Introduction - 1 Introduction to Local Area Networks (LANs)  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 (

Introduction - 2 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 Independent Devices Communicate Directly Moderately Sized Geographic Area Moderate Data Rate

Introduction - 3 Basic Requirements of a LAN  Data rate of 1 to 1000 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

Introduction - 4 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

Introduction - 5 LAN Components  Computers (Networking devices)  Transmission System (Network Cards, Cabling) 傳輸媒介 : 同軸電纜, 雙絞線, 光纖, 無線電波等等 工作站

Introduction - 6 LAN Extension LAN Segment 1 LAN Segment 2 Repeater

Introduction - 7 Network Topologies  Star Single Star (IEEE VG-AnyLAN, ATM) Multiple Star (Snowflake) (ATM)  Bus/Tree Single Bus (IEEE CSMA/CD, IEEE Token-Bus) Dual Bus (IEEE DQDB)  Ring Single Ring (IEEE Token Ring) Dual Ring (FDDI, FDDI-II)  Mesh

Introduction - 8 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

Introduction - 9 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

Introduction - 10 Network Topologies A E B D C F J G I H K O L N M 橋接器 Bridged Ring Networks C A B F D E G H... Hub or Switch

Introduction - 11 Open System Interconnection (OSI) Model-- Seven Layers 應用層 (Application Layer) 表達層 (Presentation Layer) 會議層 (Session Layer) 傳輸層 (Transport Layer) 網路層 (Network Layer) 鏈結層 (Data Link Layer) 實體層 (Physical Layer)

Introduction - 12 Open System Interconnection (OSI) Model  Physical Layer. Responsible for transmission of bit streams across a particular physical transmission medium. Retransmission is not supported.  Encoding/Decoding  Data Link Layer. Responsible for providing reliable data transmission from one node to another. Provides error-free transmission of frames.

Introduction - 13 Local Network G H WAN Local Network Local Network Local Network G G G G G H H H H H H H H H Transport Layer and up Layers (TCP/Telnet/FTP/Http) Routing (Layer 3) Layer 2

Introduction - 14 Open System Interconnection (OSI) Model  Network Layer. Concerned with routing data from one network node to another. Provides routing path selection. Establishing/maintaining/Terminating network connection  Transport Layer. Responsible for providing data transfer between two end users at an agreed on level of quality. Establishing/maintaining/Terminating transport layer connection

Introduction - 15 Open System Interconnection (OSI) Model  Session Layer. Providing services used to organize and synchronize the dialog that takes place between users and to manage the data exchange.  Presentation Layer. Responsible for the presentation of information to the network users. Character code translation/ Data conversion Data compression/expansion Encryption/Decryption

Introduction - 16 Open System Interconnection (OSI) Model  Application Layer. Provides services to application processes or users. File Transfer Protocol (FTP) Remote Login (Telnet) Transaction Server Network Management WWW Server/VoD Server Browser (HTTP) Internet Telephony/Video Streaming/IPTV

Introduction - 17 Layering Concept  Service Access Point (SAP)  Layer N provides services for layer N+1 by using the services provided by layer N-1.

Introduction - 18 Layering Concept 第 N-1 層 第 N 層 服務點 第 N+1 層 通訊軟體 第 N-1 層 第 N 層 第 N+1 層 通訊軟體 通訊協定 系統 A 系統 B

Introduction - 19 Layering Protocols 應用層 表達層 會議層 傳輸層 網路層 鏈結層 實體層 應用層 表達層 會議層 傳輸層 網路層 鏈結層 實體層 應用軟體 X 鏈結層通訊協定 傳輸媒介 應用軟體 Y 網路層通訊協定 傳輸層通訊協定 會議層通訊協定 表達層通訊協定 應用層通訊協定 實體層通訊協定 系統 A 系統 B

Introduction - 20 Basic Functions of Protocols  Encapsulation/Decapsulation  Segmentation/Reassembly  Connection Establishing  Flow Control  Error Control  Multiplexing

Introduction - 21 Encapsulation/Decapsulation Mechanisms 應用層 表達層 會議層 傳輸層 網路層 鏈結層 實體層 應用層 表達層 會議層 傳輸層 網路層 鏈結層 實體層 應用軟體 X AH PH SH TH NH 資料 F A CFCS F 位元串 通訊路徑 應用軟體 Y 往下送時訊框包裝 往上送時訊框拆裝 IP TCP/UDP FTP/HTTP/ Telnet/DNS FTP/HTTP/ Telnet/DNS TCP/UDP IP CSMA/CD 資料

Introduction - 22 Preamble/SFD DA SA LEN IP TCP FTP Data FCS < bytes version IHL Type of Service Total length Indentification Flags Fragment Offset Time to Protocol Header Checksum Source IP Address Destination IP Address Options + Padding Data

Introduction - 23 Connections Multiplexing  Upward Multiplexing: Several layer N connections should be multiplexed into a layer N-1 connection.  Downward Multiplexing: a layer N connection uses several layer N-1 connections.

Introduction - 24 Connections Multiplexing 第 N-1 層 第 N 層 服務點 一對一 向上多工 向下多工 通訊軟體

Introduction - 25 IEEE Project 802 Standards  IEEE High Level Interface IEEE 802.1D Local Bridge (Spanning Tree Algorithm) IEEE 802.1w Fast Spanning Tree Algorithm IEEE 802.1p Dynamic Multicast membership IEEE 802.1Q Virtual LAN (VLAN)  IEEE LLC (Logical Link Control)  IEEE CSMA/CD (Carrier Sense Multiple Access with Collision Detection  IEEE Token-Bus  IEEE Token-Ring  IEEE DQDB (Distributed Queue Dual Bus)

Introduction - 26 IEEE Project 802 Standards  IEEE Broadband Technical Advisory Group  IEEE Fiber Optic Technical Advisory Group  IEEE Integrated Voice and Data LAN Working Group  IEEE LAN Security Working Group  IEEE Wireless LAN  IEEE Demand-Priority (100VG-AnyLAN)  IEEE CATV Networks (HFC)  IEEE WiMAX  IEEE Resilient Packet Ring Working Group  IEEE , the Radio Regulatory Technical Advisory Group  IEEE Media Independent Handover (MIH).

Introduction CSMA/CD Token-Bus Token-Ring DQDB Isochronous Wireless VG- AnyLAN Ethernet LAN AX3T9.5 FDDI LLC 網路連結技術 實體層 媒介擷取層 鏈結層 IEEE Project 802 Standards