ASHOK GARG MOBILE :

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2 An interconnected collection of autonomous computers is called Computer Network. It means two computers are said to be interconnected if they are capable of exchanging the information.

3 Need for Networking Sharing of Hardware and Software Resources Reliability To enable different computers to communicate To reduce cost of transfer of data

4 Evolution of Networking 1. ARPANET : This was the first network which was planted in It means Advanced Research Projects And NETwork. Its aim was to connect different computers of different universities and U.S. defense to exchange messages and data. 2. NSFnet : This was the network which was started in 1980 by National Science Foundation. It was a high capacity network than ARPANET. It was used to do research work on the network.

5 3. INTERNET: Itisanetworkof networks. It is a worldwide network of Computers network.it was developed in 1990 by different companies to allow the users to connect one network to the other to communicate.it is a super network. 4. INTERSPACE : It is a client/server software program that allows multiple users to communicate online with real time audio, video and text in dynamic 3D environment.

6 Basic Terminology Nodes or Workstations The different terminals or computers which are attached to a network and are able to share the resources are called nodes workstations. or Server A Computer which facilitates the sharing of data, software and hardware resources like Printer, Modem etc. on the network is called a Server.

7 Servers are of two types Dedicated Server It is a computer which can onlybeused asaservernot asanode. Itmeansitsonly job is to provide facilities of data, software, hardware resources etc. to the nodes. Non -Dedicated Servers In a network a workstation which can double up as a server is called a nondedicated Server. It means it can be used as a server andasanode.

8 Network Interface Unit It is a device which is attached to server and all the workstations to maintain the connection between them. Communication Channels : They refer to the connecting cables that connect two or more workstations. The following are the important types of cables :

9 Types of Communication Channels 1. Guided media : The medium of communication which includes the cables.

10 ( a ) Twisted Pair Cable : This is the most common form of wiring in data communication applications. It is consisted of two identical wires wrapped together. Its main advantage is its simplicity and ease of installation. It is flexible and can be connected easily. In this the data transmission characteristics are not so good. It is incapable in carrying a signal over long distances. Its Advantages : (1) It is physically flexible and easy to install. (2) It is inexpensive and can be connected easily. Its Disadvantages : (1) It is incapable to carry a signal over long distances without the use of repeaters. (2) Its bandwidth is very low and so can not be used for broadband applications.

11 ( b ) Coaxial Cable : This type of cable is consisted of a solid wire core surrounds by one or more wire shields each separated by some insulating material. The inner core carries the signal and shield provides the ground. It is very cheap and has better transmission characteristics than twisted pair cable. Its Advantages : (1) Its bandwidth is higher than the twisted pair cable. (2) It can be used for broadband transmission. It means several channels can be transmitted simultaneously. Its Disadvantages : (1) It is more expensive than twisted pair cable. (2) It is not compatible with twisted pair cable.

12 ( c ) Optical Fibers : It is consisted of glass like material which carry light form source to the destination. Its bandwidth is very high. It is difficult to install them and they need special care. It is one of the attractive transmission indeed. Its Advantages : (1) Its bandwidth is very high and so can be used for broadband transmissions where several channels are handled in parallel. (2) It can be used for broadband transmission. It means several channels can be transmitted simultaneously. Its Disadvantages : (1) It is more expensive than other type of cables. (2) It sometimes can not be installed easily. (3) Connection loss is a common problem in optical fiber.

13 2. Unguided media : The medium of communication which includes the waves through air ( vacuum ).

14 ( a ) Micro Wave : These are the signals which are used to transmit data and are similar to the TV signals. These are used for long distances. It is a line-of-sight transmission. These signals pass through the atmosphere and they travel from one antenna to the other. It is very cheap and can be used for very long distances. Sometimes these signals are insecure. Its Advantages : (1) It has the ability to communicate over the oceans. (2) It is cheaper than laying the cables. Its Disadvantages : (1) It is an insecure communication. (2) Bandwidth allocation is very limited in microwave. (3) Is design and maintenance cost is very high.

15 ( b ) Radio Wave : These are the signals which are used to transmit data at radio frequencies. It has two parts : transmitter and receiver. The transmitter takes messages and encodes it and transmit it into radio waves which is received by receiver. It is very cheap and needs less repairing. In this communication is very easy. Sometimes these signals are insecure. Its Advantages : (1) It provides a more easy and convenient way of communication. (2) It is cheaper than laying the cables. Its Disadvantages : (1) It is an insecure communication to some extent. (2) It is susceptible to weather conditions like rain etc.

16 ( c ) Satellites : In this transmission the earth station communicate to send and receive the data using transponders. In the area coverage is more and it is very attractive. It is costly and due to atmospheric losses it has a definite limit of frequency. Its Advantages : (1) The area coverage for the transmission is very large. (2) It is cheaper than laying the cables. Its Disadvantages : (1) It is available with high investment cost and with significant probability of failure. (2) It has a high atmospheric loss above a fixed frequency.

17 TYPES OF NETWORK LOCAL AREA NETWORK (LAN ) METROPOLITAN AREA NETWORK (MAN) WIDE AREA NETWORK (WAN )

18 LOCAL AREA NETWORK ( LAN ) It is a small computer network that are confined to a localized area like an office, a building etc. Only a definite number of computers can be connected in this network to share the resources. Its range can be up to a few Kilometers.Its main features are Total diameter not more than 5 km Data communication at the rate of 100 Mbps Owned by single organization Low Error Rates Provides user access to several resources like printers, Modem etc.

19 Metropolitan Area Network ( MAN ) This network is larger in size than LAN and it spreads over a city. It means a very large number of computers can be connected in this in a city or from one city to the other.

20 WIDE AREA NETWORK ( WAN ) This network spreads across the countries and it is a group of computers that are separated by very large distances. The computers of even one continent can be connected to the other continent. Itsmainfeaturesare: Spans large geographical area, often a country or continent Helps in ing Data can be received from or sent to remote areas with the help of satellite with less cost

21 LAN WAN. Diameter of not more than a few kms. Total data rate of at least several Mbps Complete ownership be a single organization Very low error rates Span entire countries Data rate less than 1 Mbps Owned by multiple organizations Comparatively higher error rates.

22 MODEM (MOdulation/DEModulation ) The device which is used to connect and communicate with computers with the help of telephonic lines. It converts digital data into analog form and vice versa. Working :A modem is a computer peripheral that allows to connect and communicate with the other computers through telephone lines. In MoDem, Mo stands Modulation and Dem stands for Demodulation. Modulation means to convert digital signals to analog signals and Demodulation is reverse of that. The data is transferred form source to the destination through telephone wires and they can only understand analog signals so there is need to convert digital signals to analog. And computer can only understand digital signals. This conversion isdonebymodem.

23 WORKING OF MODEM MODEM Analog signals Digital Signals Analog signals MODEM Digital Signals Source Computer Destination (Remote Computer)

24 Network Switching Techniques ( 1 ) Circuit Switching : In this technique first of all the complete physical connection between two computers is established and then data is transmitted from the source computer to the destination computer. Its important property is to set up an end-toend connection between computer before any data can be sent. ( 2 ) Message Switching : In this technique the source computer sends data or the message to the switching office first which stores the data. It then looks for a free link to another switching office and then sends the data to this office. Hence it is also known as store and forward. ( 3 ) Packet Switching : In message switching there is no limit on block size but in Packet switching a fixed size of packet which can be transmitted across the network is specified. In this all the packets of fixed size are stored in the main memory. It improves the performance as the access time is reduced.

25 Network Topologies The way of interconnection of the nodes in a network is called the Topology. The different factors on which selection of a topology depends are : ( a ) Cost : A Network of computers can reduce the cost to a large extent. ( b ) Reliability : It is more reliable to work in a Computer Network. Hence if a node fails to work the data can be achieved from some other nodes. ( c ) Flexibility : The topology should allow for easy reconfiguration of the network. The different topologies are :

26 Star Topology It is consisted of a central node to which all other nodes are connected by a single path. Its different advantages and disadvantages are : Advantages : ( 1 ) One Device per connection : In this topology failure of a single connection typically involves disconnecting one node from an otherwise fully functional network. ( 2 ) Simple Access protocols : In this access protocols are very simple. Disadvantages : ( 1 ) Long Cable Length : This topology uses a very long cable as each node id directly connected to the centre. ( 2 ) Central Dependency : If the central node fails, the entire network stops working.

27 WS1 WS3 Server WS2 WS4

28 Bus or Linear Topology It is consisted of a single length of the transmission medium onto which the various nodes are attached. Its different advantages and disadvantages are : Advantages : ( 1 ) Short Cable Length : There is a single common data path connecting all nodes, so this topology uses a very short cable. ( 2 ) Easy to Expand : In this topology additional nodes can be connected at any point along its length. Disadvantages : ( 1 ) Fault detection : In this topology it is very difficult to detect a faulty node. ( 2 ) Nodes must be intelligent : All the nodes working in this topology must be intelligent.

29 Server WS1 WS2 WS3 Printer WS4

30 Ring or Circular Topology In this each node is connected to two and only two neighbouring nodes. Data is transmitted from one to another node and is transmitted onwards to another. In this topology the data travels only in one direction. Its different advantages and disadvantages are : Advantages : ( 1 ) Short Cable Length : There is very short cable which is used to develop a Computer Network ( 2 ) Suitable for optical fibers : In this topology for very fast speed transmission optical fibers can be used. Disadvantages : ( 1 ) Node Failure causes network failure : In this topology if one node fails to pass the data through itself, the entire network fails. ( 2 ) Network reconfiguration is difficult : It is not possible to shut down a small section of the ring.

31 C1 C2 C3 C6 C5 C4

32 Tree Topology A variation of bus topology is the tree topology. The shape of the network is just like an inverted tree with the central root branching and sub-branching to the extremities of the network. Advantages : ( 1 ) Easy to Expand : It is very easy expand this topology. It means nodes can be connected easily. ( 2 ) Fault isolation is easy : It is easy to find the faulty node in this topology. Disadvantages : ( 1 ) Dependency on root computer : The total dependence is on the root computer. If it fails to work, the entire network will stop working. ( 2 ) Complex Access Protocols : The protocols designed for this topology are generally very complex.

33 Server WS1 WS3 WS2 WS4 WS5 WS6

34 Backbone Network A backbone is a central interconnecting structure which is used to connect two or more networks e.g. LANs together to form a WAN e.g. FDDI Fiber Distributed Data Interface

35 REPEATER A repeater is a device that amplifies a signal being transmitted on a network for long distances. It is used in long network lines, which exceed the maximum rated distance for a single run.

36 Bridge A bridge is used to connect two LANs which are physically separated but logically same i.e. followthesametopology.

37 Router It is a device that links two networks which can handle different protocols. The routers use physical addresses. It improves the performance of the network.

38 Gateway A gateway is a device that connects dissimilar networks. It gives an intelligent connection between a local network and an external network with different structures. It is a special device which allows different networks to talk to internet that uses TCP/IP.

39 Some Important Terms ( 1 ) Data Channel : A channel is a medium that is used to carry information or data from one point to the other. ( 2 ) Baud : It is a unit to measure the rate of transfer of data. ( 3 ) bps : It stands for Bits per seconds. It is also a unit to measure the rate of transfer of data. The higher units to measure the rate of transfer of data are : ( a ) kbps : Kilo bits per seconds ( b ) mbps : mega bits per seconds ( c ) Mbps : million bits per seconds ( d ) Gbps : Giga bits per seconds ( e ) Tbps : Tera bits per seconds

40 ( 4 ) Bandwidth : It is the difference between the highest and lowest frequencies of a transmission channel. It refers the amount of the information travelling through a single channel at one point of time. High bandwidth channels are called broad bandwidth channels and low bandwidth channels are called narrow bandwidth channels. Some of the commonly used units for this are : Hz, khz, MHz, GHz, THz

41 ( 5 ) Data Transfer Rate : It means the amount of data transferred per second by a communication channel or a storage device. ( 6 ) RJ-45 Connector : It stands for Registered Jack It is a 8 wire connector which can be used to connect computers in a LAN. ( 7 ) Ethernet Card : It is LAN architecture which can be used in bus and star topologies. It can be used to transfer the data up to a rate of some Mbps. The computers which are a part of Ethernet use a special card called Ethernet Card. It has connections for coaxial and twisted pair cable. ( 8 ) Hub : It is a device that can be used to connect a number of computers. It provides a central connection point for workstations, server and other devices. It ca be of two types : ( a ) Active Hub : A hub that electrically amplifies the signals. It means it is used as a repeater. ( b ) Passive Hub ASHOK : AGARG hubmobile that : allow the signals to pass from one computer to the other without any change.

42 ( 9 ) Switch : It is a device which can be used to segment networks into different sub networks called subnets. It prevents traffic overloading in the network.it transforms the data in the form of forwarding packets and it supports packet protocols. ( 10 ) Wireless communication : It is a way to transfer data without any use of landlines. This may involve cellular phone, satellite communication etc. ( 11 ) EDGE : It stands for Enhanced Data Rates for Global Evolution. It is a radio based high speed mobile data standard. It allows data transmission speeds up to 384 kbps.

43 ( 12 ) GSM : It means Global System for Mobile communication. To connect to the specific service provider in different countries GSM users use SIM ( Subscriber Identification Module ) Card. GSM digitises and compresses the voice data.it uses narrowband TDMA (Time Division Multiple Access). ( 13 ) SIM Card : It stands for Subscriber Identification Module. It is a small removable disk which are used to slip in and out in cell phones. They store all the connection data and identification number which can be used to access. It is basically a small computer having memory, processor and ability to interact.

44 ( 14 ) CDMA : It stands for Code-Division Multiple Access. It is a digital cellular technology which does not use any specific frequency. CDMA is a form of spread spectrum that means the data is sent in small pieces over a number of discrete frequencies available to use any time in a specified range. At the receiver end the same unique code is used to recover the signal. ( 15 ) WLL : It stands for Wireless Local Loop. It is analogous with local telephone service but with more capabilities. It serves as a multiple transmit/receiver base stations. It is consisted of a radio transceiver and the WLL interface assembled in one metal box. A fax or a modem can also be connected with it for communication. Advantages : ( 1 ) WLL facilities are not suffered by weather problems. ( 2 ) It offers a better bandwidth for communication.

45 ( 16 ) 3G : It stands third generation. It is a broadband mobile communication technology in which the packet based transmission of text, digitised voice, video etc. is done. It offers a consistent set of services to the mobile computer and phone users no matter where they are located in the world. ( 17 ) Mobile Computing : It means a way to communicate where the computing device is not continuously connected to the central network e.g. laptop computer. ( 18 ) SMS : It stands for Short Message Service. It is the transmission of short text messages to and from a mobile phone, fax machine etc. In this the messages must not be longer than a fixed number of numeric characters and contain no images and graphics. The sent SMS is received by SMSC (Short Message Service Centre ) and forwarded to Home Location Register ( HLR ). ( 19 ) DNS : It stands Domain Name System. It is a character based naming system by which the servers are identified.

46 Important Definitions ( 1 ) Protocols : The protocols refer some rules and regulations that are applicable for a network. They define standardized formats for the data packets, techniques for detecting and correcting errors. Most common examples of the used protocols are : ( a ) HTTP : It stands for Hypertext Transfer Protocols and it is an application-level protocol for speed necessary and hypermedia information systems. It has various built-in request methods which allow users to read a web page. ( b ) TCP / IP : It stands for Transmission Control Protocol / Internet Protocol. It is layered set of some protocols. These protocols are responsible for making sure that the commands get through to the other end. It keeps track what is sent. If a message is very large TCP will split it up into several datagrams. ( c ) FTP : FTP stands for File Transfer Protocols.This protocols are helpful for uploading and downloading the files.

47 ( d ) SLIP :It stands for Serial Line Internet Protocols. These are used to relay over dial up lines. ( e ) PPP : It stands for Point to Point Protocols. It is layered protocols which is consisted of 3 types of Protocols. (1) IPCP : IP Control Protocols used for IP packets over PPP link. (2) NCP : Network Control Protocols used for traffic transport over PPP link. (3) LCP : Link Control Protocols used for link establishment

48 ( 2 ) Datagram : It is a collection of the data that is sent as a single message. ( 3 ) Internet : A very large network of networks is called internet. It is the world s largest network which provides facilities like : ( a ) stands for Electronic mail. It is facility of internet which can be used to send and receive messages. This facility is becoming very popular all over the world now a days. Its different advantages are : ( I ) Low Cost : It is very cheap to send or receive a message through . ( II ) Speed : The messages can be sent from one location to the other very fast. ( III ) Reliable : It is more reliable and safe to send a message by in comparison to conventional mailing system. ( IV ) Easy to use : It is also very easy to send or receive messages by this.

49 ( b ) WWW : It stands for World Wide Web. It is a set of some protocols that allows to access any document on the Internet through a naming system based on URL(Uniform Resource Locators).It also specifies a way to send and receive a document over the internet.it means it is a way of visiting a Web Site. ( c ) Video Conferencing : It is a service of internet by which the user can talk to another person via the microphone and speakers connected to the computer system. It can be used to send images and voice from one place to the other. Instead of typing messages the user can see the face of the other person and can transmit the voice and the video. ( d ) Chat : Online textual talk in real time is called Chatting. It is a service of internet by which the user can communicate with the other user by typing the messages on the screen and gets the response immediately.

50 ( 4 ) URL: It stands for Uniform Resource Locators. These are the unique addresses of the web sites in the Internet which serve as the page s worldwide address. It has three parts : 1. The Protocol 2. The DNS name of the machine on which the page is located 3. A local name uniquely indicating the specific page. It can be of three types Absolute URL, Relative URL and Fragment URL.

51 ( 5 ) Web Browser : It a software that navigates through the WWW and displays the Web Page. The different examples of Web Browser are Internet Explorer and Netscape Navigator. ( 6 ) Web Server : It is a World Wide Web Server that responds to the requests made by the web browsers. ( 7 ) Web Site : It is collection of web pages which are hyper linked with each other belonging to a particular person or organization. It may contain information in the form of text, images etc. It can be called a location on the net.

52 ( 8 ) Web Page : A web page is a single unit of information that is available through a World Wide Web. A web page is an HTML page that is stored on a web server and has a URL so that is can be accessed via the web. ( 9 ) NFS : It stands for Network File System. It means how the files are organised and retrieved on it. It depends on the operating system used by the network.

53 ( 10 ) Telnet : It is an Internet facility which allows us to log in to other computers over the internet. This facility is generally used to check the messages by the users irrespective of the physical location from where the connection has been taken. Most ISP provides this service to the account holders. This facility needs a Telnet program. After entering the user name and password this can be used. (11) ISP:It stands for Internet Service Provider.It is a company or an organization that provides the internet access.it provides domain name service etc. It also provides the technical support to the users. ( 12 ) Intranet : An intranet is a network that exists in a single organization and can be handled by it. It is based on the internet technology.

54 ( 13 ) E-Commerce : It is a collection of some tools and practices that are involved in Internet technologies which allow the users to create, maintain and optimise business relations with consumers and other businesses. ( 14 ) HTML : It stands for Hyper Text Markup Language. It is used to design the layout of a document and to specify the hyper links. This language tells the web browser how to display the contents of a hypertext document. This language provides many layout commands which are called tags.

55 ( 15 ) DHTML : It stands for Dynamic Hyper Text Markup Language. It refers to the web contents that change each time when it is viewed e.g. Time of Day, Profile of the Reader etc. This allows a web page to change after it is loaded into the web browser. ( 16 ) XML : It stands for extensible Markup Language. This language is used for the documents containing structured information which contains words and picture both. This neither specifies semantics nor a tag set. In this language there is no predefined tag set.

56 Some Common Domains are com edu gov mil co org Commercial Education Government military company Organization ( 17 ) Web Hosting : It is a way of hosting the web server application on a computer where the contents are available to any web browser clients. Its different types are : ( a ) Free Hosting : A type of web hosting which offers visiting many websites free of cost.

57 ( b ) Virtual or Shared Hosting : A type of web hosting which is provided under one s own domain. Using this one can present himself as a fully independent identity to his web audience. ( c ) Dedicated Hosting : A type of web hosting in which a company or an organization hires a web server from the hosting company. ( d ) Co-location Hosting : A type of web hosting in which a company or an organization owns its own server on which the site is hosted. In this the company owning the website is responsible for all server administration.

58 ( 18 ) Cookies : These are the messages which a web server transmits to the web browser so that the server can keep a track on the user s activities on a web site. ( 19 ) Hackers : The people who are interested in learning programming languages and computer system and can be considered computer experts. This is term is used for those who gain unauthorized access to use computer systems for stealing and corrupting data. ( 20 ) Crackers : The programmers who break into the network security system. ( 21 ) Cyber law : It refers to all the legal and regulatory aspects of Internet and the WWW. It is a way to check your legal transactions in the Internet Environment.

59 Network Security The different Prevention methods are used while working in Network environment for security. ( 1 ) Authorization : It determines whether the ISP has granted the access to the web service or not. It is done by asking the user legal login-id. ( 2 ) Authentication : It is a way to check the password protection of an authorised user. ( 3 ) Firewall : It is a system designed to prevent the unauthorised users to access to or from a private network. In this we can also encrypt the data.

60 Sno Short Form Full Form 1 3G & EDGE Third Generation, Enhanced data rates for Global Evaluation 2 ARPANET Advanced Research Projects Agency Network 3 CDMA Code Division Multiple Acess 4 DGM Data Grade Medium 5 DHTML Dynamic Hypertext Markup Language 6 DNS Domain Name System 7 FTP File Transfer Protocol 8 GSM Global System For Mobile 9 HTML Hypertext Markup Language 10 HTTP Hypertext Transfer Protocol 11 IMAP Internet Mail Access Protocol 12 IP Internet Protocol 13 ISP Internet Service Provider 14 Kbps Kilobyte per second 15 MAC Media Acess Control 16 Mbps Mega Bits Per Seconds 17 Mhz MegaHertz

61 18 MIME Multipurpose Internet Mail extension 19 MMS Multimedia Message Service 20 NIU Network Interface Unit 21 NSFnet National Science Foundation Network 22 NTP Network time Protocol 23 PDA Personal data Assistant 24 POP Post Office Protocol 25 SIM Subscriber Identity Module Extension 26 SLIP/PPP Serial Line Internet Protocol/Point to Point protocol 27 SMS Short Message Service 28 SMTP Simple Mail transfer Protocol 29 TCP/IP Transmission Control Protocol/Internet Protocol 30 TDMA Time Division Multiple Access 31 URL Uniform Resource Locator 32 VGM Voice Grade Medium 33 WLL Wireless Local Loop 34 www World Wide Web 35 XML extensible Markup Language