Operating principle of the OSI reference model

The layers of the OSI reference model are moved through sequentially and thereby divide the communications process into structured elements. During a transmission the layers are moved through from top to bottom and when receiving in the opposite order. The actual communication is found only on Level 1. Nevertheless the individual layers can use their own protocol.

The layers assume the following tasks:

Layer	Task
Application	Communication flow of the application
Presentation	System independent data representation
Session	Maintains connection over longer time periods
Transport	Provides secure connection between processes
Network	End-to-end connection between computers
Data link	Data transmission between neighbouring stations
Physical	Hardware means of transmitting signals