西安电子科技大学：《计算机通信与网络》课程教学课件（讲稿）第三部分 数据链路层 第10章 检错与纠错 Error Detection and Correction

Data Communications and Networking Forouzan Fourth Edition Chapter 10 Error Detection and Correction 检错与纠错 10.1

10.1 Chapter 10 Error Detection and Correction 检错与纠错

Note Data can be corrupted during transmission. Some applications require that errors be detected and corrected. 数据在出传输额过程中可能遭到破坏，一些 应用需要进行检错和纠错。 10.2

10.2 Data can be corrupted during transmission. Some applications require that errors be detected and corrected. 数据在出传输额过程中可能遭到破坏，一些 应用需要进行检错和纠错。 Note

10-1 INTRODUCTION Let us first discuss some issues related,directly or indirectly,to error detection and correction. 首先直接或间接地讨论有关差错检测和差错纠正的间题 Topics discussed in this section: Types of Errors 差错类型 Redundancy 冗余 Detection Versus Correction检错和纠错 Forward Error Correction Versus Retransmission前向纠错和重传 Coding 编码 Modular Arithmetic 模运算 10.3

10.3 10-1 INTRODUCTION Let us first discuss some issues related, directly or indirectly, to error detection and correction. 首先直接或间接地讨论有关差错检测和差错纠正的问题 Types of Errors 差错类型 Redundancy 冗余 Detection Versus Correction 检错和纠错 Forward Error Correction Versus Retransmission 前向纠错和重传 Coding 编码 Modular Arithmetic 模运算 Topics discussed in this section:

Note In a single-bit error,only 1 bit in the data unit has changed. 在单比特差错中，数据单位中仅有一比特发 生变化。 10.4

10.4 In a single-bit error, only 1 bit in the data unit has changed. 在单比特差错中，数据单位中仅有一比特发 生变化。 Note

Figure 10.1 Single-bit error 0 changed to 1 00000010→00001010 Sent Received 10.5

10.5 Figure 10.1 Single-bit error

Note A burst error means that 2 or more bits in the data unit have changed. 一个突发差错意味着数据单元中两位或多位 发生变化。 10.6

10.6 A burst error means that 2 or more bits in the data unit have changed. 一个突发差错意味着数据单元中两位或多位 发生变化。 Note

Figure 10.2 Burst error of length 8 Length of burst error(8 bits) Sent 0100010001000011 Corrupted bits 0101110101100011 Received 10.7

10.7 Figure 10.2 Burst error of length 8

Note To detect or correct errors,we need to send extra(redundant)bits with data. 为了检测或纠正错误，我们需要发送除了数 据外的额外（冗余）位。 10.8

10.8 To detect or correct errors, we need to send extra (redundant) bits with data. 为了检测或纠正错误，我们需要发送除了数 据外的额外（冗余）位。 Note

Figure 10.3 The structure ofencoder and decoder编码器和译码器的结构 Sender Receiver Encoder Decoder Message Message Correct or discard Generator Checker Unreliable transmission Message and redundancy Received information 10.9

10.9 Figure 10.3 The structure of encoder and decoder 编码器和译码器的结构

Note In this book,we concentrate on block codes;we leave convolution codes to advanced texts. 本课程，我们主要介绍块编码。 10.10

10.10 In this book, we concentrate on block codes; we leave convolution codes to advanced texts. 本课程，我们主要介绍块编码。 Note