1. 6.2. - LANs Cabling Topologies Segments and bridges Switches and routers

2. At the end of this session you will be able to: Describe different types of cabling and other communication methods Describe the term topology Describe the operation of different types of networks such as Bus, Ring, Star, Switched Ethernet and hubs Compare advantages and disadvantages of each Define and explain the terms Segment and Bridge and why they are used in LANs.

3. Give another name for Network Adapter A. Modem B. ASDL C. Network Interface Card D. Network Information Centre

4. Network adapter card Why are NICs used? A. Converts analogue signal into digital B. Allows the PC to send and receive data with other devices on the network. C. To connect to the Internet. D. To remotely access parts of an internal network.

5. Identify the advantage of using a bus network A. It is easy to locate a fault if a cable fails B. Easy to add more stations without disrupting the network C. If the main cable fails only one station is affected D. The performance is not affected under a heavy load

6. Give an advantage of star network A. If one cable fails, only one station is affected B. Is easy and inexpensive to install as it requires the least amount of cabling C. The whole network goes down if a cable fails at any point D. There is no central computer

7. Identify a common feature of Bus topology and Star with hub. A. Easy to expand to a larger network. B. Cheap to install and maintain. C. Every node competes for a fraction of the total bandwidth by broadcasting the packets to all nodes. D. Uses intelligent routing of packets.

8. Describe the function of the hub at the centre of a star network. A. Hub stores information temporarily then send it out to another destination on the network B. Hardware device which will enable any printer to be connected to the network C. It regenerates the incoming signals and sends them out to all nodes connected to hub.

9. Cables Twisted pair Baseband Coaxial cable (digital transmission e.g.Bus Ethernet) Broadband coaxial Cable (analog transmission e.g.cable TV – is more expensive, larger geo area) Fibre Optics

10. Other Wireless Communication methods used in LANs Radio Waves – WLAN Bluetooth (uses time division full duplex) Microwaves –max 30 miles apart because of earth’s curvature. Mobile phones Satellite – travel in Geosynchronous orbit about 22,000 miles above earth.

11. Cable versus Wireless LANs Task – 5 minutes: Group 1: Identify advantages/disadvantages of cabling over wireless Group 2 Identify advantages/disadvantages of wireless over cabling

12. Group 1 -disadvantages of cabling over wireless

13. Group 2 -disadvantages of wireless over cabling

14. Advantages/disadvantages of Wireless Wireless + Convenience - location Mobility Productivity due to increased mobility. Deployment – initial set up costs – less complexity because less cabling Expandability – easy to add devices Cost – initial cost but maintenance / expansion cost is low Wireless - Security – more complex to secure than wired LAN, wireless packets can be intercepted, encryption needed Range is limited- repeaters are required – costly Reliability – radio frequency – interference from other devices such as printers Speed –can be slow compared to slowest common wired LANs – low bandwidth

15. Advantages/disadvantages of Cabling Cable + Reliable technology Higher speed than wireless (100 Mbps Fast Ethernet ) Security – more difficult to intercept packets Cable – Static location – cost and expertise to move devices Cables and connection need to be set up -more complex and costly Expandability – more costly as extra cables are required

16. Evolution of LAN Devices NICs, Repeaters, & Hubs Bridges Switches Routers

17. NIC Specifics NICs provide hosts with access to media by using a MAC address. MAC stands for Media Access Control NICs operate at Layer 1 – Network Access layer of TCP/IP model

18. NICs, Repeaters, & Hubs To connect two computers, you must... Install a NIC card in each. The First LAN NIC Attach computers using a crossover cable

19. NICs, Repeaters, & Hubs Repeaters can be used to increase the distance What’s the maximum distance for Cat 5 cable? 100 meters or approx. 300 feet So what can we use if this distance is greater than 100 meters? NIC Repeaters amplify and retime signals

20. NICs, Repeaters, & Hubs NIC Using repeaters was fine as long as a business only needed two computers networked. What if a business wanted a third computer attached? Or a fourth? What device would they need?

21. NICs, Repeaters, & Hubs NIC A multi-port repeater! Also called a... Hub

22. A Dilemma! NIC As businesses expanded their networks, they began to cascade hubs.

23. What’s The Problem? 1) Hubs share bandwidth between all attached devices. 2) Hubs are stupid, Layer 1 devices. They cannot filter traffic. 3) Most LANs use a “broadcast topology,” so every device sees every packet sent down the media.

24. Broadcasts In this picture, all hubs forward all traffic to all devices.

25. So, if Host 1 wants contact Host 2, all hosts see the packets. This is what we mean by a broadcast topology Broadcasts 2 1 The red arrows show that all hosts receive the contact request. Only Host 2 will respond.

26. What’s The Solution? We need a smarter hub! What’s a “smarter hub” called? A Bridge! Bridges filter network traffic based on MAC addresses. Let’s take a look at how this works.

27. Segment Definition: A run of cable to which are attached a number of workstations The portion of a computer network in which computers can access each other using a Network Access layer protocol (e.g., in Ethernet, this would be the ability to send an Ethernet packet to others using their MAC addresses). In this case, it is synonymous with broadcast domain. In Ethernet a segment is also known as the collision domain This area should be kept small or heavy traffic can slow down network considerable

28. Bridge Definition: Connects two segments at MAC (Media Access Control) address level. Amplifies signal that passes through Bridge ‘learns’ address connected to ports. Examines data frame and extracts source and destination (MAC) addresses. If not on same segment as source – bridge will broadcast the frame on the other segment. Bridge Port 1 Port 2 segment

29. Bridge To lessen the amount of LAN traffic, businesses began to uses bridges to filter frames based on MAC addresses.

30. Bridge Now, if Host 1 contacts Host 2, only the hosts on that LAN segment see the packets. The bridges stop the packets. 2 1

31. Switch A switch (also know as a multi-port bridge), can effectively replace these four bridges.

32. Switch Another benefit of a switch is that each LAN segment gets dedicated bandwidth. The Cloud 10 Mbps

33. Ethernet Switch Each node can transmit to switch at same time. No collisions occur as switches can receive and send data at same time to all connections. Two wire pairs providing full duplex operation.

34. Since a switch is a multi-port bridge, we know it will stop local pings from traveling to other network segments. Switch 1 2 1 But a switch cannot stop a ping destined for a different LAN segment from traveling to all other LAN segments as it uses Mac Addresses.

35. Switch 16 1 For example, Host 1 pings Host 16. Since Host 16 is on another LAN segment, the switch will flood the ping request out all ports. What device will solve this problem?

36. Router 1 16 1 Routers filter traffic based on IP addresses. The IP address tells the router which LAN segment the ping belongs to.

37. Devices Function At Layers Know These!

38. Devices Function At Layers Also know that each device not only works at its layer, but all layers below it.

39. Devices Function At Layers For example, a router is a layer 2 device but also uses MAC addresses (layer 1) and repeats the signal (layer 1)

40. Why are LANs based on a bus topology segmented? A. Is cheaper as less wiring is required B. It reduces traffic in the LAN as the bridge will block frames by looking at destination IP address and operates at internet layer or network layer. C. It reduces traffic in the LAN as the bridge will block frames destined for an address on the same segment from being passed to the other segment and operates at Network Access layer or data link layer (physical layer).

41. Give an advantage of a Switched Star network (Ethernet) A. Collisions cannot occur B. Is easy and inexpensive to install as it requires the least amount of cabling C. Supports portable devices D. Difficult to find cable failure between node and switch.

42. What is a MAC address A. A flat 48 bit number on the network card representing the manufacturer and vendor of card. B. A dynamically assigned address representing the PC in a LAN C. A flat 32 bit number that can be used to identify a computer in WAN

43. Which of the following elements does a peer-to-peer network require? A. Workstations B. Fileserver C. Network Interface Cards