Page 1 :
UNIT –II, COMPUTER NETWORKS NOTES, , Evolution of Networking, Modern world scenario is ever changing. Data, Communication and network have changed the way, business and other daily affair works. Now, they highly, rely on computer networks and internetwork., , •, , Initially, there were only four nodes, formally, called Hosts., , •, , In 1972, the ARPANET spread over the globe, with 23 nodes located at different countries, and thus became known as Internet., , •, , By the time, with invention of new, technologies such as TCP/IP protocols, DNS,, WWW, browsers, scripting languages, etc.,Internet provided a medium to publish, and access information over the web., , Internet, Internet is defined as an Information super Highway,, to access information over the web. However, It can, be defined in many ways as follows:, •, •, •, •, , •, , •, , Advantages of internet, ➢, ➢, ➢, ➢, ➢, ➢, ➢, , Internet is a world-wide global system of, interconnected computer networks., Internet uses the standard Internet Protocol, (TCP/IP)., Every computer in internet is identified by a, unique IP address., IP Address is a unique set of numbers (such as, 110.22.33.114) which identifies a computer, location., A special computer DNS (Domain Name, Server) is used to give name to the IP Address, so that user can locate a computer by a name., Internet is accessible to every user all over the, world., , Social networking, Education and Technology, Entertainment, Online Service, Reliability, Resource sharing, Cost effective, , Disadvantages of Internet, However, Internet has proved to be a powerful source, of information in almost every field, yet there exists, many disadvantages discussed below:, Threat to personal in formation, ➢ Cyber crime, ➢ Spamming, ➢ Virus attack, , Interspace, Interspace is a client/server software program that, allows multiple users to communicate online with realtime audio, video and text chat in dynamic 3D, environments. Interspaces provides the most advanced, form of communication available on the Internet today., , Switching techniques, Switching: When a user accesses the internet or another, computer network outside their immediate location,, messages are sent through the network of transmission, media. This technique of transferring the information, from one computer network to another network is, known as switching., , Evolution, , Why is Switching Concept required?, , The concept of Internet was originated in 1969 and has, undergone several technological & Infrastructural, changes as discussed below:, •, , The origin of Internet devised from the concept, of Advanced Research Project Agency, Network (ARPANET)., , •, , ARPANET was developed by United States, Department of Defense., , •, , Basic purpose of ARPANET was to provide, communication among the various bodies of, government., , Switching concept is developed because of the, following reasons:, • Bandwidth: It is defined as the maximum, transfer rate of a cable. It is a very critical and, expensive resource. Therefore, switching, techniques are used for the effective utilization, of the bandwidth of a network., , •, , 1, , Collision: Collision is the effect that occurs, when more than one device transmits the, message over the same physical media, and

Page 2 :
Advantages Of Circuit Switching:, , they collide with each other. To overcome this, problem, switching technology is, implemented so that packets do not collide, with each other., , •, , In the case of Circuit Switching technique, the, communication channel is dedicated., • It has fixed bandwidth., Disadvantages Of Circuit Switching:, •, , Once the dedicated path is established, the, only delay occurs in the speed of data, transmission., • It takes a long time to establish a connection, approx 10 seconds during which no data can, be transmitted., • It is more expensive than other switching, techniques as a dedicated path is required for, each connection., • It is inefficient to use because once the path is, established and no data is transferred, then the, capacity of the path is wasted., In this case, the connection is dedicated therefore no, other data can be transferred even if the channel is free., , Classification Of Switching Techniques, , Message Switching, , Circuit Switching, •, , •, , •, •, •, , •, , •, , Circuit switching is a switching technique that, establishes a dedicated path between sender, and receiver., In the Circuit Switching Technique, once the, connection is established then the dedicated, path will remain to exist until the connection is, terminated., Circuit switching in a network operates in a, similar way as the telephone works., A complete end-to-end path must exist before, the communication takes place., In case of circuit switching technique, when any, user wants to send the data, voice, video, a, request signal is sent to the receiver then the, receiver sends back the acknowledgment to, ensure the availability of the dedicated path., After, receiving, the, acknowledgment,, dedicated path transfers the data., Circuit switching is used in public telephone, network. It is used for voice transmission., Fixed data can be transferred at a time in circuit, switching technology., , •, , •, , •, , •, , •, , Message Switching is a switching technique in, which a message is transferred as a complete, unit and routed through intermediate nodes at, which it is stored and forwarded., In Message Switching technique, there is no, establishment of a dedicated path between the, sender and receiver., The destination address is appended to the, message. Message Switching provides a, dynamic routing as the message is routed, through the intermediate nodes based on the, information available in the message., Message switches are programmed in such a, way so that they can provide the most efficient, routes., Each and every node stores the entire message, and then forward it to the next node. This type, of network is known as store and forward, network., Message switching treats each message as an, independent entity., , Communication through circuit switching has 3, phases:, •, •, •, , Circuit establishment, Data transfer, Circuit Disconnect, , Advantages Of Message Switching, •, , 2, , Data channels are shared among the, communicating devices that improve the, efficiency of using available bandwidth.

Page 3 :
•, •, •, , •, , Traffic congestion can be reduced because the, message is temporarily stored in the nodes., Message priority can be used to manage the, network., The size of the message which is sent over the, network can be varied. Therefore, it supports, the data of unlimited size., , •, •, •, , Disadvantages Of Message Switching, •, , •, , Virtual Circuit Switching, , The message switches must be equipped with, sufficient storage to enable them to store the, messages until the message is forwarded., The Long delay can occur due to the storing, and forwarding facility provided by the, message switching technique., , •, , Virtual Circuit Switching is also known as, connection-oriented switching., • In the case of Virtual circuit switching, a, preplanned route is established before the, messages are sent., • Call request and call accept packets are used to, establish the connection between sender and, receiver., • In this case, the path is fixed for the duration of, a logical connection., Let's understand the concept of virtual circuit, switching through a diagram:, , Packet Switching, •, , •, , •, , •, •, •, •, , The packets are reassembled at the receiving, end in correct order., In Datagram Packet Switching technique, the, path is not fixed., Intermediate nodes take the routing decisions, to forward the packets., Datagram Packet Switching is also known as, connectionless switching., , The packet switching is a switching technique, in which the message is sent in one go, but it is, divided into smaller pieces, and they are sent, individually., The message splits into smaller pieces known, as packets and packets are given a unique, number to identify their order at the receiving, end., Every packet contains some information in its, headers such as source address, destination, address and sequence number., Packets will travel across the network, taking, the shortest path as possible., All the packets are reassembled at the receiving, end in correct order., If any packet is missing or corrupted, then the, message will be sent to resend the message., If the correct order of the packets is reached,, then the acknowledgment message will be sent., , •, •, , •, •, , •, , In the above diagram, A and B are the sender, and receiver respectively. 1 and 2 are the nodes., Call request and call accept packets are used to, establish a connection between the sender and, receiver., When a route is established, data will be, transferred., After transmission of data, an acknowledgment, signal is sent by the receiver that the message, has been received., If the user wants to terminate the connection, a, clear signal is sent for the termination., , Advantages Of Packet Switching:, •, , Approaches Of Packet Switching:, There are two approaches to Packet Switching:, Datagram Packet switching:, •, , It is a packet switching technology in which, packet is known as a datagram, is considered as, an independent entity. Each packet contains the, information about the destination and switch, uses this information to forward the packet to, the correct destination., , •, , 3, , Cost-effective: In packet switching technique,, switching devices do not require massive, secondary storage to store the packets, so cost, is minimized to some extent. Therefore, we, can say that the packet switching technique is, a cost-effective technique., Reliable: If any node is busy, then the packets can, be rerouted. This ensures that the Packet Switching, technique provides reliable communication.

Page 4 :
•, , Efficient: Packet Switching is an efficient technique., It does not require any established path prior to the, transmission, and many users can use the same, communication channel simultaneously, hence, makes use of available bandwidth very efficiently., , Disadvantages Of Packet Switching:, •, , •, , Packet Switching technique cannot be implemented, in those applications that require low delay and, high-quality services., The protocols used in a packet switching technique, are very complex and requires high implementation, cost., , Transmission media, •, , •, , •, , Transmission media is a communication, channel that carries the information from the, sender to the receiver. Data is transmitted, through the electromagnetic signals., The main functionality of the transmission, media is to carry the information in the form of, bits through LAN(Local Area Network)., Different transmission media have different, properties such as bandwidth, delay, cost and, ease of installation and maintenance., , Guided Media, It is defined as the physical medium through which the, signals are transmitted. It is also known as Bounded, media., Types Of Guided media:, , Twisted pair:, •, , Some factors need to be considered for designing the, transmission media:, •, , •, , •, , Bandwidth: All the factors are remaining, constant, the greater the bandwidth of a, medium, the higher the data transmission rate, of a signal., Transmission impairment: When the received, signal is not identical to the transmitted one, due to the transmission impairment. The, quality of the signals will get destroyed due to, transmission impairment., Interference: An interference is defined as the, process of disrupting a signal when it travels, over a communication medium on the addition, of some unwanted signal., , •, •, , Twisted pair is a physical media made up of a, pair of cables twisted with each other. A, twisted pair cable is cheap as compared to other, transmission media. Installation of the twisted, pair cable is easy, and it is a lightweight cable., The frequency range for twisted pair cable is, from 0 to 3.5KHz., A twisted pair consists of two insulated copper, wires arranged in a regular spiral pattern., The degree of reduction in noise interference is, determined by the number of turns per foot., Increasing the number of turns per foot, decreases noise interference., , Causes Of Transmission Impairment:, •, , •, , •, , Attenuation: Attenuation means the loss of, energy, i.e., the strength of the signal decreases, with increasing the distance which causes the, loss of energy., Distortion: Distortion occurs when there is a, change in the shape of the signal. This type of, distortion is examined from different signals, having different frequencies. Each frequency, component has its own propagation speed, so, they reach at a different time which leads to the, delay distortion., Noise: When data is travelled over a, transmission medium, some unwanted signal, is added to it which creates the noise., , Unshielded Twisted Pair:, An unshielded twisted pair is widely used in, telecommunication. Following are the categories of the, unshielded twisted pair cable:, Category 1: Category 1 is used for telephone lines that, have low-speed data., Category 2: It can support upto 4Mbps., Category 3: It can support upto 16Mbps., , Classification Of Transmission Media:, , 4

Page 5 :
Category 4: It can support upto 20Mbps. Therefore, it, can be used for long-distance communication., Category 5: It can support upto 200Mbps., Advantages Of Unshielded Twisted Pair:, • It is cheap., • Installation of the unshielded twisted pair is, easy., • It can be used for high-speed LAN., Disadvantage:, • This cable can only be used for shorter, distances because of attenuation., , •, , Broadband transmission: It is defined as the, process of transmitting multiple signals, simultaneously., Advantages Of Coaxial cable:, • The data can be transmitted at high speed., • It has better shielding as compared to twisted, pair cable., • It provides higher bandwidth., Disadvantages Of Coaxial cable:, • It is more expensive as compared to twisted, pair cable., • If any fault occurs in the cable causes the failure, in the entire network., , Shielded Twisted Pair, , A shielded twisted pair is a cable that contains the mesh, surrounding the wire that allows the higher, transmission rate., Characteristics Of Shielded Twisted Pair:, • The cost of the shielded twisted pair cable is not, very high and not very low., • An installation of STP is easy., • It has higher capacity as compared to, unshielded twisted pair cable., • It has a higher attenuation., • It is shielded that provides the higher data, transmission rate., Disadvantages, • It is more expensive as compared to UTP and, coaxial cable., • It has a higher attenuation rate., , Fibre Optic, •, •, , •, , •, , Fibre optic cable is a cable that uses electrical, signals for communication., Fibre optic is a cable that holds the optical, fibres coated in plastic that are used to send, the data by pulses of light., The plastic coating protects the optical fibres, from heat, cold, electromagnetic interference, from other types of wiring., Fibre optics provide faster data transmission, than copper wires., , Coaxial Cable, •, , •, •, •, , •, , •, •, , Coaxial cable is very commonly used, transmission media, for example, TV wire is, usually a coaxial cable., The name of the cable is coaxial as it contains, two conductors parallel to each other., It has a higher frequency as compared to, Twisted pair cable., The inner conductor of the coaxial cable is, made up of copper, and the outer conductor is, made up of copper mesh. The middle core is, made up of non-conductive cover that, separates the inner conductor from the outer, conductor., The middle core is responsible for the data, transferring whereas the copper mesh prevents, from the EMI(Electromagnetic interference)., , Basic elements of Fibre optic cable:, •, , Core: The optical fibre consists of a narrow, strand of glass or plastic known as a core. A, core is a light transmission area of the fibre. The, more the area of the core, the more light will be, transmitted into the fibre., • Cladding: The concentric layer of glass is, known as cladding. The main functionality of, the cladding is to provide the lower refractive, index at the core interface as to cause the, reflection within the core so that the light waves, are transmitted through the fibre., • Jacket: The protective coating consisting of, plastic is known as a jacket. The main purpose, of a jacket is to preserve the fibre strength,, absorb shock and extra fibre protection., Following are the advantages of fibre optic cable, over copper:, • Greater Bandwidth: The fibre optic cable, provides more bandwidth as compared copper., , Coaxial cable is of two types:, Baseband transmission: It is defined as the, process of transmitting a single signal at high, speed., , 5

Page 6 :
•, , •, , •, , •, , Therefore, the fibre optic carries more data as, compared to copper cable., Faster speed: Fibre optic cable carries the data, in the form of light. This allows the fibre optic, cable to carry the signals at a higher speed., Longer distances: The fibre optic cable carries, the data at a longer distance as compared to, copper cable., Better reliability: The fibre optic cable is more, reliable than the copper cable as it is immune to, any temperature changes while it can cause, obstruct in the connectivity of copper cable., Thinner and Sturdier: Fibre optic cable is, thinner and lighter in weight so it can, withstand more pull pressure than copper, cable., , •, •, , Radio waves cover a large area, and they can, penetrate the walls., Radio transmission provides a higher, transmission rate., , Microwaves, , UnGuided Transmission, , An, unguided, transmission, transmits, the, electromagnetic waves without using any physical, medium. Therefore it is also known as wireless, transmission., In unguided media, air is the media through which the, electromagnetic energy can flow easily., Unguided transmission is broadly classified into three, categories:, , Terrestrial Microwave Transmission, •, , •, , Radio waves, •, , •, •, •, , •, , Radio waves are the electromagnetic waves, that are transmitted in all the directions of free, space., Radio waves are omnidirectional, i.e., the, signals are propagated in all the directions., The range in frequencies of radio waves is from, 3Khz to 1 khz., In the case of radio waves, the sending and, receiving antenna are not aligned, i.e., the wave, sent by the sending antenna can be received by, any receiving antenna., An example of the radio wave is FM radio., , •, , •, , •, , Terrestrial Microwave transmission is a, technology that transmits the focused beam of, a radio signal from one ground-based, microwave transmission antenna to another., Microwaves are the electromagnetic waves, having the frequency in the range from 1GHz, to 1000 GHz., Microwaves are unidirectional as the sending, and receiving antenna is to be aligned, i.e., the, waves sent by the sending antenna are, narrowly focussed., In this case, antennas are mounted on the, towers to send a beam to another antenna, which is km away., It works on the line of sight transmission, i.e.,, the antennas mounted on the towers are the, direct sight of each other., , Characteristics of Microwave:, ✓, , ✓, ✓, ✓, ✓, , Frequency range: The frequency range of, terrestrial microwave is from 4-6 GHz to 21-23, GHz., Bandwidth: It supports the bandwidth from 1, to 10 Mbps., Short distance: It is inexpensive for short, distance., Long distance: It is expensive as it requires a, higher tower for a longer distance., Attenuation: Attenuation means loss of signal., It is affected by environmental conditions and, antenna size., , Advantages Of Microwave:, ✓, , Applications Of Radio waves:, • A Radio wave is useful for multicasting when, there is one sender and many receivers., • An FM radio, television, cordless phones are, examples of a radio wave., Advantages Of Radio transmission:, • Radio transmission is mainly used for wide, area networks and mobile cellular phones., , ✓, ✓, , 6, , Microwave transmission is cheaper than using, cables., It is free from land acquisition as it does not, require any land for the installation of cables., Microwave transmission provides an easy, communication in terrains as the installation, of cable in terrain is quite a difficult task.

Page 7 :
✓, , Communication over oceans can be achieved, by using microwave transmission., , •, , Disadvantages of Microwave transmission:, ✓, , ✓, ✓, , ✓, , Eavesdropping: An eavesdropping creates, insecure communication. Any malicious user, can catch the signal in the air by using its own, antenna., Out of phase signal: A signal can be moved out, of phase by using microwave transmission., Susceptible, to, weather, condition: A, microwave transmission is susceptible to, weather condition. This means that any, environmental change such as rain, wind can, distort the signal., Bandwidth limited: Allocation of bandwidth is, limited in the case of microwave transmission., , Characteristics Of Infrared:, •, •, , •, •, , Satellite Microwave Communication, •, •, , •, , It is used for short-range communication such, as data transfer between two cell phones, TV, remote operation, data transfer between a, computer and cell phone resides in the same, closed area., , A satellite is a physical object that revolves, around the earth at a known height., Satellite communication is more reliable, nowadays as it offers more flexibility than cable, and fibre optic systems., We can communicate with any point on the, globe by using satellite communication., , How Does Satellite work?, The satellite accepts the signal that is transmitted from, the earth station, and it amplifies the signal. The, amplified signal is retransmitted to another earth, station., Advantages Of Satellite Microwave Communication:, ➢ The coverage area of a satellite microwave is, more than the terrestrial microwave., ➢ The transmission cost of the satellite is, independent of the distance from the centre of, the coverage area., ➢ Satellite communication is used in mobile and, wireless communication applications., ➢ It is easy to install., ➢ It is used in a wide variety of applications such, as weather forecasting, radio/TV signal, broadcasting, mobile communication, etc., Disadvantages Of Satellite Microwave Communication:, ➢ Satellite designing and development requires, more time and higher cost., ➢ The Satellite needs to be monitored and, controlled on regular periods so that it remains, in orbit., ➢ The life of the satellite is about 12-15 years. Due, to this reason, another launch of the satellite has, to be planned before it becomes non-functional., , It supports high bandwidth, and hence the data, rate will be very high., Infrared waves cannot penetrate the walls., Therefore, the infrared communication in one, room cannot be interrupted by the nearby, rooms., An infrared communication provides better, security with minimum interference., Infrared communication is unreliable outside, the building because the sun rays will interfere, with the infrared waves., , Network topologies, A network topology describes the arrangement of, systems on a computer network. It defines how the, computers, or nodes, within the network are arranged, and connected to each other., , BUS Topology, Bus topology is a network type in which every, computer and network device is connected to single, cable. When it has exactly two endpoints, then it is, called Linear Bus topology., , Infrared, •, , •, , An infrared transmission is a wireless, technology used for communication over short, ranges., The frequency of the infrared in the range from, 300 GHz to 400 THz., , Features of Bus Topology, ❖ It transmits data only in one direction., ❖ Every device is connected to a single cable, , 7

Page 8 :
Advantages of Bus Topology, ❖ It is cost effective., ❖ Cable required is least compared to other, network topology., ❖ Used in small networks., ❖ It is easy to understand., ❖ Easy to expand joining two cables together., Disadvantages of Bus Topology, ❖ Cables fails then whole network fails., ❖ If network traffic is heavy or nodes are more the, performance of the network decreases., ❖ Cable has a limited length., ❖ It is slower than the ring topology., , RING Topology, It is called ring topology because it forms a ring as each, computer is connected to another computer, with the, last one connected to the first. Exactly two neighbours, for each device., , STAR Topology, In this type of topology all the computers are connected, to a single hub through a cable. This hub is the central, node and all others nodes are connected to the central, node., , Features of Ring Topology, , A number of repeaters are used for Ring, topology with large number of nodes, because, if someone wants to send some data to the last, node in the ring topology with 100 nodes, then, the data will have to pass through 99 nodes to, reach the 100th node. Hence to prevent data, loss repeaters are used in the network., o The transmission is unidirectional, but it can be, made bidirectional by having 2 connections, between each Network Node, it is called Dual, Ring Topology., o In Dual Ring Topology, two ring networks are, formed, and data flow is in opposite direction, in them. Also, if one ring fails, the second ring, can act as a backup, to keep the network up., Advantages of Ring Topology, ❖ Transmitting network is not affected by high, traffic or by adding more nodes, as only the, nodes having tokens can transmit data., ❖ Cheap to install and expand, Disadvantages of Ring Topology, ❖ Troubleshooting is difficult in ring topology., ❖ Adding or deleting the computers disturbs the, network activity., ❖ Failure of one computer disturbs the whole, network., o, , Features of Star Topology, ❖ Every node has its own dedicated connection to, the hub., ❖ Hub acts as a repeater for data flow., ❖ Can be used with twisted pair, Optical Fibre or, coaxial cable., , Advantages of Star Topology, , ❖ Fast performance with few nodes and low, network traffic., ❖ Hub can be upgraded easily., ❖ Easy to troubleshoot., ❖ Easy to setup and modify., ❖ Only that node is affected which has failed, rest, of the nodes can work smoothly., Disadvantages of Star Topology, ❖ Cost of installation is high., ❖ Expensive to use., ❖ If the hub fails then the whole network is, stopped because all the nodes depend on the, hub., , 8

Page 9 :
❖ Performance is based on the hub that is it, depends on its capacity, , ➢ Fault is diagnosed easily., ➢ Provides security and privacy., Disadvantages of Mesh Topology, ➢ Installation and configuration is difficult., ➢ Cabling cost is more., ➢ Bulk wiring is required., , MESH Topology, It is a point-to-point connection to other nodes or, devices. All the network nodes are connected to each, other. Mesh has n(n-1)/2 physical channels to, link n devices., There are two techniques to transmit data over the, Mesh topology, they are :, • Routing, • Flooding, , TREE Topology, It has a root node and all other nodes are connected to, it forming a hierarchy. It is also called hierarchical, topology. It should at least have three levels to the, hierarchy., , MESH Topology: Routing, In routing, the nodes have a routing logic, as per the, network requirements. Like routing logic to direct the, data to reach the destination using the shortest distance., Or, routing logic which has information about the, broken links, and it avoids those node etc. We can even, have routing logic, to re-configure the failed nodes., , MESH Topology: Flooding, In flooding, the same data is transmitted to all the, network nodes, hence no routing logic is required. The, network is robust, and the its very unlikely to lose the, data. But it leads to unwanted load over the network., , Features of Tree Topology, • Ideal if workstations are located in groups., • Used in Wide Area Network., Advantages of Tree Topology, • Extension of bus and star topologies., • Expansion of nodes is possible and easy., • Easily managed and maintained., • Error detection is easily done., Disadvantages of Tree Topology, • Heavily cabled., • Costly., • If more nodes are added maintenance is, difficult., • Central hub fails, network fails., , HYBRID Topology, It is two different types of topologies which is a mixture, of two or more topologies. For example if in an office in, one department ring topology is used and in another, star topology is used, connecting these topologies will, result in Hybrid Topology (ring topology and star, topology)., , Types of Mesh Topology, Partial Mesh Topology : In this topology some, of the systems are connected in the same, fashion as mesh topology but some devices are, only connected to two or three devices., ➢ Full Mesh Topology : Each and every nodes or, devices are connected to each other., Features of Mesh Topology, • Fully connected., • Robust., • Not flexible., Advantages of Mesh Topology, ➢ Each connection can carry its own data load., ➢ It is robust., ➢, , 9

Page 10 :
➢, , Features of Hybrid Topology, • It is a combination of two or topologies, • Inherits the advantages and disadvantages of, the topologies included, Advantages of Hybrid Topology, • Reliable as Error detecting and trouble, shooting is easy., • Effective., • Scalable as size can be increased easily., • Flexible., Disadvantages of Hybrid Topology, • Complex in design., • Costly., , PAN(Personal Area Network), •, , •, , •, , COMPUTER NETWORKS TYPE, , •, , A computer network is a group of computers linked to, each other that enables the computer to communicate, with another computer and share their resources, data,, and applications., A computer network can be categorized by their size., A computer network is mainly of four types:, • LAN(Local Area Network), • PAN(Personal Area Network), • MAN(Metropolitan Area Network), • WAN(Wide Area Network), , •, , LAN(Local Area Network), ➢, , ➢, , ➢, , ➢, , Local Area Network provides higher security., , Personal Area Network is a network arranged, within an individual person, typically within a, range of 10 meters., Personal Area Network is used for connecting, the computer devices of personal use is known, as Personal Area Network., Thomas Zimmerman was the first research, scientist to bring the idea of the Personal Area, Network., Personal Area Network covers an area of 30, feet., Personal computer devices that are used to, develop the personal area network are the, laptop, mobile phones, media player and play, stations., , There are two types of Personal Area Network:, 1. Wireless Personal Area Network: Wireless, Personal Area Network is developed by simply, using wireless technologies such as WiFi,, Bluetooth. It is a low range network., 2. Wired Personal, Area Network: Wired, Personal Area Network is created by using the, USB., Example of PANBody Area Network: Body Area Network is a network, that moves with a person. For example, a mobile, network moves with a person. Suppose a person, , Local Area Network is a group of computers, connected to each other in a small area such as, building, office., LAN is used for connecting two or more, personal computers through a communication, medium such as twisted pair, coaxial cable, etc., It is less costly as it is built with inexpensive, hardware such as hubs, network adapters, and, ethernet cables., The data is transferred at an extremely faster, rate in Local Area Network., , 10

Page 11 :
establishes a network connection and then creates a, connection with another device to share the, information., , offices. This network is made by using the, telephone leased line provided by the, telecom company., , MAN(Metropolitan Area Network), •, , •, •, •, , •, , 3., , A metropolitan area network is a network that, covers a larger geographic area by, interconnecting a different LAN to form a, larger network., Government agencies use MAN to connect to, the citizens and private industries., In MAN, various LANs are connected to each, other through a telephone exchange line., The most widely used protocols in MAN are, RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL,, etc., It has a higher range than Local Area, Network(LAN)., , Advantages Of Wide Area Network:, , Following are the advantages of the Wide Area, Network:, ➢, , ➢, , Uses Of Metropolitan Area Network:, ➢ MAN is used in communication between the, banks in a city., ➢ It can be used in an Airline Reservation., ➢ It can be used in a college within a city., ➢ It can also be used for communication in the, military., , ➢, , ➢, , WAN(Wide Area Network), ➢, , ➢, ➢, , ➢, ➢, , ➢, , A Wide Area Network is a network that, extends over a large geographical area such as, states or countries., A Wide Area Network is quite bigger network, than the LAN., A Wide Area Network is not limited to a single, location, but it spans over a large geographical, area through a telephone line, fibre optic cable, or satellite links., The internet is one of the biggest WAN in the, world., A Wide Area Network is widely used in the, field of Business, government, and education., , ➢, ➢, , Geographical area: A Wide Area Network, provides a large geographical area. Suppose if, the branch of our office is in a different city then, we can connect with them through WAN. The, internet provides a leased line through which, we can connect with another branch., Centralized data: In case of WAN network,, data is centralized. Therefore, we do not need, to buy the emails, files or back up servers., Get updated files: Software companies work, on the live server. Therefore, the programmers, get the updated files within seconds., Exchange messages: In a WAN network,, messages are transmitted fast. The web, application like Facebook, Whatsapp, Skype, allows you to communicate with friends., Sharing of software and resources: In WAN, network, we can share the software and other, resources like a hard drive, RAM., Global business: We can do the business over, the internet globally., High bandwidth: If we use the leased lines for, our company then this gives the high, bandwidth. The high bandwidth increases the, data transfer rate which in turn increases the, productivity of our company., , Disadvantages of Wide Area Network:, The following are the disadvantages of the Wide Area, Network:, , Examples Of Wide Area Network:, 1. Mobile Broadband: A 4G network is, , ➢, , widely used across a region or country., 2. Private network: A bank provides a, private network that connects the 44, 11, , Security issue: A WAN network has more, security issues as compared to LAN and MAN, network as all the technologies are combined, together that creates the security problem.

Page 12 :
➢, , Needs Firewall & antivirus software: The, data is transferred on the internet which can, be changed or hacked by the hackers, so the, firewall needs to be used. Some people can, inject the virus in our system so antivirus is, needed to protect from such a virus., , 2., 3., , ➢ High Setup cost: An installation cost of the, WAN network is high as it involves the, purchasing of routers, switches., ➢ Troubleshooting problems: It covers a, large area so fixing the problem is difficult., , network (modulator) or network to digital, device (demodulator)., Half duplex − A half-duplex modem has the, capacity to transfer data in both the directions, but only one at a time., Full duplex − A full duplex modem can, transmit data in both the directions, simultaneously., , RJ45 Connector, RJ45 is the acronym for Registered Jack 45. RJ45, connector is an 8-pin jack used by devices to physically, connect, to Ethernet based local, area, networks, (LANs). Ethernet is a technology that defines protocols, for establishing a LAN. The cable used for Ethernet, LANs are twisted pair ones and have RJ45 connector, pins at both ends. These pins go into the corresponding, socket on devices and connect the device to the, network., , Network Devices, Hardware devices that are used to connect computers,, printers, fax machines and other electronic devices to a, network are called network devices. These devices, transfer data in a fast, secure and correct way over same, or different networks. Network devices may be internetwork or intra-network. Some devices are installed on, the device, like NIC card or RJ45 connector, whereas, some are part of the network, like router, switch, etc. Let, us explore some of these devices in greater detail., , Modem, Modem is a device that enables a computer to send or, receive data over telephone or cable lines. The data, stored on the computer is digital whereas a telephone, line or cable wire can transmit only analog data., , Ethernet Card, Ethernet card, also known as network interface card, (NIC), is a hardware component used by computers to, connect to Ethernet LAN and communicate with other, devices on the LAN. The earliest Ethernet cards were, external to the system and needed to be installed, manually. In modern computer systems, it is an internal, hardware component. The NIC has RJ45 socket where, network cable is physically plugged in., , The main function of the modem is to convert digital, signal into analog and vice versa. Modem is a, combination, of, two, devices, − modulator and demodulator., The modulator converts digital data into analog data, when the data is being sent by the computer., The demodulator converts analog data signals into, digital data when it is being received by the computer., , Ethernet card speeds may vary depending upon the, protocols it supports. Old Ethernet cards had maximum, speed of 10 Mbps. However, modern cards support fast, Ethernets up to a speed of 100 Mbps. Some cards even, have capacity of 1 Gbps., , Router, A router is a network layer hardware device that, transmits data from one LAN to another if both, networks support the same set of protocols. So, a router is typically connected to at least two LANs and, the internet service provider (ISP). It receives its data in, the form of packets, which are data frames with, their destination, address added., Router, also, strengthens the signals before transmitting them. That, is why it is also called repeater., , Types of Modem, Modem can be categorized in several ways like, direction in which it can transmit data, type of, connection to the transmission line, transmission mode,, etc., Depending on direction of data transmission,, modem can be of these types −, 1. Simplex − A simplex modem can transfer data, in only one direction, from digital device to, , Routing Table, 12

Page 13 :
A router reads its routing table to decide the best, available route the packet can take to reach its, destination quickly and accurately. The routing table, may be of these two types −, • Static − In a static routing table the routes are, fed manually. So it is suitable only for very, small networks that have maximum two to, three routers., • Dynamic − In a dynamic routing table, the, router communicates with other routers, through protocols to determine which routes, are free. This is suited for larger networks, where manual feeding may not be feasible due, to large number of routers., , home, office or any public space. Hotspots themselves, are connected to the network through wires., A Wi-Fi, card is, used, to, add, capabilities, like teleconferencing, downloading digital camera, images, video chat, etc. to old devices. Modern devices, come with their in-built wireless network adapter., , Data Communication Terminology, Channel, Physical medium like cables over which information is, exchanged is called channel. Transmission channel, may be analog or digital. As the name suggests, analog, channels transmit data using analog signals while, digital channels transmit data using digital signals., , Switch, , Switch is a network device that connects other devices, to Ethernet networks through twisted pair cables. It, uses packet, switching technique, to receive,, store and forward data packets on the network. The, switch maintains a list of network addresses of all the, devices connected to it., On receiving a packet, it checks the destination address, and transmits the packet to the correct port. Before, forwarding, the packets are checked for collision and, other network errors. The data is transmitted in full, duplex mode, Data transmission speed in switches can be double that, of other network devices like hubs used for networking., This is because switch shares its maximum speed with, all the devices connected to it. This helps in maintaining, network speed even during high traffic. In fact, higher, data speeds are achieved on networks through use of, multiple switches., , In popular network terminology, path over which data, is sent or received is called data channel. This data, channel may be a tangible medium like copper wire, cables or broadcast medium like radio waves., , Data Transfer Rate, The speed of data transferred or received over, transmission channel, measured per unit time, is called, data transfer rate. The smallest unit of measurement is, bits per second (bps). 1 bps means 1 bit (0 or 1) of data, is transferred in 1 second., Here are some commonly used data transfer rates −, • 1 Bps = 1 Byte per second = 8 bits per second, • 1 kbps = 1 kilobit per second = 1024 bits per, second, • 1 Mbps = 1 Megabit per second = 1024 Kbps, • 1 Gbps = 1 Gigabit per second = 1024 Mbps, , Gateway, Gateway is a network device used to connect two or, more dissimilar networks. In networking parlance,, networks that use different protocols are dissimilar, networks. A gateway usually is a computer with, multiple NICs connected to different networks. A, gateway can also be configured completely using, software. As networks connect to a different network, through gateways, these gateways are usually hosts or, end points of the network., Gateway uses packet switching technique to transmit, data from one network to another. In this way it is, similar to a router, the only difference being router can, transmit data only over networks that use same, protocols., , Bandwidth, Data transfer rates that can be supported by a network, is called its bandwidth. It is measured in bits per second, (bps). Modern day networks provide bandwidth in, Kbps, Mbps and Gbps. Some of the factors affecting a, network’s bandwidth include −, • Network devices used, • Protocols used, • Number of users connected, • Network overheads like collision, errors, etc., , Wi-Fi Card, Wi-Fi is the acronym for wireless fidelity. Wi-Fi, technology is used to achieve wireless connection to, any network. Wi-Fi card is a card used to connect any, device to the local network wirelessly. The physical area, of the network which provides internet access through, Wi-Fi is called Wi-Fi hotspot. Hotspots can be set up at, , Throughput, Throughput is the actual speed with which data gets, transferred over the network. Besides transmitting the, actual data, network bandwidth is used for transmitting, error messages, acknowledgement frames, etc., , 13

Page 14 :
Throughput is a better measurement of network speed,, efficiency and capacity utilization rather than, bandwidth., , Protocol, Protocol is a set of rules and regulations used by devices, to communicate over the network. Just like humans,, computers also need rules to ensure successful, communication. If two people start speaking at the, same time or in different languages when no interpreter, is present, no meaningful exchange of information can, occur., Similarly, devices connected on the network need to, follow rules defining situations like when and how to, transmit data, when to receive data, how to give errorfree message, etc., Some common protocols used over the Internet are −, • Transmission Control Protocol, • Internet Protocol, • Point to Point Protocol, • File Transfer Protocol, • Hypertext Transfer Protocol, • Internet Message Access Protocol, , 14