OSI Models (7 Layers)
Last updated
Last updated
The Open Systems Interconnection (OSI) model is a set of standards that defines how computers communicate over a network. In the OSI model, data flow gets broken down into seven layers that build upon each other.
The OSI model, created in 1984 by ISO, is a reference framework that explains the process of transmitting data between computers.
It is divided into seven layers that work together to carry out specialized network functions, allowing for a more systematic approach to networking.
Each layer uses data from the layer before it and serves a specific purpose in the broader network communication.
The lowest layer of the OSI reference model is the physical layer.
It is responsible for the actual physical connection between the devices.
The physical layer contains information in the form of bits.
It is responsible for transmitting individual bits from one node to the next.
Hub, Repeater, Modem, and Cables are Physical Layer devices.
It divides the data into number of frames.
It uses the MAC address for sending frames from one node to other.
It provides flow control, error control and access control.
It divides data into number of packets.
It uses IP address for routing packets to their destination.
It provides end to end connection.
It divides message into segments and also reassemble the segments to create original message.
It can be either connection-oriented or connectionless.
It uses service-point address or port address for process to process communication.
Flow control and error control also provided by transport layer.
Session Layer establishes, maintains and synchronizes the interaction among communicating systems.
The protocols of the Session layer try to recover any connection losses when they happen. It also optimizes connections:
If a connection is not used for a long period, Session-layer protocols may close it and reopen it later.
It is concerned with the syntax and semantics of the information exchanged between two systems.
It translates information from text/numeric into bit stream.
It also encrypts the information for security purpose and compress the information to reduce the number of bits in the information.
It provides the interface to the end user and supports for services such as Email, file transfer and distributed information service.
The OSI protocol stack is structured into seven conceptual layers. The layers form a hierarchy of functionality starting with the physical hardware components to the user interfaces at the software application level.
