OSI - Ref: OSI by Uyless Black, Prentice-Hall, 1991
NOTE
- Layers 1-3 (physical, data-link, network) are chained, i.e., the protocols exist between a machine and its immediate neighbours. Whereas layers 4-7 (transport, session, presentation, application) are all end-to-end where (in principle) a program on source machine has a “conversation” with programs on a destination machine.
Session layer
- Allows users on different hosts to establish sessions between them, e.g., log into remote time sharing system or transfer a file between 2 machines
- Make sure order of hosts requesting operations are maintained. Only a host holding a token can perform an operation (token management)
- Checkpoint large file transfers so that if failure occurs the file transfer will not begin from scratch (synchronization)
Reference Models/OSI layers