OSI REFERENCE MODEL
The International Organization introduced the OSI layer for Standardization (ISO) in 1984 in order to provide a reference model to make sure products of different vendors would interoperate in networks. OSI is short for Open System Interconnection. The OSI layer shows WHAT needs to be done to send data from an application on one computer, trough a network, to an application on another computer, not HOW it should be done. A layer in the OSI model communicates with three other layers: the layer above it, the layer below it, and the same layer at its communication partner. Data transmitted between software programs passes all 7 OSI layers. The Application, Presentation and Session layers are also known as the Upper Layers. The Data Link and Physical layers are often implemented together to define LAN and WAN specifications. Application Layer (Layer 7) Application Layer provides network services directly to applications. Type of software programs vary a lot: fr...