vi Contents 1.3.6 The Presentation Layer,25 1.3.7 The Application Layer,26 1.4 A Simple Distributed Algorithm Problem,26 1.5 Notes and Suggested Reading,29 Chapter 2 DATA LINK CONTROL AND COMMUNICATION CHANNELS 31 2.1 Overview,31 2.2 The Physical Layer:Channels and Modems,34 2.2.1 Filtering,35 2.2.2 Frequency Response,37 2.2.3 The Sampling Theorem,40 2.2.4 Bandpass Channels,42 2.2.5 Modulation,43 2.2.6 Frequency-and Time-Division Multiplexing,47 2.2.7 Other Channel Impairments,48 2.2.8 Digital Channels,48 2.2.9 Propagation Media for Physical Channels,49 2.3 Error Detection,50 2.3.1 Single Parity Checks,50 2.3.2 Horizontal and Vertical Parity Checks,51 2.3.3 Parity Check Codes,52 2.3.4 Cyclic Redundancy Checks,54 2.4 ARQ-Retransmission Strategies,58 2.4.1 Stop-and-Wait ARQ,59 2.4.2 ARPANET ARQ,62 2.4.3 Go Back n ARQ,63 Rules Followed by Sending DLC,66 Rules Followed by Receiving DLC,67 Go Back n with Modulus m n,68 Efficiency of Go Back n Implementations,70 2.4.4 Selective Repeat ARQ,71Contents 1.3.6 The Presentation Layer, 25 1.3.7 The Application Layer, 26 1.4 A Simple Distributed Algorithm Problem, 26 1.5 Notes and Suggested Reading, 29 Chapter 2 DATA LINK CONTROL AND COMMUNICATION CHANNELS 31 2.1 Overview, 31 2.2 The Physical Layer: Channels and Modems, 34 2.2.1 Filtering, 35 2.2.2 Frequency Response, 37 2.2.3 The Sampling Theorem, 40 2.2.4 Bandpass Channels, 42 2.2.5 Modulation, 43 2.2.6 Frequency- and Time-Division Multiplexing, 47 2.2.7 Other Channel Impairments, 48 2.2.8 Digital Channels, 48 2.2.9 Propagation Media for Physical Channels, 49 2.3 Error Detection, 50 2.3.1 Single Parity Checks, 50 2.3.2 Horizontal and Vertical Parity Checks, 51 2.3.3 Parity Check Codes, 52 2.3.4 Cyclic Redundancy Checks, 54 2.4 ARQ-Retransmission Strategies, 58 2.4.1 Stop-and-Wait ARQ, 59 2.4.2 ARPANET ARQ, 62 2.4.3 Go Back n ARQ, 63 Rules Followed by Sending DLC, 66 Rules Followed by Receiving DLC, 67 Go Back n with Modulus m > n, 68 Efficiency of Go Back n Implementations, 70 2.4.4 Selective Repeat ARQ, 71