Physical

This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.

Data-Link

Data packets are encoded and decoded into electrical signals at this layer. It furnishes transmission protocol knowledge and management.

Network

This layer creates the logical paths, known as virtual circuits, for transmitting data from node to node. Routing and Forwarding are  functions of this layer.

Transport

This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.

Session

This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.

Presentation

This layer formats and encrypts data to be sent across a network. ). Sometimes called the syntax layer.

Application

This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Application services are provided by this layer for file transfers, email, and other network software services.