Networks - PDF

# Networks ## Unit I: Communication System and Network Topology ### Learning Scope - Introduction, Communication System and its elements - Network Components - Transmission Media - Transmission Signals - Communication Resources - Computer Network, its need and advantages - T...

# Networks ## Unit I: Communication System and Network Topology ### Learning Scope - Introduction, Communication System and its elements - Network Components - Transmission Media - Transmission Signals - Communication Resources - Computer Network, its need and advantages - Types of Network - PAN - LAN - CAN - MAN - WAN - Network Topology - Types of topologies - Star - Ring - Complete - Hybrid - Multipoint ### Introduction In today's world, technology plays a crucial role in bringing people closer to each other. The internet has played an important role in connecting people and bringing them closer to each other. The BSNL's byline 'Connecting India' highlights the company's goal to act as a medium of effective communication between people belonging to far-off regions. You can access information directly by using your personal computer and connect with other internet users around the world. Thus, a computer network is a system of interconnecting computers or terminals. It shares the resources viz. computers, peripherals and terminals. It is also used for the purpose of transmitting computerised data from one location to another. The data can be in the form of text, graphics, pictures, audios or videos. ### Communication System A communication system is a collection of individual communication networks which interconnect and inter-operate to form an integrated communication environment. The purpose of a communication system is to facilitate effective communication between the source and the destination. It involves the following elements: 1. Network Components 2. Transmission Media 3. Transmission Signals 4. Communication Resources ### Network Components The components which are needed to facilitate an effective communication from the source to the destination are referred to as network components. These components help in transferring data from one point to another by using resources. This data may be analogous or digital in nature. In any communication process, three elements are essentially needed. They are: 1. **Sender:** It creates the messages to be transmitted. 2. **Medium:** It carries the transmitted messages to the destination. 3. **Receiver:** It receives the messages from the source. | Sender | Medium | Receiver | |---|---|---| | You | Telephone Line | Friend | | Computer | Satellite Link | Computer | For example, when you talk to your friend over a telephone, you are the sender of the data. The telephone line through which your voice is transmitted is the medium and your friend will be the receiver. The same concept holds true for data communications in the field of the computer and its peripherals. In a computer, the data transfer communication system, the sender and the receiver are generally machines. The transmission medium may be telephone lines, satellite links, microwave links, etc. ### Transmission Media The sender-medium-receiver concept has actually been around since a long time. However, the use of this concept has undergone a revolutionary change. Today, we have several types of physical channels (communication media) through which data can be transmitted from one point to another. The transmission media used for communication can be classified into two categories: 1. **Wire-based Transmission Media** In this mode of transmission media, the communicating devices are interconnected via a cable. The signal flows from one device to another through a connecting wire. * **Examples:** - Twisted Pair Cable - Coaxial Cable - Optical Fiber Cable 2. **Wireless Transmission** In case of wireless transmission, the communicating devices are not connected through wires. The signal from the transmitting device travels through the air in the form of electromagnetic waves to reach the receiving device. * **Examples:** - Radio Wave - Microwave (in Communication Satellite) ### Transmission Signals When data is propagated from one point to another, it is transmitted either in the form of electrical signals or digital signals. Computer-generated data is digital, whereas the telephone lines used for the data communication in the computer networks carry analog signals. The technique by which a digital signal is converted into its analog form is called **Modulation**, and the reverse process is called **Demodulation**. Thus, a **modem** is used to perform modulation and demodulation for the data transmission. #### 1. Analog Signal Any type of signal or wave which is continuously varying in nature is known as an analog signal. It always gives output in the form of a pattern which is referred to as the 'Sine' wave. By observing the pattern of the output wave, we can conclude the results. The best examples of analog signals are videos, human voice in the air, radio transmission waves, TV transmission waves, etc. Some of the analog devices are a thermometer, meter scale, wall clock, etc. #### 2. Digital Signal A digital signal works on discrete data which states only two conditions, i.e., 'True' and 'False' or 'High' and 'Low' or 'Present' and 'Absent'. These states represent either 1 (one) or 0 (zero). The pattern of the signal is referred to as the 'Square' wave which is shown in the adjacent figure. An example of a digital signal would be the data transmission in a computer. The most common digital devices are digital clocks, blood pressure measuring machines, computers, laptops, cell phones, etc. ### Advantages of Digital Signal There are many advantages of a digital signal over an analog signal. Some of them are as listed below: * They are more secure as they do not get damaged by noise. * They have a low bandwidth. * They have a higher rate of transmission. * We can translate the messages, audios and videos into different languages. ### Differences between Analog Signal and Digital Signal | Analog Signal | Digital Signal | |---|---| | It signifies a continuous signal which keeps on changing with a fixed time period. | It signifies a discrete signal which carries binary data values (0 or 1). | ### Communication Resources The communication resources refer to the data communication between devices or other media. It may be a wire or wireless based transmission to send or receive data connected to the internet. Moreover, the resources can be used directly or indirectly with the help of some technologies. These resources may follow some authentication (if necessary) while exchanging data. They mainly involve the following: 1. **Broadband** - Broadband internet access is often shortened to just broadband, which is referred to as High-Speed internet. It usually has a very high rate of data transmission as compared to other methods of internet access, such as accessing internet services, connecting with mobile hotspot. - In general, any connection which offers more than 256 Kbps is considered to be a Broadband Internet. - Earlier, the Broadband used co-axial cables or twisted pair cables for the data transmission. With the development of technology, nowadays, it uses optical fiber cable also which makes the data transmission reasonably high. Thus, one can access internet service with just a click. This marks a revolutionary change in the internet world. - Presently, the Broadband services are provided by BSNL, Airtel, Alliance Broadband, JioGiga Fibre, etc. 2. **Wi-Fi System** - Wi-Fi stands for wireless fidelity which allows wireless data transmission. Unlike mobile phones, a standard Wi-Fi device will work anywhere in the world and can transfer data through computers or mobile phones. Today, Wi-Fi is widely used in offices, hospitals, airports, corporate offices and university campuses worldwide. - A Wi-Fi enabled device, such as a PC, video game console, mobile phone or an MP3 player, can connect to the internet, when it is within the range of a wireless network, connected to the internet. Wi-Fi also allows connectivity in peer-to-peer mode (wireless ad hoc network), which enables devices to connect directly with each other. 3. **Bluetooth** - Bluetooth is one of the latest technologies which enables wireless communication between low-power consumption devices within a short range (1 meter, 10 meters, 100 meters) by using radio frequency bandwidth. This technology makes it possible for different devices to communicate with each other when they are within the range. Bluetooth provides a way to connect and exchange information between devices such as mobile phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers, digital cameras, etc. A personal computer must have bluetooth connectivity to communicate with the other bluetooth devices (such as mobile phones, mice and keyboards). However, recent laptops come with an in-built bluetooth adapter to avail this service. ### Computer Network The term 'network' means a system of interconnected points or terminals. So, a computer network is a system of interconnected computers or terminals. The network helps to share the resources of the series of interconnected computers, peripherals and terminals in the network. A part from sharing resources, a computer network also facilitates the transmission of data from one location to another. ### Need for Computer Network In the year 1960, the USSR and USA were involved in a Cold War. In order to send some urgent messages to its armed forces, the USA used the medium of electronic text to communicate with their head offices. Similarly, the disaster of Titanic could have been prevented or the rescue operations could have been intensified had the communication been done on time. It is very important to have a good communication network since it helps to keep ourselves updated about the latest trends in the technology world as well as in other fields. It also serves several purposes like keeping us updated about the election results, sensex in the share market, launching of a new product, etc. ### Advantages of a Computer Network The advantages of a computer network are: * Information can be easily shared by people. * It helps us in staying updated with the events in and around the world. * It also helps in sharing resources. * For example, a colour laser printer connected to a network can print several hard copies. * Interaction among people around the world becomes easy through chatting/video conferencing. * Email allows us to send or receive mails effortlessly. ### Types of Computer Network A computer network is a group of interconnected computers. Computer networks can be classified according to the hardware and software technology used in the networks. The most commonly used networks classified on the basis of geographical distance they cover are listed below: 1. **Personal Area Network (PAN):** This network is used to establish communication among computer devices within the range of 20 to 30 feet. This network may be wired with computer buses (e.g. USB) or may be a wireless network through Bluetooth 2. **Local Area Network (LAN):** A local area network (LAN) is a digital communication system which interconnects a large number of computers and other peripheral devices. This type of network is generally preferred within a smaller area such as an office building or a lab building (say, within the radius of half a kilometre). The configuration of a LAN can be a star, a ring or a multipoint network. The transmission channels use coaxial or fiber optic cables for high-speed transmission. Ethernet, developed by Xerox Corporation is an example of LAN. 3. **Campus Area Network (CAN):** This network connects two or more LANs that are limited to specific geographical areas viz. college campus, office building, etc. It is generally limited to an area between the local area network and the metropolitan area network. 4. **Metropolitan Area Network (MAN):** This network connects two or more local area networks or campus area networks together. The MAN is bigger than the local area network but smaller than the wide area network. This network is located on a larger geographical area whose diameter usually ranges from 5 to 50 kilometers. It prefers routers, switches and hubs but doesn't extend beyond the boundaries of the immediate town/city. 5. **Wide Area Network (WAN):** A wide area network (WAN) is a digital communication system which interconnects a large number of computers in a wide area. This type of communication network can operate worldwide. In WAN, telephone lines, microwave, satellite links, etc. can be used as transmission mediums. The ARPANET (Advanced Research Project Agency) of the U.S. Department of Defense is an example of the WAN. ### Differences between the LAN and the WAN | Local Area Network | Wide Area Network | |---|---| | A local area network is restricted to a limited geographical area. | A wide area network operates on a worldwide or nationwide basis. | | In a local area network, the computers, the terminals and the peripheral devices are connected to each other through wires and co-axial cables. | In a wide area network, there may not be physical connections between various computers. | ### Network Topology The term Network Topology refers to the arrangement of various elements (links, nodes, etc.) of a computer network, physically and logically. Essentially, it is the topological structure of a network. Physical topology refers to the physical placement of computers or nodes, including device location and cable installation. Logical topology defines as how data flows within a network, irrespective of the physical topology. The distances between the nodes, physical interconnections, transmission rates and/or signal types may differ between the two networks. The different types of topologies are: 1. Star 2. Ring 3. Complete 4. Hybrid 5. Multipoint (Bus) #### Star Topology In this topology, there is a host computer storing all the data and information, which is connected to the local computers. The local computers are however not linked directly to each other. They communicate only via the host computer through multiple communication lines. The host computer is thus responsible for establishing communication among the local computers. * **Advantages:** * If any of the local computers fail or break, the transmission system of the network remains unaffected. * The transmission delays between the two terminals do not increase by adding a new terminal. * **Disadvantage:** * The entire system depends upon the host computer. If the transmission of the host computer fails then the entire network fails. #### Ring Topology In this communication system, there is no host computer as such to transmit the data centrally. Thus, there is no 'controlling computer' in this network. All the local computers are connected to each other in a ring arrangement. Each computer in the ring communicates with the other computers. There is no master computer to control the other computers in the ring. * **Advantage:** * In ring topology, all the traffic flows in only one direction and at a very high speed. * **Disadvantage:** * The addition of a new terminal in the network delays the communication. #### Complete Topology In this topology, all the computers are connected to one another. The control is given to each computer to decide its communication priorities. Since, each computer is connected to other computer, it is called a point-to-point link of the network. * **Advantages:** * It is the fastest way to transfer data between two computers. * If any computer breaks down, communication takes place via other modes. * **Disadvantage:** * It is comparatively expensive as the number of terminals/points connected to a computer are more. #### Hybrid Topology It is defined as the combination of two or more topologies. Here, you can find that the star topology is combined with the ring topology and the complete topology. In fact, the configuration of the network depends upon the needs of the organisational structure of the company. #### Multipoint Topology (Bus Topology) In this topology, a single transmission medium is shared by all the terminals as shown in the figure. When a particular computer wants to send a message to another computer, the system checks whether the communication line is free or not. As soon as the communication line is free, the message is transmitted online and thus, it sets up a local area network. A high-speed communication channel may be used for faster communication of online messages from the source to the destination. * **Advantages:** * It is reliable as the failure of one computer within the network does not affect the entire network. * It is easier to connect a new computer into the network. * **Disadvantage:** * If the communication line fails, the entire system stops working. ### Chapter at a Glance * A computer network is a system of interconnecting computers or terminals. It shares the resources (viz. computers, peripherals and terminals) and information. * The internet is a system through which we can communicate with people, or access information from any part of the world. * Communication resources define data communication between devices used directly or indirectly with the help of some technologies. * A communication system is a collection of individual communication networks which are inter-connected and inter-operated to form an integrated communication environment. * The data can be transmitted from one point to another on the network with wires or without wires (wireless transmission). * The two types of transmission signals are the Analog and the Digital. * The analog and digital signals are used to transmit information, usually through electric signals. * An analog signal is continuous which means, that there are no breaks or interruptions. * A digital signal works on discrete data which states only two conditions i.e., 'True' and 'False' or 'High' and 'Low' or 'Present' and 'Absent'. * A broadband internet access is often shortened to just broadband, which refers to a High-Speed Internet. * The Network Topology is the arrangement of various elements of a network, physically and logically.