Computer Networks

By Matt Wright


Routers are small physical devices that join multiple networks together. It can-direct network traffic and deal with different pockets in different ways. It can protect the computers on the network by hiding them from the outside world. Some routers have a modem built in and wireless capabilities.


A switch learns which devices are on the network and only sends the data packet to the person who is the intended recipient. This is more efficient than a hub because it doesn't result in a lot of unnecessary


A hub receives all data sent over the network and sends it to all the other devices on the network. Only the device who the data pocket is for will acknowledge it; The other devices will ignore it.

Network toplogys

Ring network

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). The disadvantage of these networks is that if they can get very busy and slow. Also if there is any failure in the cable the whole network breaks down.

Star Network

Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Bus Network

Bus networks use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.


Stands for "Network Interface Card." Pronounced "nick," this is the card that physically makes the connection between the computer and the network cable. These cards typically use an Ethernet connection and are available in 10, 100, and 1000 Base-T configurations. A 100 Base-T card can transfer data at 100 Mbps. The cards come in ISA and PCI versions and are made by companies like 3Com and LinkSys. So if you want to connect your computer to a network, you better get yourself a NIC.


A personal computers or workstations (called clients) that are connected to the network.


A computer or computer program that manages access to a centralized resource or service in a network.

Different types of network


A LAN (Local Area Network) is a localized network, typically within a single building. Each LAN is separate from each other, and cannot reach each other except through a wider connection (like a WAN). LANs typically have a faster transfer rate and don't require any equipment that can't be purchased off a shelf. They typically have one or more routers hooked to several computers, workstations and/or servers. They can be used for anything from internet sharing in a home setting to internal company communications and resource sharing.


• Workstations can share peripheral devices like printers. This is cheaper than buying a printer for every workstations.

• Workstations do not necessarily need their own hard disk or CD-ROM drives which make them cheaper to buy than stand-alone PCs.

• User can save their work centrally on the network’s file server. This means that they can retrieve their work from any workstation on the network.

• They don’t need to go back to the same workstation all the time.

• Users can communicate with each other and transfer data between workstations very easily.

• One copy of each application package such as a word processor, spreadsheet etc. can be loaded onto the file and shared by all users.

• When a new version comes out, it only has to be loaded onto the server instead of onto every workstation.


• Special security measures are needed to stop users from using programs and data that they should not have access to;
• Networks are difficult to set up and need to be maintained by skilled technicians.
• If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.

Examples of use:

  • 2 or more computers connected together
  • A small office


A WAN is more expensive than a LAN. It is easier to expand a LAN than a WAN. The equipment needed for a LAN is a network interface card (NIC), a switch and a hub. On the other hand, the equipment needed to connect a WAN to the Internet is a modem and a router. The modem may be a cable modem or a DSL modem that is connected to a wall jack, while the router should be configured so that it can handle the packets traveling between the WAN and the Internet.


  • Messages can be sent very quickly to anyone else on the network. These messages can have pictures, sounds, or data included with them (called attachments).
  • Expensive things (such as printers or phone lines to the internet) can be shared by all the computers on the network without having to buy a different peripheral for each computer.
  • Everyone on the network can use the same data. This avoids problems where some users may have older information than others.
  • Share information/files over a larger area


  • Setting up a network can be an expensive and complicated experience. The bigger the network the more expensive it is.
  • Security is a real issue when many different people have the ability to use information from other computers. Protection against hackers and viruses adds more complexity and expense.
  • Once set up, maintaining a network is a full-time job which requires network supervisors and technicians to be employed.
  • Information may not meet local needs or interests
  • Volunerable to hackers or other outside threats

Examples of use:

  • Internet


A protocol is a set of rules or procedures for transmitting data between electronic devices, such as computers. In order for computers to exchange information, there must be a pre-existing agreement as to how the information will be structured and how each side will send and receive it. Without a protocol, a transmitting computer, for example, could be sending its data in 8-bit packets while the receiving computer might expect the data in 16-bit packets.

Mac Addresses

The MAC address (Media Access Control) is a hexadecimal number that is

unique to that particular device.

The MAC address is used to transmit between devices on a LAN.

If devices are going to communicate they must have a unique reference number.

It is the same principal as addressing a letter; you need to put a unique address on the front so the postman knows where to deliver it.

Within a LAN each device must have a Network Interface Card (NIC) to connect it to the network. This card will have a MAC address.

The MAC address is hard‐coded into the NIC when it is manufactured, it cannot be configured in software.

Data Packets

A packet is a basic unit of communication over a digital network. A packet is also called a datagram, a segment, a block, a cell or a frame, depending on the protocol. When data has to be transmitted, it is broken down into similar structures of data, which are reassembled to the original data chunk once they reach their destination.