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Broadband may be only hope for ISDN.


ISDN least the ISDN we've known over the past five years.

In spite of hype from regional Bell companies and several equipment manufacturers, people simply didn't buy into integrated services digital networks.

Does that mean the issue of ISDN and intelligent network services is dead? Of course not. The next generation is regularly described in the media, Communications News included. It has several names.

One is fast packet switching, a technique for moving data packets through a network faster and more efficiently than with current technology.

An extension of this is frame relay, and appears well-positioned as a key switching technique for the 1990s, in addition to fast packet.

Another is SONET, a fiber optic transmission standard.

Still another is switched multimegabit data service, or SMDS, a high-speed intermediate network service envisioned as a bridge between local and wide area networks.

A fourth is the 100 Mb/s fiber distributed data interface standard, which adds an order of magnitude speed jump for token-passing LANs.

Broadband ISDN

Finally, we have broadband ISDN. It has been around for several years> few people noticed.

Now that original baseband ISDN has effectively plateaued--in spite of opinions to the contrary--the industry needs a new network standard for the 1990s.

Unfortunately, we will propbably have several, adding to the confusion we deal with already.

Let's try to clear up some of that confusion. Broadband ISDN is the technology we should have had all along.

During first-generation ISDN, however, RBOCs were limited to existing twisted pair wires for ISDN deployment in the local loop. Digital technology at the time offered maximum affordable band-width over copper wires at the DS-1 level (1.544 Mb/s).

Basic (2B+D) and primary rate (23B+D) services were defined. These are available in most RBOC areas, as well as from many independents.

Unfortunately, user network requirements did not included ISDN. They found it difficult to justify dismantling existing networks,, replacing them with ISDN.

Most initially used ISDN for voice communications. Today, both voice and data are implemented, although voice still occupies the larger share of bandwidth.

Correctly figuring that ISDN would be a technological boondoggle for a long time, users set about up-grading their local and wide area networks on their own.

They found solutions they needed, and ISDN wasn't a part of them.

Probably the biggest hurdle for ISDN, aside from resolving standards, was identifying workable applications. After looking at dozens of them (and many were fascinating) the verdict for most users was: so what?

ISDN missed its window of opportunity. It was more complicated than anyone ever imagined. That's why it has failed so far.


ISDN continues moving forward. Tests to link different ISDNs now are scheduled. They will all be successful. Or at least we won't hear about the failures.

The fiber optic juggernaut continues rolling. News switching techniques, like fast packet, are gathering supporters, or at least a lot of press.

New information services based on the transfer of automatic number identification (ANI) data are being implemented (or stonewalled, if you're in Pen nsylvania).

Signaling System 7 now flows through most major carriers networks.

So let's move on to broadband. Higher data sppeds envisioned with broadband ISDN can now be achieved over twisted pair, as well as fiber optics.

For example, it is now possible to obtain 100 Mb/s FDDI speeds using twisted pair. This is important for local loop service deployment.

Boradband transmission systems are like a multilane highway. Large bandwidth-in-tensive applications, such as video transmission, graphics, and large file transfers are well served by broadband networks.

Aggregate bandwidths often run into the hundreds of Mb/s. These contrast with single-path, baseband networks that have proven themselves in applications requiring 10-50 Mb/s.

Multiple stations can send or receive messages on a broadband network. Data streams are separated by frequency bands. Coaxial and fiber optic cables are the most widely used media.

However, these same facilities often limited initial user acceptance of broadband because so many users were comfortable with twisted pair.

Of course, today much of that has changed with improvements in fiber optics. Bandwidth on a broadband network can support several kinds of channels:

* dedicated channels connecting comunicating devices suc as two computers>

* switched channels, connecting two devices under centralized control>

* and shared channels supporting their own network of devices using time-division techniques.

Within a cable, each information group is totally autonomous, and the cable appears an exclusive resource to each.

Even though it operates with analog transmission, a broadband network can support digital communications.

We can easily envision a typical broadband network handling multiple ISDN channels, both basic and primary rate, plus video channels and other bandwidth-intensive applications.

This is where broadband really shows its colors.

So broadband ISDN, with huge service potential, is just around the corner. Or is it?

The new network options noted earlier in this column suggest that broadband may have some stiff competition from twisted pair, digital transmission, and a hybrid of fiber to the curb linked with "supercharged" twisted pair to the desktop.

Will we someday have "intelligent dial tone" that provides the same flexibility and ease of use we get with POTS and 120V electrical outlets?

Broadband ISDN could be the answer.
COPYRIGHT 1990 Nelson Publishing
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:integrated services digital network
Author:Kirvan, Paul
Publication:Communications News
Date:Aug 1, 1990
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