ITU Group 3 Fax Modem
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The Group 3 Fax software is an implementation of Group 3 Fax standard for the TMS320C3x. The Group 
3 Fax standard defines a procedure for analog transmission of binary images on the General Switched 
Telephone Network (GSTN). The Group 3 Fax software is composed of implementations of four ITU 
(formerly CCITT) recommendations for fax control and transmission.
The Group 3 Fax software operates on 20-ms frames sampled at 8 kHz. The demodulator processes 160 
sample frames of linear PCM data and returns either 6 symbols for V.21, 24 symbols for V.27ter at 
2,400 bps, 32 symbols for V.27ter at 4,800 bps, or 48 symbols for V.29 every frame.  The modulator 
processes a buffer of symbols and generates 160 sample frames of linear PCM data. The modulator and 
the demodulator symbol word size ranges from 1 bit for V.21 at 300 bps to 4 bits for V.29 at 9,600 
bps.

Features and Benefits

•	Full Avatar™ data pump implementation
•	V.21 300-bps data pump for pre- and post-document signaling
•	Object based, C-callable functions
•	T.30 state machine processor for fax transmission control
•	V.29 data pump for transmission of binary image data at 9,600 and 7,200 bps
•	SPOX compatible
•	V.27ter data pump for transmission of binary image data at 4,800 and 2,400 bps

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Fax
•	Requirements:
All memory requirements are in units of 32-bit words. The MIPs ratings presented require the listed 
amounts of on-chip, zero-wait-state program and data memory, and a processing frame size of 160 
samples at 8 kHz. All measurements were made using an executable demo built for a third-party PC 
plug-in board.
Function
MIPS
Chip RAM
Data
Program
V.29 (Tx/Rx/Both)
2.5/10/10
0.1 k/0.4 k/0.4 k
0.7 k/1.6 k/2.3 k
2.1 k/2.8 k/4.9 k
V.27ter (Tx/Rx/Both)
2.5/7.0/7.0
0.1 k/0.5 k/0.5 k
0.8 k/2.3 k/3.1 k
2.9 k/3.7 k/6.6 k
V.21
5.0
0.2 k
1.2 k
2.8 k
T.30 (no ECM)
2.0
0.2 k
1.4 k
8.1 k
Total*
12.0
0.9 k
9.2 k
20.9 k/23.7 k/30.2 k
* Total includes Avatar common memory requirements and VMI. MIPS values are for worst case

User Functions

The Group 3 Fax implementation consists of a set of C-callable functions that perform 
modulation/demodulation, data-pump control, and status reporting. It also includes functions that 
reflect the implementation's object-based interface. The modulator/demodulator interfaces with 
arrays of linear PCM samples and 1-, 2-, 3-, or 4-bit symbols.
Interface Functions (general form)
XXX_create (...)
Dynamically allocates and initializes data memory for modem
XXX_delete (...)
Frees modem's usage of dynamically-allocated data memory
Group 3 Fax Processing Functions
VXXX_control (...)
Implements run-time control of V.XX modem
VXXX_status (...)
Provides run-time status of V.XX modem
VXXX_status (...)
Performs modulation/demodulation at the data frame rate
T30_originate (...)
Performs modulation/demodulation at the data frame rate
T30_answer (...)
Performs T.30 answer handshake procedure

Company Background and Contact Information

DSP Software Engineering, Inc (DSPSE), founded in 1989, is a leading provider of highly-complex 
digital-signal-processing software used in telecommunications and multimedia applications such as 
computer telephony, digital wireless, PSTN, and satellite communications, and videoconferencing.
Contact:	DSP Software Engineering, Inc
		175 Middlesex Turnpike
		Bedford, MA 01730  USA
		(617) 275-3733
		Fax: (617) 275-4323
		e-mail:  info@dspse.com
		www:  http://www.dspnet.com