to check to make sure you have ECM enabled? This handy ECM self-test tool can tell you in minutes.

T.38 with Fax Voip T38 Fax & Voice

FaxVoip Software develops solutions for the transmission of a fax via the Internet Telephony (FOIP). The main emphasis has been placed on the transfer T.38 and audio via SIP, H.323 and ISDN CAPI 2.0.
Fax Voip application operates with T.38 faxes via standard COM port interface.
What is Voip? For your fax or voice application, it's a Voice Fax Modem. You can setup your Fax & Voice program to operate with Fax Voip Virtual COM ports or virtual Fax Voip 14.4K TAPI Voice-Fax Modems. From the perspective of your VOIP internet network, it’s a SIP/H.323 client with T.38 and G.711 Fax support.From the perspective of your ISDN line, it’s CAPI 2.0 client with audio fax support. You can send/receive T.38 and audio (color/black-and-white) faxes and voice messages without any hardware, using your favourite Fax & Voice program. Fax Voip is the ideal solution for the implementation of Fax and Voice Mailbox into SIP/H.323/ISDN network. You can use Fax Voip with your VOIP or ISDN-based PBX or with your SIP/H.323/ISDN Provider. Up to 100 virtual modems can be used simultaneously.
Multiple SIP Registrations and Call Routing functions make your system the most flexible as well as allowing you to work with different SIP and H.323 providers simultaneously.
Fax Voip supports Caller ID and Dial a Phone Number Extension features.
You can send T.38, audio and CAPI faxes via Fax Voip Virtual Printer and receive faxes directly in TIFF, PDF or SFF files, and without limiting the number of incoming fax sessions. You can send audio messages. You can manage faxes and audio messages with Fax Voip Console.
Fax Voip is a fully-functional system for sending faxes and audio messages via e-mail (Mail to Fax and Mail to Audio) and for receiving faxes to e-mail (Fax to Mail).
Incoming Routing Methods (Route through e-mail, Store in a folder, Print) allow you to route incoming faxes to recipients on the network.
Fax on Demand function allows callers to retrieve information via fax on the same call (from a fax machine).
Fax Voip T38 Fax & Voice has been successfully tested with Microsoft Fax, CallStation, BVRP Classic Phone Tools 9, FaxTalk Messenger Pro, WinFax Pro, Venta Fax & Voice (include color faxes) and many other well-known programs.
Note that if you plan to take the free Windows 10 upgrade or reinstall the OS then you will have to pay for a new license, unless your purchase is less than a year old.
Please, visit the Fax Voip home page at http://www.t38faxvoip.com
The last version 7.6.1 can be downloaded using the following link: http://www.t38faxvoip.com/downloads/t38fv7_6_1.zip

T.38 with Fax Voip Windows Fax Service Provider

Fax Voip Windows Fax Service Provider (Fax Voip FSP) enables Microsoft Fax and Windows Fax and Scan, which are built right into Windows, to send and receive T.38 and audio (over G.711 codec) faxes using your VoIP (SIP or H.323) infrastructure without any further cost.
Windows Fax Service and Windows Fax and Scan application is an integrated fax software included in all Windows versions. It is an extensible fax platform that you can use to deploy shared fax resources in your organization. Users within an organization can install a connection to a remote fax printer on a network fax server and send and receive faxes using shared fax devices located on the server, as well as from a local fax device attached to their computers. Fax administrators can configure, manage, and monitor these shared fax resources. Centralized management of server-based shared fax devices means easier management and maintenance, and lower costs. Fax users can send and receive faxes without the need to use manual fax machines, saving time and effort.
Fax Voip FSP replaces the standard Microsoft Modem Device Provider by the Fax Voip T.38/G.711FAX Device Provider. This allows you to use the Windows Fax Service most efficiently. In particular, the ECM (Error Correction Mode) is supported. The busy signal is also detected correct way. Using Fax Service Provider (FSP) instead of Virtual COM Ports and modems significantly improves reliability of your fax system.
Fax Voip FSP allows Windows Fax and Scan to receive Caller ID and Called Number (DID) - via Routing Information field.
Multiple SIP Registrations and Call Routing functions make your system the most flexible as well as allowing you to work with different SIP and H.323 providers simultaneously.
The Mail to Fax function will let you send faxes directly from your e-mail application. The body of your e-mail messages will act as the fax cover page, while any attached documents (e.g. PDF, TIFF, or TXT formats) will be converted into additional fax pages. Faxes can be sent to multiple recipients.
Fax Voip FSP Routing Extension allows you to route incoming faxes depending on the Caller Number (Caller ID) and Called Number (DID), using the following fax routing methods: Route through e-mail, Store in a folder, Print. Custom routing for incoming faxes allows you to easy add any routing functionality by using custom application that is started after receiving a fax.
Fax Voip FSP has been successfully tested with CALLCentric, babyTEL, T38FAX and many other VoIP service providers.
Please, visit the Fax Voip FSP home page at http://www.t38faxvoip.com/fsp/
The last version 2.3.1 can be downloaded using the following link: http://www.t38faxvoip.com/downloads/fvpfsp2_3_1.zip

T.38 with Fax Voip SoftPhone

Fax Voip Softphone is a powerful and unique SIP / H.323 software telephone that lets users make phone calls, record calls, play audio files into the telephone line as well as send/receive T.38 and audio faxes from one single software application using any Voice over IP (VoIP) telephony provider. Fax Voip Softphone supports Music on Hold, Call Transfer and Call Forwarding. Hairpin Call Transfer and Hairpin Call Forwarding (2 call legs). Audio and Fax panel allows you to send pre-prepared faxes and audio messages in one click. With Log Book you can easily view call history, view received and sent faxes and listen to call recordings and sent audio messages. The Phone Book provides a convenient place to store information about your contacts. Random Phone Calls function can be useful for your business, as well as for different testing purposes. The function allows you to automatically make repetitive phone calls to one or more target phone numbers. This function allows you to play audio messages into the telephone line, as well as to record phone calls. Using the Fax Voip Softphone Control Panel, you can easily configure the softphone according to your requirements..
Please, visit the Fax Voip Softphone home page at http://www.t38faxvoip.com/phone/
The last version 2.3.1 can be downloaded using the following link: http://www.t38faxvoip.com/downloads/fphone2_3_1.zip

T.38 with Asterisk

Built in support for T.38

Digium's Fax For Asterisk is a commercial facsimile (Fax) termination and origination solution designed to enhance the capabilities of Open Source and commercial Asterisk as well as Switchvox. Fax For Asterisk bundles a suite of user-friendly Asterisk applications and a licensed version of the industry's leading fax modem software from Commetrex.
Asterisk 1.6 support G.711 and T.38 FAX origination and termination. T.38 gateway features are in Asterisk 10. Patch exist for Asterisk 1.8.

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' real-time T.38 Fax Relay technology gives the next-generation network system developer the technology needed to support standards-based fax in IP, ATM, and Frame Relay networks. As a developer of a packet-telephony system you can offer a T.38-compliant system for fax over IP, an I.366.2 system for fax over ATM, an FRF.11.1-compliant system for fax over Frame Relay, or a proprietary implementation, should it be required.

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 develops and markets enabling technologies for the gateway and media-server telecom OEM, as well as ready-to-deploy fax applications, BladeWare Fax Media Server (FMS), BladeWare Fax2Email, and BladeWare Email2Fax. Well known for its market-leading fax and other licensed media-processing technologies, Commetrex has announced its 75th T.38 FoIP customer. Commetrex' list of technology partners and licensees is a who's who of the telecom industry, including LSI, Iperia, Sonus, Marvell, OpenWave, Nortel, Amazon.com, AT&T, Broadsoft, Siemens, ShoreTel, Avaya, Interactive Intelligence, Aspect, Freescale, Portugal Telecom, Octasic, Tektronix, Pika, Empirix, LogicaCMG, and MetaSwitch. Commetrex is currently enhancing the BladeWare product family by introducing comprehensive voice capabilities with its BladeWareVXi VoiceXML interpreter initiative.

For additional information, visit the Commetrex home page at http://www.commetrex.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 open source ICTFAX

ICTFAX is an open source , multi-user and web based software solution for internet telephony service providers (ITSP) and businesses. ICTFAX is an email to fax gateway, supports G.711 faxing , PSTN faxing and T.38 origination and termination. ICTFAX based on open source Freeswitch, ICTCore and Drupal 7., ICTFAX is an email to fax, fax to email,web to fax gateway,

ICTFAX supports T.38 origination and termination, T.30 origination, termination and gateway , G.711 Foip origination, termination and gateway capabilities

Released new version of ICTCore V 0.7.5 on March 12, 2017 with following improments
Twig based template added for gateway configurations and Application data
Data and Token libraries updated
Sip, SMTP and SMPP added as provider sub-type
Multi tasking support improved for Task and Schedule
Namespaces and PSR-4 based auto-loading support added
PhpUnit support added for unit testing

for more information please visit ICTFAX home site

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.

Reliable fax with Acepacket

  • Fully support T.38
  • Dedicated fax line.
  • Virtual fax and fax to email.
  • Web based gui to send and recieve faxes online.
  • Fax solution for single and broadcasting.

See also

Created by: jht2, Last modification: Wed 28 of Feb, 2018 (22:39 UTC) by tahiralmas
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