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Note for Computer Network - CN by Mohammad Akbal

  • Computer Network - CN
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  • Computer Science Engineering
  • B.Tech
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Author : Sh. Dharmender Kumar Vetter : Dr. Manoj Dhun Lesson No. : 01 Lesson Name: Introduction Objective : To understand networking concepts, connection oriented and connection less communication, network topologies, concept of LAN, MAN, WAN ,lastly and Analysis & comparison of OSI and TCP/IP reference model for data communication. 1.1 Introduction 1.1.1 What is Network 1.1.2 Elementary Terminology 1.1.3 Applications and uses of Network 1.2 1.3 History (Development) Networking Network Topology 1.3.1 Star Topology 1.3.2 Bus Topology 1.3.3 Ring Topology 1.3.4 Tree Topology 1.3.5 Hybrid Topology Network Hardware 1.4.1 LAN 1.4.2 MAN 1.4.3 WAN 1.4.4 Wireless Network 1.4.5 Home Network 1.4.6 Internetwork Network Software 1.5.1 Protocol Hierarchies 1.5.2 Connection Oriented and Connectionless services 1.5.3 Service Primitives OSI Reference Model TCP/IP Reference Model Comparison of TCP/IP and OSI Reference Model Critique of OSI Reference model and TCP/IP reference model Summary Self Assessment Questions 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11

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1.1 INTRODUCTION Earlier, computer networks consisted of mainframes in an enclosure. Input was in the form of punch cards read by card readers and output was in the form of printed results via local printers. Local terminals were mostly used for control and programming input. All processing was on a batch basis, rather than being interactive. In other words, the input was transmitted in a batch from a card reader over a short circuit to the processor, the processor processed the program in a batch and the output to the printer was in a batch. The first true mainframe was the IBM 360, introduced in 1964. Over time, input to the mainframe was extended to multiple users at dumb terminals that connected to ports on the mainframe through terminal controllers, or cluster controllers. In parallel to the development of data networking, the computers began to change. Computers became more powerful as processor speeds increased with the development of faster microprocessors on silicon chips. Memory became more available as chip technology and hard drive technology improved. Additionally, computers became smaller and less expensive, to the point that the typical desktop PC is equivalent to an early mainframe that would have filled a moderate-size office building. As a result, all of this computing power and storage capability on all of these desktops would lead to a need to network those devices within the workplace. It has been estimated that majority of data transfer is confined to the workplace, while only small percentage travels to remote places. Therefore, it is clear that PC users need to share access to hosts, databases, printers, etc. LANs provide a solution to that requirement. Robert M. Metcalfe and his associates at the Xerox Palo Alto Research Center (Xerox PARC) first conceived LAN technology. Later on, Xerox commercialized the technology and named it The Xerox Wire. When Digital Equipment Corporation (DEC), Intel and Xerox corporate to standardize the

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technology in 1979, they named it to Ethernet. Ethernet quickly became a de facto standard. Ethernet and LANs were officially recognized when the IEEE established Project 802 at the request of members. In the end of 1982, the first standard was published and circulated. Ethernet, clearly, is still the most popular LAN standard. 1.1.1 What is Network ? Tenenbaum defines a network as an interconnected collection of autonomous computers. Two computers are said to be interconnected if they are capable of exchanging information. Central to this definition is the fact that the computers are autonomous. This means that no computer on the network can start, stop, or control another. Advantages Many organizations. already have a substantial number of computers, often located far apart. For example, a company .with many offices may have a computer at each location to keep track of customer orders, monitor sales, and do the local payroll. Previously, each of these computers may have worked in isolation from others but at some point, management decided to connect them together information about entire company. In general we can refer to it as. (I) RESOURCE SHARING. The aim is to make all programs, data and peripherals available to anyone on the network irrespective of the physical location of the resources and the user. (ii) RELIABILITY. A file can have copies on two or three different machines, so if one of . them is unavailable (hardware crash), the other copies could be used. For military, banking, air reservation and many other applications it is of great importance. (iii) COST FACTOR. Personal computers have better price/performance ratio than micro computers. So it is better to have PC's, one per user, with data stored on one shared file server machine. (iv) COMMUNICATION MEDIUM. Using a network, it is possible for managers,

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working far apart, to prepare financial report of the company. The changes at one end can be immediately noticed at another and hence it speeds up co-operation among them. 1.1.2 ELEMENTARY TERMINOLOGY OF NETWORKS It is some time to learn about the components/terms mostly used in networking. Whenever we talk about a network it includes. the hardware and the software that make up the network. Now let us have a look at some typical hardware components of network. Nodes (Workstations) The term nodes refers to the computers that are attached to a network and are seeking to share the resources of the network. Of course, if there were no nodes (also called workstations), there would be no network at all. A computer becomes a workstation of a network as soon as it is attached to a network. Server Def:. A computer that facilitates "the sharing of data" software" and hardware resources (e.g. "printers" modems etc,) on the network" is termed as a SERVER. On small networks, sometimes, all the shareable stuff (like files, data, software etc.) is stored on the server. A network can have more than one server also. Each server has a unique name on the network and all users of network identify the server by its unique name. Servers can be of two types: non-dedicated and dedicated servers. Non-dedicated Servers:. On small networks, a workstation that can double up as a server, is known as non-dedicated server since it is not completely dedicated to the cause of serving. Such servers can facilitate the resource-sharing among workstations on a proportionately smaller scale. Since one computer works as a workstation as well as a server, it is .slower and requires. more memory. The (small) networks using such a server are known as peer-to-peer networks.

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