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A computer network consists of nodes and communication links which implement its protocols. It interconnects a set of hosts which conform to the network protocols.
A network may be classified as a LAN, MAN, or WAN, depending on its geographic spread, and as private or public, depending on its access restrictions. It may employ a point-to-point or a broadcast communication
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model. A point-to-point model may be based on circuit switching or packet
The OSI model proposes a seven-layer architecture for networks. Each layer is characterized by a set of protocols. The network nodes implement only the bottom three layers, while the hosts implement all the layers.
The physical layer controls the transmission of raw data bits over communication lines. The data link layer facilitates the reliable transfer of data over communication channels. The network layer controls the end-to-end routing of data across the network. The transport layer manages the efficient and cost-effective transportation of data across the network. The session layer manages the negotiation of the establishment and termination of connections (sessions). The presentation layer provides a mutually-agreeable binary representation of application data (syntax). The application layer provides a mutually-agreeable meaning of application data (semantics).
A service primitive is an abstract representation of the interaction between a service provider and a service user, and may be of one of four types: request, indication, response, and confirmation.
A sequence diagram defines a service protocol by specifying the permissible sequence of service primitives that may be exchanged between service users and service providers.
A state transition diagram describes the various execution states a station can assume and how service primitives cause it to transit from one state to another.
Communication standards are essential in order to achieve interoperability between different equipment and networks.