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Schools opt for bridges: muxes no longer used to link terminals to Toronto-area CPU.


The Brant County public school system, an hour and a half from Toronto, has 45 elementary schools and six high schools.

For the past three years, they were connected by a computer network for electronic mail and student information and other school records.

At first we multiplexed stand-alone word processors to a central computer.

In 1989, when we opened a new resource center, we decided to consider using bridges, which have dropped considerably in price over the years, becoming more cost-effective.

Although they're still used primarily for LAN (local-area network) and WAN (wide-area network) connections, they were the best option for linking our word processors.

In fact, they're being widely used today to connect PCs (personal computers) in WANs.

A bridge provides the same performance whether users are five or 5000 miles apart.

Limit Of 16

We've always been pleased with the muxes, but they have one major drawback.

One mux can be used to connect only 16 devices for every phone line.

At our new resource center, we have 30 devices--terminals and printers--that must be connected to our central computer.

We would have needed two muxes to link that equipment to our computer.

Buying one bridge was far cheaper than buying two muxes, and the type of bridge we're using (a Cryptall 3000) series Ethernet bridge) offers a number of advantages:

* Room for growth. A mux can be expensive because it doesn't handle a large number of network devices. Generally, a bridge can route data to about 8000 devices.

* Flexibility. Our current system--with standard digital terminals in the schools and all computer power at a central location--works well for us now. Someday, however, we might want to add PCs to our network. Bridges will let us do that.

* Options for speed. We're transmitting at 56 kb/s. If we want to upgrade to higher data rates, we won't have to purchase another bridge. Our bridge will go to 10 Mb/s.

* Throughput. Many popular bridges can't send continuously at 100% capacity. Ours offers 100% of network capability 100% of the time.

* Self-learning. The bridge "learns" how to determine the appropriate path for data to travel through the network to reach its designated destination. About 15% of our users are at the resource center. Without the self-learning process, the bridge would route 100% of its packets to that location, slowing our network. A small bridge helps.

* Security. We can use security tables to restrict who receives information. We can add data encryption as an option as well.

* Installation. It took only two hours to put in our bridge.

* Easy maintenance. With a multiplexer, you have multiple connections to maintain. With a bridge, you have one connection to the LAN and one to the WAN.
COPYRIGHT 1990 Nelson Publishing
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Author:Smith, Bruce
Publication:Communications News
Date:Feb 1, 1990
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