The Transport Layer 65 The Session Layer 74 The Presentation Layer 84 The Application Layer 95 Local Area Networks 109 Telephone Networks 121

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

5.1. Transport Services 65 5.1.1. Network Types 67 5.2. Transport Protocol 67 5.2.1. TPDUs 67 5.2.2. Classes of Protocol 68 5.2.3. Segmentation 69 5.2.4. Multiplexing 69 5.2.5. Splitting and Recombining 69 5.2.6. Addressing 69 5.2.7. Flow Control 70 5.2.8. Error Checking 70 5.3. Transport Layer Standards 70 5.3.1. TCP 71 5.4. Further Reading 72

6. The Session Layer 74

6.1. Session Services 74 6.1.1. Session Layer Role 77 6.1.2. Functional Units 77 6.2. Session Protocol 78 6.2.1. Tokens 79 6.2.2. Activities and Dialogue Units 79 6.2.3. Synchronization 80 6.2.4. Error Reporting and Resynchronization 81 6.2.5. SPDUs 82 6.3. Session Layer Standards 82 6.4. Further Reading 83

7. The Presentation Layer 84

7.1. Presentation Services 84 7.1.1. Syntax 84 7.1.2. Service Primitives 87 7.1.3. Functional Units 89 7.2. Abstract Syntax Notation One 89 www.pragsoft.com Contents ix 7.2.1. Definitions in ASN.1 89 7.2.2. Basic Encoding Rules 91 7.3. Presentation Protocol 93 7.4. Presentation Standards 94 7.5. Further Reading 94

8. The Application Layer 95

8.1. Application Services 95 8.1.1. Application Entity 96 8.2. Common Application Service Elements 97 8.2.1. Association Control 97 8.2.2. Reliable Transfer 97 8.2.3. Remote Operations 98 8.3. Specific Application Service Elements 98 8.3.1. Virtual Terminal 98 8.3.2. Message Handling Systems 100 8.3.3. File Transfer, Access, and Management 104 8.4. Other Standards 108 8.5. Further Reading 108

9. Local Area Networks 109

9.1. Basic Concepts 109 9.1.1. Topologies and Access Protocols 110 9.1.2. Architecture 112 9.1.3. Transmission 113 9.2. IEEE 802 Standards 113 9.2.1. Logical Link Control 114 9.2.2. CSMACD 115 9.2.3. Token Bus 116 9.2.4. Token Ring 117 9.3. ANSI FDDI Standard 118 9.3.1. Topology 118 9.3.2. Token Ring Protocol 119 9.4. Further Reading 120

10. Telephone Networks 121

10.1. Basic Concepts 121 10.1.1. A Simple Network 122 10.1.2. Networks Topologies 123 10.1.3. Switching Systems 125 10.2. Signaling 126 10.2.1. Subscriber Signaling 127 10.2.2. Interexchange Signaling 128 x Communication Networks Copyright © 2005 PragSoft 10.2.3. Common Channel Signaling 129 10.3. Signaling System Number 7 131 10.3.1. Signaling Data Link 132 10.3.2. Signaling Link Control 132 10.3.3. Signaling Network Functions 133 10.3.4. Signaling Connection Control Part 134 10.3.5. User Parts 135 10.3.6. Operations and Maintenance Applications Part 136 10.4. Private Telephone Networks 136 10.4.1. PBX Networks 136 10.4.2. Corporate Networks 137 10.4.3. Intelligent Networks 138 10.5. Further Reading 139

11. Integrated Services Digital Network 140