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What is a LAN ?

What is a LAN ?. A LAN is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communications channel of moderate data rates. Thus Communicate Directly

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What is a LAN ?

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  1. What is a LAN ? • A LAN is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communications channel of moderate data rates. • Thus • Communicate Directly • Moderately Sized Geographic Area • Moderate Data Rate

  2. Basic Requirements of a LAN • Data rate of 1 to 100 Mbps • Geographic distances spanning at most 1-5 km • Ability to support several hundred independent devices • Simplicity, or use of the simplest mechanisms that have the required functionality and performance • Reliability and good error characteristics

  3. Basic Requirements of a LAN • Minimal dependence on any centralized components or control • Efficient use of shared resources, including the network channel • Stability under high load • Fair access (bandwidth, delay) to the network by all devices • Easy installation • Ease of reconfiguration and maintenance • Low cost

  4. 網路區段 2 網路區段 1 訊號增益器 LAN Extension

  5. Network Topologies B B B C C A A C A E D E D D E Star Ring Dual Ring A D B F D B A C B A E C C F E Bus Tree Dual Bus

  6. Network Topologies B A D A D C B F C E A C B Dual Bus Dual Bus Mesh B C A D E H F G Snowflake

  7. Network Topologies G B 橋接器 H C F A 集線器 或 中樞器 J E I D A H 橋接器 橋接器 L ... F B G D C M K E Hub or Concentrator O N Bridged Ring Networks

  8. Rules of Using Repeaters • Maximum 5 sections • Maximum 4 repeaters • Maximum 3 sections can have hosts • Within a whole collision domain Reason: Propagation round trip latency < 51.2ms 8

  9. CSMA/CD • listen before talk • listen while talking • wait before talk again BEBAAlgorithm： n : (n <= 16) collision times, more than 16 would give error message. k : Min (n,10) k=n when n<=10，k=10 when n>10 r : (unit: slot time) 0 <= r < 2krandom waiting factor Slot time = 51.2 ms. 9

  10. 整體延遲 元件 穩定延遲 前進路徑 元件數 回程路徑 元件數 元件 啟動延遲 元件 Calculation of Slot time 編碼器 0.1 ms 0.1 ms 5 5 2.0 ms 收發器電纜 5.13ns/公尺 0 300公尺 300公尺 3.08 ms 收發器（傳送路徑） 0.05 ms 0.3 m 3 3 2.10 ms 收發器（接收路徑） 0.05 ms 0.6us 3 0 1.95 ms 收發器（衝撞路徑） 0 0.9 m 0 3 2.70 ms 同軸電纜 4.33ns/公尺 0 1500公尺 1500公尺 12.99 ms 半訊號增益器間電纜 5.13ns/公尺 0 1000公尺 1000公尺 10.26 ms 電纜驅動器 0.1 ms 0 2 2 0.40 ms 電纜接收器 0.1 ms 0 2 2 0.40 ms 訊號增益器（增益路徑） 0.2 ms 0.4 ms 2 0 1.20 ms 訊號增益器（衝撞路徑） 0.2 ms 0.2 ms 0 2 0.80 ms 載波感測 0 0.2 ms 5 0 1.00 ms 衝撞偵測 0 0.2 ms 0 5 1.00 ms 訊號上升時間 0 0.1 ms 3 0 0.30 ms （至 70% 於500公尺處） 訊號上升時間（由 50% 0 2.0 ms 0 3 6.00 ms 至 94% 於 500公尺處） 衝撞分割 0 0.2 ms 0 1 0.20 ms 訊號來回傳遞最長延遲46.38 ms

  11. IEEE Project 802 Standards • IEEE 802.1 High Level Interface • IEEE 802.1D Local Bridge (Spanning Tree Algorithm) • IEEE 802.1G Remote Bridge • IEEE 802.2 LLC (Logical Link Control) • IEEE 802.3 CSMA/CD (Carrier Sense Multiple Access with Collision Detection • IEEE 802.4 Token-Bus • IEEE 802.5 Token-Ring • IEEE 802.6 DQDB (Distributed Queue Dual Bus)

  12. IEEE Project 802 Standards • IEEE 802.7 Broadband Technical Advisory Group • IEEE 802.8 Fiber Optic Technical Advisory Group • IEEE 802.9 Integrated Voice and Data LAN Working Group • IEEE 802.10 LAN Security Working Group • IEEE 802.11 Wireless LAN • IEEE 802.12 Demand-Priority (100VG-AnyLAN) • IEEE 802.14 CATV Networks

  13. IEEE Project 802 Standards 802.1 網路連結技術 LLC 802.2 LLC MAC 802.12 AX3T9.5 802.5 802.11 802.3 802.4 802.9 802.6 Wireless FDDI Token-Ring CSMA/CD Token-Bus Isochronous DQDB 100VG- AnyLAN Physical LAN Ethernet

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