Rs232 c is a popular physical layer standard for

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Unformatted text preview: ge of computers. The architecture of DECNET (Digital Equipment Corporation Network) is known as DNA (Digital Network Architecture). Like SNA, it is a private network architecture oriented only to DEC hardware. Other telecommunication protocols are BNA (Burroughs Network Architecture) by Burroughs Incorporation, DSN (Distributed Systems Network) by Hewlett Packard, PRIMENET (Prime Computers Network) by Prime Incorporation, etc. Thus the data communication protocols of one network were not compatible with any other network. Moreover, standards of the same network architecture also kept changing from time to time. For example, earlier versions of SNA were not compatible with its subsequent versions. Such incompatibilities started creating bottleneck in the efficient and proper utilization of network resources. This problem was recognized by the International Standards Organization (ISO), which established a subcommittee to develop an international standard on network architectures. The result was the Open System Interconnection (OSI) model, which is a framework for defining standards for linking heterogeneous computers in a packet switched network. Thus the standardized OSI protocols made it possible for any two heterogeneous computer systems, located anywhere in the world, to easily communicate with each other. The OSI model is also designed in a highly structured way. Its architecture is shown in Figure 17.24. It is a seven-layer architecture in which a separate set of protocols is defined for each layer. Thus each layer has an independent function and deals with one or more specific aspects of the communication. The roles of the seven layers are briefly described below. This description material has been reprinted, with permission, from the book titled Distributed Operating Systems: Concepts and Design by Pradeep K. Sinha. [© 1997 IEEE]. In actual implementation, of the seven layers, the first three layers are likely to be in hardware, the next two layers in the operating system, the presentation l...
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This document was uploaded on 04/07/2014.

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