California Educational Data Processing Association
The DataBus - Vol. 37, No. 1
December, 1996-January, 1997

ISDN vs. Spread Spectrum-Part II

Networking: Radios provide increased bandwidth and better support for Novell IPX.

Terrell Tucker, Panama-Buena Vista Union School District

The Panama-Buena Vista Union School District has been providing Internet access to schools for one year. We began providing the access with ISDN telephone service, then installed a spread spectrum link to an elementary school in the spring of 1996. As indicated in the Part I article (see The DataBus, June-July, 1996, "Spread Spectrum Wireless vs. ISDN, Part I"-ed.) , the district is pleased with the performance and reliability of the original wireless link. Unfortunately, we felt the cost was too high.

We have since installed spread spectrum links to each site previously connected with ISDN. The new equipment is made by Breeze Com and is capable of providing 3 mb of bandwidth. Two omni-directional antennas were installed at the District Office, each receiving signals from 3 schools. Our intent was to limit the number of antennas at the District Office since we plan to install a link to all 18 schools. We plan to add new schools onto the existing antennas until throughput is diminished, at which point we will add another omni-directional antenna. Sharing three sites over one antenna has proven to be more than acceptable.

Numerous problems have been encountered, primarily due to the use of omni-directional antennas. Due to the nature of the antennas, distance is severely limited. The farthest link is approximately 2 miles and the closest is one-third mile. Signal strength is very limited at greater distances, especially when a lot of mature trees are in the signal's path. The bandwidth realized seems to vary from a minimum of 1 mb up to 3 mb at the closest site. It is important at this point to realize that even though bandwidth is limited at some sites, it is still far greater than the bandwidth provided through ISDN. We have seen dramatic increases in the speed of delivery of IPX packets. We found ISDN to be unacceptable for Novell server maintenance over ISDN links.

The most pleasing aspect of our new "experiment" with wireless links is the price. Including installation, the cost of a wireless link at a school is approximately $3,200. This only includes the equipment on the school's end. After including the cost of omni-directional antennas at a central site, the cost is still less than $5,000 per site. The cost of wireless is paid off in a very short time when compared to the cost of telco equipment, installation and monthly service charges.

Breeze Com radio units are extremely small and are configured with an included bridge. Segmentation of networks is a problem with this setup, but a small price to pay to avoid the cost of routers. We will be installing dual network cards in our servers to perform the routing services. One of the cards will be a fast ethernet card to plug into an ethernet switch; the other a 10 mb card for the bridge connection.

Our goal is and has always been to provide affordable connectivity to schools, primarily for Internet access. Thus far, our new wireless solution seems to be just what we were looking for.

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