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:

• Workstations
• Server
• Network Interface Unit (NIU)
• Communication Channel

Workstations

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.

Server

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

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

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.