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1 The Medium Access Control Sublayer Chapter 4. 2 The Channel Allocation Problem Static Channel Allocation in LANs and MANs Dynamic Channel Allocation.

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Presentation on theme: "1 The Medium Access Control Sublayer Chapter 4. 2 The Channel Allocation Problem Static Channel Allocation in LANs and MANs Dynamic Channel Allocation."— Presentation transcript:

1 1 The Medium Access Control Sublayer Chapter 4

2 2 The Channel Allocation Problem Static Channel Allocation in LANs and MANs Dynamic Channel Allocation in LANs and MANs

3 3 1.Station Model. N independent stations sending messages according Poisson distribution. 2.Single Channel Assumption. A single channel is available to all stations to transmit to and receive from. 3.Collision Assumption. If stations transmit at the same time frames will collide and garbled. All stations can detect collision and retransmit frame later. 4.(a) Continuous Time: Frame can start transmission at any time. (b) Slotted Time: Frame can start transmission at given time instance. 5.(a) Carrier Sense: Stations can sense if the channel is in use and wait. (b) No Carrier Sense: Stations cant tell if the channel is free.

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

5 5 Pure ALOHA In pure ALOHA, frames are transmitted at completely arbitrary times.

6 6 Collision conditions in pure Aloha period is 2t If another frame starts here we will have collision All frames are of the same size. Frame transmission can start at any time instant.

7 7 Throughput versus offered traffic for ALOHA systems. Max throughputs: 18% at G = 0.5 for pure 37% at G = 1 for slotted. (throughput per packet time)

8 8 (1-p) carr ->random back off Persistent and Non-persistent CSMA no carr -> transmit carr -> check after random time nonpersistent no carr -> transmit with prob p. p-persistent is slotted carr -> check next slot carr ->check next slot

9 9 CSMA with Collision Detection CSMA/CD can be in one of three states: contention, transmission, or idle. Minimum contention slot is 2 where is the propagation delay between the two most remote stations.

10 10 Collision free protocols: the basic bit-map protocol.

11 11 The binary countdown protocol. A dash indicates silence.

12 12 Wireless LAN Protocols A wireless LAN. (a) A transmitting. (b) B transmitting.

13 13 Wireless MACA (Multiple Access with Collision Avoidance) a)C hears RTS to B 30 bytes frame with the length of the frame to follow. b)D hears B responding with a CTS to A (copying the length of the next frame). c)A starts transmitting.

14 14 Ethernet Ethernet Cabling Manchester Encoding The Ethernet MAC Sublayer Protocol The Binary Exponential Backoff Algorithm Ethernet Performance Switched Ethernet Fast Ethernet Gigabit Ethernet IEEE 802.2: Logical Link Control Retrospective on Ethernet

15 15 Ethernet MHz Segment length in hundredths meters Base band Vampire taps T conn.

16 16 Ethernet Cabling Three kinds of Ethernet cabling. (a) 10Base5, (b) 10Base2, (c) 10Base-T.

17 17 Ethernet coding (a) Binary encoding, (b) Manchester encoding, (c) Differential Manchester encoding.

18 18 Ethernet MAC Sublayer Protocol Frame formats. (a) DIX Ethernet, (b) IEEE Address bit 46 determines local or global address. Min frame is 64 bytes from dest. address to checksum.

19 19 Collision detection can take as long as 2 This is to sense a collision before end of the frame reach far end. In 10 Mbps LAN 1 bit is 100 nsec, and max segment 2500 m round trip delay is 2 = 50 mksec = 500 bits = 64 bytes.

20 20 Binary exponential backoff Frame Contention period Contention period Frame Idle period p = 1/2 p = 1/4 p = 1/8 If k stations contend for a channel probability that any of k gets a channel is: A = kp(1 – p) k-1 p = 1/k gives A max Average number of contention slots = jA(1 – A) j-1 = 1/A. Therefore, channel efficiency = P/(P + 2 /A)

21 21 Ethernet Performance Efficiency of Ethernet at 10 Mbps with 512-bit slot times.

22 22 Switched Ethernet A simple example of switched Ethernet.

23 23 Fast Ethernet The original fast Ethernet cabling.

24 24 Gigabit Ethernet (a) A two-station Ethernet. (b) A multistation Ethernet.

25 25 Gigabit Ethernet (2) Gigabit Ethernet cabling.

26 26 IEEE 802.2: Logical Link Control (a) Position of LLC. (b) Protocol formats.

27 27 Wireless LANs The Protocol Stack The Physical Layer The MAC Sublayer Protocol The Frame Structure Services

28 28 The Protocol Stack Part of the protocol stack.

29 29 The MAC Sublayer Protocol (a) The hidden station problem. (b) The exposed station problem.

30 30 The MAC Sublayer Protocol (2) The use of virtual channel sensing using CSMA/CA.

31 31 The MAC Sublayer Protocol (3) A fragment burst.

32 32 The MAC Sublayer Protocol (4) Interframe spacing in

33 33 The Frame Structure The data frame.

34 Services Association Disassociation Reassociation Distribution Integration Distribution Services

35 Services Authentication Deauthentication Privacy Data Delivery Intracell Services

36 36 Broadband Wireless Comparison of and The Protocol Stack The Physical Layer The MAC Sublayer Protocol The Frame Structure

37 37 The Protocol Stack The Protocol Stack.

38 38 The Physical Layer The transmission environment.

39 39 The Physical Layer (2) Frames and time slots for time division duplexing.

40 40 The MAC Sublayer Protocol Service Classes Constant bit rate service Real-time variable bit rate service Non-real-time variable bit rate service Best efforts service

41 41 The Frame Structure (a) A generic frame. (b) A bandwidth request frame.

42 42 Bluetooth Bluetooth Architecture Bluetooth Applications The Bluetooth Protocol Stack The Bluetooth Radio Layer The Bluetooth Baseband Layer The Bluetooth L2CAP Layer The Bluetooth Frame Structure

43 43 Bluetooth Architecture Two piconets can be connected to form a scatternet.

44 44 Bluetooth Applications The Bluetooth profiles.

45 45 The Bluetooth Protocol Stack The version of the Bluetooth protocol architecture.

46 46 The Bluetooth Frame Structure A typical Bluetooth data frame.

47 47 Data Link Layer Switching Bridges from 802.x to 802.y Local Internetworking Spanning Tree Bridges Remote Bridges Repeaters, Hubs, Bridges, Switches, Routers, Gateways Virtual LANs

48 48 Data Link Layer Switching Multiple LANs connected by a backbone to handle a total load higher than the capacity of a single LAN.

49 49 Bridges from 802.x to 802.y Operation of a LAN bridge from to

50 50 Bridges from 802.x to 802.y (2) The IEEE 802 frame formats. The drawing is not to scale.

51 51 Local Internetworking A configuration with four LANs and two bridges.

52 52 Spanning Tree Bridges Two parallel transparent bridges.

53 53 Spanning Tree Bridges (2) (a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree.

54 54 Remote Bridges Remote bridges can be used to interconnect distant LANs.

55 55 Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers.

56 56 Repeaters, Hubs, Bridges, Switches, Routers and Gateways (2) (a) A hub. (b) A bridge. (c) a switch.

57 57 Virtual LANs A building with centralized wiring using hubs and a switch.

58 58 Virtual LANs (2) (a) Four physical LANs organized into two VLANs, gray and white, by two bridges. (b) The same 15 machines organized into two VLANs by switches.

59 59 The IEEE 802.1Q Standard Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.

60 60 The IEEE 802.1Q Standard (2) The (legacy) and 802.1Q Ethernet frame formats.

61 61 Summary Channel allocation methods and systems for a common channel.


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