OSI Model

Open System Interconnection is a standard that describes how message  is transmitted and received between two points in telecommunication.It is developed by ISO( International Organization for Standardization ). It is a seven layer model and are labeled 1 to 7 with layer 1 at bottom(as per X.200 Recommendations).This concept of a seven-layer model was provided by the work of Charles Bachman, Honeywell Information Services.Idea behind this model was that the telecommunication between two points can be divided into layers with each layer adding its own set of special, related functions. The seven Layers are: 1)Physical Layer 2)Data Link Layer 3)Network Layer 4)Transport Layer 5)Session Layer 6)Presentation Layer 7)Application Layer. these seven layers are divided into two groups. The upper four layers are used whenever a message passes from or to a user(known as Host Layers). The lower three layers (up to the network layer) are used when any message passes through the host computer(known as Media Layers) . Messages intended for this computer pass