The OSI (open systems interconnection) Model
Many computer devices are now designed for use in networked systems. Manufacturers are tending to conform to standard protocols that make their equipment compatible with a variety of user networks. Closed networks, that are restricted to one manufacturer, are not attractive to the user, because they are restrictive.
The aim of standardisation is to achieve more open systems, which allow the users to select from a wider range of manufacturers' products. A reference model for open systems interconnection (OSI) has been under development by the International Standards Organisation (ISO) since 1977.
The OSI reference model for communications protocol identifies a hierarchy of seven layers. The layers are briefly described below:
Application layer. This is the highest layer in that it is closest to the user. It supports the transfer of information between end-users, applications programs and devices. Several types of protocol exist in this layer, including those for specific applications and those for more generalised applications, such as accounting, entry control and user identification. The applications layer hides the physical network from the user, presenting a user-orientated view instead.
Presentation layer. This layer covers the standards on how data is presented to the end-user devices. The aim is to ensure that different devices, which may be using data in different formats, can communicate with one another.
Session layer. The session layer is concerned with the exchange of information between different applications and users. It is the users interface into the network.
Transport layer. The data transmission system on any network will have its own peculiarities and the function of the transport layer is to mask out any undesirable features which may prevent high quality transmission for the network.
Network layer. The function of the network layer is to perform the routing of information around the network and also to connect one network to another. The software can also carry out accounting functions to enable the network owner to charge users.
Data Link layer. The physical data transmission media used in a network are subject to interference, which can corrupt data and other signals. The data link layer handles data transmission errors, which improves the quality of the network.
Physical layer. The physical layer provides the means to connect the physical medium and is concerned with the transmission of binary data within the communication channel. Standards are set regarding the mechanical, electrical and procedural aspects of the interface devices.
Btec First Diploma
Networking
D Stainton