A school district may decide to join an on-line curriculum project which necessitates classroom connections as well as multiple computer access in the library media centers and the administrative offices. These needs require a local area network in the building connected to a router to the Internet.
The following scenarios are presented as options that a district may pursue to get the Internet connection to their district office and their school buildings.
1. Dial-up Connection to a computer
2. Routed Dial-up Connection to a building
3. Routed connection to one school building
4. Routed connection to multiple buildings with local dial-up access
5. Wireless connection to a school building
6. Cable System Connection to a school building
NASA has developed a method for having multiple computers using a single 28.8K modem line for access to the World-Wide Web. This scenario works well if the students are generally all retrieving the same general pages off the web. The commonly accessed web pages are kept on a local server in the school – this is called caching of files locally. When a page is needed that is not local, it is then retrieved from across the network. If the numbers of pages needed that aren’t on the local server are kept to a minimum, the limited bandwidth can serve the students and teachers well.
In this scenario many buildings have permanent connections to the Hub using a leased line. All of the same line speed options are available. The selection of the router at the Hub is dependent on the number and speed of each line coming into the router at the Hub.
Dial -up capacity is limited by the size of the terminal Server and the number of modems. Some universities support banks of 500 or more modems, and still cannot sustain the demand from their users. Limitations will
need to be imposed on modem usage or fees assessed to users to help manage the demand.
Wireless technologies offer an opportunity to provide high speed access in areas where phone line charges are unreasonable, where line of sight is not a problem, and distances are within the tolerance of vendor products.
In this scenario a single building establishes a permanent connection to the Hub using a wireless connection. The
speed or bandwidth of the line is determined by the distance between the antennas, the quality of the antennas, the power level used to generate the antenna signal, and the vendor offerings. Speeds of 1 to 2 Mbps are possible from a variety of vendors using spread spectrum technology which is in the unlicensed area.
Costs range from $4,500 to about $10,000 for wireless products that support upwards of 2Mbps connectivity. The difference in costs has to do with the distance at which they operate. The $4,500 range supports distances of 3-5 miles. The $10,000 category supports the distances of up to 25-30 miles. The major costs are related to antenna costs and affect both distance and angle of dispersion of the signals. Once in place, there are no recurring line charges, although maintenance costs will be required. Maintenance costs are nominally estimated at about 15% per year of purchase price.
Care must be taken to avoid overlapping fields of transmission from the antennas and other applications of wireless technology in the area. Cellular phones and other equipment are also using similar unlicensed frequencies and may cause interference and thus degraded performance causing slower or less reliable transmissions.
Cable System Connection to a School Building:
A cable connection can provide a permanent connection. In effect, a TV channel is dedicated to data communications. One channel is used for the outbound data to user sites, and a second channel is used for all data incoming from the site back to the Internet. This means that for each data channel, one less video channel is available in the community. At times, a TV channel at a high frequency range which is not desirable for TV signals can be used. New systems with large numbers of channels may be more flexible in allocating channels just for data usage.
Many cable systems are one-way in nature, enabling TV signals to be sent throughout the system, but no reverse channel broadcasts to most sites. There are products that utilize this media to deliver high speed bandwidth to a customer site (about 2 Mbps), but use alternate return paths. One such product uses a modem for the return path. This makes for a suitable use if the user is downloading lots of information from the Internet or a server at a Hub, but not if the user wants to upload a large amount of information, since the 28.8K return path is slow.
Many cable systems are now being upgraded to support two-way communications throughout the system. There are products that make effective use of this media to allow transmission rates ranging from 512Kbps to 10Mbps.
The difference between this and a leased line is that all sites connecting to a cable TV channel, are sharing the bandwidth, whereas a leased line is dedicated solely to the site being connected. This implies that the usage of the cable channel needs to be monitored, and when traffic levels dictate, additional cable TV channels must be allocated to data communications to handle the load.