1. Sender frame Receiver datagram frame Adapter Link layer protocol

2. Recap Figure from: Douglas Comer: “Computer Networks and Internets”

3. Recap Figure from: Douglas Comer: “Computer Networks and Internets”

4. Recap Figure from: Douglas Comer: “Computer Networks and Internets”

5. (for any reason including distance, no. of users, cost)

9. Network hub’s image source: Wikimedia Commons

10. Bridge

11. Cisco Systems Catalyst Switch; Image Credit: Cisco Systems

12. Application Transport Network Data Link Destination Host (Same LAN) Bits Bridges/ Switches Repeater/ Hub Source Host Application Transport Network Data Link Bits

13. Bridge

14. From: Peterson/ Davie: “Computer Networks – A Systems Approach”

15. Exercise

19. Figure from: Peterson/ Davie: “Computer Networks – A Systems Approach”

20. From: Peterson/ Davie: “Computer Networks – A Systems Approach”

22. An example network. The numbered boxes represent bridges (number being the bridge ID). The lettered clouds represent network segments. 1

23. The smallest bridge ID is 3. Therefore, bridge 3 is the root bridge. 2

24. Assuming that the cost of traversing any network segment is 1, the least cost path from bridge 4 to the root bridge goes through network segment c. Therefore, the root port for bridge 4 is the one on network segment c. 3

25. The least cost path to the root from network segment e goes through bridge 92. Therefore the designated port for network segment e is the port that connects bridge 92 to network segment e. 4

26. This diagram illustrates all port states as computed by the spanning tree algorithm. Any active port that is not a root port or a designated port is a blocked port. 5

27. 6. After link failure the spanning tree algorithm computes and spans new least-cost tree. 6

30. Section 2.6: Direct Link Networks [P&D] Chapter 3: Packet Switching [P&D]