Inserting and Deleting Drive

Assume that the MAP command displays the following information on drives:

Drive A: maps to a local disk
DriveB: maps to a local disk
DriveC: maps to a local disk

If you would like to change the search drive mappings, you can use the INS option with the MAP command. For instance, search drive 3 currently points to the subdirectory \ACCREC. If it is to refer to the subdirectory \PUBLIC\FOXPRO, the command


will ensure that it does.

The option INS maps the next available search drive to \PUBLIC\FOXPRO, in this case search drive W:. The command further converts X: to search drive 4 and assigns W: to search drive 3. The MAP command would now display the following

Drive A: maps to a local disk
DriveB: maps to a local disk
DriveC: maps to a local disk

To delete a network drive or search path, the DEL or REM option can be used.

For instance, if you issue the command


search drive 4 will be removed and the message

'Mapping for X: has been deleted'

will be displayed.

How are Files Stored?

DOS helps you organize files by creating directories. The directory structure in DOS is a multi-level tree structure where the directories and the subdirectories correspond to the branches and the files correspond to leaves. The directory structure of Novell NetWare is similar to that of DOS. When we talk about the directory structure in Novell NetWare, we are referring to the directory structure of the file server.

On the server, the top-most level in the directory structure is the volume. Each volume has a unique name. Each file server has at least one volume called SYS. NetWare creates it when the file server is installed. A file server can have other volumes besides SYS.

Why have volumes? Well, to answer this question, let us answer a related question about the DOS directory structure: why have directories and subdirectories? The primary reason is to have a logical storage of files so that a user can easily access them. The same reason applies for NetWare. The difference between DOS and NetWare is that NetWare adds another level on top of the existing directory structure in DOS. Thus you have:

Files, which are in subdirectories, which are in directories, which are in the volumes of a file.

NetWare Directory Structure

NetWare Directory Structure

Note: The number of subdirectories and files shown in Figure 1.4 is representative and does not indicate the exact situation in NetWare.

Dividing a hard disk into several volumes divides the disk into logical chunks.

Consider an office in which a NetWare LAN is being used by two departments, Marketing and Personnel. Apart from the SYS volume that would be created anyway, there are two other volumes; one for the Marketing department that would contain files related only to the Marketing department, and the other for the Personnel department containing files related only to the Personnel department. The employees in Marketing would have access only to SYS and VOL1 (containing marketing files), the Personnel employees would have access to files in SYS and VOL2 (containing personnel files).

A volume contains directories. In NetWare, the default volume, SYS, contains four directories: SYSTEM, PUBLIC, LOGIN, and MAIL. SYSTEM contains NetWare operating system files, NetWare utilities, and programs that are reserved for the Supervisor. PUBLIC contains program files that help to execute certain utility programs of NetWare. These can be used by regular users. The LOGIN directory contains files that help a user log in to NetWare. MAIL contains program files that help the user use NetWare's E-mail facility.

Apart from these four directories, additional directories can be created in the volume SYS. More volumes (in addition to SYS) can be created on the server hard disk. These volumes in turn, have their own directories. It depends on the supervisor to decide whether the organization needs more directories within SYS, or more volumes apart from SYS.

Each directory can be further divided into subdirectories and each of these subdirectories can contain files. A directory, instead of containing subdirectories, can also contain files.

In NetWare, the path for a Foxpro file can be given as:


which indicates that the file Foxpro is in the subdirectory SW, which is in the directory PUBLIC, which is on the volume SYS, which resides on the file server NUT. The server name and the volume name need not be included if you have a LAN with a single server and a single volume. In a situation where there are more than one server on the LAN, and each server contains several volumes, if the server and volume name is not specified while giving the file and directory name, NetWare assumes the current server and the current volume name.

If a LAN has more than one server, changing over from one server to another would require a fresh login from the user. If the user is currently working on the server NIIT1 and would like to work on the server NIIT2 as USER2, the command to be issued would be:


Two additional points need to be noted here. While DOS recognizes only the backslash (\) for separating the levels of the directory structure, NetWare allows both the slash (/) and the backslash. Secondly, while DOS allows 127 characters in a directory path (including the drive letters and delimiters), NetWare allows 255 characters.


A Network user can afford to be sociable. We are referring to the facility that helps a LAN user talk to other users by sending short messages on their screen. First of all, how does a user find out who the neighbors are?

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The USERLIST command displays the list of other users who have logged into the LAN.

The command, USERLIST when typed at the command prompt displays the list of login ids of users logged in and other details, as given in Figure.

Output of the USERLIST Command

Output of the USERLIST Command

In the above list, the login id with an asterisk is your login id.

The command USERLIST /A gives additional information. It includes the network numbers and node addresses where the users are working. The connection number gives the serial number of the users in the order that they have logged in (refer Figure).

Output of the USERLIST/A Command

Output of the USERLIST/A Command

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SEND Command

This command allows the user to send brief messages to other users or user groups. The messages can be up to 45 characters. The command,

SEND "How about lunch?" TO USER JOE

will flash the message, How about lunch? on the screen of the workstation where JOE has logged in. You may include more than one user in that command, if you wish.

The command,


will flash the message on the screen of everyone belonging to the user group MKTG.

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This command flashes a message on the screens of all the users who have logged in. The message can be up to 60 characters and appears on line 25 of the screen. Thus, the command

BROADCAST There is a fire in the office. Head for fire exit.

should have the desired result. Note that the message need not be in quotes. The BROADCAST command can only be used from the server prompt and not from a workstation.

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You can give this command at the command prompt, and any user who sends you a message will get a display on the screen informing him or her that the message was not conveyed. CASTOFF does not block messages that have been flashed by the BROADCAST command.

To do this, the command CASTOFF A can be used.

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CASTON Command

If you have turned off receipt of messages and wish to establish links with other fellow-users again, you use the CASTONcommand.

LAN Community

A LAN is an organization within an organization. Just as any organization needs hierarchies and clear-cut roles and responsibilities, a LAN too needs hierarchies and groups. These hierarchies and groups help in the smooth functioning of the LAN.

All LANs, including Novell NetWare, form their own hierarchies and groups in an office, independent of the organizational structure.

A LAN contains data and software that is not meant to be used by everyone. Just imagine a LAN as a huge filing cabinet where every user has been assigned a different drawer to store his or her files. How would Tom feel if he discovers that John has got hold of the keys to his drawer and has been going through his files? Or if John's supervisor finds that John has been secretly going through the company's classified financial reports.

To implement proper security measures to manage resources, a LAN needs hierarchies and groups.

A LAN consists of users. The basic idea of having a LAN is the dissemination of information across all levels of an organization such that it can bring these levels closer and promote efficiency. Let us see how users in a LAN are organized (refer Figure).

Representation of Users in a LAN

Representation of Users in a LAN

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The Regular User

A Regular User is the person who works on the software, manages files and does not need to know the working of the network.

Each user is assigned a given area on the LAN server. This area, called the user area, could be a directory or a subdirectory, or a group of subdirectories under which the user can manage files. The user can ensure that no other user can access this area without permission. In turn, this user too cannot access other users' areas unless given permission.

Thus, a regular user of a LAN has a personalized set of rights and restrictions.

However, there are hierarchies within users themselves. In an organization, for example, a manager would be given more rights than a junior executive.

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User Group

A user group is created when a number of users have to be assigned the same set of rights and restrictions. A new LAN user can be put into one of these groups, which would automatically define the user's rights. A user can belong to more than one group. This entitles the user to the rights of the groups to which the user belongs. By default, every user, when created in NetWare, becomes a member of at least one group called EVERYONE.

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The Operator

An operator is a regular user who may be taking care of some additional operational issues of the LAN, and therefore has special privileges. For example, a user might be given special charge of making sure that the printer operates smoothly on the LAN. Therefore, special rights would be given to help the operator carry out this responsibility.

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The Supervisor

A supervisor is an administrator of the LAN. The supervisor has all the powers and rights on the LAN, and manages the day-to-day working of the LAN. The responsibilities of a supervisor are listed hereunder.

  • When new employees join the organization, the supervisors initiate them as LAN users. They assign the login ids and passwords for the new users and decide what the new users' rights are going to be.
  • For existing users, they can add or delete rights.
  • They decide the amount of disk space on the server that each user can have.
  • When user requests for additional rights to use a resource like a modem, the supervisor does the needful.

The supervisor has the right to access the user-area of any user.

Many LAN vendors define their own levels and groups for the LANs that they sell. That is to say, Novell might define levels for NetWare that are different from the ones that other vendors would define for their brands of LAN. What have been described are levels that are likely to be found across all LANs.

Novell NetWare defines one more level apart from the ones that we have described. They are called managers. They function as supervisors over a small group but do not have supervisory equivalence. Managers are of two types:

Work Group Managers

Work group manager is at a level below the supervisor. They can also be called assistant supervisors. Like all other LAN users, the supervisor creates them. They can create users and assign them to a particular group. They can restrict users' access to workstations and restrict concurrent logins. They can also change a user's password.

User Account Managers

A user account manager has the power to help the supervisor to manage a small group of LAN users and directories. User account managers have all the powers of a work group manager in their group, except that they cannot create users.

Initiation to Novell NetWare

To switch your PC from DOS to the Novell NetWare operating system, the following steps need to be followed:

  • Establish the rules for communication between the workstation and the server.
  • Establish the connection between the workstation and the server.
  • Change from the DOS drive to the Network drive.
  • Specify the login identity.
  • Specify the password.

IPX Command

The first command that you would need to use at the DOS prompt is the IPX command. Figure shows a sample output when the IPX command is executed.


IPX stands for Internetwork Packet eXchange. It establishes a communication protocol between the server and your workstation. What is a communication protocol? Assume that Kevin and Steve need to talk to each other. The intention of this conversation is an exchange of ideas. It turns out that, both, Kevin and Steve are egoists. They start talking simultaneously, then pause for breath simultaneously, and then start talking again. The resultant confusion can well be imagined. Therefore, when Kevin and Steve talk, they need to follow a set of rules. Thus, say first Kevin talks, then he gives Steve a chance to put forward his ideas, and so on.

In NetWare, the workstation and the server communicate with each other, and IPX ensures that this communication is orderly and smooth.

NetWare v3.11 - Workstation Shell

(C) Copyright 1991 Novell, INC. All

Rights Reserved

Running on DOS v 5.00

Attached to server NIIT

04-30-95         4:37:14 pm

Output of the IPX Command

NETx Command

To establish a connection between the workstation and the server, the command NETx is used:


The 'x' here should be replaced by the version of DOS that is being used, in case the DOS version on the workstation is 3.x or 4.x. Therefore, if DOS version 3.x is being used, then the command would be:


However, if DOS version 5.0 or above is being used, the command NETx should be given.

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Changing Drives

The third step is to change from the C drive (on DOS) to the NetWare drive F. To do so, type F: at the DOS prompt:


This will take you to the NetWare drive. The prompt will change from,




Note: Workstations that do not have hard disks do not boot through DOS. They boot directly through NetWare. When the user switches the workstations on, NetWare F prompt is displayed. The IPX command, the NETx command and the change from the DOS drive to the NetWare drive are not needed.

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Logging In

In NetWare, every user has a login id (identity). The login id is also known as the login name or the user id. The login id is the name by which NetWare recognizes and identifies a user. For example, the user may be given a login id User14.

To log in, you need to give the command LOGIN at the NetWare prompt.


The prompt

        Enter your login name:

is displayed on the screen.

You enter your login id against the prompt and press . Normally, your login would have a password attached to it, and you will be prompted to enter your password.

        Enter your password:

The password that you enter is not echoed on the screen for security reasons.

A password is of paramount importance in any LAN. Once you connect to a LAN by giving your user id and password, you would enter what is called your user-area where you can manage your files. No other user normally has access to this area. Also, you do ordinarily have access to the user-areas of other users. The login id identifies you as a LAN user; the password provides security to your login.

After logging in, the user can use DOS commands. Using the CD command, the user can browse through the directories. WHOAMI given at the NetWare prompt enables the user to find out his login id.

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Changing the Password

Changing the password frequently is one way of ensuring that no one gets to know your current password. The SETPASS command can be used to change the password. For this, you need to login to NetWare by giving your current password. After doing so, you give the command SETPASS. NetWare displays the following message:

        Enter old password for <server name/login id.>:

At this prompt, you need to type the current password and press . NetWare displays another prompt:

        Enter new password for <server name/login id>:

On typing the new password and pressing , NetWare displays a third prompt:

        Retype new password for <server name/login id>:

This is done to make sure that the spellings are correct. When the choice is confirmed by retyping the password, NetWare displays a message informing you that the task has been completed successfully.

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Logging Out

When you have finished your session on NetWare, you log out. Once you log out, NetWare no longer recognizes you as a user, and you are not able to use NetWare commands any longer. To use these commands, you must login again. To log out, you give the command LOGOUT at the command prompt.

NetWare displays a message giving your login id, the time and date when you last logged in, and the time and date of the logout.

It is essential to logout once you have finished working on NetWare or, for that matter, on any network. If you do not log out, your user area is still accessible and someone might tamper with or delete your files.

The Network Operating System

Now that you have looked at the typical hardware components of a LAN, let us look at another very essential element of the LAN, namely its operating system (OS). The operating system in a computer, as you know, performs the task of storage management of data and programs and the functions of input-output device management.

A LAN or any other type of network also needs an operating system. There is one vital difference between a network operating system and a single-user operating system like DOS. DOS concerns itself with the operations of a single PC. A network operating system has to concern itself with the management of the network as a whole. It has to ensure that the network of computers operates smoothly.

Some of the tasks that a network operating system performs are listed hereunder:

  • The network OS provides network services to users. The network services are:
    • Access to disk storage space: Network users can save files in a common location, i.e. the server hard disk. It is necessary to ensure that every user gets a share of disk space on the server disk.
    • Access to shared files: In a network, certain files on the server can be accessed by several workstations at the same time. The network operating system ensures that this takes place smoothly.
  • The network OS takes care of security, ensuring that files of one user are not accessed by other users.
  • It manages the sharing of peripherals like printers among workstations.

Some of the most popular network operating systems in use are -Novell NetWare from Novell Inc., Windows NT Server from Microsoft.

What are the Functions of a Network Operating System?

The network operating system provides network services to the users, takes care of the security and manages peripherals like printers among workstations.

What is The Difference between a Dedicated Server and a Non-Dedicated Server?

A dedicated server is a server whose only job is to help workstations access data, software and hardware. It does not double up as a workstation. A non-dedicated server acts as a server as well as a workstation.

Elements of a LAN

Working on a Local Area Network adds enormously to the range of things that you can do with your PC. The difference is quite simple. A non-networked, stand-alone PC limits you to its own operating system, the software available on it, and the peripherals (like printers) attached to it. But when your PC is networked, it can access the pooled resources of the network and its capabilities increase manifold.

A network encompasses the whole gamut of hardware and software components that make a computer network operate.

Some typical hardware components of a LAN are:


The term workstation refers to the computers that are attached to a LAN and share the resources of the LAN. On a LAN, there can be PCs that do not have either hard disk or floppy disk drives. Such PCs are called diskless workstations. Such workstations cannot store any data or software. They access them directly from the LAN server.

A computer (regardless of whether it has disk drives or not) is said to become a node of the LAN once you attach it to the LAN.


A server is a computer that provides the data, software and hardware resources (like printers) that are shared on the LAN. A LAN can have more than one server. Each server has a unique name on the network and all LAN users identify the server by its name.

Dedicated Server

A server that functions only as a storage area for data and software and allows access to hardware resources is called a dedicated server. Dedicated servers need to be powerful computers capable of handling the huge workloads demanded of them.

Non-dedicated Server

In many LANs, the server is just another workstation. Thus, there is a user working on the computer and using it as a workstation, but part of the computer also doubles up as a server. Such a server is called a non-dedicated server (since it is not completely dedicated, to serving). Such a server is typically used by small LAN installations that have a few workstations. Such LANs do not require a dedicated server since resource sharing amongst a few workstations is on a proportionately smaller scale.

Other Types of Servers

In large LAN installations, which have hundreds of workstations sharing resources, a single computer is often not sufficient to function as a server. Consequently, the LAN may have several servers that allow workstations to share specific resources. Some of the servers have been discussed hereunder.

  • File Server: A file server stores files that LAN workstations can access. It also decides on the rights and restrictions that the users need to have while accessing files on the LAN. For example, if an employee in the marketing department wants to access classified files of the accounts department, he or she would not be able to do that, unless the appropriate permissions are granted. The file server also allows LAN users to store files on their own hard disks. The file server regulates the amount of space allowed for each user.
  • Printer Server: A printer server takes care of the printing requirements of a number of workstations (remember one of the main advantages of a LAN is that it helps the workstations share hardware resources like printers). In a LAN with a large number of workstations, several users could give requests for printing in intervals of just a few minutes. The printer server typically stores the files to be printed on its disk, and then executes these requests (i.e. prints these files) on a first-in-first-out basis.
  • Modem Server: A modem server allows LAN users to use a modem to transmit long distance messages. Typically, in an organization, only a few users would need to use the modem. A single modem server attached to one or two modems would serve the purpose.

Network Interface Unit (NIU)

The Network Interface Unit (NIU) is a device that is attached to each of the workstations and the server. It helps the workstation to establish a connection with the network. Each NIU that is attached to a workstation has a unique number identifying it called the node address. Thus, the node address of a workstation means the address of the NIU that is attached to the workstation.

Communication Channel

In a LAN, the words communication channel mean connecting cables. The connecting cables are the life- lines of a LAN. Snap a line in any part of the LAN, and at least a part of the LAN will become inoperational. While installing a LAN in any office or factory, attention has to be given to the manner in which these wires are laid out. Care has to be taken that the layout of these wires is such that they are provided with maximum protection, and cause minimum inconvenience to the movement of employees.

The quality and performance of LAN cables has improved over time with the improvement in technology.

Let us take a look at some of the communication channels.

Twisted-pair Cables

The oldest and least expensive type of cables used for LANs are the twisted-pair cables. These cables consist of two insulated copper wires twisted around each other (refer Figure 1.1). These cables are also used for short and medium range telephone communication.

Twisted-pair Cables

Twisted-pair Cables

Co-axial Cables

A co-axial cable consists of one or more small cables in a protective covering (refer Figure 1.2). These are more expensive than twisted-pair cables but perform better.

Co-axial Cables

Co-axial Cables

Fiber-optic Cables

Fiber-optic cables are made of plastic or glass and are as thin as a human hair. These cables are highly durable and offer excellent performance. Their speed of transmission is very high. However, they are expensive and are still not widely used in LAN installations.

Benefits of a Local Area Network (LAN)

LANs do not just form a network of computers. They also form a network of people. An office, comprising diverse departments and employees working on various jobs can be made to function as one once a LAN is installed. Here are some of the ways in which a LAN can benefit an employee in an organization.

Resource Sharing

Using a LAN, expensive resources like laser printers, modems, graphic devices and data storage units can be shared. This enables several users to access these resources at the same time. Software and programs can be stored at a common location where every user who has the need can access them. Resource sharing allows organizations to purchase more sophisticated and faster equipment than would otherwise be practical for them.


Another use of a LAN is that it can help you make the computer do the job of an office intercom. You can use the computer to flash messages on the screen of other computers in the office. This would save employees the time they would spend in going to someone in another department, on some other floor to deliver a message or a memo. This also reduces the need for face-to-face meetings and the need to circulate memos among employees.


The PC is capable of storing a fair amount of information, but it is not a very secure place to store data. Using a LAN, users can store their files on a computer that is a part of the LAN. A LAN has built-in security features such that it would be virtually impossible for anyone to get hold of these files.

Expanded PC Usage

A LAN is very accommodating. It takes into consideration the fact that employees can get transferred between departments, or machines can be moved to different locations. New machines can be added, or existing ones removed. A LAN ensures that, despite these changes, a user goes through minimum inconvenience and continues to benefit from the LAN.

A Local Area Network is certainly not the only solution for an office to share computing power, but it is surely a means of combining the power of computers in an office location while maintaining the independence of the computers. It helps to make an office a more compact setup and helps increase the efficiency of its functioning.

Local Area Network (LAN)

A Local Area Network, or LAN as it is more widely called, is a group of computers in a localized area. The term localized area could mean a small room, twenty feet by ten feet, or it could mean a factory spanning several acres. Another definition, widely accepted, states that a LAN is a computer network that is confined to a building or a cluster of buildings. A LAN is a network that is typically personal to an organization and is installed for the exclusive use of a particular office or factory of a given organization. It is not often that you will come across two or more organizations in an office complex sharing a LAN.

Sending Data Across a WAN

If the technologies discussed above for data transmission are inadequate, the network administrator can consider using any of the advanced WAN technologies. Some of these technologies are:

X.25 Packet Switching

X.25 is a set of protocols included in a packet-switching network. An X.25 network uses switches, circuits and the available routes for routing at anytime.

Asynchronous Transfer Mode (ATM)

ATM is also an advanced form of packet-switching. It is a broadband method that transmits data in 53-byte cells. Each cell consists of 48 bytes of data and five bytes of header information. Therefore, the packets that are generated are consistent and uniform. ATM can be used with any media.

ATM switches are multiport devices that can act as either hubs or routers. In architectures, such as Ethernet and Token Ring where only one computer at a time may transmit, ATM uses switches as multiplexers to permit several computers to put data on a network.

Note: In asynchronous transmission, data is transmitted as a stream. Each character is converted into a string of bits. Each string is separated from the other strings by a start bit and a stop bit. In this method, there is no device or method to coordinate transmission between the sender and the receiver.

Integrated Services Digital Network (ISDN)

Basic Rate ISDN uses digital transmission that divides its bandwidth into three channels. Two of these transmit data at 64 Kbps, and the third at 16 Kbps. The 64 Kbps channels can carry voice, data or images. The slower 16 Kbps channel carries signaling data.

A computer connected to an ISDN service can use both the 64 Kbps channels to have a 128 Kbps data stream.

Fiber Distributed Data Interface (FDDI)

FDDI is a high-speed token-passing ring network that uses fiber-optic media and was developed for high-end computers.

FDDI uses a dual-ring topology. In this, there are two data streams flowing in opposite directions around two counter-rotating rings. One ring is called the primary ring and the other is called the secondary ring. The secondary ring acts as a backup. Computers may connect to one or both FDDI cables in a ring.

Wide Area Network Transmission

With components such as bridges, routers and communications service providers, local area networks can be connected to create WANs. Communications services make use of the following three types of transmission technologies:

Analog Connectivity

Analog transmission refers to telephone lines used with modems. These can be:

  • Dial-Up Lines - used for infrequent data transmissions.
  • Dedicated Lines - used for frequent and continuous data transmissions. This method provides a ready communication link.

Digital Connectivity

Digital lines provide faster and a more secure transmission as compared to the telephone lines. Digital transmission does not require the use of modems. Following are the different forms of digital lines:

  • DDS (Digital Data Service)
  • T1
  • T3
  • T4
  • Switched 56

DDS sends data through a device called a Channel Service Unit/Data Service Unit (CSU/DSU). This device converts digital signals into a form that is part of the synchronous communications.

Note: With synchronous communication, bits are sent in a timed, controlled fashion. Transmission stops at the end of one frame and starts again with a new one.

T1 and T3 use point-to-point transmission that can transmit voice, data and video signals. T1 offers high data speeds and is the most widely used type of digital line. T3 is the highest capacity leased line service available.

Switched 56 is a digital dial-up service that requires a CSU/DSU to be installed with each computer on the network.

Packet-switching Networks

Packet-switching is a fast and efficient way to transmit data over wide areas. With packet-switching, data is divided into packets of small size and a destination address is attached to each packet. This way each packet can be sent separately over the network. Packets are transmitted along the best route available between the source and the destination.

LAN Expansion

Networks cannot be made larger by simply adding new computers and more cable because each topology has its limits. However, there are certain components which can increase the size of the network within the existing environment. These components are:


A Repeater is a device that regenerates signals so that the signal can travel on additional cable segments. They do not translate or filter data. For a repeater to work, both segments that the repeater joins must have the same media access scheme, protocol and transmission technique.

Repeaters can move packets from one medium to another. Some multiport repeaters can connect different types of media. Repeaters improve performance by dividing the network into segments, thus reducing the number of computers per segment.


A Router is a device used to connect networks that use different architectures and protocols. They can switch and transfer information packets across multiple networks. This process is called routing. They can determine the best path for sending data and filtering broadcast traffic to the local segment. Routers cannot link to remote computers. They only read addressed network packets. Routers can link segments that use different data packaging and media access schemes.


A Bridge is a device that can join two LANs. However, a bridge can also divide an overloaded network into separate networks, reducing the traffic on each segment and making each network more efficient. A bridge can link unlike physical media such as twisted-pair and coaxial Ethernet. It can also link unlike network segments such as Ethernet and Token Ring.

They are also referred to as Media Access Control layer bridges. A Media Access Control layer bridge:

  • Checks the source and destination address of each packet.
  • Creates a routing table.
  • Forwards packets.
Note: A routing table stores the addresses and all the other information necessary to route information from one network to another.

If the destination address is not listed in the routing table, the bridge forwards the packets to all segments.

Multiple bridges can be used to combine several small networks into one large network. A bridge can be installed internally or externally. Bridges are faster than routers because routers perform complex functions on each packet.

The following are the differences between bridges and routers:

  • The bridge only recognizes the addresses of network cards in its own segment. Routers recognize network addresses.
  • A bridge can only recognize one path between networks. A router can search among multiple active paths and determine the best path.
  • The router only works with routable protocols.


A Brouter combines the best features of both a bridge and a router. Brouters can:

  • Route routable protocols.
  • Bridge non-routable protocols.


Gateways make communication possible between systems that use different communication protocols, data formatting structures, languages and architectures. Gateways repackage data going from one system to another. Gateways are usually dedicated servers on a network and are task-specific.

Network Operating System

A network operating system does everything a stand alone operating system does, and more in a much more complex environment. In addition to the usual lower level computing tasks, a network operating system is responsible for all the following tasks:

  • Directing data traffic through the network
  • Allowing and preventing access to data based on security requirements
  • Preventing access to data files while they are being processed
  • Managing the flow of information between a variety of workstations
  • Managing requests for printer services
  • Managing communication and messages between network users
  • Managing connections between the network and remote sites
  • Make services as transparent as possible to the user

Components of the Network Operating System

There are two main components of the network operating system. They are:

Client Software

In a network environment, when a user initiates a request to use a resource that exists on a server in another part of the network, the request has to be forwarded or redirected to the server with the requested resource. The component of the client software that does this task is the redirector.


The redirector may also be referred to as a shell or a requester. It is a small part of the network operating system that:

  • Intercepts requests in the computer.
  • Determines if the requests can be serviced by the local system itself or it needs to be forwarded to the server.


A designator is an alphabet that is assigned to each network resource. The redirector keeps track of which drive designators are associated with which network resources.

For example, to access a particular shared directory on a remote computer, we can assign a letter of the alphabet, say H, to it. We can then refer to the shared directory on the remote computer as H and the redirector will locate it.

Server Software

Server software makes it possible for users working on other machines to share the server's data and peripherals including shared directories, printers, plotters and disks.

Resource Sharing

The server software not only allows sharing of resources, but also determines the degree of sharing. The degree of sharing includes:

  • Allowing different users different levels of access to the resources. For example, a file server could give read or write or read and write permissions to different users.
  • Coordinating access to the resources to make sure that two users do not use the same resource at the same time.

Managing Users

Network operating systems make it possible for a network administrator to determine who will be able to use the network. The server software can be used to:

  • Create user privileges, which indicates who gets to use the various resources on the network.
  • Validate user names and passwords at the time of logging on.
  • Grant or revoke user privileges on the network.
  • Remove users from the list of users having access to the server.

Network Services

Network services are network operating application programs that run on the network. The network operating system installation program ensures that the user has a minimum of network services installed by default.

Some examples of services installed by the NT operating system, by default are:

  • Alerter service - notifies selected users and computers, of administrative alerts that occur on the computer. As an example, an alerter service could be set to issue alerts whenever the used space of a hard disk exceeds a particular percentage of the total hard disk space.
  • Event log service - records system, security and program events in the event log.
  • Messenger service - sends and receives messages sent by administrators or by the alerter service.
  • Other services such as the telephony service, which is used by programs to make data, fax, voice calls. These services have to be manually started by the user.

Shared Network Applications

Applications such as word processors and databases can be shared on the network like any other resource.

The advantages of shared network applications are:

  • It makes application programs less expensive because buying a site license for 200 users on an application is usually cheaper than buying 200 individual copies of the application.
  • It ensures that everyone will be using the same version of the product.
  • The information in the database that is stored on the server, can be accessed by the clients on remote machines. This model of the client/server network is the most efficient way for:
    • Database access and management.
    • Network management.
    • Centralized file storage.

How To Create Local Area Networks (LAN)

Access Methods

The set of rules defining how a computer puts data onto the network cable and retrieves data from the cable is called an access method. Access methods prevent simultaneous access to the cable. By ensuring that only one computer can put the data on the network cable, access methods keep the transmission of network data an orderly process.

  1. Carrier-Sense Multiple Access
  2. Token Passing
  3. Demand Priority

Carrier-Sense Multiple Access with Collision Detection

In the Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) method, each computer on the network senses any signal passing on the cable. The computer can only transmit if the cable is free. If two or more computers send data at exactly the same time, it will result in data collision. When a collision occurs, the two computers involved stop transmitting and then attempt to re-transmit after a certain period of time. The collision detection method is only effective up to 2,500 meters.

With more traffic, collisions tend to increase, which slows down the network. So, CSMA/CD can be a slow access method.

Carrier-Sense Multiple Access with Collision Avoidance

In the Carrier-Sense Multiple Accesses with Collision Avoidance (CSMA/CA) method, each computer signals its intent to transmit before it actually transmits data. This way, the computer can avoid collisions. CSMA/CA is a slower access method and is less popular than CSMA/CD.

Token Passing

In Token Passing, a special packet called a token circulates around the ring network in one direction. When any computer on the network wants to send data, it takes control of a free token. The computer can then transmit data. Until the token has been released by the computer sending data, no other computer can transmit. As only one computer can use the token at a time, the possibility of a collision is ruled out.

Demand Priority

Demand priority is an access method designed for the 100 Mbps Ethernet standard called 100 VG-AnyLAN. The 100VG-Anyl_AN network comprises repeaters and end nodes. An end node could be a computer, bridge, router or switch. The function of the repeater is to search for requests from all nodes on the network. In a demand priority network, computers can receive and transmit at the same time. This is because four pairs of wires are used in the cabling scheme defined for this method. In demand priority, communication is only between the sending computer, the hub or the repeater, and the destination computer. This method is more efficient than CSMA/CD, which sends transmission to the entire network.

Define Access Method

Access method is a set of rules defining how computer puts data onto the network cable and retrieves data from the cable.

List The Three Access Methods

  1. Carrier-Sense Multiple Access With
    • Collision Detection
    • Collision Avoidance
  2. Token Passing
  3. Demand Priority