1. The Medium Access Control Sublayer Chapter 4

2. The Channel Allocation Problem Static Channel Allocation Dynamic Channel Allocation  Delay for the divided channel is N times worse than if all the frames were somehow magically arranged orderly in a big central queue

3. Assumptions for Dynamic Channel Allocation 1.Station Model. 2.Single Channel 3.Collision Assumption. 4.Continuous or slotted time 5.Carrier sense or no carrier sense

4. Multiple Access Protocols ALOHA Carrier Sense Multiple Access Protocols Collision-Free Protocols Limited-Contention Protocols Wireless LAN Protocols

5. ALOHA (1) In pure ALOHA, frames are transmitted at completely arbitrary times. Collision Time User A B C D E

6. ALOHA (2) Vulnerable period for the shaded frame.

7. ALOHA (3) Throughput versus offered traffic for ALOHA systems.

8. Carrier Sense Multiple Access Protocols (CSMA)  1-persistent CSMA  Collision  Propagation delay  When the busy channel become idle  Nonpersistent CSMA  Better channel utilization  Longer delays  p-persistent CSMA  For slotted time channels

9. Persistent and Nonpersistent CSMA Comparison of the channel utilization versus load for various random access protocols.

10. CSMA with Collision Detection CSMA/CD can be in one of three states: contention, transmission, or idle.

11. CSMA with Collision Detection Collision detection can take as long as 2 .

12. Collision-Free Protocols The basic bit-map protocol.

13. Collision-Free Protocols Token Ring Station Direction of transmission Token

14. Collision-Free Protocols (2) The binary countdown protocol. A dash indicates silence.

15. Limited-Contention Protocols  Low Load  Contention Protocol o Less Delay  High Load  Collision-free protocols o More Performance

16. Limited-Contention Protocols Acquisition probability for a symmetric contention channel.

17. Adaptive Tree Walk Protocol The tree for eight stations.

18. Wireless LAN Protocols (1) A wireless LAN. (a) A and C are hidden terminals when transmitting to B.

19. Wireless LAN Protocols (2) A wireless LAN. (b) B and C are exposed terminals when transmitting to A and D.

20. Wireless LAN Protocols (3) The MACA protocol. (a) A sending an RTS to B. (b) B responding with a CTS to A.

21. Ethernet Classic Ethernet and Switched Ethernet Collision Domain

22. Switched Ethernet An Ethernet switch.

23. Ethernet & Fast Ethernet

24. Gigabit Ethernet & 10 Gigabit Ethernet

25. IEEE 802.2: Logical Link Control (a) Position of LLC. (b) Protocol formats.

26. IEEE 802.2: Logical Link Control  MAC : Physical Addressing Media Access Control  MAC Address: 48 bit 24

27. Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers.

28. Three Switch Functions at Layer 2  Address learning Layer 2 switches and bridges remember the source hardware address of each frame received on an interface, and they enter this information into a MAC database called a forward/filter table.  Forward/filter decisions When a frame is received on an interface, the switch looks at the destination hardware address and finds the exit interface in the MAC database. The frame is only forwarded out the specified destination port.

29. Three Switch Functions at Layer 2  Loop avoidance If multiple connections between switches are created for redundancy purposes, network loops can occur. Spanning Tree Protocol (STP) is used to stop network loops while still permitting redundancy.

30. Address learning

31. Loop avoidance (1) Redundant links between switches are a good idea because they help prevent complete network failures in the event one link stops working.  Broadcast storm

32. Loop avoidance (2)  Multiple frame copies  MAC Table Instability

33. Loop avoidance (2)  Spanning Tree Protocol (STP)

34. Virtual LANs (1) A building with centralized wiring using hubs and a switch.

35. Virtual LANs (2)  Organizations need several LANs.  Security  Organization Department  Eliminate Broadcast Domain  Traffic type and load

36. Virtual LANs (3) 15 machines organized into two VLANs by switches.

37. Virtual LANs (4)  Switches need to know to which VLAN an incoming frame belongs. By ports By MACs By Ips Trunk Protocols  ISL (Using Encapsulation)  IEEE 802.1Q Standard (Using Tagging)

38. The IEEE 802.1Q Standard Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.

39. The IEEE 802.1Q Standard (2) The 802.3 (legacy) and 802.1Q Ethernet frame formats.