Open Systems Interconnection (OSI) Reference Model

A joint ISO/ITU T standard [I7498 1] for a seven layer, architectural communication framework for interconnection of computers in networks. (See: OSIRM Security Architecture. Compare: Internet Protocol Suite.) Tutorial: OSIRM based standards include communication protocols that are mostly incompatible with the IPS, but also include security models, such as X.509, that are used in the Internet. The OSIRM layers, from highest to lowest, are (7) Application, (6) Presentation, (5) Session, (4) Transport, (3) Network, (2) Data Link, and (1) Physical. Usage: This Glossary refers to OSIRM layers by number to avoid confusing them with IPS layers, which are referred to by name. Some unknown person described how the OSIRM layers correspond to the seven deadly sins: 7. Wrath: Application is always angry with the mess it sees below itself. (Hey! Who is it to be pointing fingers?) 6. Sloth: Presentation is too lazy to do anything productive by itself. 5. Lust: Session is always craving and demanding what truly belongs to Application's functionality. 4. Avarice: Transport wants all of the end to end functionality. (Of course, it deserves it, but life isn't fair.) 3. Gluttony: (Connection Oriented) Network is overweight and overbearing after trying too often to eat Transport's lunch. 2. Envy: Poor Data Link is always starved for attention. (With Asynchronous Transfer Mode, maybe now it is feeling less neglected.) 1. Pride: Physical has managed to avoid much of the controversy, and nearly all of the embarrassment, suffered by the others. John G. Fletcher described how the OSIRM layers correspond to Snow White's dwarf friends: 7. Doc: Application acts as if it is in charge, but sometimes muddles its syntax. 6. Sleepy: Presentation is indolent, being guilty of the sin of Sloth. 5. Dopey: Session is confused because its charter is not very clear. 4. Grumpy: Transport is irritated because Network has encroached on Transport's turf. 3. Happy: Network smiles for the same reason that Transport is irritated. 2. Sneezy: Data Link makes loud noises in the hope of attracting attention. 1. Bashful: Physical quietly does its work, unnoticed by the others.