ISDN saves over T1 on college campus - West Virginia University

ISDN SAVES OVER T1 ON COLLEGE CAMPUS

Jeffrey Fritz has found a way to save Ethernet users a lot of money on linkups.

As datacomm analyst at West Virginia University, he has used ISDN successfully in two test Ethernet applications.

First, he tested ISDN as a backup to a T1 network.

T1 is a data link, usually supplied by a telco, that runs at 1.544 Mb/s and is commonly used to connect LANs together--two 10-Mb/s Ethernets, for example.

"The problem for us, and for many users, is that T1 is very costly," Fritz says.

A typical T1 line can cost West Virginia University more than $2000 per month. And if the link goes down, WVU has big problems.

The university has several heavily used Ethernets.

The one at the Engineering Science building is connected to the West Virginia Network for Educational Telecomputing (WVNET), an affiliated educational computing service supporting major colleges throughout the state.

West Virginia University is WVNET's major customer.

The Engineering Science Ethernet runs over a microwave link.

If that link goes down, a lot of users are left stranded. That's what happened while the ISDN backup was being tested.

Heavy rain caused a rock-slide. The Department of Highways dynamited away the debris and ordered all radio communications in the area shut off, including the microwave link.

Fortunately, Fritz realized he could use basic-rate ISDN.

"Sixty-four kilobits is not T1 speed, but it's a lot letter than being off the air," Fritz says. "So we developed it as a backup possibility. It gives us link redundancy."

WVU's second ISDN application allows Fritz to bridge an Ethernet to another network, though the Ethernet users cannot afford the cost of a T1 line as a link.

"Under certain conditions--for example if there are a lot of interactive users not doing a lot of large file transfers, or it it's a small Ethernet--they really don't need T1 bandwidth. They can do quite nicely with ISDN."

Tests showed the best the school could expect on a 64-kb/s link was about 54- or 55- kb/s bandwidth.

Depends On Intensity

"It depends on what the people are doing," Fritz says.

"You could have an Ethernet with three people, and all of them trying to transfer 2-megabyte files at the same time, and you can bring the house down.

"But you could have a local-area network with 100 people. They're all sitting at terminals looking at a database--not bringing up any information, just bringing screen information back and forth. All 100 will probably work very nicely over a 64-kilobit-per-second link."

Fritz' strategy is to combine multiple ISDN B channels.

For example, if he determines that one B channel will be enough, he installs a pair of bridges and uses a single B channel to connect them.

This way, he can get a university-department hookup started without major costs.

Then, he can add the ISDN line's second 64-kb/s B-channel link if the traffic requires it.

If that's still not enough, he will add a second ISDN line to take the user up to 256 kb/s.

At WVU, Fritz sees two ISDN lines as a practical limit.

"If they exceed that, then they might as well go to T1 anyway," he says. "Two ISDN lines on our campus would cost the user about $200 per month. They might want to go higher. We haven't gone that far down the road with it yet."

Compare that ISDN user cost of $200 per month ($100 for each ISDN line) with a T1 cost of $1000 to $2000 per month, and you can see why he's excited about it.

"You have to find a bridge that has a very good routing algorithm," Fritz says. "You must use a multiport bridge.

"The idea would be to share a bunch of B channels among all those ports and send them off the same way."

In theory, that should work well with a bridge that can route multiple serial parallel paths.

"But the bridge has to be able to use that complete bandwidth. And we had some problems getting the bridges we were using to do that."

Fritz hasn't yet overcome this problem.

Fortunately, he doesn't have an application where it becomes critical.

What he has is functional, but the traffic is limited by bridge bandwidth.

He has been working with Vitalink bridges and likes the support that supplier has given his testing.

Microcom brought in a beta-test version of an ISDN bridge it was developing, and so WVU has been working with Microcom bridges.

The testing done, Fritz is waiting for a user request to install the first permanent ISDN link.

COPYRIGHT 1990 Nelson Publishing
COPYRIGHT 2004 Gale Group