Ch12_ECOA2e - Chapter 12 Network Organization and...

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Chapter 12 Network Organization and Architecture
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2 Chapter 12Objectives Become familiar with the fundamentals of network architectures. Learn the basic components of a local area network. Become familiar with the general architecture of the Internet.
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3 12.1 Introduction The network is a crucial component of today’s computing systems. Resource sharing across networks has taken the form of multitier architectures having numerous disparate servers, sometimes far removed from the users of the system. If you think of a computing system as collection of workstations and servers, then surely the network is the system bus of this configuration.
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4 12.2 Early Business Computer Networks The first computer networks consisted of a mainframe host that was connected to one or more front end processors. Front end processors received input over dedicated lines from remote communications controllers connected to several dumb terminals. The protocols employed by this configuration were proprietary to each vendor’s system. One of these, IBM’s SNA became the model for an international communications standard, the ISO/OSI Reference Model.
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5 12.3 Early Academic and Scientific Networks In the 1960s, the Advanced Research Projects Agency funded research under the auspices of the U.S. Department of Defense. Computers at that time were few and costly. In 1968, the Defense Department funded an interconnecting network to make the most of these precious resources. The network, DARPANet, designed by Bolt, Beranek, and Newman, had sufficient redundancy to withstand the loss of a good portion of the network. DARPANet, later turned over to the public domain, eventually evolved to become today’s Internet.
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6 12.4 Network Protocols I ISO/OSI Reference Model To address the growing tangle of incompatible proprietary network protocols, in 1984 the ISO formed a committee to devise a unified protocol standard. The result of this effort is the ISO Open Systems Interconnect Reference Model (ISO/OSI RM). The ISO’s work is called a reference model because virtually no commercial system uses all of the features precisely as specified in the model. The ISO/OSI model does, however, lend itself to understanding the concept of a unified communications architecture.
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7 The OSI RM contains seven protocol layers, starting with physical media interconnections at Layer 1, through applications at Layer 7. 12.4 Network Protocols I ISO/OSI Reference Model
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8 OSI model defines only the functions of each of the seven layers and the interfaces between them. Implementation details are not part of the model. 12.4 Network Protocols I ISO/OSI Reference Model
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9 The Physical layer receives a stream of bits from the Data Link layer above it, encodes them and places them on the communications medium. The Physical layer conveys
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Ch12_ECOA2e - Chapter 12 Network Organization and...

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