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Chapter 6 Medium Access Control Protocols and Local Area Networks

Chapter 6 Medium Access Control Protocols and Local Area Networks. Chapter Figures. 3. 2. 4. 1. Shared multiple access medium. 5. M. . Figure 6.1. Medium sharing techniques. Static channelization. Dynamic medium access control. Scheduling. Random access. Figure 6.2.

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Chapter 6 Medium Access Control Protocols and Local Area Networks

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  1. Chapter 6Medium Access Control Protocols and Local Area Networks Chapter Figures

  2. 3 2 4 1 Shared multiple access medium 5 M  Communication Networks Figure 6.1

  3. Medium sharing techniques Static channelization Dynamic medium access control Scheduling Random access Communication Networks Figure 6.2

  4. Satellite channel = fin = fout Communication Networks Figure 6.3

  5. Inbound line Outbound line Host computer Stations Communication Networks Figure 6.4

  6. (a) (b) Communication Networks Figure 6.5

  7. Communication Networks Figure 6.6

  8. Distance d meters tprop = d /  seconds A transmits at t = 0 A B B transmits before t = tprop and detectscollision shortly thereafter A B A detects collision at t = 2 tprop A B Communication Networks Figure 6.7

  9. E[T]/X Transfer delay 1 r rmax 1 Load Communication Networks Figure 6.8

  10. a > a E[T]/X a a Transfer Delay 1 r rmax rmax 1 Load Communication Networks Figure 6.9

  11. First transmission Retransmission t t0 t0+X t0-X t0+X+2tprop + B t0+X+2tprop Vulnerable period Backoff period B Time-out Retransmission if necessary Communication Networks Figure 6.10

  12. 0.368 Ge-G S 0.184 Ge-2G G Communication Networks Figure 6.11

  13. t (k+1)X t0+X+2tprop kX t0+X+2tprop+ B Vulnerableperiod Retransmission if necessary Backoff period B Time-out Communication Networks Figure 6.12

  14. Station A begins transmission at t=0 A Station A captures channel at t=tprop A Communication Networks Figure 6.13

  15. Sensing Communication Networks Figure 6.14

  16. S 0.53 1-Persistent CSMA 0.01 0.45 0.16 0.1 G 1 Communication Networks Figure 6.15 – part 1

  17. S 0.81 Non-Persistent CSMA 0.01 0.51 0.14 0.1 G 1 Communication Networks Figure 6.15 – part 2

  18. A begins to transmit at t = 0 A B B begins to transmit at t = tprop- ; B detects collision at t = tprop B A A detects collision at t= 2 tprop-  A B Communication Networks Figure 6.16

  19. (a) Busy Contention Busy Idle Contention Busy Time (b) Pmax n Communication Networks Figure 6.17

  20. CSMA/CD 1-P CSMA Non-P CSMA max Slotted ALOHA ALOHA a Communication Networks Figure 6.18

  21. Reservation interval Data transmissions d r d d r d d d Time Cycle n Cycle (n + 1) r = M 1 2 3 Communication Networks Figure 6.19

  22. (a) 5 r 3 5 3 3 r 3 5 r 3 r 5 r 8 8 t (b) 8 5 r 3 5 3 3 r 3 5 r 3 r 5 r 8 8 t Communication Networks Figure 6.20

  23. Shared inbound line (a) Outbound line Central controller (b) (c) Central controller Communication Networks Figure 6.21

  24. Polling messages … 2 M 1 2 1 3 4 5 t Packet transmissions Communication Networks Figure 6.22

  25. Listen mode Transmit mode Input from ring Output to ring Delay Delay From device To device Communication Networks Figure 6.23

  26. d a) b) c) d d d d d d d d d d d d d d Free token Busy token Communication Networks Figure 6.24

  27. M = 50 Multiple token operation M = 10 M = 50 Maximum throughput M = 10 Single packet operation Single token operation a  Communication Networks Figure 6.25

  28. M=16 M=8 M=4 M=2 M=1 E[T]/X ρ Communication Networks Figure 6.26

  29. Frequency Guard bands 1 2 W … M–1 M Time Communication Networks Figure 6.27

  30. Guard time Frequency W 3 M 1 2 1 ... Time One cycle Communication Networks Figure 6.28

  31. Transmitter from one user Binary information R1 bps W1 Hz Radio antenna   R >> R1bps W >> W1 Hz Unique user binary random sequence Digital modulation Signal and residual interference   Binary information Signals from all transmitters Digital demodulation Correlate to user binary random sequence Communication Networks Figure 6.29

  32. g2 g3 g0 Time R0R1R2 0 1 0 0 1 0 1 0 2 1 0 1 3 1 1 0 4 1 1 1 5 0 1 1 6 0 0 1 7 1 0 0 Sequence repeats from here onwards R0 R1 R2 output g(x) = x3 + x2 + 1 The coefficients of a primitive generator polynomial determine the feedback taps Communication Networks Figure 6.30

  33. Frequency Code 1 Code M W Time Communication Networks Figure 6.31

  34. Channel 1:110 -> +1+1+1 -> (-1,-1,-1,-1),(-1,-1,-1,-1),(+1,+1,+1,+1) Channel 2:010 -> -1+1-1 -> (+1,-1,+1,-1),(-1,+1,-1,+1),(+1,-1,+1,-1) Channel 3:001 -> -1-1+1 -> (+1,+1,-1,-1),(+1,+1,-1,-1),(-1,-1,+1,+1) Sum Signal: (+1,-1,-1,-3),(-1,+1,-3,-1),(+1,-1,+3,+1) Channel 1 Channel 2 Channel 3 Sum Signal Communication Networks Figure 6.32

  35. Sum Signal: (+1,-1,-1,-3),(-1,+1,-3,-1),(+1,-1,+3,+1) Channel 2 Sequence:(-1,+1,-1,+1),(-1,+1,-1,+1),(-1,+1,-1,+1) Correlator Output: (-1,-1,+1,-3),(+1,+1,+3,-1),(-1,-1,-3,+1) Integrated Output: -4, +4, -4 Binary Output: 0, 1, 0 Sum Signal Channel 2 Sequence Correlator Output +4 Integrator Output -4 -4 Communication Networks Figure 6.33

  36. 0 0 0 1 0 0 0 1 0 0 0 1 W1= 0 W2= W4= 0 0 0 1 1 1 1 0 W8= 0 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 1 1 1 0 0 0 0 1 1 1 1 0 Communication Networks Figure 6.34

  37. (a) A B A B Frequency 825 MHz 845 MHz 870 MHz 890 MHz (b) A B A A B A A A B B Frequency 824 MHz 849 MHz 894 MHz 869 MHz Communication Networks Figure 6.35

  38. Base to mobile 4 1 6 1 2 5 6 2 3 3 Time Mobile to base 2 1 2 3 4 5 1 3 6 4 Time 40 ms Communication Networks Figure 6.36

  39. (a) Initial GSM Existing services Existing services Initial GSM 890 MHz 915 MHz 935 MHz 960 MHz 905 MHz 950 MHz (b) Slow Associated Control Channel Slow Associated Control Channel Traffic Channels #0-11 Traffic Channels #13-24 8 0 7 21 3 17 6 20 2 9 16 5 19 1 15 22 4 18 14 10 24 13 23 12 11 25 1 multiframe = 26 frames 120 ms long 0 1 2 3 4 5 6 7 1 TDMA frame = 8 slots 1 slot = 114 data bits / 156.25 bits total Communication Networks Figure 6.37

  40. I short code spreading sequence (a) Walsh channel j sequence baseband filter I(t) Error coding, repetition, interleaving 19,200 sym/s 9600 bps User info baseband filter Q(t) 19200 sym/s User mask (ESN) Long code generator Decimator Q short code spreading sequence 1.2288 Mcps (b) I short code spreading sequence Walsh channel 0 sequence baseband filter I(t) Pilot channel all 1s baseband filter Q(t) Q short code spreading sequence Communication Networks Figure 6.38

  41. I short code spreading sequence baseband filter I(t) 307,200 sym/s Error coding, repetition, interleaving 9600 bps 1/2 chip delay User info baseband filter Q(t) D User mask (ESN) Long code generator Q short code spreading sequence 1.2288 Mcps Communication Networks Figure 6.39

  42. Our frame finishes transmission Our frame arrives and finds two frames in queue (a) Second frame transmitted First frame transmitted t 0 3 6 9 (b) Our frame finishes transmission Our frame arrives and finds two frames in queue t 0 1 3 4 6 7 9 First frame transmitted Second frame transmitted Communication Networks Figure 6.40

  43. 10 5 1 τ΄X a΄ = .5 E[T]/X 0 ρ Communication Networks Figure 6.41

  44. 10 1 Average wait 0 0.1  Communication Networks Figure 6.42

  45. 10 Average wait 1 0, 0.1  Communication Networks Figure 6.43

  46. 1 10 Average wait 0.1 0  Communication Networks Figure 6.44

  47. (a) (b) Ethernet Processor RAM RAM ROM Communication Networks Figure 6.45

  48. Network layer Network layer 802.2 Logical link control LLC Data link layer 802.11 Wireless LAN Other LANs 802.3 CSMA-CD 802.5 Token Ring MAC Physical layer Various physical layers Physical layer IEEE 802 OSI Communication Networks Figure 6.46

  49. Unreliable Datagram Service MAC MAC MAC PHY PHY PHY Communication Networks Figure 6.47

  50. C A Reliable frame service A C LLC LLC LLC MAC MAC MAC PHY PHY PHY Communication Networks Figure 6.48

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