PC Construction and Maintenance Week 7

1. PC Construction and MaintenanceWeek 7 Networks

2. Introduction to networks • In computing, the term Network generally means connecting two or more machines together • Networking covers a wide area of computing. • Networking is becoming increasingly important, even in the home environment • The cost of networking hardware has dropped considerably

3. Why have networks? • The main reason is to share resources between computers • Many computers can share a printer • Internet access can be shared amongst a number of machines • Access to information and resources shared across a network is often useful in practice

4. Type of networks • We are concerned with building a small LAN (Local Area Network) in order to enable file and printer sharing • Also, a connection to the internet is desirable, for the download of drivers, patches, BIOS upgrades etc • The word internet literally means between networks • The internet is really just a large collection of networks, themselves networked together

5. The theory behind networks • Network theory could itself encompass a whole course • We are going to explore the tip of the ice-berg of network theory • We only need to know the key points in order to have enough knowledge to understand how a small home or business network functions • There are a just few fundamental facts of computer networking that interest us

6. Network Theory – Key Points • All networks are based on a layered model. The ISO 7-layered model is the theoretical ideal model of a computer model • Real networks are based on a simplified models of the theoretical ideal. But always retain the “layered” quality. • We are interested primarily in TCP/IP networks. TCP/IP is the protocol that runs the Internet • We need at the very least to know the essential properties of the layered model in order to configure and troubleshoot basic networks

7. ISO 7-layer reference model • 7. Application • 6. Presentation • 5. Session • 4. Transport • 3. Network • 2. Data Link (Hardware Interface) • 1. Physical Hardware Connection

8. ISO layers explained • Physical Layer:  Transmitting data bits. Voltages, timing factors, cable standards, etc.Data Link Layer:  Managing basic transmission circuit.  Error detection and correction; message delimitation.Network Layer:  Addressing and routing of packets.Transport Layer:  Establish, maintain, and terminate logical connections. Generating addresses; breaking packets: eliminating duplicate packets; flow control.Session Layer:  Initiating, maintaining, terminate logical session. Presentation Layer:  Display, formatting, encryptionApplication Layer:  Applications.

9. The TCP/IP model

10. The Physical Layer • For ordinary networks, there are two common ways of hooking up several computers • One way is to use BNC cabling, provided the network cards have a BNC connector on them. • The most common way at the present time is to use UTP (Unshielded Twisted Pair) cable, in combination with a Hub

11. BNC based network • All machines are daisy chained together via BNC cabling and T-pieces • There is no need for a hub • If a single wire is disconnected, then the whole network fails • A terminator is plugged in to both ends of the network • This sort of arrangement is known as “BUS topology” • A 10-Mbit BNC network is known as 10-BASE2

13. BUS topology (BNC networks)

14. UTP based network • Several machines are connected together via a hub • Several hubs can be chained together to form a larger networks • For the simple case of a two-computer network, you don’t need a hub, you can just use a ‘crossover cable’ • UTP based networks are fast and reliable • If one wire is disconnected, then only one computer is affected. The remaining network still functions correctly • UTP networks are known as 10BASE-T, or 100BASE-T, depending on the speed

16. Star Topology (UTP based networks)

17. UTP Cable Wiring

18. UTP Cable Wiring

19. UTP Cable Wiring Reference • 1 White/Orange • 2 Orange • 3 White/Green • 4 Blue • 5 White/Blue • 6 Green • 7 White/Brown • 8 Brown

20. UTP cables • A standard UTP network cable is known as a straight cable, or a patch cable • If the pairs #2 and #3 are swapped with each other, then we have a crossover cable • Straight cables are the most common, and are used to connect a PC to a hub • Crossover cables are used to connect a PC to a PC (2 PC network) or , a hub to another hub

21. Receive/Transmit swapping • In the 10-base T case. One twisted pair is for receiving a signal (Rx), and the other for transmitting (Tx) • The hub swaps these over internally so that (Tx) of machine A connects to (Rx) of machine B • Straight cables do not swap Tx and Rx, crossover cables do. • If the number of “swaps” between the source and destination machines is odd, then they are wired correctly, else they will not talk to each other

22. The datalink layer • The datalink layer deals with transfer of binary data from one network interface card to another • The dominant datalink protocol used at the current time in a LAN environment is Ethernet • Some other datalink protocols are still found on LANs (e.g. token ring), but these seem to be dying out • Because of widespread use of Ethernet equipment, it is now very cheap

23. Ethernet Networks • In the Ethernet environment, every network card on the planet has a unique MAC address • The Media Access Code is used to address different devices on the network • On a simple network, any device on the network can address any other device within a given subnet using its MAC address • Devices cannot address other devices on other subnets by using a MAC address • This is because the datalink protocol is non-routable

24. The network layer • IP is the network protocol that drives the Internet (simply IP=InteRnet Protocol) • It became widely used on UNIX systems to start off with, but has now spread to virtually every other operating system • IP is needed to ‘surf the web’ • Unlike the datalink layer, IP is a routable protocol and therefore can be used to build large networks (e.g. the Internet)

25. IP architecture • In the IP scheme of things, the network as a whole is treated as an interconnected set of subnets • Each subnet allows communication within itself using the aforementioned datalink protocol • Subnet A is connected to Subnet B via a device known as a router • Each machine on the network (even on the public internet) must have a unique IP address

26. IP addresses • IP addresses have a four byte form and are normally written using a dotted notation • For example 150.204.51.254 • One some networks, static I.P addresses are used, which means that each machine handles it’s own IP configuration locally • Some networks employ protocols to allow an IP address to be assigned dynamically at boot time

27. Configuring IP under windows 95 • As a test case, we will go through the steps of configuring IP networking under windows 95 • Firstly, we need to have a network adapter available • We need to check using device manager that a network card is installed

29. Installing the network card driver • If windows has automatically recognised the card, then we will see it in device manager • If not, we may need to use the “add hardware wizard” • Sometimes, windows can see the card, but doesn’t know what type it is. In this case, it will show up as “Unknown device”, next to a question mark symbol • If this happens, remove the unknown device from device manager and reboot the PC • Windows should then properly detect the card on the next boot

30. Installing the network components • Once we have the card install correctly, we need to add the TCP/IP component • Right-click on Network-Neighbourhood (Or select network) in Control Panel, and then click on “Add” to add a protocol (You will need the windows CD in the drive) • The protocol is Microsoft -> TCP/IP

32. TCP/IP Parameters • After adding the TCP/IP protocol, we need to configure the relevant settings to run the machines on our network • The main setting is IP address (I have reserved a separate address for each group, written on a list) • The other settings are Subnet Mask,Gateway, DNS servers and WINS servers

33. Subnet mask • For our network, the subnet mask is always 255.255.252.0 • The subnet mask defines how we choose to split our physical subnet into logical subnets • The non-zero (left hand portion) defines the network part of the address • The zero portion (right hand portion) defines the host part of the address

34. Gateway • For our network, the address of the gateway (a.k.a the router) is 150.204.51.254 • The router is just a box that bridges the gap between our network and the outside world • The network could work as a self contained entity without a router (e.g. as in a home network) • The router is needed to access the internet

35. DNS servers • DNS servers are just other computers on our network that translate things like web-site names into IP addresses • Without them, we could theoretically still browse the internet, but we would have to refer to websites by number, rather than by name • The address of the three DNS servers on our network are 150.204.51.1 150.204.51.5 150.204.51.17

36. WINS Servers • WINS servers are used to translate between Microsoft networking names and IP addresses • We need to configure WINS servers to allow are machines to use Microsoft network resources such as shared printers and files • Our WINS servers are 150.204.13.108 and 150.204.40.1

37. Completing the configuration • Any other protocols on the system, such as NetBUI and IPX should be removed on PCs on our network • After rebooting, the machine should be enabled for TCP/IP • This can be tested by launching Internet explorer • If that fails, then try “ping 150.204.51.254” to bounce a packet of data off the router from the DOS prompt.

38. Notes on home networking • In the home environment, there are typically no WINS or DNS servers available • In that case, it is still possible to run TCP/IP over the network • Its just that local file configurations are used instead of network servers • Local file configuration becomes impractical when working with a large number of machines though • Microsoft’s custom protocols may sometimes be more suited to a small home network (but not for internet sharing)