Computer network

A computer network is a group of computers that are connected to each other for the purpose of communication. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network.

Introduction

A computer network allows computers to communicate with many other and to share resources and information. The Advanced Research Projects Agency (ARPA) funded the design of the "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first operational computer network in the world.[1] Development of the network began in 1969, based on designs begun in the 1960s.

Network classification

Connection method:-
Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.
Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.
ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.
Wired Technologies:-
Twisted-Pair Wire - This is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per second to 100 million bits per second.
Coaxial Cable – These cables are widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
Fiber Optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective layer. It transmits light which can travel over long distance and higher bandwidths. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of times faster than twisted-pair wire.
Wireless Technologies:-
Terrestrial Microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
Communications Satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANS use spread spectrum technology to enable communication between multiple devices in a limited area. Example of open-standard wireless radio-wave technology is IEEE 802.11b.
Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances.
The Wireless Web – The wireless web refers to the use of the World Wide Web through equipments like cellular phones, pagers,PDAs, and other portable communications devices. The wireless web service offers anytime/anywhere connection.
Scale:-
Networks are often classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area Network (CAN), Storage Area Network (SAN), etc. depending on their scale, scope and purpose. Usage, trust levels and access rights often differ between these types of network - for example, LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations (such as a building), while WANs may connect physically separate parts of an organization to each other and may include connections to third parties.

Types of networks

Below is a list of the most common types of computer networks in order of scale.

Personal area network

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. Such a PAN may include wired and wireless connections between devices. The reach of a PAN is typically at least about 20-30 feet (approximately 6-9 meters), but this is expected to increase with technology improvements

Local area network

A local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)[2].For example, a library may have a wired or wireless LAN for users to interconnect local devices (e.g., printers and servers) and to connect to the internet. On a wired LAN, PCs in the library are typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through a system of interconnected devices and eventually connect to the Internet. The cables to the servers are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or possibly 802.11n. The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.

Campus area network

A campus area network (CAN) is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. It can be considered one form of a metropolitan area network, specific to an academic setting.In the case of a university campus-based campus area network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls. A campus area network is larger than a local area network but smaller than a wide area network (WAN) (in some cases).The main aim of a campus area network is to facilitate students accessing internet and university resources. This is a network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, office building, or a military base. A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a smaller area than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.

Metropolitan area network

A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network.

Wide area network

A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose communications links cross metropolitan, regional, or national boundaries [1]). Less formally, a WAN is a network that uses routers and public communications links. Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

Global area network

A global area networks (GAN) (see also IEEE 802.20) specification is in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial WIRELESS local area networks (WLAN).

Virtual private network

A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.A VPN allows computer users to appear to be editing from an IP address location other than the one which connects the actual computer to the Internet.

Internetwork

An Internetwork is the connection of two or more distinct computer networks or network segments via a common routing technology. The result is called an internetwork (often shortened to internet). Two or more networks or network segments connect using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.In modern practice, interconnected networks use the Internet Protocol. There are at least three variants of internetworks, depending on who administers and who participates in them:IntranetExtranetInternetIntranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internet

The Internet consists of a worldwide interconnection of governmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the U.S. Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun, for historical reasons and to distinguish it from other generic internetworks.Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Basic hardware components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable ("optical fiber"). An Ethernet card may also be required.

Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.

Repeaters

A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable which runs longer than 100 meters

Hubs

A network hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.

Bridges

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.Bridges come in three basic types:Local bridges: Directly connect local area networks (LANs)Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Switches

A network switch is a device that forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets.[6] This is distinct from a hub in that it only forwards the packets to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (OSI Layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch.[7]Switch is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI model layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

COMPUTER INTRODUCATION HARDWARE & SOFTWARE

INTRODUCTION

•DEFINITION OF COMPUTERS
•TYPES OF COMPUTERS
•GENERATION OF COMPUTERS

DEFINITION OF COMPUTERS

•An electronic device that has the ability to store, retrieve, and process data, and can be programmed with instructions that it remembers.
•A computer is a machine that accepts data (in digital form) and manipulates it for some result based on a program (sequence of instructions) which describes how data is to be manipulated or processed.

TYPES OF COMPUTERS

•The Types Of Computers: Analog and Hybrid (classification based on operational principle)
1. Analog Computer
2. Hybrid Computer
3. Microcomputer
4. Mini computer
5. Super Computer

1. Analog Computers

The analog computer is almost an extinct type of computer these days. It is different from a digital computer in respect that it can perform numerous mathematical operations simultaneously. It is also unique in terms of operation as it utilizes continuous variables for the purpose of mathematical computation. It utilizes mechanical, hydraulic, or electrical energy or operation.

2. Hybrid computers

These types of computers are, as the name suggests, a combination of both Analog and Digital computers. The Digital computers which work on the principle of binary digit system of “0” and “1” can give very precise results. But the problem is that they are too slow and incapable of large scale mathematical operation. In the hybrid types of computers the Digital counterparts convert the analog signals to perform Robotics and Process control.

2. The Microcomputer

•These are the most frequently used computers better known by the name of “Personal computers”. This is the type of computer meant for public use. Other than Desktop Computer the choice ranges as follows:

•Personal Digital Computer
•Tablet PC
•Towers

•Work Stations

•Laptops

•Hand Held Computer

3. The Mini computer

The Mini computer – Mini computers like the mainframe computers are used by business organization. The difference being that it can support the simultaneous working of up to 100 users and is usually maintained in business organizations for the maintenance of accounts and finances.

4.Super Computers.

•4. Yet another category of computer is the Super Computers. It is somewhat similar to mainframe computers and is used in economic forecasts and engineering designs. Today life without computers is inconceivable. Usage of different types of computers has made life both smooth and fast paced.

GENERATION OF COMPUTERS

1. First Generation (1941-1956)
2. Second Generation Computers (1956-1963)
3. Third Generation Computers (1964-1971)
4. Fourth Generation (1971-Present)

First Generation (1941-1956)

•World War gave rise to numerous developments and started off the computer age.

•Electronic Numerical Integrator and Computer (ENIAC) were produced by a partnership between University of Pennsylvania and the US government•It consisted of 18,000 vacuum tubes and 7000 resistors.

•It was developed by John Presper Eckert and John W. Mauchly and was a general purpose computer.

•"Von Neumann designed the Electronic Discrete Variable Automatic Computer (EDVAC) in 1945 with a memory to hold both a stored program as well as data."

Second Generation Computers (1956-1963)

•The invention of Transistors marked the start of the second generation. These transistors took place of the vacuum tubes used in the first generation computers.

•First large scale machines were made using these technologies to meet the requirements of atomic energy laboratories.

•One of the other benefits to the programming group was that the second generation replaced Machine language with the assembly language. Even though complex in itself Assembly language was much easier.

•Second generation computers also started showing the characteristics of modern day computers with utilities such as printers, disk storage and operating systems. Much financial information was processed using these computers

•In Second Generation computers, the instructions (program) could be stored inside the computer's memory. High-level languages such as COBOL (Common Business-Oriented Language) and FORTRAN (Formula Translator) were used, and they are still used for some applications nowadays.

Third Generation Computers (1964-1971)

•Although transistors were great deal of improvement over the vacuum tubes, they generated heat and damaged the sensitive areas of the computer

•The Integrated Circuit(IC) was invented in 1958 by Jack Kilby. It combined electronic components onto a small silicon disc, made from quartz.

•More advancement made possible the fittings of even more components on a small chip or a semi conductor. Also in third generation computers, the operating systems allowed the machines to run many different applications. These applications were monitored and coordinated by the computer's memory.

Fourth Generation (1971-Present)

•FourthGeneration computers are the modern day computers.

•The Size started to go down with the improvement in the integrated circuits. Very Large Scale (VLSI) and Ultra Large scale(ULSI) ensured that millions of components could be fit into a small chip

•It reduced the size and price of the computers at the same time increasing power, efficiency and reliability.

•"The Intel 4004 chip, developed in 1971, took the integrated circuit one step further by locating all the components of a computer (central processing unit, memory, and input and output controls) on a minuscule chip."

•Due to the reduction of cost and the availability of the computers power at a small place allowed everyday user to benefit.

•First came the minicomputers, which offered users different applications, most famous of these the word processors and spreadsheets, which could be used by non-technical users

•Video game systems like Atari 2600 generated the interest of general populace in the computers.

•In 1981, IBM introduced personal computers for home and office use

•Computer size kept getting reduced during the years. It went down from Desktop to laptops to Palmtops.

•Macintosh introduced Graphic User Interface in which the users didn’t' have to type instructions but could use Mouse for the purpose.

Out Put Device

Electronic devices used to view or print the results of data processing done on a computer.

Centeral Processing Unit (C.P.U)

Principal component of a digital computer, composed of a control unit, an instruction-decoding unit, and an arithmetic-logic unit. The CPU is linked to main memory, peripheral equipment (including input/output devices), and storage units. The control unit integrates computer operations. It selects instructions from the main memory in proper sequence and sends them to the instruction-decoding unit, which interprets them so as to activate functions of the system at appropriate moments. Input data are transferred via the main memory to the arithmetic-logic unit for processing (i.e., addition, subtraction, multiplication, division, and certain logic operations). Larger computers may have two or more CPUs, in which case they are simply called "processors" because each is no longer a "central" unit. See also multiprocessing.

Storage Device

Storage Device:-

Storage Device is used to store (Save) the Data.

Follings are the kinds of Storage Device.

INPUT DEVICEC

Hardware Device

COMPUTER HARDWARE AND SOFTWARE

COMPUTER SYSTEM

•A computer system is a combination of five elements
1. Hardware
2. Software
3. People
4. Procedures
5. Data/ information
Software:-
•Software is the term used to describe the instructions that tell the hardware how to perform a task
People:-
•People constitute the most important component of the computer system. People operate computer hardware; they create the computer software instructions
Data:-
•Data is raw unevaluated facts and figures, concepts or instructions. This raw material is processed into useful information

Peripheral device

•In computer hardware, a peripheral device is any device attached to a computer in order to expand its functionality basically input and output devices together are known peripherals). Some of the more common peripheral devices are printers, scanners, disk drives, tape drives, microphones, speakers, and cameras. Peripheral devices can also include other computers on a network system.

COMPUTER HARDWARE

1. INPUT HARDWARE
2. STORAGE HARDWARE
3. PROCESSING HARDWARE
4. OUT PUT HARDWARE

INPUT HARDWARE

•The purpose is to collect data and convert it into a form for computer processing
•The most common input device is a keyboard
•It looks much like a type writer keyboard with rows of keys arranged in a typical typewriter layout
•As well as a number of additional keys used to enter special computer related codes

STORAGE HARDWARE

•The purpose is to provide a means of storing computer instructions and data in a form that is relatively permanent, or non volatile
•And easy to retrieve when needed for processing
•Storage hardware serves the same basic functions as do office filing systems except that it stores data as electromagnetic signals, commonly on disk or tape, rather than on paper

PROCESSING HARDWARE

•purpose is to retrieve, interpret, and dirct the execution of software instructions provided to the computer.
•The most common components of processing hardware are the central processing unit and main memory•
CPU is the brain of the computer
•It reads and interprets software instructions and coordinates the processing activities that must take place
•The design of CPU affects the processing power and the speed of the computer, as well as the amount of main memory it can use effectively
•With a well designed CPU the computer can perform highly sophisticated tasks in a very short time
•Main memory ( also called internal memory, primary storage or just memory) can be thought of as an electronic desktop
•The more desk surface you have in front of you the more you can place on it
•Similarly if your computer has a lot of memory you can place more software instructions in it
•The amount of memory available determines whether you can run simple or sophisticated software
•A large memory is more capable of holding the thousands of instructions that are contained in the more sophisticated software programs
•Large memory allows to work with and manipulate great amount of data and information at one time

OUTPUT HARDWARE

Provide the user with the means to view information produced by the computer system•Information is output in either hardcopy or softcopy form•Hardcopy output can be held in your hand such as paper with text or graphics printed on it•Softcopy output is displayed on a monitor, televisionlike screen on which you can read text and graphics•A computer is an inanimate device that has no intelligence of its own and must be supplied with instructions so that it knows what to do and how and when to do it•These instructions are called software•Software is made up of a group of related programs•Each of which is a group of related instructions that perform very specific processing tasks.

COMPUTER SOFTWARE

A computer is an inanimate device that has no intelligence of its own and must be supplied with instructions so that it knows what to do and how and when to do it•These instructions are called software•Software is made up of a group of related programs•Each of which is a group of related instructions that perform very specific processing tasks•Software acquired to perform a general business function is often referred to as a software package•Software packages, which are usually created by professional software writers, are accompanied by documentation –user’s manuals-that explain how to use the software

KIND OF SOFTWARE

1. SYSTEM SOFTWARE 2. APPLECATION SOFTWARE

SYSTEM SOFTWARE

Programs designed to allow the computer to manage its own resources are called system software•System software is any computer software which manages and controls computer hardware so that application software can perform a task.•This software runs the basic operations; it tells the hardware what to do and how and when to do it•However it does not solve specific problems relating to a business or profession•Operating systems, such as Microsoft Windows, Mac OS X or Linux, are prominent examples of system software•System software contrasts with application software, which are programs that enable the end-user to perform specific, productive tasks, such as word processing or image manipulation.

APPLICATION SOFTWARE

Any instructions or collection of related programs designed to be carried out by a computer to satisfy a user’s specific needs are application software•Application software is a subclass of computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform•Typical examples of software applications are word processors, spreadsheets, and media players.