Tips for Handling Tasks
Managing Cyberspace Communications
Data communications schemes come in a variety of flavors, with a range
of prices to match.
By Glenn K. Schulke
The rapid growth of the Internet, combined with the confluence of technologies
from what used to be distinct industries, is adding to the complexity and
size of data communications requirements for individuals and companies alike.
A company's need for speed and bandwidth has to be continually evaluated
to see whether there are tangible benefits from adopting new technologies.
Should you, say, upgrade the single 2400-baud modem that's only for a dial-out
e-mail connection to a 28.8 kilobits-per-second (kbps) connection for company
remote access use? Set up your own company World Wide Web site to provide
better customer service? Establish a high-speed connection for video conferencing?
With data communications--as with traveling physically from one city to
another--there are many ways to get there. Today's alphabet soup of data
communications can be foreboding and is cryptic at best. It is difficult
to determine what is the most effective (or cheapest) method.
A Spectrum of Options
There are several options for data communications, including standard dial-up
or dedicated circuits with voice-grade analog lines, and dedicated digital
circuits in various speeds and flavors with varying equipment requirements,
availability, service rates, and installation and maintenance costs.
At the low end, standard dial-up lines offer reasonable, cost-effective
performance for most dial-in remote access applications. Although faster
modem speeds are now available, line quality hasn't necessarily improved,
as most modems shipping today offer some form of line conditioning or error
correction (such as V.42, PEP or MNP 3 and 4) to improve data integrity
and support higher line speeds. Typical modem speeds start with at least
14,400 to 28,800 bits per second (bps or baud) and some support speeds up
to 115.2kbps with data compression methods like MNP Class 5, which has a
2:1 compression ratio, or V.42bis with a 4:1 compression ratio (28.8 x 4
= 115.2kbps). Given today's modem prices of typically under $300 for a full-featured
28.8kbps modem with V.34 and V.42bis--and with only a standard phone line
required--availability of these data speeds is easy to get and relatively
painless to the pocketbook.
If you are planning to establish a full-time connection with another site
or an Internet service provider (ISP), check the costs for installation,
basic monthly charges and connection fees, as well as evaluating your own
particular requirements. Some ISPs charge a fee for the number of minutes
connected (though they usually include a fixed amount of connect time per
month, such as 20 hours), and you may also be able get a dial-up connection
with your ISP that allows for unlimited connect time (typically for a higher
monthly fee). With the latter solution, you will generally stay connected
If you are considering a full-time connection to your remote site or ISP
with your company's Web server, you might wish to use the higher speed,
and potentially higher reliability, of a dedicated 56kbps (56K for short)
or T-1 line. Though the speeds and capabilities differ between a dedicated
56K and T-1 line (the T-1 line supports speeds of up to 1,500kbps or 1.5mbps),
they both use the same underlying mechanisms to achieve the connection.
Both are dedicated point-to-point connections, have the same underlying
protocols and use similar equipment.
Both 56K and T-1 dedicated lines use a form of serial communications by
transmitting encapsulated packets of data over serial point-to-point links.
Point-to-Point Protocol (PPP) uses the High-Level Data Link Control (HDLC)
protocol as a basis for creating these encapsulated packets of data or datagrams.
HDLC breaks the data to be transferred into variable length segments and
creates a "frame" or packet of information that is then transferred.
The frame of data contains a number of fields, including a beginning and
ending field, and address, control, data and checksum fields.
The Old Bottom Line
It is important to note that dedicated 56K and T-1 lines are typically expensive
to install and maintain. I received quotes on full T-1 lines of upwards
of $3,000 per month in some areas--plus installation and equipment. Moreover,
unless you are planning to use the entire bandwidth of the T-1 lines internally
or sell segments of your lines, it probably is not economically sensible.
Variations on a theme are available, though.
The 56K frame relay and fractional T-1 line are potential lower cost alternatives.
The 56K frame relay also gives you 56kbps of available bandwidth, but it
connects to a "frame cloud" at the phone company rather than directly
to your ISP. By this method, all of the ISP's incoming frame relay lines
are grouped together into a single T-1 line. This reduces the number of
lines the ISP requires and hence the cost of the line, as the ISP has to
purchase equipment only for the T-1 line, not numerous point-to-point lines.
Although the equipment required at your end will be the same, the monthly
cost will be much less. The principal advantage of the frame relay cloud
is that connections are priced at a low fixed cost per month and a "permanent
virtual circuit" links you to any other single site--anywhere within
the cloud--for the same cost. This distance-insensitive pricing can yield
A fractional T-1 line is just what the name indicates: a fraction of a T-1
line. Probably you will have to pay the installation charge for a full T-1
line at your location, but you have access to only a fraction of it. These
fractions or channels are each capable of a bandwidth of 64kbps and are
typically sold in pairs. You can therefore lease channel pairs up to the
maximum of the T-1 line (24 channels). This will save on your monthly service
fees, though it may not change either the installation cost or the cost
of the equipment required to establish the connection. However, when your
data communications needs increase, you can easily add more channels and
only be charged a small setup fee plus the additional monthly fees.
The equipment required to connect 56K, 56K frame relay, T-1 and fractional
T-1 is similar. You (and those on the other end) will require a channel
service unit/data service unit (CSU/DSU) and a router. The CSU/DSU required
for a 56K frame relay is different to the units required for the T-1 or
fractional T-1, so when selecting equipment, make sure you check with your
ISP to see which type of unit will be required. For 56K lines they start
at around $200, and for T-1 lines you can plan on $1,500 or so for each
unit. The router can be either a stand-alone piece of equipment or (in most
cases) a PC configured with routing software. The stand-alone units can
be expensive, eclipsing $3,000 in some cases, whereas the PC configured
with routing software can be nothing more than a 386 with a 56K or T-1 interface
ISDN Finally Here
Integrated Services Digital Network (ISDN) is gaining much publicity of
late, since it is finally being deployed after a decade of promises. There
are two primary types of ISDN service: basic rate interface (BRI) and primary
rate interface (PRI). BRI ISDN consists of up to three distinct channels
on one pair of copper wires: one or two B (bearer) channels and one D (delta)
channel. The two B channels can be combined for data rate speeds of up to
128kbps before compression. With compression, users in many applications
today can achieve throughput speeds of from 256kbps to more than 1,024kbps--over
a megabit per second. Because the lines are digital, they are almost totally
error-free, which means that the slowdowns and errors typically encountered
in today's modem transmissions are no longer a problem.
A single ISDN line can serve as many as eight devices: digital telephones,
fax machines, desktop computers, video units and more. Each device, in turn,
can be assigned its own telephone number, so incoming calls can be routed
directly to the appropriate device. Any two of these devices can be in use
at the same time for voice or data transmissions, and the lines can also
be combined for higher data speeds. It should be noted that in most cases,
the same copper wires used today for what is typically called plain old
telephone service (POTS) can be used successfully for ISDN. This means that
most homes and offices are ISDN-ready.
ISDN has a few additional advantages going for it. It's cheap in most areas,
with rates of $70 a month for 200 hours of connection time and only a nominal
setup fee ($100 or so). Equipment costs are reasonable; ISDN terminal adapters
start at around $400 each. ISDN terminal adapters connect and operate just
like standard modems, but they are designed specifically for ISDN services.
If you are planning to connect to an ISP using ISDN, make sure that the
service is available through the ISP and that you have compatible ISDN terminal
PRI is a service configuration that provides 23 B channels in the U.S. and
Japan (other parts of the world have 30 B channels) and one D channel, for
a total transmission rate of 1.544 mbps, which is equivalent (in cost also)
to a T-1 line. Each 64kbps B channel carries user information, such as voice
calls, circuit-switched data or video. The D channel is a 64kbps channel
used to carry the control or signaling information.
As you can see, there is quite a bit of overlap, but for my money the new
fast modems and ISDN warrant careful consideration before investing big
bucks in 56K or T-1 technologies.
Glenn K. Schulke is president of Open Technologies, Inc.,
a systems integrator specializing in software integration services, located
in Tempe, AZ. He can be reached at email@example.com.