OSI Model
OSI (Open Systems Interconnection) is reference model for how messages should be transmitted between any two points in a telecommunication network. A reference model is a framework for understanding relationships. The purpose of the OSI reference model is to guide vendors and developers so that the digital communication products and software programs they create will interoperate. The OSI reference model defines seven layers of functions that take place at each end of a communication.
Layers of OSI:-
Layer 7:-The application layer - This is the layer at which communication partners are identified, quality of service (QoS) is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.)
Layer 6:-The presentation layer - This is a layer, usually part of an operating system (OS), that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly- arrived text).
Layer 5:-
The session layer - This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.
Layer 4:-The transport layer - This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.
Layer 3:-The network layer - This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding.
Layer 2:-The data-link layer - This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management. This layer has two sub layers, the Logical Link Control Layer and the Media Access Control Layer.
Layer 1:-The physical layer - This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier network.