OSI reference models

The OSI reference model and TCP/IP reference model are the two most important network architectures used in layered networks. The OSI model was developed by international standards organization. OSI stands for open systems interconnection. The OSI model has seven layers. They are physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The physical layer deals with the transmission of raw bits over a communication channel. The data link layer transforms raw transmission facility into a line that appears free of undetected transmission errors to the network layer. Operation of the subnet is controlled by the network layer. Transport layer accepts data and splits the data into smaller units. Session layer offers various services for users such as dialog control, token management, synchronization etc. The prime objective of presentation layer is to deal with syntax and semantics of the information transmitted. The application layer contains a variety of protocols that are commonly needed by users. One example is Hyper Text Transfer Protocol (HTTP) which is the basis of World Wide Web.