The Open Systems Interconnection (OSI) is a model that was developed by the ISO (International Organization for Standards ) and it describes how information from a software application in one computer, moves through a network medium to a software application in another computer.
The Upper Layers : This deals with Application issues and generally are implemented only in software. The highest layer, application layer is closest to the end user. This layer is where communication from one end user to another begins through the interaction between the application layer processes and the end user.
The Lower layers : This handles Data transport issues. The physical layer and Data link layers are implemented in hardware and software.
Provides physical interface for transmission of information.
Defines rules by which bits are passed from one system to another on a physical communication medium.
Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.
A given layer within the OSI model communicates with three other layers:the layer directly above it, the layer directly below it and it’s peer layer in other networked computer system. In the diagram below, the data link layer in system A, communicates with the network layer and physical layer of system A. It also communicates with the data link layer of system B.