Network Hierarchy Concept: The OSI Reference Model

Application	Network service part of applications Provides network services to applications (e.g. protocols to applications such as snmp)
Presentation	Data presentation Presents data in the right format to the application layer (includes encryption, reformating, restructuring of data)
Session	Interapplication communication Maintains sessions between applications
Transport	End-to-end connection Ensures data transport reliability, information flow (includes maintaining of virtual circuits between hosts)
Network	Data delivery Provides routes between two host systems (might be at different locations) (includes network discovery and routing decision)
Data Link	Access to media Defines the data format and how the access to the media is controlled (includes bit-error correction)
Physical	Binary transmission on a physical link Electrical, mechanical, procedural, and functional specification