RFC 994 December 1986 Contents 1 Scope and Field of Application 6 2 References 7 SECTION ONE. GENERAL 9 3 Definitions 9 3.1 Reference Model Definitions . . . . . . . . . . . . . . . . . 9 3.2 Service Conventions Definitions . . . . . . . . . . . . . . . 9 3.3 Network Layer Architecture Definitions . . . . . . . . . . . . 9 3.4 Network Layer Addressing Definitions . . . . . . . . . . . . . 10 3.5 Additional Definitions . . . . . . . . . . . . . . . . . . . . 10 4 Symbols and Abbreviations 11 4.1 Data Units . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 Protocol Data Units . . . . . . . . . . . . . . . . . . . . . 11 4.3 Protocol Data Unit Fields . . . . . . . . . . . . . . . . . . 11 4.4 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.5 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Overview of the Protocol 12 5.1 Internal Organization of the Network Layer . . . . . . . . . . 12 5.2 Subsets of the Protocol . . . . . . . . . . . . . . . . . . . 12 5.3 Addresses and Titles . . . . . . . . . . . . . . . . . . . . . 13 5.3.1 Addresses . . . . . . . . . . . . . . . . . . . . . . 13 5.3.2 Network-entity Titles . . . . . . . . . . . . . . . . 13 5.4 Service Provided by the Network Layer . . . . . . . . . . . . 14 5.5 Underlying Service Assumed by the Protocol . . . . . . . . . . 14 5.5.1 Subnetwork Points of Attachment . . . . . . . . . . . 15 5.5.2 Subnetwork Quality of Service . . . . . . . . . . . . 15 5.5.3 Subnetwork User Data . . . . . . . . . . . . . . . . 16 5.5.4 Subnetwork Dependent Convergence Functions . . . . . . 16 5.6 Service Assumed from Local Environment . . . . . . . . . . . . 16 SECTION TWO. SPECIFICATION OF THE PROTOCOL 18 6 Protocol Functions 18 6.1 PDU Composition Function . . . . . . . . . . . . . . . . . . . 18 6.2 PDU Decomposition Function . . . . . . . . . . . . . . . . . . 19 6.3 Header Format Analysis Function . . . . . . . . . . . . . . . 19 ISO 8473