1. Basic Model MEDIUM Distributed Sources Fig.13 Generic Model for Media Access Systems

3. Message Delay - FDMA

4. Example FDMA 50 kbps line - 1000 bit frames to be transmitted from four sources Two Approaches 1) All traffic on 50 kps line 2) 12.5 kbps dedicated to each source MUX

5. Four 12.5 kbps lines One 50 kbps lines Average delay(sec) Load

6. L=1 L=4 L=16 L=64 Load Average delay(sec) Continuation FDMA

8. Message Delay - TDMA

9. L=64 L=16 L=4

11. Cycle time Delay

17. P(Collision)= Total traffic New trafficRetransmitted traffic Assumption: Total lineflow,  Poisson Define  M, total load and , load due to new traffic

20. P(Collision)= Total traffic New trafficRetransmitted traffic Define  M, total load and , load due to new traffic

21. Delay Analysis

22.  Average Delay/Retransmission Interval Pure ALOHA Slotted ALOHA

24. Carrier Sense Multiple Access Collision avoided by sensing line for other users Three strategies: 1-persistent - Transmit when line sensed idle p-persistent - Transmit with probability p when line sensed idle nonpersistent - random timeout before new attempt Problem: Two terminals transmit within  seconds of one another - collision results

25. Propagation delay -  seconds Terminal A transmits Terminal B transmits  2  Contention Interval Duration of Conflict

26. Arrival Rate Throughput a=1 a=.1 a=.01 a=.001 a=0 nonpersistent CSMA a=a= round trip delay message transmission time

27. Ethernet Protocol CSMA/CD Carrier Sense Multiple Access with Collision Detection line length 1 km  5  sec a =.01 and 10 Mbps rate B=5000 Same technique with optical fiber? R=1 Gbps a=  B/R)=1 Reduced efficiency

28. Polling model appropriate

29. Central Processor Broadcast Polls Bridge Physical Tree Logical Tree 000 001 010 011100 101 110 111 0 1 0 0 01 10 11

30. 0 1 0 0 01 10 11 Terminal with message 011 Example Polling - eight steps Probing - four steps General result for light loading Polling - N steps Probing - log N steps

31. 0 1 0 0 01 10 11 011 Contention Resolution in Random Access 101

32. Code Division Multiple Access (pages 271-275) User data #1 User data #2 User data #N Code seq #1 Code seq #2 Code seq #N CHANNELCHANNEL Code seq #1 Code seq #2 Code seq #N User data #1 User data #2 User data #N

33. Two kinds of code sequences Direct sequence TCTC TBTB 1/T B =Data rate 1/T C =Chip rate Processing gain= T B /T C Hard to generate “fast” sequences

34. Frequency Hopping TCTC TBTB 1/T B =Data rate 1/T C =Chip rate Processing gain= T B /T C

35. Orthogonality of Code Sequences Code sequence A Code sequence B

37. Star Coupler Wavelength Division Multiple Access(WDMA) Tuneable Transmitters and/or Receivers All optical no electronic bottleneck

39. 802.3 - Derived from Ethernet

41. 10base10 Core Vapire tap Core 10base5 Connector 10baseT Hub Physical Arrangements Twisted pairs coax

42. Topologies Cable snaking through offices Backbone up an elevator shaft

43. Tree Repeater Greatest length=2.5 km and four repeaters roundtrip delay=51.2  seconds = 512 bit times

44. Preamble Destn Addrss Source Addrss Data Bytes 7 1 2 or 6 2 or 6 2 0-1500 0-46 4 PadCksm 802.3 Frame Format Start of frame delimiter Length of data field Dotting pattern Addressing - broadcast, multicast, local, global Minimum frame length - 64 bytes

45. Binary Exponential Backoff Algorithm Initial transmission collision slot time= 51.2  seconds = 512 bit times collision retransmission Process continues to ten retransmissions-1023 slots

46. Efficiency k statons with messages each transmits in a slot with prob P slot = 2  =2line length(km)/propagation speed(km/sec)=2L/c A=P(one successful)=P(only one transmits)=kp(1-p) k-1 If p=1/k A is maximum (dA/dP=0) A max =e -1 for k>>1 P(j slot in contention interval)=A(1-A) j-1 Average number of slots in a contention interval=1/A Average duration contention interval=2  /A=< 2  e=5.4  P=average frame transmission time = average length(bits)/line rate(bps)=F/B Efficiency=P/(P+ 2  /A)=1/(1+2BLe/cF)

47. 802.4 Token Bus Logical ring Direction of token motion  ohm broadband coax Speeds - 1,5 and 10 Mbps

48. Four priority classes - 0(lowest), 2, 4, 6 (highest) Token passing sequence Class 6 stations Class 4 stations Class 2 stations Class 0 stations Start

49. Preamble Destn Addrss Source Addrss Data Bytes 1 1 1 2 or 6 2 or 6 0-8182 4 1 Cksm 802.4 Frame Format Start of frame delimiter Length of data field frame control end delimiter

50. 802.5 Token Ring Station Interface

51. Two Modes for Interface Station One bit delay Ring Interface Station One bit delay Ring Interface Listen Transmit

52. Speeds-1, 4 and 16 Mbps velocity = 1.8 x 10 5 km/sec Bits circulating in ring B=N+LR/V =No stations +Line length x bit rate/ Signal velocity Padding to transmit entire token

53. No restriction on message length

54. Wire Center Wire center Connector Bypass relay Cable

55. 802.5 Frame Format Starting delimiter access control (ACK) SD AC ED 1 1 1 10 msec frame holding time Token format Destn Addrss Source Addrss Data Bytes 1 1 1 2 or 6 2 or 6 no limit 4 1 1 Cksm Length of data field frame control ending delimiter SD AC FC ED FS frame status Violations of differential Manchester coding for control Data frame format

56. Comparison of 802 LANs

58. Bus A Bus B Data flow Head end Data flow MAN-Distributed Queue Dual Bus(DQDB) IEEE 802.6

59. Distributed Queue Protocol Station with a message for station to right(left) sends request left(right) and puts message on internal stack for right(left) Each station counts requests from right(left) and increases the right(left)stack by one for each Each station counts empty frames from left(right) and decreases right(left)stack by one Transmit message when it comes to head of line

60. LLC MAC Network layer Data link layer Physical layer Packet LLC PacketLLCMAC Network 802.2-Logical link control Service options: unreliable datagram ACKed datagram connection-oriented

61. BBBB Work stations File servers Backbone LAN Bridge Cluster on single LAN Bridges

62. Reasons for Bridges Connect different kinds of LANs in an organization Connect dispersed LANs Handle growth by splitting LANs Increasing distance constraints Reliability Security

63. Host A Higher levels Network LCC MAC Physical Host B Higher levels Network LCC MAC Physical 802.3802.4 MAC Physical MAC Physical Bridge Pkt Path

64. 802.3 802.4 802.5 Preamble Start limiter Access control Frame control addresses Length Data Pad Chcksm End delimiter Frame status Problem for Bridges - different formats

65. Transparent or Spanning tree Bridges Flooding and backward learning Spanning tree topology prevents looping sub-optimum use of bandwidth Source Routing Bridges discovery frames Destination addresses

66. Comparison Transparent and Source Routing Bridges Issue Transparent Source Routing

67. High-speed LANs FDDI-Fiber Distributed Data Interface Fast Ethernet(802.3u) HIPPI - High-Performance Parallel Interface Fibre Channel

68. FDDI High-speed optical ring 100 Mbps 200 km 1000 stations Multimode fiber LEDs FDDI - II PCM voice ISDN traffic

69. Topology Failure mode A A A B B

70. Destn Addrss Source Addrss Data Bytes >7 1 1 2 or 6 2 or 6 no limit 4 1 1 Cksm Length of data field frame control ending delimiter ED FS frame status Start delimiter FDDI Frame Blocks of 5 bits 16 data symbols 3 delimiter symbols 2 control symbols 3 hardware signaling 8 spare Synchronous frames every 125  sec - 96 bytes of data each