Introduction 1 The Physical Layer 18 The Data Link Layer 36 The Network Layer 52

vi Communication Networks Copyright © 2005 PragSoft Contents Contents 6 Preface 10

1. Introduction 1

1.1. Network Components 2 1.2. Network Types 2 1.3. The OSI Model 4 1.3.1. The Physical Layer 7 1.3.2. The Data Link Layer 7 1.3.3. The Network Layer 8 1.3.4. The Transport Layer 9 1.3.5. The Session Layer 9 1.3.6. The Presentation Layer 10 1.3.7. The Application Layer 10 1.4. Protocol Notations 11 1.4.1. Service Primitives 11 1.4.2. Sequence Diagrams 12 1.4.3. State Transition Diagrams 12 1.5. Standards 13 1.6. Further Reading 14 1.7. Summary 15 1.8. Exercises 16

2. The Physical Layer 18

2.1. Equipment 19 2.1.1. Equipment Types 19 2.1.2. Connection Types 19 2.2. Transmission 20 2.2.1. Signal Types 20 2.2.2. Modulation 21 2.2.3. Digitization 22 2.2.4. Synchronization 23 2.2.5. Transmission Media 24 2.3. Multiplexing 27 2.3.1. Space Division Multiplexing SDM 28 www.pragsoft.com Contents vii 2.3.2. Frequency Division Multiplexing FDM 28 2.3.3. Time Division Multiplexing TDM 29 2.3.4. Concentration 29 2.4. Physical Layer Standards 30 2.4.1. RS-232 30 2.4.2. CCITT X.21 32 2.5. Further Reading 33 2.6. Summary 33 2.7. Exercises 34

3. The Data Link Layer 36

3.1 Link Protocol Types 37 3.1.1. Synchronous Protocols 37 3.1.2. Asynchronous Protocols 38 3.1.3. Master-Slave Protocols 38 3.1.4. Peer-to-Peer Protocols 38 3.2. Link Protocol Functions 38 3.2.1. Acknowledgments 39 3.2.2. Timers 39 3.2.3. Error Checking 40 3.2.4. Retransmission 42 3.2.5. Flow Control 42 3.3. Sliding Window Protocol 43 3.4. Data Link Layer Standards 45 3.4.1. BSC 45 3.4.2. HDLC 46 3.5. Further Reading 48 3.6. Summary 49 3.7. Exercises 50

4. The Network Layer 52

4.1. Network Services 53 4.2. Switching Methods 55 4.2.1. Circuit Switching 55 4.2.2. Packet Switching 57 4.3. Packet Handling 59 4.3.1. Packet Structure 60 4.3.2. Routing 60 4.3.3. Congestion Control 63 4.3.4. Error Handling 63 4.4. Internetworking 64 4.4.1. Network Sublayers 65 viii Communication Networks Copyright © 2005 PragSoft 4.5. Network Layer Standards 66 4.5.1. CCITT X.25 66 4.5.2. CCITT X.75 69 4.5.3. IP 70 4.5.4. ISO 8473 71 4.6. Further Reading 72 4.7. Summary 72

5. The Transport Layer 65