Each layer provides services to the higher levels.
Each layer behaves as a black box.
Layer n on one machine talks to layer n on another machines.
The corresponding layer in the layered structure are called peers .
The communication between peers must follow certain rules, known as protocol .
No data are directly transferred between layers. Actual communication is through a physical medium below layer 1.
An Analogy Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Dutch I like rabbits Message Information for the remote translator Information for the remote secretary Ik vind konijnen leuk L: Ducth Fax:# Ik vind konijnen leuk L: Ducth J’aime bien les lapins Urdu & English Chinese & French Professor B Translator Secretary use fax use Dutch Secretary Translator Professor A
Open Systems Interconnection (OSI) Reference Model Application Presentation Session Transport Network Data Link Physical
Provides user interface
Transfer data into standard format before transmission
Keeps data different applications’ data separate
Control the data exchange
End-to-end data error free data transmission
Logical addressing for data packets Routing and error handling