OSI Model Summary

In summary, Table 4.1 lists the seven layers of the OSI model and describes some of the most significant points of each layer.

Table 4.1. OSI Model Summary

OSI Layer	Major Functions
Physical (Layer 1)	Defines thephysical structure of the network and the topology.
Data-link (Layer 2)	Provides error detection and correction. Uses two distinct sublayers: the Media Access Control (MAC) and Logical Link Control (LLC) layers. Identifies the method by which media is accessed. Defines hardware addressing through the MAC sublayer.
Network (Layer 3)	Handles the discovery of destination systems and addressing. Provides the mechanism by which data can be passed from one network system to another.
Transport (Layer 4)	Provides connection services between the sending and receiving devices and ensures reliable data delivery. Manages flow control through buffering or windowing. Provides segmentation, error checking, and service identification.
Session (Layer 5)	Synchronizes the data exchange between applications on separate devices.
Presentation (Layer 6)	Translates data from the format used by applications into one that can be transmitted across the network. Handles encryption and decryption of data. Provides compression and decompression functionality. Formats data from the application layer into a format that can be sent over the network.
Application (Layer 7)	Provides access to the network for applications.