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The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes the communication functions of computing systems.

Layer Name Data Unit
7 Application Data
6 Presentation Data
5 Session Data
4 Transport Segment
3 Network Packet
2 Data link Frame
1 Physical Bit

Application Layer

High-level APIs, including resource sharing, remote file access


Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption


Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes.

Transport Layer

Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing

Network Layer

Structuring and managing a multi-node network, including addressing, routing and traffic control

Reliable transmission of data frames between two nodes connected by a physical layer

Physical Layer

Transmission and reception of raw bit streams over a physical medium