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Scientific and Technical Computing

In this module some of the basic aspects of computer networks are presented in two lessons
. In lesson  the historical background of computer networks is presented
. Then different type of networks and their classification on the basis of transmission technology and scale are considered
. In the next section important applications of computer networks, which spans over different areas in a common man life are discussed
. Lesson  presents the important concepts of layering
. The basic terminologies in the context of layered architecture are also covered in this section
. Then this lesson provides an introduction of PSI layered architecture - Open System Interconnection Reference Model
. Basic functionalities of different layers of PSI and concept of service access points and information exchange will also be dealt in this lesson.  

Scientific and Technical Computing

Scientific and Technical Computing – Client Server Model, Distributed Processing Parallel Processing, Communication Media Commercial – Advertisement, Telemarketing, Teleconferencing – Worldwide Financial Services – Network for the People (this is the most widely used application nowadays) – Medicine, Distance Education, Access to Remote Information, Person-to Person Communication, Interactive Entertainment Course Outline Over the years the subject of computer networks has grown with advancement of technology and the emergence of new technologies and new applications
. In this course, this massive subject has been divided into comprehensible parts and arranged in a structured and logical manner
. It is organized in the following eight modules:
• Introduction
 • Data Communication Fundamentals
 • Data Link Control 
• Switched Communication Networks 
• Broadcast Communication Networks
 • Internet working
 • Routing and Congestion Control
 • Network Security

Communication network based on point-to-point communication

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 (EDIT): DIE 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 equipment's 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
. Summary: The main area of applications can be broadly classified into following categories:  

Communication network based on point-to-point communication

includes telescoping, which uses order-entry computers or telephones connected to order processing network, and online-reservation services for hotels, airlines and so on. 

Communication network based on point-to-point communication

In a short period of time computer networks have become an indispensable part of business, industry, entertainment as well as a common-man's life
. 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 inquiry 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 1990,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 

Communication network based on point-to-point communication

Internet is a collection of networks or network of networks
. Various networks such as LAN and WAN connected through suitable hardware and software to work in a seamless manner
. 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
. The basic difference between WAN and Internet is that WAN is owned by a single organization while internet is not so
. But with the time the line between WAN and Internet is shrinking, and these terms are sometimes used interchangeably. 

Communication network based on point-to-point communication

WAN provides long-distance transmission of data, voice, image and information over large geographical areas that may comprise a country, continent or even the whole world
. In contrast to LAN's, Awns may utilize public, leased or private communication devices, usually in combinations, and can therefore span an unlimited number of miles as shown  

Communication network based on point-to-point communication

MAN is designed to extend over the entire city
. It may be a single network as a cable TV network or it may be means of connecting a number of LAN's into a larger network so that resources may be shared as shown in Fig
 For example, a company can use a MAN to connect the LAN's in all its offices in a city 
. MAN is wholly owned and operated by a private company or may be a service provided by a public company
. Figure  Metropolitan Area Networks (MAN) The main reason for distinguishing Mans as a special category is that a standard has been adopted for them. It is DB (Distributed Queue Dual Bus) or IEEE 

Communication network based on point-to-point communication

LAN typically used transmission technology consisting of single cable to which all machines are connected
. Traditional LAN's run at speeds of 10 to 100 Mbps (but now much higher speeds can be achieved)
. The most common LAN typologies are bus, ring and star
. A typical LAN is shown in Fig

Communication network based on point-to-point communication

Figure  Communication network based on point-to-point communication As a general rule (although there are many exceptions), smaller, geographically localized networks tend to use broadcasting, whereas larger networks normally use are point-to point communication
. Classification based on Scale Alternative criteria for classifying networks are their scale
. They are divided into Local Area (LAN), Metropolitan Area Network (MAN) and Wide Area Networks (WAN)
. Local Area Network (LAN) LAN is usually privately owned and links the devices in a single office, building or campus of up to few kilometers in size
. These are used to share resources (may be hardware or software resources) and to exchange information
. LAN's are distinguished from other kinds of networks by three categories: their size, transmission technology and topology
. LAN's are restricted in size, which means that their worst-case transmission time is bounded and known in advance
. Hence this is more reliable as compared to MAN and WAN
. Knowing this bound makes it possible to use certain kinds of design that would not otherwise be possible
. It also simplifies network management.  

Network Technologies

This system generally also allows possibility of addressing the packet to all destinations (all nodes on the network)
. 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 Multi casting
 Point-to-Point Networks A network based on point-to-point communication is shown in Fig
. 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
. It uses FEM or TAM for node-to-node communication
. 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. 

Network Technologies

 Network Technologies There is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: Transmission Technology and Scale
. The classifications based on these two basic approaches are considered in this section
.Classification Based on Transmission Technology Computer networks can be broadly categorized into two types based on transmission technologies: • Broadcast networks • Point-to-point networks Broadcast Networks Broadcast network have a single communication channel that is shared by all the machines on the network as shown in Fig sand  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. 

Computer Science and Engineering

The bandwidth was clearly a problem, and in the late 1970,s and early,another new communication technique known as Local Area Networks (LAN,s) 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.  

Historical Background of Computer Science and Engineering

With the advancement of VLASIC technology, and particularly, after the invention of microprocessors in the early 1970,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 VLASIC 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
. One significant development was the APPARENT (Advanced Research Projects Agency Network)
. Starting with four-node experimental network in 1969, it has subsequently grown into a network several thousand computers spanning half of the globe, from Hawaii to Sweden
. Most of the present-day concepts such as packet switching evolved from the PLANETARY project
. The low bandwidth (kHz on a voice grade line) telephone network was the only generally available communication system available for this type of network. 

Historical Background

 Historical Background The history of electronic computers is not very old
. It came into existence in the early 1950,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 1960,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. 

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