A network consists of two or more computers that are linked in order to

share resources (such as printers and CD-ROMs), exchange files, or allow

electronic communications. The computers on a network may be linked through

cables, telephone lines, radio waves, satellites, or infrared light beams.

 

The three basic types of networks include:

 

· Local Area Network (LAN)

· Metropolitan Area Network (MAN)

· Wide Area Network (WAN)

· Campus Area Network (CAN)

· Home Area Network (HAN)

 

(A) Local Area Network

 

A Local Area Network (LAN) is a network that is confined to a relatively

small area. It is generally limited to a geographic area such as a writing lab,

school, or building. Rarely are LAN computers more than a mile apart.

In a typical LAN configuration, one computer is designated as the file

server. It stores all of the software that controls the network, as well as the

software that can be shared by the computers attached to the network.

Computers connected to the file server are called workstations. The workstations

can be less powerful than the file server, and they may have additional software

on their hard drives. On most LANs, cables are used to connect the network

interface cards in each computer.

 

(B) Metropolitan Area Network

 

A Metropolitan Area Network (MAN) covers larger geographic areas, such

as cities or school districts. By interconnecting smaller networks within a large

geographic area, information is easily disseminated throughout the network.

Local libraries and government agencies often use a MAN to connect to citizens

and private industries.

One example of a MAN is the MIND Network located in Pasco County,

Florida. It connects all of Pasco's media centers to a centralized mainframe at the

district office by using dedicated phone lines, coaxial cabling, and wireless

communications providers.

 

(C) Wide Area Network

 

Wide Area Networks (WANs) connect larger geographic areas, such as

Florida, the United States, or the world. Dedicated transoceanic cabling or

satellite uplinks may be used to connect this type of network.

Using a WAN, schools in Florida can communicate with places like Tokyo

in a matter of minutes, without paying enormous phone bills. A WAN is

complicated. It uses multiplexers to connect local and metropolitan networks to

global communications networks like the Internet. To users, however, a WAN will

not appear to be much different than a LAN or a MAN.

 

(D) Campus Area Network

 

Campus Area Networks are LANs whose computers are within a limited

geographic area, such as a school campus or a military base.

 

(E) Home Area Network

 

Home Area Networks are networks contained within a user’s home that

connect a person’s digital devices.

 

(F) Point-to-point and broadcast networks

 

Network may also be classified based on how messages are sent from the

sender to the receiver, thus point-to-point networks and broadcast networks.

In point-to-point networks, the transmission lines (wires, radio links,

telephone lines, etc.) connect pairs of hosts. Messages move from one host to

another until they reach their destination. The main issues with the design of this

type of network are the topology of the network (which node are connected to

each other) and the routing of information from one node to another.

In broadcast networks, on the other hand, all host share a single

communication channel. A message sent by one host is received by another host

even though this host is not the final destination of the message. In short the

message is broadcast to everyone in the network. The main problem with this

type of network is the arbitration between competing host that want to use the

channel at the same time. One example of broadcast network is the satellite

network. A satellite network is an application of a broadcast network where

satellite provides a shared channel between hosts that maybe widely distributed

geographically.

 

Advantages of Installing a Network

 

· Speed. Networks provide a very rapid method for sharing

and transferring files. Without a network, files are shared by

copying them to floppy disks, then carrying or sending the

disks from one computer to another. This method of

transferring files (referred to as sneaker-net) is very timeconsuming.

 

· Cost. Networkable versions of many popular software

programs are available at considerable savings when

compared to buying individually licensed copies. Besides

monetary savings, sharing a program on a network allows

for easier upgrading of the program. The changes have to

be done only once, on the file server, instead of on all the

individual workstations.

 

· Security. Files and programs on a network can be

designated as "copy inhibit," so that you do not have to

worry about illegal copying of programs. Also, passwords

can be established for specific directories to restrict access

to authorized users.

 

· Centralized Software Management. One of the greatest

benefits of installing a network at a school is the fact that all

of the software can be loaded on one computer (the file

server). This eliminates that need to spend time and energy

installing updates and tracking files on independent

computers throughout the building.

 

· Resource Sharing. Sharing resources is another area in

which a network exceeds stand-alone computers. Most

schools cannot afford enough laser printers, fax machines,

modems, scanners, and CD-ROM players for each computer.

However, if these or similar peripherals are added to a

network, they can be shared by many users.

 

· Electronic Mail. The presence of a network provides the

hardware necessary to install an e-mail system. E-mail aids

in personal and professional communication for all school

personnel, and it facilitates the dissemination of general

information to the entire school staff. Electronic mail on a

LAN can enable students to communicate with teachers and

peers at their own school. If the LAN is connected to the

Internet, students can communicate with others throughout

the world.

 

· Flexible Access. School networks allow students to access

their files from computers throughout the school. Students

can begin an assignment in their classroom, save part of it

on a public access area of the network, then go to the media

center after school to finish their work. Students can also

work cooperatively through the network.

 

· Workgroup Computing. Workgroup software (such as

Microsoft BackOffice) allows many users to work on a

document or project concurrently. For example, educators

located at various schools within a county could

simultaneously contribute their ideas about new curriculum

standards to the same document and spreadsheets.

 

Disadvantages of Installing a Network

 

· Expensive to Install. Although a network will generally

save money over time, the initial costs of installation can be

prohibitive. Cables, network cards, and software are

expensive, and the installation may require the services of a

technician.

 

· Requires Administrative Time. Proper maintenance of a

network requires considerable time and expertise. Many

schools have installed a network, only to find that they did

not budget for the necessary administrative support.

 

· File Server May Fail. Although a file server is no more

susceptible to failure than any other computer, when the

files server "goes down," the entire network may come to a

halt. When this happens, the entire school may lose access

to necessary programs and files.

 

· Cables May Break. The Topology chapter presents

information about the various configurations of cables. Some

of the configurations are designed to minimize the

inconvenience of a broken cable; with other configurations,

one broken cable can stop the entire network.