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Fax Modulation

Fax Modulation Software
Fax Modulation solutions are available for Group 3 Fax optimized for a wide variety of platforms. This includes complete and robust implementations for ITU-T modulations V.34, V.17, V.29, V.27ter, and V.21 channel 2. Contact us to discuss your fax modem application requirements.

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Fax Modulation Software

  • V.34 fax – 2400 to 33,600 bps
  • V.17 – 7200, 9600, 12,000 and 14,400 bps
  • V.33 – 12000 and 14400 bps
  • V.29 – 7200 and 9600 bps
  • V.27ter – 2400 and 4800 bps
  • V.21 Channel 2 – 300 bps FSK

VOCAL’s fax modulation software is optimized for DSPs and conventional processors from TI, ADI, Intel, ARM and other vendors. Our software is available for licensing as a standalone algorithm or library. Custom solutions are also available for your unique application requirements.

High Speed Fax

As an option, these modulations can be combined with VOCAL’s V.34Fax to provide image transfer rates of up to 33600 bps. The V.21 channel 2 and V.27ter are the minimum requirements for Group 3 Fax. For non V.34fax, V.21 channel 2 is used to transfer T.30 control frames. The “high speed” modulations V.27ter, V.29 and V.17 are used for the “compressed image” transfer. The term “compressed image” is used loosely here, as the high speed data may in actuality be other data, such as in the case of binary file transfer (BFT).

Fax Control Services

Using the Command Set Controller (CSC) in VOCAL’s T.30 library or with VOCAL’s facsimile service Class 1 Command Set(EIA-578 and T.31) all of the facsimile modulations and data streams can be controlled. The T.30 library could in turn be controlled by VOCAL’s facsimile service Class 2 Command Sets T.32 (Fax Class 2.1), EIA-592 (Fax Class 2.0), or industry standard (Fax Class 2). With Fax Class 1, most of the protocol is executed in software, with the advantage that any changes don’t require hardware modifications. This is in contrast to Fax Class 2, where image processing is handled by the modem.

The line interface may be an analog front end (codec and DAA) or a digital interface such as T1/E1, Switched 56, and ISDN. The upper end of this software offers a direct binary and HDLC interface.


  • Fully compliant with ITU Recommendations
  • Modular software suite available with controller code
  • Optimized for high performance on leading edge DSP architectures
  • Multi-tasking environment compatible
  • Multichannel implementation


  • DAA interface using linear codec at 7.2 kHz, 8.0 kHz or 16.0 kHz sample rate
  • Direct interface to 8.0 kHz PCM data stream (A-law or μ-law)
  • North American and International Dialing/Telephony dialing functions available
  • Facsimile protocol layer (T.30 with ECM/BFT) available
  • Facsimile service class 1 command sets (T.31 and EIA-578) available
  • Facsimile service class 2 command sets (T.32, EIA-592 and industry standard fax class 2) available.
  • System can be combined with V.34fax facsimile modulations and startup procedures (V.8 and V.8bis).
VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713