RACAL-DATACOM DISCUSSES STATUS OF GLOBAL V.FAST MODEM STANDARD 

June 22, 1993 -- SUNRISE, FL. -- This is an interview with Veda Krishnan,
Senior Fellow, Racal-Datacom engineering, to update news media and
interested individuals about the current status of the "V.fast" standard
for high speed modems. She represents Racal in TIA TR 30.1, the American
committee of approximately 35 persons representing about 25 companies
developing positions on core modem data pump issues for ITU-TSS Study
Group 14.

Formerly known as CCITT (Consultative Committee International for
Telegraphy and Telephony), ITU-TSS (International Telecommunications Union
- Telecommunications Standards Sector) is the Geneva-based advisory
committee established by the United Nations to recommend worldwide
transmission standards. ITU-TTS Study Group 14 consists of about 50-60
scientific and industrial organizations, including manufacturers, and user
groups such as national telephone administrations. Study Group 14 is
developing the "V.fast" Recommendation for two-wire duplex modems with
data rates beyond 14.4 kilobits per second (Kbps).

QUESTION: How soon can we expect to see a formal "V.fast" standard adopted
by ITU-TSS?

KRISHNAN: We expect the standard to be adopted in 1994. "V.fast" is a
nickname that emphasizes the goal of this standard, specifying a modem
that will achieve the maximum data rate that the channel can support. Once
ITU-TTS adopts the standard, it will be assigned a V series number. 

QUESTION: How fast is "V.fast"?

KRISHNAN: The V.fast modem will accommodate data signalling rates from
2,400 to 28,800 bits per second in 2,400 bps increments. The modem is
intended for connection to general switched telephone networks and on
point-to-point two-wire leased telephone-type circuits. It will provide
duplex operation using echo cancellation techniques and half-duplex
operation. 

QUESTION: How is the data rate maximized? 

KRISHNAN: Higher data rate is achieved by taking advantage of the fact that
the network is rapidly becoming digital and consequently offers wider
bandwidth for signalling than the previous analog network. V.fast utilizes
this new wider bandwidth to achieve faster data transmission, up to 28.8
Kbps. 

QUESTION: How is performance improved? 

KRISHNAN: Many new performance enhancing algorithms will be included in
this standard compared to the V.32bis standard. A better trellis coder and
a block shaper are under consideration to increase immunization to
gaussian noise. There will be line dependent algorithms such as adaptive
pre-emphasis to offer better performance. 

QUESTION: How much data rate improvement over V.32bis is expected? 

KRISHNAN: The data throughput improvement is line dependent and also
impairment dependent. It is an improvement between 10 and 40 percent for
lines with distortion and impairments and increases to 100 percent for
good lines with high signal-to-noise ratio.

For example, at the signal-to-noise level where V.32bis modulation can
support 14,400 bits per second, V.fast modulation can support 20,200 bits
per second. Better signal-to-noise ratio will lead to higher speed data
rates, up to 28,800 bps. 

QUESTION: How will the training schemes of V.fast differ from those adopted
for the V.32 standard? 

KRISHNAN: An ad hoc group is working on training schemes for V.fast. The
training will automode to V. series modems supported by V.32bis automode
procedures and Group 3 fax machines. The modems will exchange capability
parameters and selected modes of operation before the training of echo
cancellers and equalizers. A faster than V.32 training is intended, with
training time less than five seconds. 

QUESTION: How would you summarize the benefits of the V.fast standard to
users?

KRISHNAN: With the V.fast standard, we are attempting to specify a modem
that will maximize throughput over the analog, ADPCM, PCM and cellular
links and also will improve support for data, facsimile, TDD and
multi-media applications.

Rascal-Datacom Inc
1601 North Harrison Parkway, Sunrise, FL 33323-2899
PO Box 40744, Fort Lauderdale, FL 33340-7044
305-846-1601;  fax: 305-846-3935

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