OSI model

OSI model: The Open Systems Interconnection model (OSI model) was a product of the open system effort at the International Organization for Standardization.

Open system interconnection is divided into 7 layers.

1.      Physical Layer: The Physical Layer defines electrical and physical specifications for devices. In particular, it defines the relationship between a device and a transmission medium, such as a copper or optical cable. This layer specifies what will be the system speed, modem speed and what will be the voltage level.

2.      Data Link Layer: The Data Link Layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical Layer.

3.      Network Layer: The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source host on one network to a destination host on a different network.

4.      Transport Layer: The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. 

5.      Session Layer: The Session Layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes check pointing, adjournment, termination, and restart procedures.

6.      Presentation Layer: The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them.

7.      Application Layer: The Application Layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application.