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LAN Chp11

Abolanle Sule English 93 cards

Cards in this deck (93)

  1. 1LAN are usually owned by -Organization
  2. 2Does LAN have more capacity than WAN?Yes, LAN has more capacity than WAN.
  3. 3what is Topology?Topology refers to the way in which the end points or station attached to network are interconnected.
  4. 4List the common topology types?Bus, Star, Tree and Ring topologies.
  5. 5Define Bus topology?In Bus topology all stations attach through a tap directly to a linear transmission bus.
  6. 6Define Star topology?In Star, each station connects to a common central-node via 2pt to pt links, one for reception and one for transmission.
  7. 7Disadvantages of Bus topology?Transmission from any station can be received by others.
    Regulating transmission mechanism is required.
    One station can continuously transmit, blocking others.
    Messages can be overlapped/garbled if 2 stations transmit same time.
  8. 8A Star topology is physically star but logically -Bus.
  9. 9Functions of IEEE 802 Model -Physical Layer?1. Encoding and Decoding Signals.
    2. Preamble generation sync.
    3. Bit Transmission.
    4. Medium and Topology.
  10. 10LLC is acronym forLogical Link Control
  11. 11MAC is acronym for -Media Access Control
  12. 12What does LLC does?LLC specifies addressing and data control exchange between 2 users, based on HDLC standard/format.
  13. 13Name 3 services provided as alternatives for attached devices?1. Unacknowledged Connectionless Service -datagram-styled.
    2. Connection Mode Service - similar to HDLC.
    3. Acknowledged Connectionless Service - across between above two, no prior logical setup required.
  14. 14Asynchronous systems can be -1. Round Robin - each station given turn to transmit.
    2. Reservation - divided medium slots, good for stream traffic.
    3. Contention - all stations content for time, good for bursty traffic.
  15. 15MAC layer receives data from -LLC layer.
  16. 16PDU is referred to asMAC frame.
  17. 17LLC optionally retransmits -unsuccessfully frames.
  18. 18What is a Bridge?A Bridge connects similar LAN with identical physical and link layer protocols.
  19. 19Reasons for using Bridges?Reliability
    Performance
    Security
    Geography
  20. 20Functions of Bridge connecting A and B?Read all the frames transmitted on A.
    Accepts those addressed to B.
    Using MAC protocol on B, retransmit each frame.
    Do same for B to A traffic.
  21. 21Does Bridge make modification and encapsulation on the content/format of transmitted frames?No, Bridge does not make any modification.
  22. 22Bridge is transparent to -stations.
  23. 23Bridges can connect more than 2 LANs?Yes
  24. 24Bridge can function at -MAC level.
  25. 25Mention 3 types of Routing?Fixed Routing.
    Flooding.
    Adaptive Routing.
  26. 26Fixed Routing uses -Least Cost Algorithm.
  27. 27Flooding uses -Minimum Hop Count.
  28. 28Adaptive uses -Neither least cost nor minimum hop count.
  29. 29What is Spanning Tree approach?is a mechanism in which bridges automatically develop a routing table and update the table in response to changing network topology.
  30. 30The Algorithm consists of 3 mechanisms?Frame Forwarding.
    Address Learning.
    Loop Resolution.
  31. 31Frame Forwarding meansmaintaining forwarding database for each port.
  32. 32Address Learning meanscan preload forwarding databases and set timer on each entry.
  33. 33Alternative route meansthere is a closed loop.
  34. 34For any connected graph there is a spanning tree maintaining connectivity with -no closed loops.
  35. 35What are Hubs?Hubs are active central element for star layout.
  36. 36Hubs acts as a -repeaters.
  37. 37Length of a line is limited to about100m
  38. 38Length of Optical fiber maybe about -500m
  39. 39What is Layer2 switch?Layer2 switch replaced the Hub for high speed LANs.
    Its also referred to as Switching Hub.
  40. 40Benefits of Layer2 Switch?No change to the software / hardware.
    Dedicated capacity equal to original LAN.
    Scales easily.
  41. 41Types of Laye2 Switches?Store and Forward switch.
    Cut - through switch.
  42. 42Store and Forward switch- Accepts and buffers briefly then route to appropriate output line.
    - There is delay between sender and receiver.
  43. 43Cut - through switch- Uses destination address at beginning of frame and begins repeating immediately as soon as destination address is recognized.
    - Yields the highest possible throughput.
    - Risk of propagating bad frames.
  44. 44Difference between Bridges and Switches?Bridges - frame handling in software
    Switches - frame handling in hardware.
    Bridge analyzes and forward one frame at a time.
    Switches - can handle multiple frames at a time.
    Bridge uses store-and forward operation,
    Switches uses cut-through operation.
  45. 45Circuit Switching is dominant in -Voice communications.
  46. 46Packet Switching is dominant in -Digital Data communications.
  47. 47Beyond LAN, transmitting data on WAN requires -intermediate switching nodes.
  48. 48Switching nodes are not concerned about data content rather they provide -a switching facility to move data from node to node.
  49. 49Devices attached to the network are called -stations.
    e.g. computer, terminals, telephones or other communication devices.
  50. 50A collection of nodes is called -communication network.
  51. 51Internal node connects only to -other nodes within the network.
  52. 52Others attached to one/more stations aside from providing switching function -Node - Station Links.
  53. 53Node -Node are usually -FDM or TDM.
  54. 54Circuit switching implies there is a -dedicated connection path between two stations.
  55. 55Circuit Switching has 3 phases -Establish connection.
    Transfer.
    Disconnect.
  56. 56A public telecom network has 4 generic architectural components -Subscribers - device attached to network.
    Subscriber Line - called Local/ subscriber Loop.
    Exchanges - switching centers.
    Trunks - branches btw the exchanges.
  57. 57Circuit switching is well suited for -Analog voice signals.
  58. 58Circuit switching can be either -Blocking - unavailable all parts are in use.
    Non-Blocking - permit stations to connect at once provided its free.
  59. 59Space Division Switching - signal paths are physically separated from one another -using a metallic cross-point or semi-conductor gate.
    When the # of cross-pts grows its costly for a large switch.
  60. 60Multiple-stage helps to reduce -# of cross-pts & increases crossbar utilization.
    There more than one path to connect 2 end-pts, thus increases reliability.
  61. 61Packet Switching was designed for -data.
    Transmit in small packets containing user & control infor. Packets are received buffered briefly and passed to the next node.
  62. 62What are the requirements for routing function?Correctness
    Simplicity
    Robustness
    Stability
    Fairness
    Optimality
    Efficiency.
  63. 63Elements of Routing Techniques -* Performance - # of hops, cost, delay, throughput.
    ** Decision time - datagram / virtual.
    *** Decision place - distributed(each node), centralized or originating node(source).
  64. 64Minimum - hop -route is the -one that passes through the least # of nodes.
  65. 65A more generalized minimum-hop criterion is the -Least-cost routing.
  66. 66The higher the data rate on a link, the lower the assigned -cost of the link.
  67. 67The Least-cost-route should provide the highest -throughput.
    Also minimize delays.
  68. 68The Least-cost-route is more flexible than the -minimum-hop-criterion.
  69. 69Fixed Routing uses a -single permanent route for each source to destination pair. Is fixed until network topology changes. It is simple and does not react to network failure/congestion.
  70. 70Flooding sends packets to -every neighbor, multiple copies arrives at destination, each packet is uniquely numbered to avoid duplicates are discarded, no network infor required.
  71. 71Random Routing has the simplicity & robustness of flooding but with -far less traffic load. Node selects only out going path for retransmission of incoming packet. Selection can be random or round robin, based on probability calculation. No network infor is required.
  72. 72Adaptive Routing is used by most packet switch networks with routing decision based on -changes in the condition of the network, e.g. failure to links or congestion of nodes.
  73. 73Disadvantages of Adaptive Routing -Complex decision.
    Network infor required.
    Information itself constituent load.
    Reacting quickly causes oscillation.
    Reacting slowly means infor maybe irrelevant.
  74. 74Advantages of Adaptive Routing -Improved performance.
    Aid in congestion control.
  75. 75Dijkstra's algorithm -Finds the shortest path from a given source to other nodes, develops in increasing path length, runs in stages:
    *Initialization
    **Get next node
    ***Update Least-cost-paths.
  76. 76Bellman Ford's Algorithm -Finds the shortest paths from a given node subject to constraint that path contain at most one link, next at most two links and proceeds in stages:
    *Initialization Ln(s) = 0 & Lo(n) = infinity
    **Update.
  77. 77Congestion occurs when the # of packets being transmitted through a network beings to -a packet-handling capacity of the network.
  78. 78Congestion control maintains the # of packets within the network -below which performance falls off dramatically.
  79. 792 general strategies applied to congested nodes -* Discard any incoming packet for which there is no available buffer space.
    ** Exercise flow control to its neighbors.
  80. 80Mechanism for Congestion control -*Backpressure
    **Choke packet
    ***Implicit signaling(responsibility of end-systems).
    ****Explicit signaling(responsibility of network nodes).
  81. 81LAPF control is capable of detecting -lost frames.
  82. 82Explicit signaling can be either -Forward - congestion avoidance notice in opposite direction to packet required.
    Backward - congestion avoidance notice in same direction as packet required.
  83. 83Categories of Explicit signaling -Binary - A bit set in packet indicates congestion.
    Credit Based - how many packets source may send.
    Rate Based - supply explicit data rate limit.
  84. 84Leaky Bucket is used mostly in -Asynchronous transfer mode. -ATM
  85. 85Leaky Bucket empties at a -constant rate.
  86. 86While Token Bucket empties at -input data rate.
  87. 87In Token Bucket, as the rate of incoming packets rise, the output of the system also -speeds up.
  88. 88Token Bucket is widely used and provides the input parameters for a policing function but its -not for traffic policing but for traffic shaping. Its smooth out burst of cells.
  89. 89Token Bucket does not generally -Discard the packet.
  90. 90Fixed Routing -Least-cost algorithm.
  91. 91Flooding -Minimum-hop-count.
  92. 92Adaptive -Neither least cost nor minimum hop count.
  93. 93—

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LAN Chp11
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Abolanle Sule
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