OSI Model - Open Systems Interconnecting Model

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Layer number layer name Protocol data unit (PDU) What runs ‘on it’ Function of layer
7 Application HTTP, SMTP, SMB High-level APIs, including resource sharing, remote file access
6 Presentation Data AVI, GIF ,JPEG, MKV Translation of data between a networking service and an application; including character encoding, data compression and encryption/decryption
5 Session Session management (sockets) Managing communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes
4 Transport Segment (TCP) / Datagram (UDP) Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing
3 Network Packet IP addresses, Routing Structuring and managing a multi-node network, including addressing, routing and traffic control
2 Data link Frame Switching, MAC addresses Reliable transmission of data frames between two nodes connected by a physical layer
1 Physical Bit Data cables, CAT5e, CAT6 Transmission and reception of raw bit streams over a physical medium

Protocol data unit

Stands for “Protocol Data Unit.” A PDU is a specific block of information transferred over a network. It is often used in reference to the OSI model, since it describes the different types of data that are transferred from each layer.