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                            Look Before You Leap
                            56K Modem Technology

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(Editors note: This is the second edition of our White Paper on 56K modem
technology. Information is developing so fast that we plan to update this
document on a regular basis for the next few months. Since the first
edition, information has surfaced about FCC regulations that appears to
limit the technologys speed, about advances in an interim standard being
established by the Telecommunications Association (TIA), and about the
effect that suburban Subscriber Link Concentrators (SLCs) will have on
performance.

Multi-Techs position about the 56K modem technology has always been that
the technology promises to be one of the most important modem developments
in recent years. However, we believe that it has been prematurely introduced
and over hyped to the point that its real potential to improve performance
has been obscured and its reputation potentially damaged. Our efforts, such
as this white paper, are attempts to keep in focus this very important
technological development. As deployment of 56K modem technology comes
closer to reality, our enthusiasm for its potential continues to grow.)

                                Introduction

One of several new modem technologies on the horizon that promises to
dramatically increase data communications speeds is the 56K modem
technology. This newest iteration of what technologists have long claimed to
be at the top end of the envelope promises to double the speed of current
28.8K bps modems that follow the ITU V.34 standard. What is this new
technology? How does it work? How well will it work? When should you invest
in it? And, will it really perform as promised? These are some of the
questions todays modem buyer must ask. This white paper will address some
of these issues, plus provide a picture of the Multi-Tech solutions with 56K
modem technology performance.

Certainly the driving forces behind the need for faster modems are headed by
the rapid growth of remote access applications such as the Internet. In the
past, few new data communications applications created as much excitement in
the information business as the Internet. With such a rapid expansion over
the past couple of years, it was inevitable that requested services would
eventually become overburdened. This overburdening of the system is one of
the reasons behind the search for a faster modem. However, keep in mind that
the modem is only one piece of the system. Besides modems needing increased
speed, the capacity of the infrastructure and server capacity may also cause
problems. Phone lines and communications links between Central Offices (COs)
were primarily designed to handle voice traffic of a relatively short
duration, an average of about 3 minutes, not Internet calls with an average
of over 30 minutes. In addition, the Internet Service Providers (ISPs) who
sell Internet access time utilize sophisticated servers to handle the data
traffic and keep track of activity. With the rapid expansion of Internet
services, these ISP servers can become over burdened (especially during peak
business hours). This can also cause slower access to the Internet. Even the
PC used to connect to the Internet can be the culprit. An under powered PC
can struggle to handle tasks such as complex graphics that require extensive
data processing. All of these factors can make it seem that the modems
speed is the problem.

Besides the Internet, other forces driving the quest for faster modems
include desktop video conferencing, telecommuting, and entertainment (games)
software. In many of these cases, 56K modem technology will not enhance such
applications because 56K modem technology does not work in an
analog-modem-to-analog-modem connection. The 56K modem technology requires
that there is a digital ISP-type system on one end. And finally, some
applications, like groupware involving updates from a central server, will
be accelerated more in one direction than the other. That is because the 56K
modem technology transfers data faster from the server than to the server.

The jump to 56K modem technology is different than the modem speed increases
of the past. In this latest case, there are a number of limitations inherent
in the technology and the communications infrastructure. First of all, the
technology will only work over high-quality lines, otherwise the modems will
drop back to traditional V.34 speeds. The industry has already seen this
phenomena with the V.34 modems that have problems connecting at the highest
speeds over poor-quality lines. 56K modem technology also will not work over
any link that has more than one analog-to-digital or digital-to-analog
conversion, nor internationally where a conflicting digital conversion may
be used. It will not work if there is an ADPCM compression in the link, or
if any voice enhancer such as AT&Ts True Voice is employed. In addition,
there are incompatible versions of 56K modem technology on the market, so
the ISP equipment must be using the same 56K modem technology flavor as
the dial-in modem. And finally, the two leading technology versions are
headed for a showdown at the standards committee which may delay a unified
standard.

The message here is that 56K modem technology is very exciting and holds the
promise to improve performance of many data communications applications, but
selecting the applications is key. Like any technology promise, one has to
become familiar with the pros and cons before one can make an intelligent
decision on when to invest, or even if 56K modem technology is the best
technology for the task.

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                                How it Works

The new 56K modem technology is one of the most talked about datacomm
advances in recent history simply because it promises to double the speeds
and throughput of todays V.34 modems.

The reason such high speeds are even possible is due to the increasingly
digital nature of Plain Old Telephone Service (POTS) via the Public Switched
Telephone Network (PSTN). Over the past two decades, the communications
infrastructure between central offices (COs) has been almost completely
converted to a digital network. As a result, the analog modem used to
connect a PC to a distant computer or server uses analog communications for
a very small part of the link. Most probably, at the first CO, the analog
signal is converted to digital and remains so until the last mile where
the call is connected to the modem on the other end. That means there is a
analog-to-digital (A/D) conversion to get the signal onto the digital
infrastructure, and a digital-to-analog (D/A) conversion at the other end.

The way 56K modem technology works is that the data is intercepted in its
digital form by central site/ISP equipment and never has to go through the
second conversion. Digital lines are cleaner (less noise) and faster. By
dealing only with one analog to digital conversion, higher speed is
inherently possible.

To achieve maximum throughputs, the link needs to have such digital ISP
equipment on one end. Two 56K modem technology client modems cannot
establish a 56K bps link because of the additional A/D conversion). In
addition, the ISP equipment must be of the same 56K modem technology
flavor as the client modem for the whole thing to operate. As stated
earlier there is more than one 56K modem technology available, and they do
not yet interoperate.

As explained in the following section, transmissions between a 56K modem
technology client modem and ISP are not at maximum possible speeds in both
directions. Data from the ISP to the client modem will be up to the maximum
possible speed approaching 56K bps, but data transfers from the client modem
to the ISP equipment will be less. For the interim standard proposed by the
TIA, this speed will be 33.6K bps per the enhanced V.34 standard. If the
technology used is Lucent-based, future releases could very well include
speeds up to 40K in the up-stream and even 45K bps in a full duplex mode.

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                Shannons Law and Analog Data Communications

Shannons Law states that the theoretical maximum rate for error-free data
communications over the PSTN (i.e., a defined bandwidth channel with noise
present) is about 35K bps depending on the noise in the telephone link. This
theoretical limit is for two analog modems communicating over the PSTN. The
new 56K modem technology doesnt violate this limit because the data
communications is not between two modems but between a modem and a digital
ISP system which creates a reduced-noise link environment.

The diagram illustrating 56K modem technology communications shows two
modems connected through the PSTN along with a digital ISP system.
Communications between the ISP and modem are shown as up to 55K bps
downstream and 33.6K bps upstream. Communications between the two modems are
shown as 33.6K bps.

In client-to-client modem connections, the telephone network first converts
the transmitted analog signal to a digital signal and then transmits that
digital signal from one CO to the second CO. At the second CO, the digital
signal is converted back to an analog signal and then sent via an analog
phone line to the second modem. The noise introduced by the telephone
networks Analog-to-Digital converter is called quantization noise. In this
type of connection, Shannons Law determines the maximum speed to be around
35K bps. In a home-to-server type of connection 56K modem technology takes
advantage of the fact that the network has no Analog-to-Digital conversions
in the end users downloading (downstream) path and effectively avoids the
quantization noise impairments introduced by the telephone network.
Therefore the theoretical line speed will be ultimately bounded by the
telephone network capacity.

For upstream channel (data upload from client site to server site), this
direction includes a phone network PCM encoder (Analog-to-Digital
Converter); therefore, the quantization noise mentioned above does exist and
limits the maximum data rate in the upstream direction. Therefore 56K modem
technology will offer asymmetrical maximum speeds for end users downloading
and uploading data exchanges with servers digitally connected to the PSTN.

As we know, the PSTN developed as a voice-only network. Modems were
developed for communicating data over those voice-oriented networks by
converting the digital signals of a computer into analog signals that could
be transmitted as sounds. The newest V.34 modems are the most efficient
examples of this technology. But, with the widely deployed digital
technology existing in todays PSTN, it only makes sense to look to a
technology that is not limited to the assumption that both ends of a data
communications link are analog. Thats exactly what the 56K modem technology
does.

The way the analog signal coming from a modem to a CO is converted into a
digital signal is called Pulse Code Modulation (PCM mentioned earlier). The
way it works is that the incoming analog waveform is sampled 8,000 times
per second; the resulting values are transformed into eight bit PCM codes.

To transmit the resulting PCM codes, it takes 64K bps digital bandwidth (8
bits, 8,000 times/second). This 64K signal is transmitted over any number of
64K bps pipes in the telephone system as a single channel (or DS0) of a T1
communications line. In fact a channelized T1 link can carry 24 of these
signals. There are more efficient digitizing methods which may use less than
64K such as 32K ADPCM. These methods cannot be used for 56K modem technology
transmission.

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                    Applications for 56K Modem Technology

Just understanding the technology will go a long way in helping to plan how
to use it. By knowing that there must be a digital end involved for a 56K
modem technology link to work, certain applications are eliminated (e.g.,
those consisting of client-to-client modem communications.) But even keeping
in mind these basics, one still needs to approach this technology with
realistic expectations.

The true picture of 56K modem technology development is that it is too
early to tell what kind of throughput can be expected when the technology is
deployed. Weve already learned that the signal level of digital
transmission equipment, as regulated by the FCC, appears to limit the speed
of 56K modem technology to under 56K bps. This is because, unlike any other
modems, the performance of 56K modem technology is directly dependent on the
transmission level of the modem transmitter signal. The actual speed limit
will be dependent on a number of factors which can be different for each
specific link. This factors include the quality of the line, and the number
of analog to digital or digital to analog conversions.

Assuming that the technology turns out to provide an acceptable increase in
throughput over conventional modem to modem links, the best use for this new
approach will obviously be the Internet. The higher speed downstream data
rates mesh nicely with an application where a few keystrokes make a request
that results in a large amount of data being sent in response to the
request. Thats often what the Internet does. On the other hand, an
application like Internet phone or Lotus Notes, where updates in both
directions require extensive data transfers, the faster transmission in one
direction will help to a lesser degree.

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                      56K Modem Technology Limitations

By calling this new technology 56K bps, the industry has once more set the
users expectation too high, reminiscent of V.34s claims of 28.8K bps. Just
as V.34 modems fail to connect at 28.8K over many phone lines, the new 56K
technology modems may not provide 56K speeds even with one end fully
digital. In fact, as mentioned earlier, until such time that the FCC changes
its regulations regarding the signal strength of digital transmission
equipment, the top speed of this modem technology will probably not be 56K
bps. The truth is that no one knows what kind of performance can be
expected. Currently there is no test equipment available to simulate 56K
operation, so the only valid tests will be in real-life deployment. As 56K
modem technology modems roll out this year, and the various testing labs
around the country start to work them over, the real performance of these
products will become known.

The Regional Bell Operating Companies (RBOCs) have been silent about this
technology. As we know, the infrastructure is already being burdened by the
extras local traffic due to Internet calls, so a large increase of modem
traffic due to 56K modem technology will certainly not help the situation.
In fact it could be speculated that when the FCC investigates the
possibility of increasing signal strength of digital lines to help
facilitate 56K bps speeds, the RBOCs and other carriers will not be too
eager to allow it. Other technologies like ADSL will promise to offer higher
speeds and off-load data traffic from CO switches. Add to that the fact that
ADSL, like ISDN, will give RBOCs the chance to raise prices, and one see why
RBOCs may not be 56K modem technology supporters.

As stated earlier, claiming that 56K modem technology alone is going to
speed up Internet access is very misleading, because slow speeds on the
Internet are often caused by heavy traffic, overloaded servers, and
under-powered PCs. When a user is connected to the Internet, and the
send/receive lights of the modem flash once every 10 or 20 seconds, it does
not matter how fast the modem is, the problem is that the net is congested.
Its kind of like driving a Porsche during rush hour. The heavy traffic over
the Internet has gotten lots of attention, and indeed, the infrastructure is
being upgraded. The question is, will yet faster modems clog up the net even
more? Related to that question is whether the server hardware now in
existence can handle more data. A recent article in Data Communications
magazine (October 1996) titled Close-Up on Remote Access Servers, tested
several ISP hardware solutions with the results showing that as traffic
increases, the throughput of the servers decreases per connection. This is a
reflection of a server design that is not optimized for many users doing
heavy data transfer, but optimized for something lower.

The modem industry lost some of its credibility with the introduction of
28.8K bps modems a few years ago. Before V.34 was released, there were
pre-standard modems being sold as if they were standard. 28.8K was also the
first speed plateau where users could not often get the stated speed.
Previously every new speed plateau (2400, 9600, 14.4K and 19.2K) had modems
which connected at the stated speed. That was not the case at 28.8K bps for
number of reasons, all of which boil down to the technology approaching its
physical limit. Tech support departments of all modem companies and ISPs are
still explaining why users 28.8K bps modems dont achieve the highest
speeds labeled on the box. This scenario is found to repeat itself with the
premature introduction of 56K technology modems which, as previously
mentioned, will not be able to achieve 56K bps speeds at all. The same set
of problems for tech support will exist with 56K bps, but with the extra
complication of never having been designed to do client-to-client modem or
56K bps upstream transfers.

Also, 56K bps modem technology will not work where there are any conversions
of the digital signal within the link. Such conversions are done when
communicating between the US and Europe (A-law to - or mu-law or vice
versa.). Conversions are also done when the more efficient ADPCM compression
is used instead of PCM, as in some international links.

And lastly, 56K technology will not work if there is more than one
conversion in the link. As it turns out, much of the U.S. is now wired with
remote CO equipment that concentrates analog phone lines into digital T1
lines before sending the signals to the CO. This process is done by the use
of Subscriber Line Concentrators (SLCs). Some SLC technology uses multiple
analog/digital conversions for the process. Suburbs equipped with such SLCs
will reportedly not benefit from 56K modem technology. This is, again, an
area where the actual effect of an inhibiting factor on the technology is
not known. It is being reported that this could affect a large number of
potential customers.

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                 The Standardization of 56K Modem Technology

As in all modem communications, interoperability through standards
compatibility is the key to wide acceptance. The standards for 56K modem
technology operation will eventually be set by the International
Telecommunications Union (ITU). The U.S. organization which submits
recommendations to the ITU is the Telecommunications Industry Association
(TIA). The standardization process through the ITU is long, complicated, and
has been known to take years to complete.

In the mean time, there are two different 56K technologies currently being
developed by their respective groups. One group is headed by Lucent and
Rockwell, whose current modem technologies are installed in over 70% of the
central site/ISP systems. The second group is headed by U.S. Robotics. U.S.
Robotics strength is in retail and they are heavily marketing their version
of 56K to that user segment.

Considering the importance of 56K modem technology, Lucent and Rockwell are
supporting an interim standard via the TIA. This interim standard, called
K56flex, is expected to be passed by the TIA this year. One of the key
provisions of the K56flex standard is that the upstream data flow will be
ITU standard V.34. While this does not reflect the eventual higher speed
capability of the Lucent technology, it will make for faster approvals
internationally and the quicker deployment of the technology in the U.S.

The obvious problem is that the Lucent/Rockwell and USR technologies do not
interoperate, and until a standard is defined by the ITU, no one knows if
the modems being sold today as upgradeable will be upgradeable to that
standard. The first meeting of the ITU which includes an agenda item for 56K
modem technology, will be in March of 1997.

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                       Multi-Techs 56K Modem Products

Multi-Techs 56K modem technology products include central site ISP server
systems, plus both internal and external client modems. The technology used
follows the K56flex interim standard proposal by Lucent and Rockwell. By
using Lucents K56flex chips in these products, Multi-Tech expects to
provide even better performance in the future. As stated earlier, the
K56flex interim standard uses V.34 speeds of up to 33.6K bps for upstream
(modem to server) communications, but the Lucent technology is capable of
more than that. It is expected that future upgrades of Multi-Tech products
will allow upstream speeds to 40K bps and even full-duplex communications to
45K bps.

The Multi-Tech central site server system is the CommPlete Communications
Server, and the announced client modems include an external MultiModemZDX
(model MT5634ZDX), an internal ISA-bus MultiModemZPX (model MT5634ZPX), and
a Windows 95 ISA-bus internal MultiModemZPW (model MT5634ZPW.)

The CommPlete Communications Server combines dial-in/dial-out operation with
digital channelized T1 and ISDN PRI WAN access in one system. In addition,
the new CommPlete Communications Server features management via web
browsers, SNMP, telnet and FTP clients. The CommPlete system allows remote
users to dial into an IP or IPX network using analog or ISDN modems
utilizing all-digital communications links. The question of server power is
addressed by the systems high-end processors and segmented multiple bus
design. It utilizes one Pentium processor per segment/T1 line, to ensure
that each port has sufficient processing power for high-speed file
transfers. The CommPlete system was designed for 56K modem technology
products. It includes flash upgradeable modems to ensure that the latest
standards and features are just a modem connection away.

There are four segments in each rack with each segment containing one server
and four device slots. Each segment can be configured for either direct T1
or PRI interface. Each segment also can be set up to run the same remote
access solution as on all other segments or different remote access
solutions per segment to provide access for different remote clients. The
independent nature of each segment allows for greater flexibility when
providing access to the Internet or corporate intranets. The CommPlete
Communications Servers multiple bus backplane includes four buses involved
in the transfer of data. Each segment has a 16 meg data bus for data moving
to the RAS segment server, a T1 bus for calls coming in (used to provide the
signal interface between the T1 daughter board and modem boards and to
assign time slots for each modem), a control bus which spans the segments,
and the 10 meg Ethernet bus which takes the data from all four RAS segment
servers and puts it onto one Ethernet port.

The new 56K modem technology MultiModemZPX is an internal ISA-bus modem for
PC applications. It will work with any PC operating system and hardware
platform. In addition to supporting the K56flex interim standard, it also
supports standard V.34 and lower speeds along with V.17/Group 3 fax
operations.

The new 56K modem technology MultiModemZPW is a Windows 95 Plug and Play
compatible internal ISA-bus modem that supports the ITU V.80 standard is
used with video conferencing applications. In addition to supporting the
K56flex protocol, this modem will also support traditional V.34 datacomm and
V.17 faxing, plus voice mail, telephone answering machine, and
fax/document-on-demand operations via the bundled Windows 95 based
communications software.

The new 56K modem technology MultiModemZDX is ideal for both large business
and SOHO applications that require moderately priced modems. Also supporting
V.34 ITU datacomm and V.17 fax operation, the MultiModemZDX comes bundled
with data communications and fax software. Computer access is via an RS232
DB-25S connector. Advanced modem features such as remote configuration,
caller ID reporting (select models) and data/fax auto detect, makes this
modem perform to the highest application demands.

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                                 Conclusion

As the old saying goes, those who ignore history are doomed to repeat it.
V.34 (28.8K bps) modems were introduced in a mad scramble that sidestepped
important procedures for testing and standardizing. Such testing and
standardization is vital for the promised performance to be enjoyed by the
vast majority of users. Now we have modem makers throwing 56K modem
technology modems at the public before a standard is set, while two distinct
technologies are at odds, and while a basic understanding of what the higher
speed can and cannot do is largely absent. Its deja vu all over again.

Hopefully this White Paper has given cause to step back and evaluate any
planned move to 56K modem technology. It promises to bring yet another
incredible performance increase to the modem market, but it must be
understood before it can be properly applied. Specifically, keep in mind
these points:

* 56K modem technology makes sense in some applications, and not in others.
For instance, modem-to-modem links (desktop video conferencing,
telecommuting, and games) cannot run at the higher speeds, because a digital
ISP-type system is required at one end.

* Internet access is an ideal application for 56K modem technology, but
higher speeds apply only from the server to the client. Upstream links from
client modem to server may not be faster than V.34. Also keep in mind that
many of the delays encountered on the Internet are traffic-related and
cannot be improved by increased modem speed.

* Two 56K modem technologies are under development. One, headed by Lucent
and Rockwell, is incorporated in technology currently installed in over 70%
of central site/ISP systems, and it is the heart of the proposed TIA interim
standard. The other, headed by U.S. Robotics, is being incorporated (some
say prematurely) into products directed and heavily marketed to the retail
segment of the market. Both are vying for satisfaction from standards
organizations.

The best advice in selecting your 56K modem technology is to be an informed
buyer, and call your ISP to find out which technology it will be supporting
before you select a modem. Until standards are established and incorporated
into products on the shelf, it is the best way to ensure you will get the
performance you deserve. We hope this white paper will be of some help in
the selection process. Call us at (800) 328-9717, visit us on the Internet
at http://www.multitech.com, or email us at info@multitech.com.

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      Copyright  1997 by Multi-Tech Systems, Inc. All rights reserved

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Tech Support: (800) 972-2439 ---Fax Back System: (612) 717-5888 ---Web Site:
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