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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 M
2、oderate Data Rate,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 c
3、haracteristics,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
4、 maintenance Low cost,LAN Extension,Network Topologies,A,C,E,A,E,B,D,B,D,F,A,E,B,D,A,E,B,D,C,E,B,D,F,A,A,B,C,C,C,C,Star Ring Dual Ring,Bus Tree Dual Bus,Network Topologies,A,B,C,A,B,C,D,A,C,E,B,D,F,Dual Bus Dual Bus Mesh,A,G,B,E,D,F,C,H,Snowflake,Network Topologies,A,E,B,D,C,F,J,G,I,H,K,O,L,N,M,橋接器,
5、橋接器,橋接器,Bridged Ring Networks,C,A,B,F,D,E,G,H,集線器 或 中樞器,.,Hub or Concentrator,8,Rules of Using Repeaters,Maximum 5 sections Maximum 4 repeatersMaximum 3 sections can have hostsWithin a whole collision domain Reason: Propagation round trip latency 51.2 ms,9,CSMA/CD,listen before talklisten while talk
6、ingwait before talk againBEBA Algorithm：n : (n 10r : (unit: slot time) 0 = r 2k random waiting factorSlot time = 51.2 ms.,Calculation of Slot time,元件,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
7、 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 m
8、s 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,元件穩定延遲,元件啟動延遲,前進路徑元件數,整體延遲,回程路徑元件數,訊號來回傳遞最長延遲 46.38 ms,IEEE Project 802 Standards,IEEE 802.1 High Level Interface IEEE 802.1D Local Bridge (Spanning Tree Algorithm) IEEE 802.1G Remote Bridge IEE
9、E 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),IEEE Project 802 Standards,IEEE 802.7 Broadband Technical Advisory Group IEEE 802.8 Fiber Optic Techni
10、cal 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,802.3,CSMA/CD,802.4,Token-Bus,802.5,Token-Ring,802.6,DQDB,802.9,Isochronous,802.11,Wireless,802.12,100VG- AnyLAN,Ethernet,LAN,AX3T9.5,FDDI,802.2 LLC,802.1 網路連結技術,Physical,MAC,LLC,IEEE Project 802 Standards,
