ITU V.22bis Modem
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The ITU (formerly CCITT) V.22bis software is an implementation of ITU V.22bis for the TMS320C3x. 
V.22bis is an international standard for 2,400 bps full-duplex data communication on the General 
Switched Telephone Network (GSTN) and on point-to-point two-wire leased telephone-type circuits. 
The ITU V.22bis also includes the fall-back capability to provide compatibility with V.22 1,200-bps 
modems.
V.22bis software operates on 20-ms frames sampled at 8 kHz. The demodulator processes 160 sample 
frames of linear PCM data and returns 12 symbols every frame. The modulator processes 12 symbols 
and generates 160 sample frames of linear PCM data. The modulator and the demodulator symbol word 
size is 2 bits for 1,200-bps operation and 4 bits for 2,400 bps. 

Features and Benefits

•	Full Avatar™ implementation
•	ITU V.25 answer tone capability
•	Object-based, C-callable functions
•	Rate retrain and rate renegotiation capability
•	ITU V.22bis and V.22 compatible and interoperable
•	V.54 local loopback test (loop 3) capability
•	Full-duplex "splitband" modem operation at 2,400 and 1,200 bps
•	SPOX compatible

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Vocoder
•	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 demonstration built for a 
third-party PC plug-in board.
Function
MIPS
Chip RAM
Data
Program
Transmitter/Receiver
5.0
0.5 k
2.5 k
8.1 k
Total *
5.0
0.5 k
4.0 k
13.1 k
* Total includes Avatar common memory requirements.

User Functions

The V.22bis 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 and demodulator interface with 
arrays of linear PCM samples and 2- or 4-bit symbols.
V.22bis modem
V22_create (...)
Dynamically allocates and initializes data memory for encoder
V22_delete (...)
Frees encoder's usage of dynamically-allocated data memory
V22_control (...)
Implements run-time control of V.22bis modem
V22_status (...)
Provides run-time status of V.22bis modem
V22_modem (...)
Performs V.22bis modulation and demodulation at the data frame rate

Algorithm Verification

•	Call DSPSE for verification details

Availability

•	Source and object code currently available for licensing.

Company Background and Contact Information

DSP Software Engineering, Inc. 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