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V.34, V.FC and V.FAST--The 28.8 Protocols
by Karl Willdig (from the Internet)
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I get many calls everyday asking me have I got v.FAST modems in
stock, or asking other questions because of the large amount of
confusion out in the world about the 28.8k protocols. I hope in
this article to help clear up your mind about these protocols so
you can make a good buying decision. It starts off simple, and
gets a little technical explaining the v.34 toolbox.

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V.FAST - This name appeared about 2-3 years ago as the "NEW"
28.8k (28,800bps) protocol. It was actually a working name for
v.34 (more on that later) and was dropped just as the working
name for Windows 95 was Chicago, which people still insist on
calling it. People still refer today to v.FC or v.34 as v.FAST,
which could led to some problems when you are talking to
different people.

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V.FC - This is the 28.8k protocol invented, designed and (for the
most part) manufactured by Rockwell, the giant modem chip
manufacturer. Rockwell saw the need for a 28.8k protocol and the
fact that an international standard was some time off, designed
their own. V.FC or V.FAST CLASS is Rockwell's baby, and has been
sold in modems since late 1993.

It is a simple but effective 28.8k standard which a small
proportion of the population purchased, but the majority of
people have been waiting for the v.34 modems. Those people who
purchased 28.8k modems from NZ suppliers which are upgradeable to
v.34 should all be able to upgrade to v.34 within a couple of
months. Modems that have been imported by yourself or purchased
from unapproved resellers will either have great troubles
upgrading or have a costly upgrade path.

You will need to ring your dealer (or the importer) for
information regarding upgrades. Modems which are able to be
upgraded include MicroCom, USR Courier and Practical Peripherals.
Modems which definitely aren't upgradeable are Dynalinks, Ellcon
and a variety of other cheaper modems. Modems that you may have
troubles upgrading are Supra and Zoom and anything you or a
friend imported, as many US companies won't support a product
outside USA unless they have sold the modems direct to a
distributor in that country.

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V.34 - The much awaited and International ITU-T approved 28.8k
protocol hit the scene in July last year. Production of v.34
modems started in August with the DSP (Digital Signal Processor
or modems with a DSP co-processor for a datapump) modems being
the first to sell v.34 modems. It wasn't until early this year
that Rockwell based modems (Rockwell modems not having a DSP
Datapump) started coming out with the v.34 protocol.

ALL 19.2k and 28.8k modems are backward compatible with 14.4k and
slower speeds, and all have Group 3 Class 1 or 2 14.4k fax
capabilities. So when you buy a 28.8k modem you will still be
able to connect to slower modems.

Which modem is the best to buy? Well, that is a question you
should ask your dealer if they are knowledgeable about modems and
have a range of modems, they will be able to suggest the best
modem for your needs. Some modems are more reliable than others
for certain purposes, and some have features you may need, or
will want in the future.

In recent trials in the U.S. the Motorola v.34 modems came out No
1, with US Robotics Courier coming 2nd. The reason these modems
are better at the v.34 protocol is they both use 100% of the v.34
code. Most know the saying "you pay for what you get". It is the
same with modems, the cheaper brands on the market will only have
the vital parts of the v.34 code (making the modem cheaper to
produce) so these modems have proven not to be as reliable as a
modem with all or most of the v.34 code.

What about v.FC ? Well, v.FC is out of date, and if you can still
buy the modems which are v.FC only (not v.34) then I would
seriously consider you don't buy from that dealer again! V.FC
modems are being phased out, already our v.34 sales this year
have surpassed all our v.FC sales for all of last year, and with
a number of manufacturers making v.34 only modems (not v.FC
compatible) at lot of people with v.FC modems will find they have
a 14.4k modem by the years end. If you know you need to be able
to connect to a v.FC modem, your best buy would be a "Dual
Standard" modem, which is both v.FC and v.34 compatible. The USR
Courier is the best in this field, but its price tag will put
many home users off, ask your dealer, and check to find out how
much of the v.34 code is in the v.34 modems before buying, and
ensure you can return a modem if you're not satisfied within at
least 7 days.

Again I would recommend you talk to a dealer with some good
knowledge that can advise you on your best buy, as many brands on
the market are of good to high quality, but also many are of low
quality.

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Why is V.34 better than V.FC ??

V.34 has been under development for a number of years, and a
large number of modem manufacturers help in designing this code
including ; Motorola, US Robotics and Rockwell.

V.34 has a number of features that make it superior to v.FC of
which the most substantial advancement is the modems "adaptive
intelligence capability. Unlike previous standards v.34 employs
multiply modulation methods (MODEM = Modulator/Demodulator) and
multiple impairments compensation techniques. This allows it to
intelligently choose the optimum set of modulation tools to adapt
to the telephone lines.

The only other modem that is selling on the market in any sort of
quantity is v.32bis (14,400 baud) modems. These modems as you can
tell by the name are half the speed of a 28,800 baud modem and
have the following differences;

                 V.32bis                 V.34
Modem Types     Fixed Modulation  Adaptive Intelligence
Data Rates     14,400 - 7200 bps  28,800 - 2400 bps
Bandwidth     Fixed                   Variable
Trellis Coding   2 Dimensional           4 Dimensional
Adaptive
Equalization     Linear                  Preceding
Mapping          2D Shell Mapping       16 D Shell Mapping
Aux Channel     None                    200 bps
Operating
Modes            Full & 1/2 Duplex(Fax)  Full, 1/2 (Fax) and
                                         Asymmetric

Even if you don't understand the jargon above (Some even I don't
know about) you can see that v.34 is a more flexible, higher
quality transmission protocol. V.34 is also very flexible in the
manufacturing stage. Modem manufacturers are able to select from
a "toolbox" various features they want to include in their
modems. This way they only pay for the features they use, meaning
cheap modems can be built which although are 28.8k they are not
using all the great features of v.34 making them less reliable,
etc. than a modem with all the features. This has been proven by
the fact that the two best v.34 modems on the market (Motorola
and USR Courier) are fully v.34 compliant or have all the v.34
toolbox.

1. V.8 Negotiation handshake
2. Line Probing
3. Precoding
4. Adaptive Pre-Emphasis
5. Adaptive Power Control
6. Multi-dimensional Trellis Coding
7. Shell Mapping (aka shaping)
8. Warping
9. Fast Train & Training Recovery Procedures 10. High Speed DTE
Interface

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V.8 MODEM NEGOTIATION HANDSHAKE - A new handshake start up
procedure developed for v.34 products. V.8 is backwards
compatible to all lower speed modems. V.8 is the first noise you
will hear from your modem between two v.34 modems. V.8 is an
intelligent procedure allowing for a quick connection. V.8 has
been built flexible, and can be easily upgraded in the future if
the need arises.

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LINE PROBING - Line probing is the most significant tool in the
toolbox. It allows the v.34 modem to intelligently choose the
optimum operating parameters for any given telephone channel.
Line Probing is a bi-directional exchange which is performed
immediately after v.8 negotiation and involves the transmission
of complex signals that allow the distant receiver to analyze the
characteristics of the telephone channel before entering data
transmission. This analyzing sets a number of key parameters
including:

* Carrier Frequency and Symbol Rate. Sets optimum bandwidth and
placement from 11 combinations with 6 different symbol rates,
each with 2 possible carrier frequencies

* Pre Emphasis Selection. Modems choose the optimum transmit pre-
emphasis filter from menu of 10 defined filters.

* Power Control Selection. Modems choose the optimum transmitter
output power level.

The line probing features are performed on initial connecting and
when ever line conditions change, which is very handy if you're
connected for long periods of time, especially over leased lines
or microwave links.

****
PRECODING - Very techo, but basically for the best connection and
to use all frequencies available on the line. Precoding uses DFE
or Decision Feedback Equalizers to compensate for ISI
(Intersymbol Interference).
****
ADAPTIVE PRE-EMPHASIS - This is an amazing feature which can
compensate for known channel distortions learnt during Line
probing. The modem has a selection of 10 different filters to
choose from so that it can get the signal through as best as
possible to the receiver.
****
ADAPTIVE POWER CONTROL - Proper selection of transmitter power is
critical in high speed modems to stop echo, and to maintain
signal to noise ratio. Adaptive power control is an intelligent,
adaptive scheme which automatically selects the optimum transmit
level based on line probing results.
****
MULTIDIMENSIONAL TRELLIS CODING - Trellis coding simply put is a
forward error correction coding scheme. The value of the coding
is expressed as a "coding gain" which is a measure of the modem's
error rate improvement over an uncoded modem. The effective
coding gain of the three new v.34 codes employed work to be the
best trade-off between performance, delay and complexity.
****
SHELL MAPPING - Shell mapping is a signal constellation mapping
technique which attempts to distribute these signal points in the
2 dimensional space in such a way as to improve the resultant
noise immunity by approximately 1 dB.
****
WARPING (aka Non-linear Encoding) - Warping is another form of
signal space coding specifically designed to combat the effects
of signal dependent distortion also known as non-linear
distortion or harmonic distortion.
****
FAST TRAINING & TRAINING RECOVERY - Training is a general term
used to describe the process by which the modem's receiver
synchronizes on the remote modem's transmit signal at initial
connection. It is also performed when extreme disruptions (line
noise) occur. The v.34 training sequences are receiver timing
based, therefore the time to complete a train can be minimized.
Recovery is built into the v.34 code unlike v.32bis modems,
allowing for quick detection and recovery from line noise.
****
HIGH SPEED DTE INTERFACE - The v.34 specifications defines two
interface connections, the preferred interface is a 25 or 26 pin
physical interface utilizing a mix of v.10 and v.11 electrical
standards. This is very similar to X.21 and will likely become
the preferred interface for synchronous PC users. The alternative
interface is backward compatible with the installed EIA232 based
(Your standard 25 or 26 pin serial port on most computers
including Amiga, IBM PC and the modified Macintosh interface).

(c) Copyright as well!
Thanks to Motorola for help.
This is (c) copyright 1995 by Karl Willdig. All rights reserved.
This file may be freely distributed as long as it remains intact.
