Section 4 – Computer Networks

1. Section 4 – Computer Networks Network Hardware

2. Lesson Objectives • By the end of this lesson you will be able to: • Describe a routerand its purpose • Describe other common network devices

3. Hub • A hub is a hardware device that connects multiplecomputers together in a network and allows them to share data packets. • You can also 'daisy chain' hubs to allow even more computers to join the network. However there is a problem with doing this - see 'Switches' for more details.

4. Hub

5. Switch • A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). • Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. • Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately.

6. Switch

7. Router • A Router is a device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route. • In order to do this, the router has a micro computer inside it. This holds a table in memory that contains a list of all the networks it is connected to, along with the latest information on how busy each path in the network is, at that moment. This is called the 'routing table‘ • When a data packet arrives, the router does the following • Reads the data packet's destination address • Looks up all the paths it has available to get to that address • Checks on how busy each path is at the moment • Sendsthe packet along the least congested (fastest) path

8. Router

9. Repeaters • All signals fadeas they travel from one place to another. • Each type of network cable has a maximum useable length. If you go beyond that length, the signal will be too weak to be useful. • Of course, computers on a real network can easily be more than 200 metres apart. Therefore the network cable is split up into segments. Each segment is less than the maximum length allowed. Joining the segments together is a device known as a 'Repeater'. • A Repeater boosts the signal back to its correct level. Here are some typical maximum cable lengths: • Copper cable - 100m • Thick Ethernet - 500m • Thin Ethernet - 185m

10. Repeater

11. Bridge • A Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network • A bridge is not as capable as a Router and it is less expensive. • Both networks have to be using the same protocol (rules)

12. Bridge

13. Network Card • Network cards are needed if the computer does not have a built-in network chips on the motherboard. They allow the signal from the network to be transmitted to the machine this could be via a fixed cable.

14. Network Card

15. Server • A computer or device on a network that manages network resources. There are many different types of servers. For example: • File server: a computer and storage device dedicated to storing files. Any user on the network can store files on the server. • Print server: a computer that manages one or more printers, and a network server is a computer that manages network traffic. • Database server: a computer system that processes database queries. • Servers are often dedicated, meaning that they perform no other tasks besides their server tasks

16. Server

17. Proxy Server • A proxy server is a server that takes client computer requests and forwards them to other servers. The proxy server sits between the server of the network you are using and the server of the system outside of your network that you need to access. A proxy server can be a major component of a firewall. • Here are some uses: • Schools use proxy servers to block offensive content • They can be used to protect anonymity on the internet. Every server connected to the internet will have an IP address. Using the proxy server means that the main server for the network being protected is anonymous to all the other servers on the internet.

18. Task • Create a PowerPoint summarising all the points made above. • You must include a picture for each slide and make a minimum of 4 points per slide. Use the iGCSE website. • Hub • Switch • Router • Repeater • Bridge • Network Card • Server • Proxy Server

19. Exam Questions • What three items of hardware are used to network computers together. Hub Printer Scanner Switch Bridge Monitor

20. Exam Questions • Complete each sentence below using one item from the list A Hub, A WAN, An Intranet, A WLAN, A Proxy Server • ……is a device used to connect computers together to form a LAN • …….is a network with restricted access • …… can allow networked computers to connect to the internet • …… is a wireless local area netwok

21. Exam Questions • Complete each sentence below using one item from the list below A Bridge, A Hub, A Proxy Server, A Switch • …… does not manage any of the data traffic through it • …… forwards data packets to computers and printers • …… can be a major component of a firewall • …… usually only has two ports

22. Exam Questions • A manage wants to buy a router to connect the LAN’s. Describe the function of a router.