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Overview

To understand the full potential of computers we need to examine the computer network. A computer network consists of two or more computers and/or other peripheral devices, called resources, linked together to form a communication system that allows users to share information and resources. In contrast, a stand-alone computer stores all data on its own disk drives and is physically connected to each of its peripheral devices.

The primary advantage of using a network is that resources, applications, and data can be shared. The following three examples illustrate these advantages. The first example relates to sharing resources. In a school computer lab with thirty stand-alone computers you would need to purchase thirty printers if you wanted each student to print from his/her computer. In contrast, if you had thirty networked computers (called workstations) each of them could print over the network to a single printer.

The second example concerns the storage of applications. As stand-alone machines, each computer would need every program installed on the local hard drive (the C: drive). If you wanted to change the settings or add another application you would need to carefully repeat the process for each computer and hopefully the local hard disks would be large enough. On a network, settings need to be changed only once to impact all workstations, and programs need to be installed only once on a network drive for everyone's access.

A final example involves the storage of data. In a stand-alone environment students must sit at the same computer to access files stored on their hard drive. If a student comes in during lunch to work on a report, for example, and someone is already working at that specific computer, the student cannot access the report file. In a networked lab students can sit at any workstation and retrieve files from a network drive.

Networked computers have many other advantages. Electronic messages (called e-mail) can be instantly sent over a network. Communication can be improved with information broadcast to all appropriate people with less effort than a phone call or typewritten memo. Electronic purchases can be made without stepping into a mall or using a car. And finally, students can access encyclopedias and library resources across the globe without ever leaving their bedroom. As networks have become a common thread opening communication between millions of people throughout the world, it is important to understand more about how networks function.

Network Basics

We know the purpose of a network is to connect to another computer to communicate and share resources. Every computer on a network needs to have a communication interface that provides that connection. Examples of these interfaces are the network card that is plugged inside the computer, or a serial port.

Workstations can be physically connected through a system of cables, phone lines, or data lines. A wireless connection of infrared light, microwave, or satellite can also be used.

A workstation on a network may also be referred to as a host. These hosts are connected to various specialized computers that perform specific functions or resource sharing. These specialized computers are called servers. A file server refers to the special computer on a network that is used to serve the workstations with their applications and data. A print server is used to manage the printing jobs over the network and send them to the appropriate printer. A CD-ROM server has many CD-ROMs that it makes available to the hosts. Organizations might employ application servers that only store and manage specific programs of the organization such as a large database of information. Other servers include remote communication servers, mail servers, web servers, and domain name servers (more on these terms later).

Sharing of resources such as printers is an important use of a network. Other resources that can be shared over a network include modems, CD-ROMs, and tape back-ups.

Network Types

Operating System

Just as a stand-alone computer needs an operating system to control its processing, a network needs an operating system too. There are two types of network operating systems: peer to peer and client-server.

A peer is a person of equal standing. For example, a student's peer would be another student, while a teacher's peer would be another teacher. In a peer to peer network all workstations have equal functionality and all their resources can be shared by any other workstation on the network. For example, each workstations' hard disk or CD-ROM drive may be considered a resource that all the other workstations could access. No single computer manages or controls the peer to peer network; all workstations are equal. Examples of peer to peer network operating systems are Windows for Workgroups, Windows95, and Artisoft Lantastic.

On a client-server network that relationship between computers is not of equality, but of customer and owner. The client (customer) is the workstation that connects to a server (owner), which in turn provides services. In a client-server network the servers are not usually used as a workstation because they are dedicated to the task they perform (serving CD-ROMs, files, applications, etc.). Examples of client-server network operating systems are Novell Netware, Banyan Vines, WindowsNT Server, and OS/2 Warp Server.

Location

Another way to define a network deals with location. Beginning with the most concise network is the local area network known as a LAN. A LAN connects computers and other resources in a workgroup, department, or building. A networked computer lab is an example ofa LAN. Next is an internetwork. An internetwork is a collection of LANs within a building, group of buildings, or campus area. A computer lab that is also connected to a library network would be an example of an internetwork. Finally, a wide area network, or WAN, is an internetwork that spans geographically remote areas. Because of its distance a WAN requires public or private communication links such as phone lines or dedicated lines (such as ISDN) to interconnect each area. An example of a WAN is a connection between two campuses that are miles away from each other.

Accessing the Network

Logging In

People using networked computers are called users. When many users have access to data and applications over a network there needs to be a system to protect sensitive information and ensure that users are given access to resources they need. It is the Network Manager's responsibility to handle these tasks. For example, a Network Manager would add a new user to the system and determine to which resources, applications, and data the user can access (called assigning rights).

Networks employ several methods and levels of security in order to protect the integrity and privacy of all stored information. Assigning rights is one method that restricts users to specific predetermined data and resources of the network. A second method of securing the network is achieved through the process of gaining access to the network that is called logging in. Although the process of logging in may vary slightly, in general there are three steps. The information below refers to Novel Netware. The three steps of logging in can be compared to what you do when you go to a friend's house.

STEP ONE: Knock on your friend's door. The file server needs to know that you would like access to it. In order to "knock on the file server's door" you need to use the command LOGIN. When you type the word LOGIN and press ENTER you are telling the computer to begin the process of giving you access to its resources. In some operating systems such as Windows95 a dialog box appears to help you through this log in process.

STEP TWO: Answer the question "Who is it?" Once you have the file server's attention with the command LOGIN, it asks you the question "Who are you?" Since it cannot orally ask you this, it displays the phrase Enter your login name on the bottom of the monitor. Every network user has a unique user name that is also called the login name. The login name is assigned by the Network Manager.

STEP THREE: Verify that you are who you say you are. If you were knocking at your friend's door he/she might recognize your voice or peer through the peep hole to confirm that you are in fact who you say you are. Since the file server cannot do this, it uses a secret password to confirm who you are. Your unique password is assigned by the Network Manager and it should be changed frequently. When you type in this password you will notice that as you type nothing appears on the monitor. This is the way the file server keeps your password secret-it does not display anything on the monitor as you type. If you make a mistake, press the BACKSPACE key until you hear the beeping sound. Otherwise, just press ENTER once finished typing. If you have logged in correctly, the system will present you with your main menu or application as defined by your login name.

Rights

Using the example of visiting a friend described above, depending on how good of a friend you are, you may not be allowed to enter all rooms in the house. The same is true with the file server. Your rights to files, programs, and resources on the file server are determined by your login name. For example, students who log in to a networked computer lab should not have access to teacher's tests and grades. Students might have the right to create files in certain folders, but they may be restricted from deleting files or modifying certain ones. A user might not be able to print on certain networked printers, access a certain network drive, or start a particular application program. These rights associated with the login name and password make it critical that younot share your password with anyone if you want your data to be secure. But remember, just as it is wrong to knock on a door and say you are a person other than yourself, using someone else's login name and password are also wrong and can result in severe consequences.

Logging Out

When you are ready to leave your friend's home you would always say good-bye and close the door after yourself. You would never think of just walking away and leaving the door open, would you? The same is true with the network. Until you officially say good-bye, a procedure called logging out, you are leaving the door wide for an intruder to steal or modify your files.

To logout, close all programs and enter the command LOGOUT. In Windows95 the Shut Down dialog box gives you the option to "Close all programs and log on as a different user." Once you log out the workstation is no longer linked to the file server using your login name and password. Again, remember that if you realize someone forgot to logout, that does not give you license to access that user's files. Just as we do not walk into a home if someone accidentally left the door open, we do not use someone else's rights because he or she forgot to logout.

 

Last modified: January 10, 2005
Yannis Grammatis