Topic 19: Networks

Topic 19: Networks

1. What is a network?

   • A network is when two or more computers are connected together to exchange data, share resources and communicate.

2. LAN & WAN

   • LAN stands for Local Area Network which is a network of computers within the sam building or on the same site.
     • Generally found in homes, offices and schools and they are connected using cabling or wirelessly.
   • WAN stands for Wide Area Network which is a network of computers connected over a wide geographic area.
     • The internet is an example of a WAN.

3. Network Topology

   • Bus Network: Each computer is linked to the 'back bone' and data travels in both directions.
     • Bus networks are the cheapest to set up and if one computer on the network fails the others computers can still work. However, the speed of the data communication is slow.
   • Star Network: Connected to a central computer (hub) which directs the flow of data within the network.
     • If one computer fails then the others can carry on working and it is faster and more reliable than a bus network because each computer has a direct link to the hub. However, if the hub fails all the computers will fail and it is more expensive than a bus network because more cabling is needed.
   • Ring Network: All computers in the network are connected to each other in a continuous loop. The computers communicate by sending data around the loop until it reaches the receiving computer.
     • If one computer or cable breaks then all the other computers will be affected

4. Internet, Intranet and Extranet

   • The internet is a network of computers across the world that uses telephone links and satellite to communicate. It allows resources and data to be shared.
   • The intranet is a network providing similar services to the internet however, it is generally limited to one organisation and there are restrictions are to who can use it etc.
   • The extranet is a part on an intranet that is able to be accessed by authorised members of the public using the internet

5. Network Components

   • A router is a device that forwards packets along a gateway and communicate with other routers by determining the best pathway to take.
   • A switch is a device that filters packets and forwards the packets between segments of the network.
   • A gateway is a system that allows a LAN to connect to a WAN.
   • A bridge connects a LAN to another LAN.

6. Packet Switching

   • Packet switching is the process of each network checking each packet to look at its address and direct it along the correct route.
   • Advantages of packets: ~if one packet fails to reach the destination only one packet has to be resent, ~ packets from different transmissions can take different routes but still get to the same destination.
   • Packets consist of control data, address of where the packet is going to and the data its delivering.

7. Stock control & Order Processing

   • Controlling the amount of stock in a shop is important because: ~ too much stock of one item means it may not be possible to sell all stock, ~some stock is perishable and may go bad before its sold, ~it can reduce wastage, ~running too low on stock can disappoint or anger customers.
   • Automatic stock control systems are designed to make sure no item of stock runs out, makes sure no stock is ever over-ordered, to keep track of stock levels and order more good from the suppliers if the stock level falls below the reorder level.
   • Reports can be produced giving information such as total sale figures, life of best/worst selling items or items that need reordering.

8. Point of Sale Systems (POS)

   • Data can be input to a POS system using a barcode scanner, a keypad, electronic scales or a magnetic strip.
     • Data can be output to a display screen, a printer or a speaker.
   • Information that is sent from the POS system to the computer can include barcodes of items, number of items scanned, weight of certain items, the cashier who scanned it, time they were scanned at etc.
   • The system processes the information in real time and sends back information such as descriptions of the items, total of all the prices, date and time of purchase etc.
   • 1. The item is scanned using a barcode scanner, 2. Once the barcode is scanned the database can find the product details that the barcode relates to, 3. Data about the items are sent back to POS terminal for the customer to see e.g. price or weight.
     • The barcode contains data about the type of product, size, manufacturer and the country of origin.
     • The barcode also contains a check digit so that the computer can validate that the data has been read correctly.

9. Networks VS. Standalone

   • ~ Standalone is less vulnerable to hacking compared to network computers
   • ~ Network computers can communicate with each other but standalone computers can't, ~ Hardware and software can be shared over a network, ~ Standalone computers aren't as easily controlled as a network manager can put certain restrictions on things that affect all computers within the network, ~ Networks allow easier scheduled backups for files that are stored on several different computers.