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& myCBSExguide.com, A Complete guide for CBSE students, , CBSE Class 12 Computer Science, UNIT 5 : Communication and Network Concepts, Network, , e The collection of interconnected computers is called a computer network., e Two computers are said to be interconnected if they are capable of sharing and, , exchanging information., , , , Need, , e Resource Sharing, , e Reliability, , e Cost Factor, , e 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, , Material downloaded from myCBSEguide.com. 1/14
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& myCBSEguide.com, , A Complete guide for CBSE students, , 1. ARPANET: In 1969, The US govt. formed an agency named ARPANET (Advanced Research, Projects Agency NETwork) to connect computers at various universities and defense, agencies. The main objective of ARPANET was to develop a network that could continue, to function efficiently even in the event of a nuclear attack., , 2. Internet (INTERconnection NETwork): The Internet is a worldwide network of, computer networks. It is not owned by anybody., , 3. Interspace: InterSpace is a client/server software program that allows multiple users to, communicate online with real — time audio, video and text chat in dynamic 3D, environments., , SWITCHING TECHNIQUES, Switching techniques are used for transmitting data across networks., Different types are:, , 1. Circuit Switching: In the Circuit Switching technique, first, the complete end-to-end, transmission path between the source and the destination computers is established and, then the message is transmitted through the path. The main advantage of this technique, is guaranteed delivery of the message. Mostly used for voice communication., , 2. Message Switching: In the Message switching technique, no physical path is established, between sender and receiver in advance. This technique follows the store and forward, mechanism., , 3. Packet Switching: In this switching technique fixed size of packet can be transmitted, across the network., , , , , , , , , , , , Comparison between the Various Circuit Message Packet, Switching Techniques: Criteria Switching Switching Switching, Path established in advance Yes No No, , Store and forward technique No Yes Yes, Message follows multiple routes No Yes Yes:, , , , , , , , , , , , DATA COMMUNICATION TERMINOLOGIES, , Material downloaded from myCBSEguide.com. 2/14
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& myCBSEguide.com, , A Complete guide for CBSE students, , Data channel :- The information / data carry from one end to another in the network by, channel., , Baud & bits per second (bps) :- It’s used to measurement for the information carry of a, communication channel., , Measurement Units :- bit, , 1 Byte= 8 bits, , 1 KBPS ( Kilo Byte Per Second)= 1024 Bytes, , 1 Kbps (kilobits Per Second) = 1024 bits, , 1 Mbps ( Mega bits Per Second )=1024 Kbps, , Bandwidth :- It is amount of information transmitted or receives per unit time., Transmission media:, , 1. Twisted pair cable: - It consists of two identical 1 mm thick copper wires insulated and, twisted together. The twisted pair cables are twisted in order to reduce crosstalk and, electromagnetic induction., , Advantages:, i It is easy to install and maintain., ii It is very inexpensive, , Disadvantages:, i. Itis incapable to carry a signal over long distances without the use of repeaters., ii. Due to low bandwidth, these are unsuitable for broadband applications., 2. Co-axial Cables: It consists of a solid wire core surrounded by one or more foil or, braided wire shields, each separated from the other by some kind of plastic insulator. It is, mostly used in the cable wires., , Material downloaded from myCBSEguide.com. 3/14
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S myCBSEguide.com, , A Complete gride for CBSE students, , , , , plastic jacket, , dielectric insulator, , metallic shield, , , , centre core, , Advantages:, i Data transmission rate is better than twisted pair cables., ii. It provides a cheap means of transporting multi-channel television signals around, metropolitan areas., Disadvantages:, i. Expensive than twisted pair cables., ii. Difficult to manage and reconfigure., 3. Optical fiber: - An optical fiber consists of thin glass fibers that can carry information in, the form of visible light., , , , Advantages:, , i. Transmit data over long distance with high security., , ii, Data transmission speed is high, iii’ Provide better noise immunity, , iv. Bandwidth is up to 10 Gbps., , Disadvantages:, , i. Expensive as compared to other guided media., ii. Need special care while installation?, 4. Infrared: - The infrared light transmits data through the air and can propagate, , Material downloaded from myCBSEguide.com. 4/14
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& myCBSEguide.com, A Complete guide for CBSE students, , throughout a room, but will not penetrate walls. It is a secure medium of signal, transmission. The infrared transmission has become common in TV remotes, automotive, garage doors, wireless speakers etc., , 5. Radio Wave: - Radio Wave an electromagnetic wave with a wavelength between 0.5 cm, and 30,000m. The transmission making use of radio frequencies is termed as radio-wave, transmission, Advantages:, , i. Radio wave transmission offers mobility., ii, It is cheaper than laying cables and fibers., iii. It offers ease of communication over difficult terrain., Disadvantages:, i. Radio wave communication is insecure communication., ii, Radio wave propagation is susceptible to weather effects like rains, thunder storms, etc., , 6. Microwave Wave: - The Microwave transmission is a line of sight transmission., Microwave signals travel at a higher frequency than radio waves and are popularly used, for transmitting data over long distances., , Advantages:, i It is cheaper than laying cable or fiber., ii. It has the ability to communicate over oceans., Disadvantages:, i. Microwave communication is an insecure communication., ii Signals from antenna may split up and transmitted in different way to different, antenna which leads to reduce to signal strength., iii. Microwave propagation is susceptible to weather effects like rains, thunder storms, etc., iv. Bandwidth allocation is extremely limited in case of microwaves., 7. Satellite link: - The satellite transmission is also a kind of line of sight transmission that, is used to transmit signals throughout the world., Advantages:, i Area covered is quite large., ii. No line of sight restrictions such as natural mountains, tall building, towers etc., iii. Earth station which receives the signals can be fixed position or relatively mobile., , Material downloaded from myCBSEguide.com. 5/14