Chap 9: Using Telephone and Cable Networks for Data Transmission

Chap 9-1 Telephone Network

Point of oresences(POPs)

Note: The tasks of data transfer and signaling are seperated in modrn telephone networks: data transfer is done by one network,signaling is by another.

Chap 9-2 Dial-Up Models

*　Ｍodem stands for modulator/demodulator

Chap 9-3 Digital Subscribe Line

Note: ADSL is an asymmetric communication technology designed for residential users; it is not suitable for business.

NOte: ADSL is an adaptive tecknology. The system uses a data rate based on the condition of the local loop line.

ADSL Bandwidth对照频段功能ADSL modemDSLAM

Chap 9-4 Cable TV Networks

Note: Communication in the "traditional cable" TV network can be budirectional.

Note: Communication in an "HFC cable" TV network can be budirectional.

Chap 9-5 Cable TV for Data Transfer

Chap 10: Error Detection and Correction

Note: Data can be corrupted durong transmission. Some applications require that errors be detected and corrected.

Chap 10-1 Introduction

Error

Single bit error(整个讯息错一个以上)Burst error(整个讯息错两个以上)

Note: In a single-bit error, only 1 bit in the data unit has changed.

Note: A burst error means that 2 or more bits int the data unit have changed.

Redundancy

用于作为检查码(detect and correct errors)

To detect or correct eooros, we need to send extra(redundant) bits with data.

Detection

Only给予有错或没错的回覆

Crrection

要给出错在哪里，并且更正错误

Forward error corrction => 继续传送，并且检查错哪里Retransmission => 直接重传，花频宽The structure of encoder and decoder

Note: In this book, we concentrate on(专注于) "block codes"; we leave convolution codes to advanced texts.

In modulo-N arithmetic, we use only the intergers in the range 0 to (N-1), inclusive.

Chap 10-2 Block Coding

先把资料切为blocks，并放入一些bits为datawords，放入k bits，并再放入r bits for redundant bits，最为codewords

Note: An error-detecting code can detect only the types of errors for which it is designed; other types of errors may remain undetected.

Note: The Hamming destance between two words is the number of differences between corresponding bits.

The minimum Hamming distance is the smallest Hamming distance between all poossible pairs in a set of words.

Note: To guarantee the detection of up to s errors in all cases, the minimum Hamming distance in a block code must be d_min = s + 1

The guarantee correction of up to t errors in all cases, the minimum Hamming distance in a block code must be d_min = 2t + 1

Chap 10-3 Linear Block Codes

note: In a linear block code, the exclusive OR(XOR) of any two valid codewords creaes another valid codeword.

Note: A simple parity-check code is a single-bit error-detecting code in which n = k+1 with d_min = 2

2 dimensional parity-check code

Note: All Hamming codes discussed in this book have d_min = 3. The relationship between m data and n in these codes is n = 2m -1.

Chap 10-4 Cyclic Codes

Hardwared design

Chap 10-5 Checksum