This is the
Jourth of a six-
part series on
Imtegrated Ser.
vices Digital
Network, or
ISDN, a commu:
nication technol-
ogy that will
have great stra-
tegic impor-
tance in the
future.

How ISDN ser-
vices develop
will depend on

individual countries and network Opera-
tors. The main users will be Corpora-
tions trying to rationalize much of their
existing wide-area telecommunications
facilities. With ISDN, corporations can
make a general, integrated voice and
data network available to all users.

It would be WTOng to assume that
ISDN can fulfill all of a corporation's
Communications reguirements. The high-
est-capacity ISDN channel, the Primary
Rate Access, operates at either 1.544M
bps or 2.084M bps, significantly slower
is currently in operation. Also,
Primary Rate Access is not generally
available for communication between in-
dividual users. Some potential dra:

— MARTIN

— this co

ISDN Benefits

There are many areas, however,
where ISDN services can bring major
benefits. The progressive deployment of
ISDN across Europe, North America and
Asia will encourage the expansion of
wide-area, integrated voice and data
Communications. By providing two 64K-
bps (144K) clear information channels
and a separate 16K-bps channel for sig-
naling, ISDN makes a wide range of fea-
tures and services available to the
whole community of telephone users.

A major advantage of ISDN to the
subscriber, the ability to integrate voice
and data over the two 64K-bps chan-
nels, is that while a User accesses one of

the 64K-bps channels for a telephone
|. Senversation, the other 64K-bps channel
can be used to either send or receive
data. With common-channel signaling,
telephone users will have displayed on
Pa nandsets the names or numbers of
ini

If the line is busy, the called party's
one ril dimla and/o,

n person call,
viding the option of taking the incoming
Call or maintaining the existing one.

The caller will also be able to send a

ISDN Boosts Lo

functions of the telephone and the PC to
be integrated.

The illustration shows an example of
an ISDN integrated workstation. The PC
Can contain a database of telephone
numbers that can be dialed from the
computer's keyboard. The telephone
electronics can be built into the comput-
er so that all the user needs is a simple
handset attached to the PC's keyboard.
A speaker built into the computer can
provide speech functions and hands-free
dialing.

For the first time, mixed voice, text or
data communications can be handled by
a single terminal device. Along with a
telephone call, a user can send informa-

—JSDN Will Integra
- Telephone and PC

PG WEEKNAPPLIGATION DEVELOPMENT — O

wer Level Net Communications .

ISDN standards place on user band-
width is not sufficient for applications
such as large file-transfer, graphics, mi-
ero-to-mainframe links and so on. For
these types of applications, the integrat-
ed workstation must have access to a
high-speed local area network, čither
through a direct connection or via the
PBX.

However, applications such as elec-
tronic mail can be handled adeguately
at lower bandwidths; that is, at 64K bps
or less.

Though costly in terms of circuit and
eguipment charges, videoconferencing
has obvious benefits, such as reduced
travel costs and better management of

Communication Services

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'communications
will be
handled by
a single
device

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Maryelen Zawatski

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The main ISDN users will be companies trying to rational.
ize existing wide-area telecommunications facilities, ISDN

tion on the screen or exchange data
with a central computer—all via one
line and one communication number,

- Data-Communications Features

ISDN will provide a number of basic
ao pe ala Platona tar
lould be a: to all users, includ-
ing electronic mail and compatibili
mmunications devices

makes an inlegrated voice/data network

geographically dispersed plants and of.
fices. Better methods Of video-signal.
Compression have reduced the band.
widths necessary for full-motion, color
ME AE speeds in the re-
on of 384K bps (corresponding to the
capacity of the proposed ISDN ie >

1 video-

information being stored electronically
s ing all tij ča

thi

APRIL 3, 1989

eration of PC/integrated workstations
will provide video communication as a
standard application.

As ISDN networks continue to emerge
in both the public and private sectors,
the impetus to develop integrated voice
and data workstations will increase. As
ISDN and Open Systems Interconnection
(OSI) standards mature, standard com-
munications applications most probably
will be built into all PCs,

Low-cost ISDN chip sets and an in-
creasing emphasis on OSI application
standards will mean that integrated
voice and data will become the norm
for the 19905.

ISDN Shortcomings
ISDN is not the solution for all com-
puter-to-computer communications. Per-

haps the most obvious shortcoming of
ISDN is its limited available bandwidth.
For communicating in and around the
office, the 144K-bps Basic Rate Access is
significantly slower than most existing
local area networks (which operate at
about 10M bps). For applications such
as file transfer, computer-aided design
and host-to-host communications, 144K
bps isn't fast enough. Very large
databases are common in many of to-
day's corporations, and the volume of

creasing all
Local ar : ANs)'are
dominant data-communications medium
in most large corporations. With the in-
troduction of fiber optics into LANSs, a
standard transmission rate of 100M bps
is readily achievable, either for worksta-
tion-to-workstation communications or
as a high-speed link interconnecting two
or more networks.

Given these shortcomings, is ISDN
"too little, too late?" For many large cor-
porations with applications that reguire
high-speed local and wide-area data
Communications, ISDN in its current for-
Mat is not enough. However, not all us-
ers have such reguirements,

ISDN should be viewed as a means of
enhancing the lower levels of a commu-
nications network architecture, provid-
ing improved integrated voice and data
Communications, better access to public
digital networks, and new network
services. :

One of the great strengths of ISDN is
e avallability of standards. Standard