V.34 Fax/Facsimile Software

VOCAL’s V.34 fax/facsimile software implements recommendation ITU-T V.34 which defines the modulation methods and operating sequences for a fax modem used on General Switched Telephone Networks (GSTNs) and on point-to-point 2-wire leased telephone-type circuits. The V.34 facsimile software supports:

• Both full duplex and half-duplex modes.
• Data rates in the range of 2400 bps to 33600 bps, in incremental steps of 2400 bps.
• Symbol rates of 2400, 2743, 2800, 3000, 3200, and 3429 symbols per second.

Using Quadrature Amplitude Modulation (QAM) with synchronous line transmission, selectable mandatory rates for the V.34 protocol are 2400, 3000, and 3200 symbols/s with optional rates of 2743, 2800 and 3429 symbols/s. Asymmetric symbol and data rates are also supported. Negotiation and training sequences at startup establish the data rate. Control channel rates are 1200 and 2400 bps, with an optional auxiliary channel with a synchronous data signalling rate of 200 bit/s. Trellis coding for all signaling rates and shell mapping permit satisfactory performance even over noisy channels. V.34 protocol adaptive techniques enable the modem to achieve close to the maximum data signaling rate that a channel can support on each connection.

VOCAL’s V.34 fax modem software uses state-of-the-art line probing analysis to automatically determine maximum channel capacity. It also supports MSE fallback/fallforward threshold control to adjust the tradeoff between higher data channel rates and symbol error rates. V.34 channel separation is accomplished using echo cancellation techniques.

Command Set Control

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), application software developers can control all of the V.34 modulations and data streams . 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 Class 1, most of the V.34 protocol is executed in software, with the advantage that any changes don’t require hardware modifications. This is in contrast to Class 2, where image processing is handled by the modem.

The line interface for the V.34 facsimile software 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.

Features

• Fully compliant Group 3 Facsimile Support
• Full and half duplex modes
• Primary data channel supports 14 data rates from 2400 to 33600 bps, in increments of 2400 bps
• Control channel rates are 1200 and 2400 bps
• Optimized for high performance on leading edge DSP architectures
• Multichannel implementation
• Multi-tasking environment compatible

Configurations

• 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.
• Use with VOCAL’s Command Set Controller (CSC) and T.30 library.
• System can be combined with other Group 3 fax modulations (V.17/V.29/V.27ter/V.21 channel 2).