Computer Science, Class XII ( ) Chapter No.14 (Networking Concepts)

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1 Chapter No.14 (Networking Concepts) Network The collection of interconnected computers is called a computer network. Two computers are said to be interconnected if they are capable of sharing and exchanging information. Advantage/Goal/Application of Networking Resource Sharing Reliability Cost Factor Communication Medium Resource Sharing means to make all programs, data and peripherals available to anyone on the network irrespective of the physical location of the resources and the user. Reliability means to keep the copy of a file on two or more different machines, so if one of them is unavailable (due to some hardware crash or any other) them its other copy can be used. Cost factor means it greatly reduces the cost since the resources can be shared. Communication Medium means one can send messages and whatever the changes at one end are done can be immediately noticed at another. Evolution of Networking First network came into existence is ARPANET. (ADVANCED RESEARCH PROJECT AGENCY NETWORK) The goal was to connect computers at different universities and US defense. MID 80 S - NSFNET (NATIONAL SCIENCE FOUNDATION NETWORK) A high capacity network to be used strictly for academic and engineering research. In 1990, the internetworking of ARPANET, NSFnet and other private networks named as Internet. Internet is a world wide network of computer networks. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

2 Diagrammatic presentation for slow learners Computer Science, Class XII ( ) 1980 NSFnet 1969 ARPANET A high capacity network to be used strictly for academic and engineering research INTERNET To connect computers at U.S. defense and different universities. The internetworking of ARPANET, NSFnet and other private networks Interspace: A client server software program that allows multiple users to communicate online with real time audio, video and text chat in dynamic 3D environments. Differentiate between Internet and Intranet. Internet is a Network of networks spread over the Globe which are interconnected by various media known as backbone and satellite also. Intranet is a network that exists exclusively within an organization and that is based on Internet Technology and designed to facilitate the customers as well as concerned people. SWITCHING TECHNIQUES Switching techniques are used for transmitting data across networks. Different types are: Circuit Switching Message Switching Packet Switching Circuit Switching In Circuit switching a complete physical connection between two computers is established and then the data are transmitted from the source computer to the destination. When a computer places a telephone call, the switching equipment within the telephone system seeks out a physical copper path all the way from the sender to the receiver. Message Switching Entire message is sent to the destination. It reaches through different intermediate nodes following the store and forward approach. In message switching the data packets are stored in disk. No dedicated connection is required. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

3 Packet Switching Packet switching introduces the idea of cutting data i.e. at the source entire message is broken in smaller pieces called packets which are transmitted over a network without any resource being allocated. Then each packet is transmitted and each packet may follow any rout available and at destination packets may reach in random order. At the destination when all packets are received they are merged to form the original message. In packet switching all the packets of fixed size are stored in main memory. DATA COMMUNICATION TERMINOLOGIES Data channel: The channel is the medium to carry information or data from one point to other. BAUD: It is the unit of measurement for the information carrying capacity of a communication channel. Measurement Units:- bit 1 Byte= 8 bits. 1 Kbps ( Kilo Byte Per Second)= 1024 Bytes, 1 kbps (kilo bits Per Second) = 1024 bits, 1 Mbps (Mega bytes Per Second )=1024 Kbps Bandwidth: It refers to the difference between the highest and lowest frequencies of a transmission channel. Data transfer rate: It is amount of information transmitted or receives per second by a communication channel. It is measuring in Kbps/Mbps etc. Transmission Media It means communication channel of network. The data is transmitted over copper wires, fiber optic cable, radio and microwaves etc. Two categories: Guided media and Unguided media. Guided media includes cables. Eg. Twisted pair cables, Coaxial cables, Optical fiber cables. Unguided media includes waves through air, water and vacuum. Eg. Microwaves, Radiowaves, Satellite. Twisted Pair Cable These cables consist of two insulated identical copper wires wrapped/twisted together in a double helix. Twisting of wires reduces crosstalk which is bleeding of a signal from one wire to another that can corrupt signal and cause network error. Segment length up to 100 m. Types: Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP) Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

4 STP offers greater protection from interference and crosstalk due to shielding. But it is heavier and costlier than UTP. USE: 1. In local telephone communication. 2. For digital data transmission over short distances up to 1 km. Advantages: Easy to install and maintain Simple and flexible. Inexpensive Low weight Suitable for small (Local) Networks Disadvantages: Due to high attenuation, it is incapable to carry signal over long distances without use of repeaters. Low bandwidth support. Low Speed. Coaxial cable Coaxial cable consists of a solid copper wire core surrounded by a plastic cladding shielded in a wire mesh. Shield prevents the noise by redirecting it to ground. Types: Coaxial cable comes in two sizes which are called thinnet and thicknet. Thicknet : segment length upto 500 m Thinnet : segment length upto 185 m USE: In Cable TV channel communication. Advantages: Better than twisted wire cable. Popular for TV networks. Offers higher bandwidth & Speed Disadvantages: Expensive than twisted wires. Not compatible with twisted wire cable. Optical Fibres Thin strands of glass or glass like material designed to carry light from one source to another. Source converts (Modulates) the data signal into light using LED (Light Emitting Diodes) or LASER diodes and send it over the Optical fiber. It consists of three parts: 1. The core: glass or plastic through which the light travels. 2. The cladding : covers the core and reflects light back to the core. 3. Protective coating : protects the fiber Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

5 Advantages Not affected by any kind of noise. High transmission capacity. Speed of Light. Suitable for broadband communication. Computer Science, Class XII ( ) Disadvantages Installation requires care. Connecting two Optical fibers is difficult. Optical fibers are more difficult to solder Most expensive Microwaves It transmits data without the use of cables. They are similar to television or radio signals & used for long distance communication. The transmitters placed at very high towers transmits signal to the receivers at a long distance. A 100 m high tower send signal up to distance of 100 km. Microwaves are transmitted in line of sight fashion, and also propagated through the surface. Advantages Maintenance easy than cables. Suitable when cable can not be used. Freedom from land acquisition rights. Ability to communicate over oceans. Disadvantages Insecure communication. Susceptible to weather effects like rain, storms etc. Less Bandwidth available. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

6 Radiowaves It use radio frequency for transmission in a range of about 10 miles. Any radio setup has two parts the transmitter to send signals and receiver to receive signal. Advantages It offers mobility. Maintenance easy than cables. Freedom from land acquisition rights. Disadvantages Insecure communication. Susceptible to weather effects like rain, storms etc. Satellite Geostationary satellites are placed around KM away from the earth s surface. In satellite communication transmitting station transmits the signals to the satellite. (It is called up-linking). After receiving the signals (microwaves) it amplifies them and transmit back to earth in whole visibility area. Receiving stations at different places can receive these signals. (It is called down-linking). Advantage Area coverage is too large Disadvantage High investment Infrared This transmission uses infrared light to send data. Eg. TV remote, Wireless speakers, Mobiles etc. Laser It uses laser transmitter and a photo sensitive receiver at each end. It has much higher speed than microwave. Network devices Modem A modem is a computer peripheral that allows you to connect and communicate with other computers via telephone lines. Modem means Modulation/ Demodulation. Modulation: A modem changes the digital data from your computer into analog data, a format that can be carried by telephone lines. Demodulation: The modem receiving the call then changes the analog signal back into digital data that the computer can digest. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

7 External Modem Computer Science, Class XII ( ) Internal Modem External modem: The modems that are connected externally to a computer. Internal modem: The modems fixed within computer. RJ- 45 Connector RJ-45 is short for Registered Jack-45. It is an eight wire connector which is commonly used to connect computers on the local area networks i.e., LAN. Network Interface Cards (Ethernet Card) Ethernet is a LAN architecture which uses either bus or star topology and supports data transfer rates up to 10 Mbps. The computers that are part of Ethernet, have to install a special card called Ethernet Card. 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. A MAC address is a 6 byte address with each byte separated by colon like 10:B3:03:63:2E:FC. It allows users to connect to each other either by using cables or wirelessly. It is an interpreter that helps to establish communication between the server and clients/workstations. Repeaters A repeater is a network device that receives a signal and amplifies it for retransmitting it at a higher level so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable runs longer than 100 meters. Hubs A hub is a network device used to connect several computers together. A Hub shares and distributes bandwidth among all the connected computers. Hubs can be either passive or active. Active Hubs: It amplify the signal as it moves from one connected device to another. Passive Hubs: It allow the signal to pass from one computer to another without any change. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

8 A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. Bridges A bridge is a network device that establishes an intelligent connection between two local networks with same protocol but with different types of cables. Switches A switch is a network device that is used to segment networks into different sub-networks called subnet. A switch does not share bandwidth rather each computer gets full bandwidth. Segmenting the network into smaller subnets, prevents traffic overloading in a network. It is responsible for filtering/forwarding data packets between LAN segments. Routers A Router is a network device that is used to separate different segments in a network to improve performance and reliability. A router works like a bridge but can handle different protocols. Routers forward data packets between networks using headers to determine the best path/route to forward the packets. GATEWAY A Gateway is a network device that connects dissimilar networks having different protocols. It established an intelligent connection between a local area network and external networks with completely different structures. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

9 Network Topologies and Types Network topology: The pattern of interconnection of nodes in a network is called network topology. Mesh Topology In this topology each node is connected to other nodes directly i.e. there is a direct link between each node. Star Topology Server The type of network topology in which each of the nodes of the network is connected to a central node with a point-to-point link. All data that is transmitted between nodes in the network is transmitted to this central node, which is usually some type of device that then retransmits the data to some or all of the other nodes in the network. Advantages Centralized distribution and control. Easy to build and access Disadvantages Central node dependency Long cable length Difficult to expand Bus Topology Server The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints. All data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

10 Advantages Short cable length. Easy to extend Disadvantages Fault diagnosis is difficult Nodes must be intelligent. Ring Topology Server The type of network topology in which each of the nodes of the network is connected to two other nodes in the network and with the first and last nodes being connected to each other, forming a ring. Advantages Short cable length. No wiring closet space required Suitable for optical fibers Computer Networks All data that is transmitted between nodes in the network travels from one node to the next node in a circular manner and the data generally flows in a single direction only. Disadvantages Fault diagnosis is difficult Node failure causes network failure. A computer network means a group of networked computers to share data and resources. Local Area Network (LAN) Small computer networks that are confined to a localized area such as building, campus, office and organization are known as Local Area Network (LAN). Current LANs are most likely to be based on Ethernet technology. For example, a computer lab will have a wired or a communications network of two or more computers connected to share data and resources. The simple idea behind computer networking is to allow users to access more information and give them access to devices not directly attached to their local system, such as printers or storage devices. Metropolitan Area Network (MAN) A Metropolitan Area Network is a network that spread over a city but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. eg- cable TV. Multiple routers, switches & hubs are connected to create a MAN. Wide Area Network (WAN) These are the networks spread over large distances, say across countries or even continents (i.e. one city to another and one country to another country). It can even include a group of LANs connected together. Personal Area Network (PAN) A PAN is the network of various IT devices within the range (i.e.10 m) of an individual person. Eg. Sharing information between mobile phone and laptop. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

11 80-20 rule of networking Computer Science, Class XII ( ) The rule of network says that: 80% of the traffic on given network segment should be local and not more than 20% of the network traffic should need to move across a backbone. i.e. the spine connecting various subnetworks. Network protocol Protocols A protocol means the set of rules that two or more devices must follow to exchange the information over a network. Types of protocols are: 1. HTTP 2. FTP 3. TCP/IP 4. SLIP/PPP Hyper Text Transfer Protocol (HTTP) is a communications protocol for the transfer of information on the intranet and the World Wide Web. Its original purpose was to provide a way to publish and retrieve hypertext pages over the Internet. FTP (File Transfer Protocol) is the simplest and most secure way to transfer files from one system to another system over the Internet. The objectives of FTP are: - To promote sharing of files (computer programs and/or data). - To encourage indirect or implicit use of remote computers. TCP/IP (Transmission Control Protocol / Internet Protocol) TCP - is responsible for verifying the reliable delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received. IP - is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address (the IP address) by selecting the best route for transmission. An Internet Protocol (IP) address is a numerical identification and logical address that is assigned to a devices connected in a computer network which is used to uniquely identify devices on the Internet and so one can quickly know the location of the system in the network. Eg SLIP/PPP (Serial Line Internet Protocol / Point to Point Protocol) SLIP is used for relaying IP packets over dial up lines. PPP is used for relaying IP packets over serial lines Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

12 Telnet- It is an internet utility that lets us log on to remote computer system. Remote login is the process of accessing a network from the remote place without actually being present at the actual place of working. Wireless/Mobile Computing Wireless communication is simply data communication without the use of landlines. Mobile computing means that the computing device is not continuously connected to the base or central network. 1. GSM (Global System for Mobile communication): It is leading digital cellular system. In covered areas, cell phone users can buy one phone that will work anywhere where the standard is supported through SIM cards. It uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA technology uses time division multiplexing and divides a radio frequency into time slots and then allocates these slots to multiple calls thereby supporting multiple, simultaneous data channels. 2. CDMA (Code Division Multiple Access): It is a digital cellular technology that uses spread-spectrum techniques where data is sent in small pieces over a number of discrete frequencies available for use. CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. 3. WLL (Wireless in Local Loop): WLL is a system that connects subscribers to the public switched telephone network (PSTN) using radio signals as a substitute for other connecting media. 4. (Electronic Mail): is sending and receiving messages by computer. Advantages Low cost. Speed Waste reduction Disadvantages Hardware requirement Hard to convey emotions. 5. Chat: Online textual talk in real time, is called Chatting. 6. Voice mail: An system that support audio. i.e. the user can leave spoken messages for one another. 7. Video Conferencing: A two way videophone conversation among multiple participants is called video conferencing. 8. SMS (Short Message Service): SMS is the transmission of short text messages to and from a mobile phone, fax machine and or IP address. 9. 3G and EDGE: 3G is a specification for the third generation of mobile communication technology. It is broadband packet based transmission of text, voice, video and multimedia at data rate up to 2 mbps or more by offering a consistent set of service to mobiles no matter where they are located in world. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

13 EDGE (Enhanced Data rates for Global Evolution) is a radio based high speed mobile data standard. It is developed to meet bandwidth need of 3G & allow data transmission speeds of 384 kbps. NETWORK SECURITY CONCEPTS While ensuring network security, the concerns are to make sure that only legal or authorized users and programs gain access to information resources like databases. Protection methods: 1. Authorization- Authorization determines whether the service requestor is entitled to perform that operation by asking the user a legal login-id. 2. Authentication Authentication involves providing a valid password by service requester and validating them against an authority. 3. Encryption The conversion of the data from one form to another coded form i.e. encrypted data so that hackers or crackers can not recognize it. 4. Biometric System It involves unique aspect of a person's body such as Finger-prints, retinal patterns etc. to establish his/her identity. 5. Firewall- A system designed to prevent unauthorized access to or from a private network is called firewall. It can be implemented in both hardware and software or a combination of both. It is used to define limited access of network resources. Cookies - Cookies are messages that a web server transmits to a web browser so that the web server can keep track of the user s activity on a specific or particular web site. Cookies have few parameters like name, value, expiration date etc. Hackers and crackers - Hackers- are more interested in gaining knowledge about computer systems and possibly using this knowledge for playful pranks. These are the persons who get unauthorized access to the websites and replace them with other website or unlawful information Crackers- are the malicious programmers who break into secure systems. The Persons by using certain software to trap authenticated information to crack the security codes such as user names and password to illegally access the information on computers are called crackers. Cyber Law- It is a generic term, which refers to all the legal and regulatory aspects of internet and the World Wide Web. In India the cyber law are contained in the IT Act (Information Technology Act-2000) which governs the legal infrastructure for e-commerce in India. Cyber Crime: It is an unlawful act where the computer is either a tool or a target or both. The IT Act deals with the following cyber crimes. 1. Tampering with computer source documents. 2. Hacking 3. Publishing of information which is obscene in electronic form 4. Child pornography. 5. Accessing protected system. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

14 IPR Issues: The intellectual property may be defined as a product that has commercial value including copy righted property such as artistic works and ideational property. WEB SERVERS WWW (WORLD WIDE WEB) It is a kind of Application of internet which is a set of protocols that allows us to access any document on the Internet through a naming system based on URLs. WWW is like a truck which uses the highway Internet. Web server- It is a WWW server that responds to the requests made by web browsers. E.g: Apache, IIS etc. Web browser- It is a WWW client that navigates through the World Wide Web and displays web pages. E.g: Netscape Navigator, Internet Explorer, Mozilla, Opera, Google Chrome etc. Web sites- A location on a net server where different web pages are linked together by dynamic links is called a web site. Each web site has a unique address called URL. Eg. Web page - A document that can be viewed in a web browser and residing on a web site is a web page. Home page- A web page that is the starting or first page and acts as an indexed page of a website is called home page. Domain name- An internet address which is a character based is called a Domain name. Some most common domains are com, edu, gov, mil, net, org, and co. Some domain names are location based also. For e.g. au for Australia, uk for United Kingdom, in for India etc. URL- A URL (Uniform Resource Locator) that specifies the distinct address for each resource on the internet. e.g. Web Hosting - means hosting web server application on a computer system through which electronic content on the internet is readily available to any web browser client. HTML - It stands for Hyper Text Markup Language that facilitates to write coding for a static web page that can be interpreted by any web browser. It provide certain tags that are interpreted by the browser, how to display and act with the text, graphics etc. tags are specified in < >. For e.g. <body bgcolor=green> it is opening tag </body> it is closing tag. body is the tag with bgcolor attributes. XML (extensible Markup Language) XML is a markup language for documents containing structured information. Structured information contains both content (words, pictures etc.) and some indication of what role content plays. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

15 What is the difference between XML and HTML? Write two differences. XML HTML -Doesn t specify either semantics or tag set. -The semantics and tag set are fixed. -It is a language for documents containing -It is a language used to design the layout of a structured information and all semantics are document and to specify the hyperlinks. defined by the applications that process them. DHTML- It stands for Dynamic Hyper Text Markup Language. DHTML refers to Web content that changes each time it is viewed i.e. dynamic web page. For example, the same URL could result in a different page depending on any number of parameters, such as: *geographic location *time of the day *previous pages viewed by the user *profile of the reader It enables a web page to react to user input without sending requests to web servers. WEB SCRIPTING The process of creating and embedding scripts/code in a web page is known as web-scripting. SCRIPT: A Script is a list of commands embedded in a web page. Scripts are interpreted and executed by a certain program or scripting engine. Types of Scripts: 1. Client Side Script: Client side scripting supports interaction within a web page. It is browser dependent. It is affected by processing speed of user s computer. Some popular client-side scripting languages are VBScript, JavaScript, PHP (Hyper Text Preprocessor). 2. Server-Side Scripts: Server-side scripting supports execution at server end. It is not dependent on browsers. It is affected by processing speed of host server. Some popular server-side Scripting Languages are PHP, Perl, ASP(Active Server Pages), JSP(Java Server Pages) etc. TERMINOLOGY & DEFINITIONS: OPEN SOURCE TERMINOLOGIES Free Software: The S/W s is freely accessible and can be freely used, changed, improved, copied and distributed by all and no payments are needed to be made for free S/W. Open Source Software: S/w whose source code is available to the customer and it can be modified and redistributed without any limitation. OSS may come free of cost or with a payment of nominal charges in the name of charge of support and development of S/W. FLOSS (Free Libre and Open Source Software) : S/w which is free as well as open source S/W. ( Free S/W + Open Source S/W). GNU (GNU s Not Unix): GNU project emphasize on the freedom and its objective is to create a system compatible to UNIX but not identical with it. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

16 FSF (Free Software Foundation): FSF is a non profit organization created for the purpose of the free s/w movement. Organization funded many s/w developers to write free software. OSI (Open Source Initiative): Open source software organization dedicated to cause of promoting open source software. W3C (World Wide Web Consortium) : W3C is responsible for producing the software standards for World Wide Web. Proprietary Software: Proprietary Software is the s/w that is neither open nor freely available, normally the source code of the Proprietary Software is not available but further distribution and modification is possible by special permission by the supplier or vendor. Freeware: Freeware are the software freely available, which permit redistribution but not modification (and their source code is not available). Freeware is distributed in Binary Form (ready to run) without any licensing fees. Shareware: Software for which license fee is payable after a limit of certain time period, its source code is not available and modification to the software are not allowed. Viruses are malicious program that damage data and files and cause harm to computer system and make a system sick just like a real virus. E.g- Trojan horses, worms. It can corrupt files, create bad sectors on disk, decrease space on hard disks, destroy exe files, cause system to hang etc. Trojan Horses: It is a code hidden in a program such as a game or spreadsheet that looks safe to run but has hidden side effect. It actually destroying, damaging, or altering information in a file. Worms: A worm is a self sustaining program designed to replicate so that it can decrease the space on hard disks by duplicating files. Spam mails, also known as junk , is a subset of spam that involves nearly identical messages sent to numerous recipients by . We can protect our mailbox from spam by creating appropriate filters. Web 2.0: Web 2.0 refers to added features and applications to WWW that makes the web more interactive, support easy online information exchange. Some features of Web 2.0 are blogs, wikis, video sharing websites, social networking websites. etc. Cloud Computing: Cloud computing describes computation, software, data access, and storage services that do not require end-user knowledge of the physical location and configuration of the system that delivers the services. It is a technology that uses the internet and central remote servers to maintain data and applications. Cloud computing allows consumers and businesses to use applications without installation and access their personal files at any computer with internet access. This technology allows for much more efficient computing by centralizing storage, memory, processing and bandwidth. A simple example of cloud computing is Yahoo or Gmail etc. We don t need software or a server to use them. All a consumer would need is just an internet connection and we can start sending s. The server and management software is all on the cloud ( internet) and is totally managed by the cloud service provider Yahoo, Google etc. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,

17 Features of Cloud Computing 1) On demand self service 2) Wide range of network access capabilities. 3) Device and location independence enable users to access systems using a web browser regardless of their location or what device they are using (e.g., PC, mobile). 4) Multi-tenancy enables sharing of resources and costs across a large pool of users 5) Security could improve due to centralization of data, increased security-focused resources, etc. 6) Quality of service. Mohd. Hashim, PGT (Computer Sc.), hashim_mbd@yahoo.co.in,