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Fax over IP Server Library (FXSRV)

faxsrv_image2From document management, to bulk fax delivery systems, VOCAL’s Fax Over IP Server Library is designed to allow Linux and Windows developers the ability to create fax endpoints supporting both t.38 and t.30.  Interoperability with fax devices of all types – whether they are fax machines, servers, gateways or cloud-fax, is a must – and FXSRV delivers.

The ability to build fax infrastructure that can handle all of the variations of fax equipment out there is built in to this library: from the legacy low speed machines that are still in use all over the world, to Internet fax endpoints that can be running high speed fax with all the latest features.

Supported Modulations

  • V.34 fax data channel – full and half duplex modulation for data rates from 2400 bps to 33600 bps.
  • V.34 fax control channel – 1200/2400 bps modulation for use with half duplex procedures
  • V.17 – 7200, 9600, 12,000 and 14,400 bps trellis coded modulation
  • V.29 – 7200 and 9600 bps modulation
  • V.27ter – 2400 and 4800 bps modulation
  • V.21 Channel 2 – 300 bps modulation

T.38 Fax Software Features

  • Fully integrated Group 3 Facsimile processing system
  • Configurable for both TCP/IP and UDP/IP modes of data transmission
  • Configurable type/amount of redundant information for UDP/IP service
  • Configurable for UDPTL forward error correction messages
  • Configurable high speed training mechanism – Local TCF generation or TCF transmitted between end-terminals
  • Optimized for high performance on leading edge DSP architectures
  • Multi-channel implementation
  • Multi-tasking environment compatible
  • Programmable Precise Tone Detector
  • Fax/Data Modem
  • Fax CNG
  • Calling Tone (used by V.90, V.34, K56flex)
  • CED/Answer Tone (used by Fax, V.90, V.34, K56flex)
  • V.21 Ch 2 HDLC flags

VOCAL has configurations supporting a broad range of fax needs. And because VOCAL has supplied the fax code for the fax gateways of the analog telephony world,  you know that the modems are industrial grade.  Vocal servers come in a variety of configurations which cover the full range of ITU T-series and V-series Fax protocols.  The server has a simple yet full featured C-callable API.  This allows it to easily fit into currently existing systems. Configuration and control are flexible, to meet the needs of already deployed infrastructure and applications. In addition, VOCAL can customize or build to suit, in order to meet very specific system requirements.


  • 100% software solution easily migrates to the cloud
  • Runs on any standard Linux or Windows distribution
  • Replaces configurations where analog lines are being replaced with VoIP (SIP/RTP) lines
  • Scalable – from single client applications to a large number of fax modems on a single server (10s to 100s depending on server and modem rates)
  • Registers with one or more SIP servers (can be phone number per line, modem pool hunt, or other combinations)
  • SRTP and Secure SIP options available
  • Dialing commands will make outgoing SIP/G.711 call (with true modulation data in the stream)
  • Requires no analog audio interface (but can be used with one)
  • Slaves to far end modem clock to eliminate skew
  • High speed fax modulation – V.34
  • Low speed fax modulations – V.17, V.29, V.27ter, V.21
  • Supports standard protocols such as t.30, t.38 , t.4, t.6

More Information

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supported platforms

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713