Whether youre connecting a LAN to the Internet or using your palmtop computer to
link with a PC at the office, youll need oneand the faster, the better.
One what? One modulator demodulator, or modem, which converts your signal from digital
computer language to a signal compatible with your communications service.
If youre transmitting data over a standard dial-up voice line, youll need a
true modem. But if youre working with digital service, you wont use a modem.
Instead, youll use a terminal adapter, such as an Integrated Services Digital
Network device, which allows voice and data transmissions on the same line.
Digital connections are so much more efficient than analog that, were we building a
telecommunications infrastructure from scratch, it would certainly be all digital. The
reason we have modems at all is because the United States essentially invented large
telephone systems and began building them decades ago, using analog equipment. Most
surviving analog equipment exists only between the telephone company switch office and
your desktop; everything else is digital.
But it means that digital data from your computer is converted to analog by modem, sent
through the wires to the telephone substation and converted to digital again, and vice
versa for information sent to your computer.
V.3433.6-Kbpsmodems assume an analog-to-digital/digital-to-analog
conversion will occur at both ends of a data call, whether upstream or downstream.
If you dont have a digital connection, such as a T1 line, and place a data call
using a 56-Kbps modem, the call travels over the local analog loop to the public switched
telephone network via a two-wire, twisted-pair copper line.
At the central site T1-connected modem, a hybrid generator terminates the two-wire
connection, converting it to four-wire.
The four-wire connection connects to a coder/decoder at the central site. The codec,
which is designed for voice, not data, converts the data from analog waveforms to digital
binary bits and sends it along the digital network.
Equalizing the signal from analog to digital is more difficult than the reverse and
shows up as quantization noise, which slows the transmission rate to about 30 Kbps.
V.9056-Kbpsmodems assume only one conversion in a downstream transmission
path. The assumption is accurate in about 80 percent of instances. Most central site
modems have a digital connection such as a T1 line with the network, and most Internet
service providers have a digital connection with the Internet.
But the modems also probe the connecting lines to detect conversions. To connect at the
56-Kbps rate, there must be no conversions of the digital signal within the network.
A data call initiated at a server modem with all-digital connections skips the
analog-to-digital connection and therefore can travel, optimally, at the Federal
Communications Commission transmission limit of 53.3 Kbps. That limit is under
consideration by the FCC now, with an expected lifting of the limit by years end.
But even if you have all-digital connections, you may not get 56-Kbps speeds. At the
beginning of a data call, the modems identify themselves and their capabilities. Modems
with different 56-Kbps technology will not connect at that rate. With adoption of the V.90
standard, however, that will cease to be a problem.
Your 56-Kbps modem and all-digital lines wont do you any good in communications
with the European Community. EC countries use E1 lines, which operate at 2.048 Mbps and
combine the equivalent of 30 voice lines, instead of T1 lines, which operate at 1.544 Mbps
and combine the equivalent of 24 voice lines.
Neither will you get the 56-Kbps speed if your line goes through a private branch
exchange. Conversions to Adaptive Differential Pulse Code Modulation, such as those that
occur with data calls over transatlantic submarine cables, and other conversions such as
AT&T Corp.s TrueVoice, also will slow transmission rates.
But with the acceptance of the V.90 standard Sept. 16 by the International
Telecommunication Union, the problem of buying into the right 56-Kbps technology is a
thing of the past. Since then, vendors have almost daily announced compliance of one
product or another with the new standard.
But the older modems are out there, so if you buy a 56-Kbps modem, its best to be
certain it is V.90, not just V.90 upgradable.
If you buy an upgradeable 56-Kbps, make sure it is controlled by Flash memory, not ROM.
Flash memory costs more but can easily be updated.
Although all the x2 and K56Flex modems are supposedly upgradable to the new standard,
reports indicate that some upgrade procedures just dont work. For this reason, I
wouldnt recommend buying an older x2 or K56Flex modem with the thought of upgrading
But should you upgrade at all? If your office is loaded with older 28.8-Kbps or
33.6-Kbps modems, does it make sense to spend the money on an upgrade to the faster
When deciding, there are some general points to consider:
Surfing may not benefit from faster connections, but if your major activity is
downloading large files, even a small improvement in throughput or modem speed can make a
big difference. Upgrading hardware from 33.6-Kbps to 56-Kbps connections can be
If youre sending files from your PC, an upgrade wont help. The 56-Kbps
modems wont improve upload speeds.
You can go ahead and buy a V.90 modem today, even if your connection isnt 56
Kbps. But you wont see a difference from your old 33.6-Kbps modem in both directions
until your remote connection upgrades to V.90 for downloads to your computer.
If your Internet service provider offers K56Flex or x2 56-Kbps connections, limit your
buys to modems that come with support for both your providers standard and the V.90
Some modems are used mostly for fax transmission and reception. As the fastest fax
connection is only 14.4 Kbps, no upgrade is cost effective.
Direct connections between remote computers or networks were once a tangle of complex
communications software, but the Internet has made it easy to link remote offices. In
fact, the Web is so easy to use that it may make sense to connect two LANs on the same
floor, not by direct cable connections but through the Internet.
But 56-Kbps modems are far from the only game in town. ISDN uses almost all the same
hardware but eliminates the analog local loop.
Because they dont use analog technology, ISDN connectors between your computer or
LAN and the telephone companys wiring are terminal adapters rather than modems.
Base rate ISDN carries up to 64 Kbps for each B-channel, which is only a bit faster
than the latest crop of analog modems.
To get really impressive speed, you need to tie two ISDN lines together for 128-Kbps
rates. But you can do the same far more cheaply with analog lines.
Like other high-speed connections using phone wiring, ISDN only works if your office is
close to the telephone switch station or central office18,000 feet, or about 3.4
At 1.5 Mbps, broadband ISDN is much faster, but because it requires fiber-optic
connections, it is rarely used.
The latest entry in the standards race is asymmetric digital subscriber line (ADSL),
which uses regularunshielded twisted paircopper wire to achieve transmission
speeds of up to 9 Mbps. Therein lies the great strength of ADSL: It can operate over
ordinary telephone wiring, which already connects every government office, business and
virtually every home in the country.
Asymmetric indicates that the downstream rate differs from the upstream rate, which is
the same as the 56-Kbps analog modem standards. An ADSL adapter includes an RJ-11
telephone connector and an RJ-45 Ethernet hookup to provide both computer data and
standard voice communications.
ADSL has a mixed history and is making spotty progress toward implementation.
Initially, it was a way for telephone companies to compete with cable companies in
delivering movies to homes. As interest in the Internet grew, telephone companies began
touting ADSL as competition for cable modems.
ADSL has been endorsed by Compaq Computer Corp., Intel Corp. and Microsoft Corp., and
accepted by nearly a hundred other information technology companies in the Universal ADSL
Working Group (UAWG). For more on UAWGs support, see http://www.uawg.com.
Support for UAWG by the ADSL Forum was announced in January; see http://www.adsl.com.
Besides the wrangling between companies offering different standards, ADSL also faces
the problem of proximity or, more exactly, the lack of it. Unless your computer is within
9,000 feet (1.7 miles) of a telephone substation, top performance is 9 Mbps.
The UAWG proposal supports something called G.Lite, which offers low-end ADSL
performance but at longer distances.
Several U.S. and Canada test sites exist or are proposed. According to Bell Atlantic
Corp. and America Online, testing is ongoing in Northern Virginia and Washington. But,
according to information on the Web, at http://www.adsl.com,
tests are limited to maximum download speeds of 1.5 Mbps.
Follow a link to Bell Atlantics Web site for information on what the company
calls Infospeed DSL. Oddly, the information page compares ADSL speeds to the speed of
out-of-date 28.8-Kbps modems, although elsewhere it compares performance of its ADSL
product to 56-Kbps modem performance.
The Bell Atlantic Web page offers higher-speed ADSL linksup to 7 Mbps. Costs for
a home ADSL link are $99 for installation, $325 for an ADSL modem, and monthly charges
from $40 (640 Kbps) to $109 (7.1 Mbps).
Adding Bell.Nets Internet link raises the top monthly cost to $190 per month.
The real promise of ADSL, or Bell Atlantics Infospeed DSL, is in providing
telecommuters with high-speed access to agency LANs, making home installations highly
relevant to government users.
Then, theres T1. Designed by AT&T Corp. to connect PBX telephone systems, a
T1 digital leased line connection to a system only works within 5,000 feet of a telephone
A full T1 line consists of 24 separate 64-Kbps lines, each of which can be used for
voice or data communications for a maximum speed of 1.544 Mbps per T1 installation, about
20 percent as fast as an Ethernet LAN connection. A T3 connection includes 672 64-Kbps
A point-to-point T1 connection has been an expensive way to connect distant offices,
but by connecting through the Internet, backbone prices have become reasonable. T1
connections are now often used to connect LANs to the Internet. Competition from various
vendors has begun driving T1 costs even lower.
For more details on how T1 and other T lines work, see http://www.dcbnet.com/notes/9611t1.html.
If you think T1 sounds a lot like ISDN, youre right. But although the two
technologies offer similar performance, they are not identical.
T1 lines use channel service unit/data service unit (CSU/DSU) hardwarenetwork
links also require a router; ordinary phone lines use modems; and ISDN lines use terminal
adapters. T1 can also be scaled up to provide much faster service than ISDN.
Typical business rates for full T1 connections are $200 and up per month, with T1
Internet links adding another $800 per month. One-time installation costs start at $200.
Special government discounts may apply for some agencies.
For practical purposes, the major difference between T1 and ISDN is that conventional
T1 is a permanent, leased-line connection while ISDN is a dial-up connectionalthough
switched T1 is like a dial-up connection.
As leased lines, T1 costs are fixed, while ISDN links are billed by the minute.
Because costs for leased lines are easy to manage, T1 connections can be cost-effective
if your traffic volume justifies using them.
If you get a T1 line, be sure to get a T1 router, which can roll over your T1 traffic
to an ISDN line if the T1 line is overloaded or goes down.
If you use a dial-up Internet service provider, cable modems will offer faster Internet
But the speed results from more than the faster data transfer capabilities of the
hardware. The bigger pipeline connecting the local server to the Internet backbone also
plays a big part.
Dial-up connections through the telephone substation are limited by a 56-Kbps
modems capabilities. In some cases, too many modems are trying to suck data through
too few high-speed T1 connections from the backbone.
The pipeline bottleneck is less likely to occur if you can get a cable modem
connection. And theres no doubt that a cable modem is fast.
A voice-grade analog phone line, which is all the phone company guarantees from a
regular telephone connection, has a service bandwidth of about 3.3 kilohertz. Data must be
squeezed into that small slice of bandwidth.
The North American Television Standards Committee analog television signal in wide use
in the United States has a width of 6 MHz. This wider bandwidth is why cable modems are so
Cable modem implementation problems stem from the TV cable systems design for
one-way, not two-way, transmissions.
Security problems with cable modems are essentially the same as those network
administrators face daily in accessing the Internet, and cable modem prices are comparable
to those of dial-up services.
Cable modems are usually thought of in the context of home use, but a government office
could take advantage of the high-speed connection if a cable passes near the office. But
for now, a cable modems best use is probably as a way for telecommuters to connect
to the office.
Another reason not to rush to cable modems is that the fast connections of today may
well slow down when cable Internet connections become more common and traffic increases.
Another way to speed Internet access is via satellite. A satellite Internet connection
is similar to a cable modem link, except that it is a one-way service.
With a small satellite dish, you can download data at high speeds directly from a
satelliteand you dont have to work for the Pentagon or own a transponder to do
it. A satellite system offers fast downloads, but if your only uplink is an analog dial-up
modem, your upload speed is restricted to 33.6 Kbps.
With a satellite connection, you cant send data or requests directly to the
satellite; you must use a local Internet account. Hughes Network Systems Inc. of
Germantown, Md., for example, offers 400-Kbps downloads via satellite, but you need a
local Internet account to carry uploads and requests, essentially doubling your base cost
for Internet connections.
Pricing presents another drawback. Charges for cable modems and local dial-up Internet
service arent based on how much data you transfer, but satellite connections are.
Costs can easily run to hundreds of dollars per month.
The pricing structure causes two problems: costs arent easily predictable, and
managers must more carefully supervise Web use.
Like cable modems, satellite links are being marketed to home users. And the links make
the most sense for branch offices with few workers in relatively remote locations where a
T1 or ISDN connection either is not available or is not cost-effective.
For remote videoconferencing or remote training, a combination of ISDN, T1, or ADSL
local connections, along with a satellite service for very fast downloads, might be a good
To keep prices low, some PC makers are using an internal modem that is a sort of
enhanced serial port using host signal processing. Called a software modem, it shifts most
signal processing functions usually found in modem hardware to software. Such modems are
easy to upgrade, but because the workload falls on the PCs processor, all other
operations are slowed. None could be considered a fast modem.
A fairly recent development are dual-line modems, in which two phone lines share
You can create a dual-line modem using software or a combination of software and two
modems in the same box, effectively doubling the performance you get from a single 56-Kbps
One final word about speed. Many people are confused by the high numberssuch as
115,200 bit/secdisplayed by some LCD-equipped external modems or software tell-tales
for connections. This is the data terminal equipment rate. It tells only how fast data can
be moved between your computer and your modem.
The 115.2-Kbps rate frequently seen is the maximum data handling capacity of the RS-232
standard serial port.
The data communications equipment speed is the transmission rate of your modem over the
phone line; its established during the handshake between your modem and the remote
The speed of early, analog modems was governed by
the initial Bell Telephone Co. 101A standard, which allowed transmission speeds up to 300
baud, or a maximum of about 25 characters per second.
Baud, an old telegraphy term referring to Morse code transmission
speeds, indicated the number of high-low tone changes per second. It had a certain
validityslow modems work by sending a two-tone signal to indicate the zeros and ones
of binary data.
Todays higher speed modems use a different system, and
speeds are measured in bits per second (bps).
The number of bytes-per-second transmitted can vary, depending on
how you define byte and how much error correction is needed. A normal byte is eight bits
in length, but at slower modem speeds you also need a start bit and stop bit. Packet
framing further reduces throughput.
A 28.8-Kbps modem, for example, can send or receive about 3,300
characters per second, uncompressed. The rating is raw data transfer speed, however. The
amount of information exchanged can be considerably higher.
Most files that were not precompressed by an algorithm intended
for data or graphics files will be compressed by the transmitting modems hardware
and uncompressed at the other end.
The Universal Asynchronous Receiver Transmitter (UART) is a chip in your
computer that moves the data between your serial port connector or internal-mount modems
and the system bus.
No matter how fast your modem is, it cant move data any faster on a sustained
rate than your UART can process it.
Early IBM Corp. PCs used a 4.55-MHz eight-bit wide UART, a standard replaced by the
16-bit wide 16450 UART standard. All olderand many newercomputers use the
This presents more than a modem problem. Because the CPU must service the UART to
prevent data overrunlost informationan old UART tied to a fast modem can slow
the entire systems performance.
A 16550 UART that includes data buffers is necessary for data transmissions of 28.8
Except for very low-end boxes, most new computers use the faster UART. You can upgrade
the serial port on older PCs by adding a new serial board with the faster UART.
Although the 16550 serial controller UART chip found in most of todays computers
can handle up to 115.2 Kbps, all modems can compress the data stream. If you use 56-Kbps
modems or external Integrated Services Digital Network modem connections, even the 16550
UART can cripple your modems performance.
The 16550 chip,with a 16-byte buffer, provides 115,200 bits-per-second maximum
The original National Semiconductor 16550 UART had some bugs, which have been
eradicated, and now all 16550s are 16550A-compatible. But neither one is reliable in
The 16650 UART features a larger 32-byte buffer and provides up to 460,800-bps
throughput. It handles multitasking communciations port operations well.
One vendor of the 16550 and the faster 16650 UART port boards is LavaComputer
Manufacturing Inc. of Rexdale, Ontario, Canada.
LavaPort cards support more than 400 Kbps data transfer speedsenough for external
ISDN and 56-Kbps modems.
For more information about LavaComputer products, visit the companys Web site at http://www.lavalink.com.
The 16750 is a 64-byte version of 16550 but with the same interrupt problems that
restrict the 16550s use with modern operating systems and places a high load on the
Telltales in Win95 show the
sources of communications delays.
For Web surfing, a dial-up connection or slow modem usually
isnt responsible for a slowdown. Most delays are caused by a slow Internet backbone
or the originating server.
Most browsersthe software that lets you navigate the
Hypertext Markup Language pages found on the Internetor operating environments
provide some way to view how much data is moving through your internal modem connection.
With external modems, LED displays show the same thing.
Microsoft Windows 95 usersthe biggest segment of the
government marketcan usually find a telltale near the system time on the tool bar.
What you learn from watching the indicators is whether your
communications delays are due to slow modem performance or delays that are beyond the
control of your software and hardware.
The two telltales show incoming and outgoing data flows. If one
or both are lit most of the time, your modem is running at its full potential, and getting
a faster modem wont really improve your Internet access.
Poor phone line quality, slow Internet backbone, overloaded Web
site servers and a slow serial port connection in your PC can cause such delays.
Most users can improve their systems performance by adding
caching software, which loads Web page link information while youre reading the
current page. If you regularly do complex searches and generate dozens or hundreds of
links, many of which you need to explore, preloading can be useful; when you click on a
link the chances are your software has already loaded the page so it just pops up.
But if you often look at a few pages but seldom follow their
links, preloading cache software will waste bandwidth. And adding cache may increase
overall Internet traffic.
Another alternative is to keep multiple Internet sessions active
simultaneously. You can use different browsersa boon on the sites optimized for use
with one browser or another. This often lightens the load on the Internet backbone and
servers, and doesnt usually increase the load on a network if you access the Net via
a LAN link.
Normally, you would open your browser, go to a Web site, click on
a link and wait. The problem is that to do research on the Web, you must keep switching
between Web pages. Some are automatically cached by your computer, but some must be
reloaded each time through your network connection. Often, after youve followed
multiple links, clicking on the original page in the list of links is fruitlessyou
must start the search again.
But by using multiple instances of a browser or browsers, you
avoid the problem. You could, for example, open Netscape Navigator, go to a site, click on
a link, then switch to Microsoft Internet Explorer and do the same with a second site. You
can keep a single page in one window, making it simple to switch between sessions to
compare prices or specifications, for example.
Try this while watching the telltales, and youll see that
this sort of window switching in multibrowser sessions creates no extra data traffic.
Theres no penalty for individual users, but check with your
network administrator if youre on a LAN. In certain configurations this might
increase the network load.
901 Explorer Blvd.
Huntsville, Ala. 35814
Alpha Telecom Inc.
7501 South Memorial Parkway
Huntsville, Ala. 35802
Apple Computer Inc.
1 Infinite Loop
Cupertino, Calif. 95014
Ascend Communications Corp.
1701 Harbor Bay Parkway
Alameda, Calif. 94502
Best Data Products Inc.
21800 Nordhoff St.
Chatsworth, Calif. 91311
Black Box Corp.
PO Box 12800
Pittsburgh, Pa. 15241
Boca Research Inc.
1377 Clint Moore Road
Boca Raton, Fla. 33487
Cardinal Technologies Inc.
1827 Freedom Road
Lancaster, Pa. 17601
Chase Research Inc.
545 Marriott Drive
Nashville, Tenn. 37214
Cisco Systems Inc.
170 West Tasman Drive
San Jose, Calif. 95134
Diamond Multimedia Systems Inc.
2880 Junction Ave.
San Jose, Calif. 95134
Digi International Inc.
11001 Bren Road E.
Minnetonka, Minn. 55343
Eicon Technology Corp.
14755 Preston Road
Dallas, Texas 75240
E-Tech Research Inc.
1800 Wyatt Drive
Santa Clara, Calif. 95054
Hadax Electronics Inc.
310 Phillips Ave.
South Hackensack, N.J. 07606
P.O. Box 105203
Atlanta, Ga. 30348
Old Orchard Road
Armonk, N.Y. 10504
5200 N.E. Elam Young Parkway
Hillsboro, Ore. 97124
P.O. Box 3000
San Gregorio, Calif. 94074
1303 East Algonquin Road
Schaumburg, Ill. 60196
Multi-Tech Systems Inc.
2205 Woodale Drive
Mounds View, Minn. 55112
Newbridge Networks Inc.
600 March Road
Kanata, Ont., Can. K2K 2E6
Osicom Technologies Inc.
2800 28th Ave.
Santa Monica, Calif. 90405
1601 N. Harrison Parkway
Sunrise, Fla. 33323
20370 Town Center Lane
Cupertino, Calif. 95014
745 Camden Ave.
Campbell, Calif. 95008
5400 Bayfront Plaza
Santa Clara, Calif. 95052
Xircom Systems Division
2300 Corporate Center Drive
Thousand Oaks, Calif. 91320
4920 E. LaPalma Ave.
Anaheim, Calif. 92807
AG Communication Systems Corp.
1000 Mansell Exchange W.
Alpharetta, Ga. 30202
2043 Samaritan Drive
San Jose, Calif. 95124
1 Oak Park
Bedford, Mass. 01730
Cisco Systems Inc.
170 West Tasman Drive
San Jose, Calif. 95134
Efficient Networks Inc.
4201 Spring Valley Road
Dallas, Texas 75244
Escalate Networks Inc.
46575 Fremont Blvd.
Fremont, Calif. 94538
2200 Mission College Blvd.
Santa Clara, Calif. 95051
601 S. Union St.
Lawrence, Mass. 01843
12303 Technology Blvd.
Austin, Texas 78727
Orckit Communications Ltd.
574 Heritage Road
Southbury, Conn. 06488
620 Stetson Ave.
St. Charles, Ill. 60174
5400 Bayfront Plaza
Santa Clara, Calif. 95052
John McCormick, a free-lance writer and computer consultant, has been working with
computers since the early 1960s.