What is mean by data communication? Data communication is the exchange of data in the form of 1s and 0s between two devices via some form of transmission medium such as a wire cable. What are the three criteria necessary for an effective and efficient network? The most important criteria are performance, reliability and security. Security issues include protecting data from unauthorized access and viruses. What are the three fundamental characteristics determine the effectiveness of the data communication system?

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In simple terms it means an interconnected set of some objects. For decades we are familiar with the Radio, Television, railway, Highway, Bank and other types of networks. In recent years, the network that is making significant impact in our day-to-day life is the Computer network. By computer network we mean an interconnected set of autonomous computers.

The term autonomous implies that the computers can function independent of others. However, these computers can exchange information with each other through the communication network system. Computer networks have emerged as a result of the convergence of two technologies of this century- Computer and Communication as shown in Fig. The consequence of this revolutionary merger is the emergence of a integrated system that transmit all types of data and information.

There is no fundamental difference between data communications and data processing and there are no fundamental differences among data, voice and video communications. After a brief historical background in Section 1. A brief overview of the applications of computer networks is presented in Section 1. Finally an outline of the entire course is given in Section 1. Computer networks 1.

It came into existence in the early s and during the first two decades of its existence it remained as a centralized system housed in a single large room.

In those days the computers were large in size and were operated by trained personnel. To the users it was a remote and mysterious object having no direct communication with the users. Jobs were submitted in the form of punched cards or paper tape and outputs were collected in the form of computer printouts. The submitted jobs were executed by the computer one after the other, which is referred to as batch mode of data processing. In this scenario, there was long delay between the submission of jobs and receipt of the results.

In the s, computer systems were still centralize, but users provided with direct access through interactive terminals connected by point-to-point low-speed data links with the computer. In this situation, a large number of users, some of them located in remote locations could simultaneously access the centralized computer in time-division multiplexed mode.

The users could now get immediate interactive feedback from the computer and correct errors immediately. Following the introduction of on-line terminals and time-sharing operating systems, remote terminals were used to use the central computer.

With the advancement of VLSI technology, and particularly, after the invention of microprocessors in the early s, the computers became smaller in size and less expensive, but with significant increase in processing power.

New breed of low-cost computers known as mini and personal computers were introduced. Instead of having a single central computer, an organization could now afford to own a number of computers located in different departments and sections.

Side-by-side, riding on the same VLSI technology the communication technology also advanced leading to the worldwide deployment of telephone network, developed primarily for voice communication.

An organization having computers located geographically dispersed locations wanted to have data communications for diverse applications. Communication was required among the machines of the same kind for collaboration, for the use of common software or data or for sharing of some costly resources. This led to the development of computer networks by successful integration and cross-fertilization of communications and geographically dispersed computing facilities. Starting with four-node experimental network in , it has subsequently grown into a network several thousand computers spanning half of the globe, from Hawaii to Sweden.

The low bandwidth 3KHz on a voice grade line telephone network was the only generally available communication system available for this type of network. The bandwidth was clearly a problem, and in the late s and early 80s another new communication technique known as Local Area Networks LANs evolved, which helped computers to communicate at high speed over a small geographical area.

In the later years use of optical fiber and satellite communication allowed high-speed data communications over long distances. The classifications based on these two basic approaches are considered in this section.

All the machines on the network receive short messages, called packets in certain contexts, sent by any machine. An address field within the packet specifies the intended recipient. Upon receiving a packet, machine checks the address field. If packet is intended for itself, it processes the packet; if packet is not intended for itself it is simply ignored. Figure 1. When such a packet is transmitted and received by all the machines on the network. This mode of operation is known as Broadcast Mode.

Some Broadcast systems also supports transmission to a sub-set of machines, something known as Multicasting. The end devices that wish to communicate are called stations. The switching devices are called nodes. Some Nodes connect to other nodes and some to attached stations.

There may exist multiple paths between a source-destination pair for better network reliability. The switching nodes are not concerned with the contents of data. Their purpose is to provide a switching facility that will move data from node to node until they reach the destination.

These are used to share resources may be hardware or software resources and to exchange information. LANs are distinguished from other kinds of networks by three categories: their size, transmission technology and topology. Computer networks LANs are restricted in size, which means that their worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain kinds of design that would not otherwise be possible.

It also simplifies network management. Traditional LANs run at speeds of 10 to Mbps but now much higher speeds can be achieved. The most common LAN topologies are bus, ring and star. A typical LAN is shown in Fig. It may be a single network as a cable TV network or it may be means of connecting a number of LANs into a larger network so that resources may be shared as shown in Fig.

MAN is wholly owned and operated by a private company or may be a service provided by a public company. In contrast to LANs, WANs may utilize public, leased or private communication devices, usually in combinations, and can therefore span an unlimited number of miles as shown in Fig.

A WAN that is wholly owned and used by a single company is often referred to as enterprise network. Schematic diagram of the Internet is shown in Fig. It allows various applications such as e-mail, file transfer, remote log-in, World Wide Web, Multimedia, etc run across the internet.

But with the time the line between WAN and Internet is shrinking, and these terms are sometimes used interchangeably. These applications have changed tremendously from time and the motivation for building these networks are all essentially economic and technological.

Initially, computer network was developed for defense purpose, to have a secure communication network that can even withstand a nuclear attack. After a decade or so, companies, in various fields, started using computer networks for keeping track of inventories, monitor productivity, communication between their different branch offices located at different locations. For example, Railways started using computer networks by connecting their nationwide reservation counters to provide the facility of reservation and enquiry from any where across the country.

And now after almost two decades, computer networks have entered a new dimension; they are now an integral part of the society and people. In s, computer network started delivering services to private individuals at home.

These services and motivation for using them are quite different. Some of the services are access to remote information, person-person communication, and interactive entertainment.

So, some of the applications of computer networks that we can see around us today are as follows: Marketing and sales: Computer networks are used extensively in both marketing and sales organizations. Marketing professionals use them to collect, exchange, and analyze data related to customer needs and product development cycles.

Sales application includes teleshopping, which uses order-entry computers or telephones connected to order processing network, and online-reservation services for hotels, airlines and so on. Financial services: Today's financial services are totally depended on computer networks.

Application includes credit history searches, foreign exchange and investment services, and electronic fund transfer, which allow user to transfer money without going. Computer networks into a bank an automated teller machine is an example of electronic fund transfer, automatic pay-check is another. Manufacturing: Computer networks are used in many aspects of manufacturing including manufacturing process itself.

Two of them that use network to provide essential services are computer-aided design CAD and computer-assisted manufacturing CAM , both of which allow multiple users to work on a project simultaneously. Directory services: Directory services allow list of files to be stored in central location to speed worldwide search operations. Information services: A Network information service includes bulletin boards and data banks.

A World Wide Web site offering technical specification for a new product is an information service. Electronic data interchange EDI : EDI allows business information, including documents such as purchase orders and invoices, to be transferred without using paper. Electronic mail: probably it's the most widely used computer network application.

Teleconferencing: Teleconferencing allows conference to occur without the participants being in the same place. Applications include simple text conferencing where participants communicate through their normal keyboards and monitor and video conferencing where participants can even see as well as talk to other fellow participants.

Different types of equipments are used for video conferencing depending on what quality of the motion you want to capture whether you want just to see the face of other fellow participants or do you want to see the exact facial expression. Voice over IP: Computer networks are also used to provide voice communication. This kind of voice communication is pretty cheap as compared to the normal telephonic conversation. Video on demand: Future services provided by the cable television networks may include video on request where a person can request for a particular movie or any clip at anytime he wish to see.

Explain functions of the seven layers of OSI Model 1. In the past, vendors developed their own architectures and required that other vendors conform to this architecture if they wanted to develop compatible hardware and software. The previous strategy, where the computer network is designed with the hardware as the main concern and software is afterthought, no longer works. Network software is now highly structured. To reduce the design complexity, most of the networks are organized as a series of layers or levels, each one build upon one below it.

The basic idea of a layered architecture is to divide the design into small pieces. Each layer adds to the services provided by the lower layers in such a manner that the highest layer is provided a full set of services to manage communications and run the applications.

The benefits of the layered models are modularity and clear interfaces, i.







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