1. 1 Chapter 8-10 Local Area Networks (LANs)

2. Comparison 4e and 5e  Ch 7, 4eCh 8, 5e Ch 10, Forouzan  Ch 8, 4eCh 14, 5e Ch 13, Forouzan  Ch 9, 4eCh 13, 5e Ch 14, Forouzan  Ch 10, 4eCh 15, 5e Ch 14, Forouzan 2

3. 3 Classification Terminology  Network technologies classified into three broad categories  Local Area Network (LAN)  Metropolitan Area Network (MAN)  Wide Area Network (WAN)  LAN and WAN most widely deployed

4. 4 The Local Area Network (LAN)  Engineering classification  Extremely popular (most networks are LANs)  Many LAN technologies exist

5. 5 Key Features of a LAN  High throughput  Relatively low cost  Limited to short distance  Often rely on shared media

6. 6 Scientific Justification For Local Area Networks A computer is more likely to communicate with computers that are nearby than with computers that are distant  Known as the locality principle

7. 7 Topology  Mathematical term  Roughly interpreted as “geometry for curved surfaces”

8. 8 Network Topology  Specifies general “shape” of a network  Handful of broad categories  Often applied to LAN  Primarily refers to interconnections  Hides details of actual devices

9. Fully connected mesh topology (for five devices)

10. 10 Bus Topology  Shared medium forms main interconnect  Each computer has a connection to the medium

11. 11 Ring Topology  No central facility  Connections go directly from one computer to another

12. 12 Star Topology  Central component of network known as hub  Each computer has separate connection to hub

13. 13 Example Bus Network: Ethernet  Most popular LAN  Widely used  IEEE standard 802.3  Several generations  Same frame format  Different data rates  Different wiring schemes

14. 14 Shared Medium in a LAN  Shared medium used for all transmissions  Only one station transmits at any time  Stations “take turns” using medium  Media Access Control ( MAC ) policy ensures fairness

15. 15 Illustration of Ethernet Transmission  Only one station transmits at any time  Signal propagates across entire cable  All stations receive transmission  CSMA/CD media access scheme

16. 16 CSMA/CD Paradigm  Multiple Access ( MA )  Multiple computers attach to shared media  Each uses same access algorithm  Carrier Sense ( CS )  Wait until medium idle  Begin to transmit frame  Simultaneous transmission possible

17. 17 CSMA/CD Paradigm (continued)  Two simultaneous transmissions  Interfere with one another  Called collision  CSMA plus Collision Detection (CD)  Listen to medium during transmission  Detect whether another station’s signal interferes  Back off from interference and try again

18. 18 Backoff After Collision  When collision occurs  Wait random time t1, 0 < t1 < d  Use CSMA and try again  If second collision occurs  Wait random time t2, 0 < t2 < 2*d  Double range for each successive collision  Called exponential backoff

19. 19 Media Access on a Wireless Net  Limited range  Not all stations receive all transmissions  Cannot use CSMA/CD  Example in diagram  Maximum transmission distance is d  Stations 1 and 3 do not receive each other’s transmissions

20. 20 CSMA/CA  Used on wireless networks  Both sides send small message followed by data transmission  “ X is about to send to Y ”  “ Y is about to receive from X ”  Data from sent from X to Y  Purpose: inform all stations in range of X or Y before transmission  Known as Collision Avoidance (CA)

21. 21 Identifying a Destination  All stations on shared-media LAN receive all transmissions  To allow sender to specify destination  Each station assigned unique number  Known as station’s address  Each frame contains address of intended recipient

22. 22 Assignment of physical address  The stations may get their address in different ways:  Static  Configurable  Dynamic

23. 23 Ethernet Addressing  Standardized by IEEE  Each station assigned by unique 48-bit address e.g. 00:30:65:52:2E:96 in hexadecimal form  Address assigned when network interface card ( NIC ) manufactured (In most cases)

24. 24 Ethernet Address Recognition  Each frame contains destination address  All stations receive a transmission  Station discards any frame addresses to another station  Important: interface hardware, not software, checks address

25. 25 Possible Destinations  Packet can be sent to:  Single destination ( unicast )  All stations on network ( broadcast )  Subset of stations ( multicast )  Address used to distinguish

26. 26 Advantages of Address Alternatives  Unicast  Efficient for interaction between two computers  Broadcast  Efficient for transmitting to all computers  Multicast  Efficient for transmitting to a subset of computers

27. 27 Broadcast on Ethernet  All 1 s address specifies broadcast (FF:FF:FF:FF:FF:FF in hexcode)  Sender  Places broadcast address in frame  Transmits one copy on shared network  All stations receive copy  Receiver always accepts frame that contains this address

28. 28 Multicast  Half of addresses reserved for multicast  Network interface card  Always accepts unicast and broadcast  Can accept zero or more multicast addresses  Software  Determines multicast address to accept  Informs network interface card

29. 29 Promiscuous Mode  Designed for testing / debugging  Allows interface to accept all packets  Available on most interface hardware

30. 30 Identifying Frame Contents  Integer type field tells recipient the type of data being carried  Two possibilities  Self-identifying or explicit type (hardware record type)  Implicit type (application sending data must handle type)

31. 31 Conceptual Frame Format  Header  Contains address and type information  Layout fixed  Payload  Contains data being sent

32. 32 Illustration Of Ethernet Frame  Sender places  Sender’s address in source  Recipient’s address in destination  Type of data in frame type  Cyclic redundancy check in CRC

33. Figure 14.3 Minimum and maximum length

34. 34 Example Ethernet Types

35. 35 When Network Hardware Does Not Include Types  Sending and receiving computers must agree  To only send one type of data  To put type information in first few octets of payload  Most systems need type information

36. 36 Illustration of Type Information Added to Data  In practice  Type information small compared to data carried  Format of type information standardized

37. 37 A Standard For Type Information  Defined by IEEE  Used when hardware does not include type field  Called LLC / SNAP header  Logical Link Control  SubNetwork Attachment Point

38. 38 Demultiplexing On Type  Network interface hardware  Receives copy of each transmitted frame  Examines address and either discards or accepts  Passes accepted frame to system software  Network device software  Examines frame type  Passes frame to correct software module

39. 39 Network Analyzer  Device used for testing and maintenance  Listens in promiscuous mode  Produces  Summaries (e.g., % of broadcast frames)  Specific items (e.g., frames from a given address)

40. 40 Bus Topology  Any user with a Network Analyzer can read all packets!

41. 41 Star Topology  Star Topology and Bus Topology are equal fom security point!

42. 42 Ethernet Wiring  Three schemes  Correspond to three generations  All use same frame format

43. 43 Original Ethernet Wiring  Used heavy coaxial cable  Formal name 10Base5  Called thicknet

44. 44 Second Generation Ethernet Wiring  Used thinner coaxial cable  Formal name 10Base2  Called thinnet

45. 45 Modern Ethernet Wiring  Uses a hub  Formal name 10Base-T  Called twisted pair Ethernet

46. 46 Ethernet Wiring In An Office

47. 47 A Note About Ethernet Topology  Apparently  Original Ethernet used bus topology  Modern Ethernet uses star topology  In fact, modern Ethernet is  Physical star  Logical bus  Called star-shaped bus

48. 48 Higher Speed Ethernets  Fast Ethernet  Operates at 100 Mbps  Formally 100Base-T  Two wiring standards  10/100 Ethernet devices available  Gigabit Ethernet  Operates at 1000 Mbps (1 Gbps)  Slightly more expensive

49. 49 Another LAN Using Bus Topology  LocalTalk  Developed by Apple Corp. 1984  Simple to use  Slow by current standards  (230,4 kbps)

50. 50 Illustration Of LocalTalk  Transceiver required per station  Transceiver terminates cable

51. 51 Ring Topology  Second most popular LAN topology  Bits flow in single direction  Several technologies exist

52. 52 Token Passing  Used with ring topology  Guarantees fair access  Token  Special (reserved) message  Small (a few bits)

53. 53 Token Passing Paradigm  Station  Waits for the token to arrive  Transmits one packet around ring  Transmits token around ring  When no station has data to send  Token circulates continuously

54. 54 Token Passing Ring Transmission  Station waits for token before sending  Signal travels around entire ring  Sender receives its own transmission

55. 55 Strengths of Token Ring Approach  Easy detection of  Broken ring  Hardware failures  Interference

56. 56 Weaknesses of Token Ring Approach  Broken wire disables entire ring  Point-to-point wiring  Awkward in office environment  Difficult to add / move stations

57. 57 Token Passing Ring Technologies  ProNet-10  Operated at 10 Mbps  IBM Token Ring  Originally operated at 4 Mbps  Later version operated at 16 Mbps  Fiber Distributed Data Interconnect (FDDI)  Operated at 100 Mbps

58. 58 FDDI Terminology  FDDI  Uses optical fibers  High reliability  Immune to interference  CDDI  FDDI over copper  Same frame format  Same data rate  Less noise immunity

59. 59 FDDI Hub Technology  Part of FDDI standard  Stations attach to hub  Same frame format and data rate as FDDI  Called star-shaped ring

60. 60 FDDI Failure Recovery  Uses two rings  Automatic failure recovery  Terminology  Dual-attached  Counter rotating  Self healing

61. 61 Illustration of FDDI Failure Recovery

62. 62 Another Example of a Physical Star Topology  Asynchronous Transfer Mode (ATM)  Designed by telephone companies  Intended to accommodate  Voice  Video  Data

63. 63 ATM  Building block known as ATM switch  Each station connects to switch  Switches can be interconnected

64. 64 Details of ATM Connection  Full-duplex connections  Two fibers required

65. 65 ATM Characteristics  High data rates (e.g. 155 Mbps)  Fixed size packets  Called cells  Important for voice  Cell size is 53 octets  48 octets of data  5 octets of header

66. 66 Summary  Local Area Networks  Designed for short distance  Use shared media  Many technologies exist  Topology refers to general shape  Bus  Ring  Star

67. 67 Summary (continued)  Address  Unique number assigned to station  Put in frame header  Recognized by hardware  Address forms  Unicast  Broadcast  Multicast

68. 68 Summary (continued)  Type information  Describes data in frame  Set by sender  Examined by receiver  Frame format  Header contains address and type information  Payload contains data being sent

69. 69 Summary (continued)  LAN technologies  Ethernet (bus)  IBM Token Ring  FDDI (ring)  ATM (star)

70. 70 Summary (continued)  Wiring and topology  Can distinguish  Logical topology  Physical topology (wiring)  Hub allows  Star-shaped bus  Star-shaped ring

71. Figure 14.1 Three generations of Ethernet

72. Figure 14.5 Unicast and multicast addresses

73. Figure 14.6 Physical layer

74. Figure 14.7 PLS

75. Figure 14.8 AUI

76. Figure 14.9 MAU (transceiver)

77. Figure 14.10 Categories of traditional Ethernet

78. Figure 14.11 Connection of a station to the medium using 10Base5

79. Figure 14.12 Connection of stations to the medium using 10Base2

80. Figure 14.13 Connection of stations to the medium using 10Base-T

81. Figure 14.14 Connection of stations to the medium using 10Base-FL

82. Figure 14.15 Sharing bandwidth

83. Figure 14.16 A network with and without a bridge

84. Figure 14.17 Collision domains in a nonbridged and bridged network

85. Figure 14.18 Switched Ethernet

86. Figure 14.19 Full-duplex switched Ethernet

87. 14.2 Fast Ethernet MAC Sublayer Physical Layer Physical Layer Implementation

88. Figure 14.20 Fast Ethernet physical layer

89. Figure 14.21 MII

90. Figure 14.22 Fast Ethernet implementations

91. Figure 14.23 100Base-TX implementation

92. Figure 14.24 Encoding and decoding in 100Base-TX

93. Figure 14.25 100Base-FX implementation

94. Figure 14.26 Encoding and decoding in 100Base-FX

95. Figure 14.27 100Base-T4 implementation

96. Figure 14.28 Using four wires in 100Base- T4

97. 14.3 Gigabit Ethernet MAC Sublayer Physical Layer Physical Layer Implementation

98. Figure 14.29 Physical layer in Gigabit Ethernet

99. Figure 14.30 Gigabit Ethernet implementations

100. Figure 14.31 1000Base-X implementation

101. Figure 14.32 Encoding in 1000Base-X

102. Figure 14.33 1000Base-T implementation