Physical Layer - 1 Physical Layer  All rights reserved. No part of this publication and file may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of Professor Nen-Fu Huang (

Physical Layer - 2 Transmission Medium, Technologies, and Encoding Schemes  Transmission Medium Twisted Pair Coaxial Cable Fiber Optic Radio  Transmission Technologies Baseband Broadband

Physical Layer - 3 Encoding Schemes  Encoding Schemes RS-232C encoding Zero-Complemented Encoding Manchester Encoding Differential Manchester Encoding

Physical Layer - 4 Twisted Pair  Two insulated wires arranged in a spiral pattern  The wires are copper or steel coated with copper  A cable may have many pairs  Twisting minimizes electromagnetic interference between pairs  Noise Immunity: Good at low frequency  Least expensive  High data error rate : 1 x  Typical data rate: 10/100 Mbps (within 100m)

Physical Layer - 5 Twisted Pair

Physical Layer - 6 Coaxial Cable  Consist of two conductors, operate over a wider range of frequency  50 Ohm cable: Baseband digital signaling Manchester Encoding, 12 Mbps, a few Kilometers Support on the order of 100 devices per segment Less signal loss in the insertion of the Taps  75 Ohm cable: Community Antenna Television (CATV) Broadband Analog signaling with FDM u MHz u In CATV, each channel has 6 MHz bandwidth

Physical Layer - 7 Coaxial Cable Single-Channel Broadband for High Speed Analog or Digital Signaling (No FDM) u Digital Signaling : Up to 50 Mbps u Analog Signaling (PSK): Up to 50 Mbps Support thousands of devices depending on data rates Tens of Kilometers depending on data rates  Moderate cost, components readily available

Physical Layer - 8 Coaxial Cable 中心導體 絕緣層 外層網狀導體 保護外皮 中心導體 (Conducting Core) 絕緣層 (Insulation) 外層網狀導體 (Conducting Mesh or Sleeve) 保護外皮 (Protective Jacket)

Physical Layer - 9 Fiber Optic  Use optical signals instead of electrical signals  Light sources : LED ( 發光二極體） Laser Diode  Optical Fibers Single Mode Stepped Index Graded Index  Detector: Photoelectric Diodes 光纖 外圍材料 保護外皮

Physical Layer - 10 Fiber Optics Characteristics  Dielectricity (free from interference)  Low Attenuation over distance  Small size, light weight  Good bandwidth (Up to 3.3 GHz)  Support long distance  Bendable (Minimum bend radius 200mm - 5 mm)  Relative Expensive

Physical Layer - 11 強化彎曲物 密集裝捆之光纖 管狀包裝層 保護層

Physical Layer - 12 A B C C A B 可接受入射角度 

Physical Layer - 13 Optical Transmission System 傳送器 接收器 驅動器 光源 光偵 測器 接收器 （電子） 光纖纜線 光纖 光訊號連接器 數位訊號 類比或 輸入 數位訊號 類比或 輸出 電子訊號連接器 （電子）

Physical Layer - 14 Transmission Techniques  Baseband : Digital Signaling  Broadband: Analog Signaling

Physical Layer - 15 Baseband  Signals sent at their original form  In LAN, baseband usually refers to digital signaling  In baseband coaxial cable (50 OHM) 500 meters 50-OHM Terminators at both end Distance between two Taps - multiples of 2.5 m to ensure no reflection from adjacent Tap At most 100 Taps

Physical Layer - 16 Baseband A D B C E 同軸電纜 收發器電纜 終端器 連接拴 同軸電纜區段（最長 500 公尺） （每區段最多接 100 個） （最長 50 公尺） 工作站

Physical Layer - 17 Broadband  Signals are modulated before transmission and demodulated after receiving, 75-OHM coaxial cable  Need modem : Modulation/Demodulation  Unidirectional transmission  Multiple/Single channel broadband  Cover a larger distance  Cascaded amplifiers can result in loss of data integrity at high data rates  System Configuration Single-cable system Dual cable system

Physical Layer - 18 Broadband 低速數據通道 交換聲音 / 數據通道 高速數據通道 視訊通道 保留 10MHz 25MHz 55MHz 75MHz 175MHz 210MHz 240MHz 310MHz 寬頻 同軸電纜 300MHz

Physical Layer - 19 Single Cable System  Headend (Central Retransmission Facility) Consist of amplifiers, filters, and signal modulators

Physical Layer - 20 工作站 數據機 傳送頻道 MHz 接收頻道 MHz 頻率轉換設備 MHz MHz 緩衝頻帶

Physical Layer - 21 Dual Cable System  Entire bandwidth is available for transmission in both directions  A passive connector is used to connect two cables  Higher cost for cable and taps

Physical Layer - 22 工作站 300 MHz 數據機 300 MHz 傳送 接收

Physical Layer - 23 Comparison of Baseband and Broadband Technologies 基頻技術 寬頻技術 較便宜（不須數據機） 資料容量大 網路架構較簡單 網路架構較有彈性 安裝容易 可傳送多種型態資料 傳送距離較長 較成熟的 CATV 技術 傳送單一型態資料 需要數據機 資料容量較小 安裝維護較複雜 傳送距離較短 二倍傳遞延遲時間 （二倍長的電纜線） 優點 缺點

Physical Layer - 24 Encoding Schemes V 0 V 位元時間 V - V Start BitData bits Stop Bit RS-232C Zero Complemented

Physical Layer - 25 Encoding Schemes V - V 位元時間 V - V 位元時間 Manchester Differential Manchester V - V 取樣時間 Sampling at Receiver side

Physical Layer - 26 Access Control Methods  Network Topologies Star Topology Bus/Tree Topology Ring Topology Mesh Topology  Transmission Control Random Transmission Control Distributed Transmission Control Centralized Control

Physical Layer - 27 Transmission Control  Random Transmission Control ALOHA Network, Slotted Aloha, Wireless LAN Carrier Sense multiple access with collision detection (CSMA/CD) Slotted Ring Register Insertion Ring

Physical Layer - 28 Transmission Control  Distributed Transmission Control Token Passing : Token-Ring (FDDI), Token-Bus (GM, MAP) Carrier Sense multiple access with collision avoidance (CSMA/CA) Distributed Queue Dual Bus (DQDB)

Physical Layer - 29 Transmission Control  Centralized Control Polling Circuit Switching (X.25, Frame-Relay, ATM network) Time-division Multiple Access (TDMA) Frequency-division Multiple Access (FDMA) Wavelength-division Multiple Access (WDMA) Code-division Multiple Access (CDMA)