UNIT 3 - NETWORKS

UNIT 3 - NETWORKS

1. ADVANTAGES (GENERAL)

   • Sharing devices such as printers saves money.
   • Site (software) licences are likely to be cheaper than buying several standalone licences.
   • Files can easily be shared between users.
   • Network users can communicate by email and instant messenger. Security is good - users cannot see other users' files unlike on stand-alone machines.
   • Data is easy to backup as all the data is stored on the file server.

2. DISADVANTAGES (GENERAL)

   • Purchasing the network cabling and file servers can be expensive.
   • Managing a large network is complicated, requires training and a network manager usually needs to be employed.
   • If the file server breaks down the files on the file server become inaccessible. Email might still work if it is on a separate server. The computers can still be used but are isolated.
   • Viruses can spread to other computers throughout a computer network.
   • There is a danger of hacking, particularly with wide area networks. Security procedures are needed to prevent such abuse, eg a firewall.

3. NETWORK STRUCTURES

   • Bus NETWORK
     • In a bus network all the workstations, servers and printers are joined to one cable (the bus). At each end of the cable a terminator is fitted to stop signals reflecting back down the bus.
       • ADVANTAGES
         • Easy to install.
         • Cheap to install, as it doesn’t require much cable.
       • DISADVANTAGES
         • If the main cable fails or gets damaged the whole network will fail.
         • As more workstations are connected the performance of the network will become slower because of data collisions.
         • Every workstation on the network "sees" all of the data on the network – this is a security risk.
   • RING NETWORK
     • In a ring network each device (workstation, server, printer) is connected to two other devices, this forms a ring for the signals to travel around. Each packet of data on the network travels in one direction and each device receives each packet in turn until the destination device receives it.
       • ADVANTAGES
         • This type of network can transfer data quickly, even if there are a large number of devices connected because the data only flows in one direction, so there won’t be any data collisions.
       • DISADVANTAGES
         • If the main cable fails or any device is faulty then the whole network will fail.

4. WHAT IS A NETWORK?

   • A computer network is a number of computers linked together to allow them to share resources. Networked computers can share hardware, software and data.
     • Most computer networks have at least one server. A server is a powerful computer that provides one or more services to a network and its users. For example, file storage and email.

5. LAN AND WAN

   • There are two main types of network:
     • Local-Area Network (LAN)
       • A LAN covers a small area such as one site or building, eg a school or a college.
         • A school network is usually a LAN.
         • LANs are often connected to WANs, for example a school network could be connected to the Internet.
     • Wide-Area Network (WAN)
       • A WAN covers a large geographical area. Most WANs are made from several LANs connected together.
         • The Internet is a WAN.
         • A network of bank cash dispensers is a WAN.
         • WANs can be connected together using the Internet, leased lines or satellite links.

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