Computer OSI several layers model

The year 1980s the Europeans-dominated International Standards Organization(ISO) networking suite. OSI has two majors components an abstract model of networking and a set of concrete protocols.
Parts of OSI has influenced Internet protocols development, but none more than the abstract model itself, documented in OSI 7498 and its various addenda. In the model, a networking system is divided into layers. Inside each layer, one or more entities implement its functionality. Each entity interacts directly only with the layer immediately beneath it, and provides facilities for us by the layer above it. Protocols enable and entity in one host to interact with a corresponding entity at the same layer in a remote host.

The seven layers of OSI Basic reference Model:
1) The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. It defines the size of the Ethernet coaxial cable, the type of BCN connector used, and the termination method.
2) Data Link Layer describes the logical organization of data bits transmitted on a particular medium. It defines the framing, addressing and check summing of Ethernet packets.
3) Network layer describes how a series of exchanges over various data links can deliver data between any two nodes in network. It defines the addressing and routing structure of internet.
4) Transport Layer describes the quality and nature of the data delivery. It defines if and how retransmissions will be used to ensure data delivery.
5) Session Layer describes the organization of data sequences layer than the packets handled by lower layers. It describes how request and reply packets are paired in remote procedure call.
6) Presentation Layer describes the syntax of data being transferred. It describes how floating point numbers can be exchanged between hosts with different math formats.
7) Application Layer describes how real work actually gets done. It implements file system operations.

The original Internet protocol specification defined a four-level model,and protocols designed around it(like TCP) have difficult fitting neatly into the seven-layers model. Most newly designed use the seven-layer.

OSI Basis Reference Model has enjoyed a far greater acceptance than the OSI protocols themselves. There are several reasons for this. OSI's committee-based design process bred overgrown, unimaginative protocols that nobody ever accused of efficiency.