July 5, 2021

INTERNET OF THINGS (IOT) The internet of things, or IoT, is a system of interrelated computing devices, mechanical and digital machines, objects, animals or people that are provided with unique identifiers (UIDs) and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. A thing in the internet of things can be a person with a heart monitor implant, a farm animal with a biochip transponder, an automobile that has built-in sensors to alert the driver when tire pressure is low or any other natural or man-made object that can be assigned an IP address and is able to transfer data over a network. Why IoT is important The internet of things helps people live and work smarter as well as gain complete control over their lives. In addition to offering smart devices to automate homes, IoT is essential to business. 1. IoT provides businesses with a real-time look into how their companies’ systems really work, delivering insights into everything from the performance of machines to supply chain and logistics operations. 2. IoT enables companies to automate processes and reduce labor costs. It also cuts down on waste and improves service delivery, making it less expensive to manufacture and deliver goods as well as offering transparency into customer transactions. 3. IoT touches every industry, including healthcare, finance, retail and manufacturing. Smart cities help citizens reduce waste and energy consumption and connected sensors are even used in farming to help monitor crop and cattle yields and predict growth patterns. 4. As such, IoT is one of the most important technologies of everyday life and it will continue to pick up steam as more businesses realize the potential of connected devices to keep them competitive. Benefits of IoT The internet of things offers a number of benefits to organizations, enabling them to: • Monitor their overall business processes; • Improve the customer experience; • Save time and money; • Enhance employee productivity; • Integrate and adapt business models; • Make better business decisions; and • Generate more revenue. IoT encourages companies to rethink the ways they approach their businesses, industries and markets and gives them the tools to improve their business strategies. Some of the advantages of IoT include: • Ability to access information from anywhere at any time on any device; • Improved communication between connected electronic devices; • Transferring data packets over a connected network saves time and money; • Automating tasks helps improve the quality of a business’ services and reduces the need for human intervention. Some disadvantages of IoT include: • As the number of connected devices increases and more information is shared between devices, the potential that a hacker could steal confidential information also increases; • Enterprises may eventually have to deal with massive numbers — maybe even millions — of IoT devices and collecting and managing the data from all those devices will be challenging. • If there’s a bug in the system, it’s likely that every connected device will become corrupted; • Since there’s no international standard of compatibility for IoT, it’s difficult for devices from different manufacturers to communicate with each other. Consumer and enterprise IoT applications There are numerous real-world applications of the internet of things, ranging from consumer IoT and enterprise IoT to manufacturing and industrial IoT (IoT). IoT applications span numerous verticals, including automotive, telecom and energy. In the consumer segment, for example, smart homes that are equipped with smart thermostats, smart appliances and connected heating, lighting and electronic devices can be controlled remotely via computers and smartphones. 1. In healthcare, IoT offers many benefits, including the ability to monitor patients more closely to use the data that’s generated and analyze it. Hospitals often use IoT systems to complete tasks such as inventory management, for both pharmaceuticals and medical instruments. 2. Smart buildings can, for instance, reduce energy costs using sensors that detect how many occupants are in a room. The temperature can adjust automatically — for example, turning the air conditioner on if sensors detect a conference room is full or turning the heat down if everyone in the office has gone home. 3. In agriculture, IoT-based smart farming systems can help monitor, for instance, light, temperature, humidity and soil moisture of crop fields using connected sensors. IoT is also instrumental in automating irrigation systems.

NETWORK SECURITY AND CLOUD COMPUTING Ways to Enhance Network Security 1. Create a Security Culture: Instilling a security culture that is integrated into the daily work of all employees. Culture starts at the top, and leadership committed to security is imperative. It’s not just a way to operate an organization, it’s a mindset. 2. Implement Network Security Policy: Network security policy is a written document customized to a particular business. The document outlines the rules and procedures relevant to Information Technology assets. This exercise help to determine the use of these assets, the information that is shared and who has access to it. The key to the success of a network policy is to provide training to all employees on every aspect of security. Training will help preserve the confidentiality, availability and integrity of technology systems and data. 3. Keep Network Updated: Given the pace at which technology changes today, keeping current with security takes constant monitoring. It involves keeping tabs on what the hackers are doing, apply the appropriate security software updates and patches to keep secure the business data, customers’ and suppliers’ data too. 4. Have a Secure Back-up Plan: A data back-up plan protect valuable data in the event of a server failure, accidental deletion or outside hacker attack. Back-up solution is dependent upon risk tolerance in a company. Minimum back up is daily with full back up weekly. Periodically testing back-up process and ability to restore data. Better is to store copies off-site. Security can further be increase by using removable data storage media that can be stored separate from the system. 5. Consider Third-Party Services: An added level of security, especially for small to mid-sized businesses, is to outsource data storage. A third-party provider already has technology that may be out of reach of your company’s budget. State-of-the-art (the most recent stage in the development of a product, incorporating the newest ideas and features) products and technologies through a third party can help ensure your business recovers from a data breach or loss of data. An off-site copy of data can help to quickly recover and keep business. CLOUD COMPUTING Cloud The term Cloud refers to a Network or Internet. In other words, we can say that Cloud is something, which is present at remote location. Cloud can provide services over public and private networks, i.e., WAN, LAN or VPN. Applications such as e-mail, web conferencing, customer relationship management (CRM) execute on cloud. Cloud Computing Cloud Computing refers to manipulating, configuring, and accessing the hardware and software resources remotely. It offers online data storage, infrastructure, and application. There are certain services and models working behind the scene making the cloud computing feasible and accessible to end users. Following are the working models for cloud computing: • Deployment Models • Service Models 1. Deployment Models Deployment models define the type of access to the cloud, i.e., how the cloud is located? Cloud can have any of the four types of access: Public, Private, Hybrid, and Community. i. Public Cloud The public cloud allows systems and services to be easily accessible to the general public. Public cloud may be less secure because of its openness. ii. Private Cloud The private cloud allows systems and services to be accessible within an organization. It is more secured because of its private nature. iii. Community Cloud The community cloud allows systems and services to be accessible by a group of organizations. iv. Hybrid Cloud The hybrid cloud is a mixture of public and private cloud, in which the critical activities are performed using private cloud while the non-critical activities are performed using public cloud. 2. Service Models Cloud computing is based on service models. These are categorized into three basic service models which are – • Infrastructure-as–a-Service (IaaS) • Platform-as-a-Service (PaaS) • Software-as-a-Service (SaaS) Benefits of Cloud Computing Cloud Computing has numerous advantages. Some of them are listed below – • One can access applications as utilities, over the Internet. • One can manipulate and configure the applications online at any time. • It does not require installing software to access or manipulating cloud application. • Cloud Computing offers online development and deployment tools, programming runtime environment through PaaS model. • Cloud resources are available over the network in a manner that provide platform independent access to any type of clients. • Cloud Computing offers on-demand self-service. The resources can be used without interaction with cloud service provider. • Cloud Computing is highly cost effective because it operates at high efficiency with optimum utilization. It just requires an Internet connection • Cloud Computing offers load balancing that makes it more reliable. Risks related to Cloud Computing Although cloud Computing is a promising innovation with various benefits in the world of computing, it comes with risks. Some of them are discussed below: A. Security and Privacy: It is the biggest concern about cloud computing. Since data management and infrastructure management in cloud is provided by third-party, it is always a risk to handover the sensitive information to cloud service providers. Although the cloud computing vendors ensure highly secured password protected accounts, any sign of security breach may result in loss of customers and businesses. B. Lock In: It is very difficult for the customers to switch from one Cloud Service Provider (CSP) to another. It results in dependency on a particular CSP for service. C. Isolation Failure: This risk involves the failure of isolation mechanism that separates storage, memory, and routing between the different tenants. D. Management Interface Compromise: In case of public cloud provider, the customer management interfaces are accessible through the Internet. E. Insecure or Incomplete Data Deletion: It is possible that the data requested for deletion may not get deleted. It happens because either of the following reasons Extra copies of data are stored but are not available at the time of deletion • Disk that stores data of multiple tenants is destroyed Characteristics of Cloud Computing There are four key characteristics of cloud computing. 1. On

PURPOSE AND LIMITATIONS OF NETWORKING Computer networking has various purposes which include: Resource sharing, remote communication, distributed processing facilities, cost effectiveness and reliability. 1.8.0 PURPOSE OF NETWORKING ✓ Resource Sharing Anything available on the same network environment is referred to as a resource this include: printers, fax machines, data/information, modems, files etc. Resource sharing is the idea of computers sharing resources in a common network. For example: in a computer lab, all computers can be able to share the same printer or scanner. Also, information can be shared in all computers ✓ Remote Communication Remote communication refers to the transmission of data signals between two communication devices located at different locations. A computer that tries to access resources from another computer on the network is called a remote client while the computer being accessed is called a remote host. Remote communication has been made possible by use of wireless transmission media such as radio waves, microwave and satellite ✓ Distributed Processing Facilities Distributed data processing is a computer-networking method in which multiple computers across different locations share computer-processing capability. This is in contrast to a single, centralized server managing and providing processing capability to all connected systems. Computers that comprise the distributed data-processing network are located at different locations but interconnected by means of wireless or satellite links. Files reside on the user’s computer rather than on a central computer. Branch offices in a large organization have their own servers that store data, information and other resources required for the daily operations. These servers would periodically update the central computer. Advantages of Distributed Processing i. The failure of the central computer does not affect the operations of the other terminals (reliability) processing load is shared equally hence no time wastage (improved performance and reduced time wasting) ii. Relatively cheap -Distributed data processing considerably lowers the cost of data sharing and networking across an organization by comprising several minicomputers that cost significantly less than mainframe machines. iii. The system is flexible in sharing of processing activities also in terms of increasing or decreasing processing power. For example, adding more nodes or computers to the network increases processing power and overall system capability, while reducing computers from the network decreases processing power. iv. Cost Effectiveness- Even though the initial cost is higher, the savings experienced and the value added to service delivery make them a ready choose for enterprising managers. Networks greatly increase the efficient use of scarce resources thus saving operational costs v. Reliability- A computer network is reliable because: a. Data can be transferred with minimum error from source to destination b. In case one computer breaks down, a user can still access data and information from other computers on the same network. Advantages of Computer Networking 1. Easy Communication: It is very easy to communicate through a network. People can communicate efficiently using a network with a group of people. They can enjoy the benefit of emails, instant messaging, telephony, video conferencing, chat rooms, etc. 2. Ability to Share Files, Data and Information: This is one of the major advantages of networking computers. People can find and share information and data because of networking. This is beneficial for large organizations to maintain their data in an organized manner and facilitate access for desired people. 3. Sharing of Resources: Another important advantage of networking is the ability to share hardware/software. For an example, a printer can be shared among the users in a network so that there’s no need to have individual printers for each and every computer in the company. This will significantly reduce the cost of purchasing hardware. 4. Speed: Sharing and transferring files within networks is very rapid, depending on the type of network. This will save time while maintaining the integrity of files. 1.8.1 LIMITATIONS (DISADVANTAGES) OF NETWORKING 1. Security Issues: Data and information is more prone to illegal access than where there is no networking. Computer crimes like tapping of information is common 2. High Initial Costs: Initial costs of acquiring network resources like hardware and software is high 3. Moral and Cultural Effects: Large networks like the internet have chat rooms and messaging services that enable underage children to meet peers and adults on the net some of whom may have bad intentions. E.g. access to drugs information and pornographic contents 4. Spread of Terrorism and Drug Trafficking: The easy flow of information keeps even those who are on the wrong side of the law communicating easily. Terrorists and drug traffickers use information networks for their business communications 5. Over – Reliance on networks: All businesses these days is dependent on computer networks. And if a network fails, businesses will halt to a standstill and bring enormous losses. 6. Bandwidth Issues: In a network there are users who consume a lot more bandwidth than others. Because of this some other people may experience difficulties.  

Infrared Waves Infrared waves, with frequencies from 300 GHz to 400 THz, can be used for short-range communication. Infrared waves, having high frequencies, cannot penetrate walls. This advantageous characteristic prevents interference between one system and another, a short-range communication system in on room cannot be affected by another system in the next room. When we use infrared remote control, we do not interfere with the use of the remote by our neighbours. However, this same characteristic makes infrared signals useless for long-range communication. In addition, we cannot use infrared waves outside a building because the sun’s rays contain infrared waves that can interfere with the communication. Applications of Infrared Waves • The infrared band, almost 400 THz, has an excellent potential for data transmission. Such a wide bandwidth can be used to transmit digital data with a very high data rate. • The Infrared Data Association (IrDA), an association for sponsoring the use of infrared waves, has established standards for using these signals for communication between devices such as keyboards, mouse, PCs and printers. • Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.  

UNBOUNDED OR UNGUIDED TRANSMISSION MEDIA Unguided medium transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. The below figure shows the part of the electromagnetic spectrum, ranging from 3 kHz to 900 THz, used for wireless communication Propagation Modes • Ground Propagation: In this, radio waves travel through the lowest portion of the atmosphere, hugging the Earth. These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. • Sky Propagation: In this, higher-frequency radio waves radiate upward into the ionosphere where they are reflected back to Earth. This type of transmission allows for greater distances with lower output power. • Line-of-sight Propagation: in this type, very high-frequency signals are transmitted in straight lines directly from antenna to antenna. We can divide wireless transmission into three broad groups: 1. Radio waves 2. Micro waves 3. Infrared waves A. Radio Waves Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are normally called radio waves. Radio waves are omnidirectional. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. A sending antenna send waves that can be received by any receiving antenna. The omnidirectional property has disadvantage, too. The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signal suing the same frequency or band. Radio waves, particularly with those of low and medium frequencies, can penetrate walls. This characteristic can be both an advantage and a disadvantage. It is an advantage because, an AM radio can receive signals inside a building. It is a disadvantage because we cannot isolate a communication to just inside or outside a building. Applications of Radio Waves • The omnidirectional characteristics of radio waves make them useful for multicasting in which there is one sender but many receivers. • AM and FM radio, television, maritime radio, cordless phones, and paging are examples of multicasting. B. Micro Waves Electromagnetic waves having frequencies between 1 and 300 GHz are called micro waves. Micro waves are unidirectional. When an antenna transmits microwaves, they can be narrowly focused. This means that the sending and receiving antennas need to be aligned. The unidirectional property has an obvious advantage. A pair of antennas can be aligned without interfering with another pair of aligned antennas. The following describes some characteristics of microwaves propagation: • Microwave propagation is line-of-sight. Since the towers with the mounted antennas need to be in direct sight of each other, towers that are far apart need to be very tall. • Very high-frequency microwaves cannot penetrate walls. This characteristic can be a disadvantage if receivers are inside the buildings. • The microwave band is relatively wide, almost 299 GHz. Therefore, wider sub-bands can be assigned and a high date rate is possible. • Use of certain portions of the band requires permission from authorities. Unidirectional Antenna for Micro Waves Microwaves need unidirectional antennas that send out signals in one direction. Two types of antennas are used for microwave communications: Parabolic Dish and Horn. A parabolic antenna works as a funnel, catching a wide range of waves and directing them to a common point. In this way, more of the signal is recovered than would be possible with a single-point receiver. A horn antenna looks like a gigantic scoop. Outgoing transmissions are broadcast up a stem and deflected outward in a series of narrow parallel beams by the curved head. Received transmissions are collected by the scooped shape of the horn, in a manner similar to the parabolic dish, and are deflected down into the stem. Applications of Micro Waves Satellite Microwave This is a microwave relay station which is placed in outer space. The satellites are launched either by rockets or space shuttles carry them. These are positioned 36000 Km above the equator with an orbit speed that exactly matches the rotation speed of the earth. As the satellite is positioned in a geo-synchronous orbit, it is stationery relative to earth and always stays over the same point on the ground. This is usually done to allow ground stations to aim antenna at a fixed point in the sky. Features of Satellite Microwave • Bandwidth capacity depends on the frequency used. • Satellite microwave deployment for orbiting satellite is difficult. Advantages of Satellite Microwave • Transmitting station can receive back its own transmission and check whether the satellite has transmitted information correctly. • A single microwave relay station which is visible from any point. Disadvantages of Satellite Microwave • Satellite manufacturing cost is very high • Cost of launching satellite is very expensive • Transmission highly depends on whether conditions, it can go down in bad weather

TRANSMISSION MEDIUMS IN COMPUTER NETWORKS Data is represented by computers and other telecommunication devices using signals. Signals are transmitted in the form of electromagnetic energy from one device to another. Electromagnetic signals travel through vacuum, air or other transmission mediums to move from one point to another (from sender to receiver). Electromagnetic energy (includes electrical and magnetic fields) consists of power, voice, visible light, radio waves, ultraviolet light, gamma rays etc. Transmission medium is the means through which we send our data from one place to another. The first layer (physical layer) of Communication Networks OSI Seven-layer model is dedicated to the transmission media, we will study the OSI Model later. Factors to be considered while selecting a Transmission Medium 1. Transmission Rate 2. Cost and Ease of Installation 3. Resistance to Environmental Conditions 4. Distances BOUNDED OR GUIDED TRANSMISSION MEDIA Guided media, which are those that provide a conduit from one device to another, include Twisted-Pair Cable, Coaxial Cable, and Fibre-Optic Cable. A signal travelling along any of these media is directed and contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. Optical fibre is a cable that accepts and transports signals in the form of light. A. Twisted Pair Cable This cable is the most commonly used and is cheaper than others. It is lightweight, cheap, can be installed easily, and they support many different types of network. Some important points: • Its frequency range is 0 to 3.5 kHz. • Typical attenuation is 0.2 dB/Km @ 1kHz. • Typical delay is 50 μs/km. • Repeater spacing is 2km. A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together. One of these wires is used to carry signals to the receiver, and the other is used only as ground reference. The receiver uses the difference between the two. In addition to the signal sent by the sender on one of the wires, interference (noise) and crosstalk may affect both wires and create unwanted signals. If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relative to the noise or crosstalk sources. This results in a difference at the receiver. Twisted Pair is of two types: • Unshielded Twisted Pair (UTP) • Shielded Twisted Pair (STP) Unshielded Twisted Pair Cable It is the most common type of telecommunication when compared with Shielded Twisted Pair Cable which consists of two conductors usually copper, each with its own colour plastic insulator. Identification is the reason behind coloured plastic insulation. Advantages of Unshielded Twisted Pair Cable • Installation is easy • Flexible • Cheap • It has high speed capacity, • 100-meter limit • Higher grades of UTP are used in LAN technologies like Ethernet. It consists of two insulating copper wires (1mm thick). The wires are twisted together in a helical form to reduce electrical interference from similar pair. Disadvantages of Unshielded Twisted Pair Cable • Bandwidth is low when compared with Coaxial Cable Provides less protection from interference. Shielded Twisted Pair Cable This cable has a metal foil or braided-mesh covering which encases each pair of insulated conductors. Electromagnetic noise penetration is prevented by metal casing. Shielding also eliminates crosstalk (explained in KEY TERMS Chapter). It has same attenuation as unshielded twisted pair. It is faster the unshielded and coaxial cable. It is more expensive than coaxial and unshielded twisted pair. Advantages of Shielded Twisted Pair Cable • Easy to install • Performance is adequate • Can be used for Analog or Digital transmission • Increases the signaling rate • Higher capacity than unshielded twisted pair • Eliminates crosstalk Disadvantages of Shielded Twisted Pair Cable • Difficult to manufacture • Heavy  

Computer Networking -Wireless Networks                                                                                                                     Digital wireless communication is not a new idea. Earlier, Morse code was used to implement wireless networks. Modern digital wireless systems have better performance, but the basic idea is the same. Wireless Networks can be divided into three main categories: 1. System interconnection 2. Wireless LANs 3. Wireless WANs System Interconnection System interconnection is all about interconnecting the components of a computer using short-range radio. Some companies got together to design a short-range wireless network called Bluetooth to connect various components such as monitor, keyboard, mouse and printer, to the main unit, without wires. Bluetooth also allows digital cameras, headsets, scanners and other devices to connect to a computer by merely being brought within range. In simplest form, system interconnection networks use the master-slave concept. The system unit is normally the master, talking to the mouse, keyboard, etc. as slaves. Wireless LANs These are the systems in which every computer has a radio modem and antenna with which it can communicate with other systems. Wireless LANs are becoming increasingly common in small offices and homes, where installing Ethernet is considered too much trouble. There is a standard for wireless LANs called IEEE 802.11, which most systems implement and which is becoming very widespread. Wireless WANs The radio network used for cellular telephones is an example of a low-bandwidth wireless WAN. This system has already gone through three generations. • The first generation was analog and for voice only. • The second generation was digital and for voice only. • The third generation is digital and is for both voice and data. Inter Network Inter Network or Internet is a combination of two or more networks. Inter network can be formed by joining two or more individual networks by means of various devices such as routers, gateways and bridges.

TYPES OF COMMUNICATION NETWORKS Communication Networks can be of following 5 types: 1. Local Area Network (LAN) 2. Metropolitan Area Network (MAN) 3. Wide Area Network (WAN) 4. Wireless 5. Inter Network (Internet) Local Area Network (LAN) It is also called LAN and designed for small physical areas such as an office, group of buildings or a factory. LANs are used widely as it is easy to design and to troubleshoot. Personal computers and workstations are connected to each other through LANs. We can use different types of topologies through LAN, these are Star, Ring, Bus, Tree etc. LAN can be a simple network like connecting two computers, to share files and network among each other while it can also be as complex as interconnecting an entire building. LAN networks are also widely used to share resources like printers, shared hard-drive etc. Characteristics of LAN • LAN’s are private networks, not subject to tariffs or other regulatory controls. • LAN’s operate at relatively high speed when compared to the typical WAN. • There are different types of Media Access Control methods in a LAN, the prominent ones are Ethernet, Token ring. • It connects computers in a single building, block or campus, i.e. they work in a restricted geographical area. Applications of LAN • One of the computers in a network can become a server serving all the remaining computers called clients. Software can be stored on the server and it can be used by the remaining clients. • Connecting locally all the workstations in a building to let them communicate with each other locally without any internet access. • Sharing common resources like printers etc. are some common applications of LAN. Advantages of LAN • Resource Sharing: Computer resources like printers, modems, DVD-ROM drives and hard disks can be shared with the help of local area networks. This reduces cost and hardware purchases. • Software Applications Sharing: It is cheaper to use same software over network instead of purchasing separate licensed software for each client a network. • Easy and Cheap Communication: Data and messages can easily be transferred over networked computers. • Centralized Data: The data of all network users can be saved on hard disk of the server computer. This will help users to use any workstation in a network to access their data. Because data is not stored on workstations locally. • Data Security: Since, data is stored on server computer centrally, it will be easy to manage data at only one place and the data will be more secure too. • Internet Sharing: Local Area Network provides the facility to share a single internet connection among all the LAN users. In Net Cafes, single internet connection sharing system keeps the internet expenses cheaper. Disadvantages of LAN • High Setup Cost: Although the LAN will save cost over time due to shared computer resources, but the initial setup costs of installing Local Area Networks is high. • Privacy Violations: The LAN administrator has the rights to check personal data files of each and every LAN user. Moreover, he can check the internet history and computer use history of the LAN user. • Data Security Threat: Unauthorized users can access important data of an organization if centralized data repository is not secured properly by the LAN administrator. • LAN Maintenance Job: Local Area Network requires a LAN Administrator because, there are problems of software installations or hardware failures or cable disturbances in Local Area Network. A LAN Administrator is needed at this full-time job. • Covers Limited Area: Local Area Network covers a small area like one office, one building or a group of nearby buildings. Metropolitan Area Network (MAN) It was developed in 1980s.It is basically a bigger version of LAN. It is also called MAN and uses the similar technology as LAN. It is designed to extend over the entire city. It can be means to connecting a number of LANs into a larger network or it can be a single cable. It is mainly hold and operated by single private company or a public company. Characteristics of MAN • It generally covers towns and cities (50 km) • Communication medium used for MAN are optical fibers, cables etc. • Data rates adequate for distributed computing applications. Advantages of MAN • Extremely efficient and provide fast communication via high-speed carriers, such as fibre optic cables. • It provides a good back bone for large network and provides greater access to WANs. • The dual bus used in MAN helps the transmission of data in both directions simultaneously. • A MAN usually encompasses several blocks of a city or an entire city. Disadvantages of MAN • More cable required for a MAN connection from one place to another. • It is difficult to make the system secure from hackers and industrial espionage (spying) graphical regions. It is also called WAN. WAN can be private or it can be public leased network. It is used for the network that covers large distance such as cover states of a country. It is not easy to design and maintain. Communication medium used by WAN are PSTN or Satellite links. WAN operates on low data rates.  

INTRODUCTION TO COMPUTER NETWORKS A set of devices often mentioned as nodes connected by media link is called a Network. A node can be a device which is capable of sending or receiving data generated by other nodes on the network like a computer, printer etc. These links connecting the devices are called Communication channels. Computer network is a telecommunication channel using which we can share data with other computers or devices, connected to the same network. It is also called Data Network. The best example of computer network is Internet. A network must be able to meet certain criteria’s, these are mentioned below: i. Performance ii. Reliability iii. Scalability Computer Networks: Performance It can be measured in the following ways: • Transit time: It is the time taken to travel a message from one device to another. • Response time: It is defined as the time elapsed between enquiry and response. Other ways to measure performance are: • Efficiency of software • Number of users • Capability of connected hardware Computer Networks: Reliability It decides the frequency at which network failure take place. More the failures are, less is the network’s reliability. Computer Networks: Security It refers to the protection of data from any unauthorized user or access. While travelling through network, data passes many layers of network, and data can be traced if attempted. Hence security is also a very important characteristic for Networks. Properties of a Good Network 1. Interpersonal Communication: We can communicate with each other efficiently and easily. Example: emails, chat rooms, video conferencing etc, all of these are possible because of computer networks. 2. Resources can be shared: We can share physical resources by making them available on a network such as printers, scanners etc. 3. Sharing files, data: Authorized users are allowed to share the files on the network. USES OF COMPUTER NETWORKS 1. Computer Networks: Business Applications Following are some business applications of computer networks: i. Resource Sharing: The goal is to make all programs, equipment’s (like printers etc.), and especially data, available to anyone on the network without regard to the physical location of the resource and the user. ii. Server-Client model: One can imagine a company’s information system as consisting of one or more databases and some employees who need to access it remotely. In this model, the data is stored on powerful computers called Servers. Often these are centrally housed and maintained by a system administrator. In contrast, the employees have simple machines, called Clients, on their desks, using which they access remote data. iii. Communication Medium: A computer network can provide a powerful communication medium among employees. Virtually every company that has two or more computers now has e-mail (electronic mail), which employees generally use for a great deal of daily communication iv. eCommerce: A goal that is starting to become more important in businesses is doing business with consumers over the Internet. Airlines, bookstores and music vendors have discovered that many customers like the convenience of shopping from home. 2. Computer Networks: Home Applications Some of the most important uses of the Internet for home users are as follows: • Access to remote information • Person-to-person communication • Interactive entertainment • Electronic commerce 3. Computer Networks: Mobile Users Mobile computers, such as notebook computers and Mobile phones, is one of the fastest-growing segments of the entire computer industry. Although wireless networking and mobile computing are often related, they are not identical, as the below figure shows.

Terms used in Data communication A. Data Signal Analog signal is one type of continuous time-varying signals, and these are classified into composite and simple signals. A simple type of analog signal is nothing but a sine wave, and that can’t be decomposed, whereas a composite type analog signal can be decomposed into numerous sine waves. An analog signal is not resistant toward the noise, therefore; it faces distortion as well as reduces the transmission quality. The analog signal value range cannot be fixed. Digital signals -These signals are discrete or not continuous. A digital signal carries the data in the form of binary because it signifies in the bits. These signals can be decomposed into sine waves which are termed as harmonics. Digital signals are more resistant toward the noise; therefore, it barely faces some distortion. Modulation and demodulation Modulation is the process of encoding information in a transmitted signal, while demodulation is the process of extracting information from the transmitted signal. A device that performs both modulation and demodulation is called a modem — a name created by combining the first letters of Modulator and Demodulator. Multiplexing and Demultiplexing Multiplexing is a technique used to combine and send the multiple data streams over a single medium. The process of combining the data streams is known as multiplexing and hardware used for multiplexing is known as a multiplexer. Multiplexing is achieved by using a device called Multiplexer (MUX) that combines n input lines to generate a single output line. Multiplexing follows many-to-one, i.e., n input lines and one output line. Demultiplexing is achieved by using a device called Demultiplexer (DEMUX) available at the receiving end. DEMUX separates a signal into its component signals (one input and n outputs). Therefore, we can say that demultiplexing follows the one-to-many approach. The ‘n’ input lines are transmitted through a multiplexer and multiplexer combines the signals to form a composite signal. The composite signal is passed through a Demultiplexer and demultiplexer separates a signal to component signals and transfers them to their respective destinations. Advantages of Multiplexing: • More than one signal can be sent over a single medium. • The bandwidth of a medium can be utilized effectively. D. Transmitter A set of equipment used to generate and transmit electromagnetic waves carrying messages or signals. The transmitter’s function is to convert the message signal into a form which is suitable for transmission over the communication channel or medium. E. Receiver A receiver is a hardware module or device used to receive signals of different kinds, depending on the context of the application. It may receive analog electromagnetic signals or waves, or digital signals through wired media. It is the device that receives and decodes signals and then conditions or transforms them into something that another machine or computer understands. F. Bandwidth Is defined as a range within a band of frequencies or wavelengths. Bandwidth is also the amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz). G. Base band Signal Is an original transmission signal that has not be modulated, or has been demodulated to its original frequency? Most telecommunications protocols require baseband signals to be converted, or modulated, to a higher frequency so they can be transmitted over long distances. H. Attenuation Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances. Attenuation occurs on computer networks because of: • Range – over longer distances both wired and wireless transmissions gradually dissipate in strength • Interference – radio interference or physical obstructions, such as walls, dampen communication signals on wireless networks • Wire size – thinner wires suffer from more attenuation than thicker wires on wired networks Transmission Modes in Computer Networks Transmission mode refers to the mechanism of transferring of data between two devices connected over a network. It is also called Communication Mode. These modes direct the direction of flow of information. There are three types of transmission modes. They are: i. Simplex Mode ii. Half duplex Mode iii. Full duplex Mode Synchronous and Asynchronous Synchronous Transmission In synchronous transmission, data moves in a completely paired approach, in the form of chunks or frames. Synchronization between the source and target is required so that the source knows where the new byte begins, since there are no spaces included between the data. Synchronous transmission is effective, dependable, and often utilised for transmitting a large amount of data. It offers real-time communication between linked devices. An example of synchronous transmission would be the transfer of a large text file. Before the file is transmitted, it is first dissected into blocks of sentences. The blocks are then transferred over the communication link to the target location. Because there are no beginning and end bits, the data transfer rate is quicker but there’s an increased possibility of errors occurring. Over time, the clocks will get out of sync, and the target device would have the incorrect time, so some bytes could become damaged on account of lost bits. To resolve this issue, it’s necessary to regularly re-synchronize the clocks, as well as to make use of check digits to ensure that the bytes are correctly received and translated.

PRINCIPLE OF DATA COMMUNICATION AND COMPUTER NETWORKS DATA COMMUNICATION Refers to a process of transmitting data signals form one point through the network. Basic Communication Model A Communication model is used to exchange data between two parties. For example: communication between a computer, server and telephone (through modem). i. Communication Model: Source Data to be transmitted is generated by this device, example: telephones, personal computers etc. ii. Communication Model: Transmitter The data generated by the source system is not directly transmitted in the form its generated. The transmitter transforms and encodes the data in such a form to produce electromagnetic waves or signals. iii. Communication Model: Transmission System A transmission system can be a single transmission line or a complex network connecting source and destination. iv. Communication Model: Receiver Receiver accepts the signal from the transmission system and converts it into a form which is easily managed by the destination device. v. Communication Model: Destination Destination receives the incoming data from the receiver. Types Data Communication The exchange of data between two devices through a transmission medium is called Data Communication. The data is exchanged in the form of 0’s and 1’s. The transmission medium used is wire cable. For data communication to occur, the communication device must be a part of a communication system. Data Communication has two types – Local and Remote which are discussed below: i. Data Communication: Local Local communication takes place when the communicating devices are in the same geographical area, same building, or face-to-face etc. ii. Data Communication: Remote Remote communication takes place over a distance i.e. the devices are farther. The effectiveness of a data communication can be measured through the following features: a. Delivery: Delivery should be done to the correct destination. b. Timeliness: Delivery should be on time. c. Accuracy: Data delivered should be accurate. Components of Data Communication i. Message: It is the information to be delivered. ii. Sender: Sender is the person who is sending the message. iii. Receiver: Receiver is the person to whom the message is being sent to. iv. Medium: It is the medium through which the message is sent. For example: A Modem. v. Protocol: These are some set of rules which govern data communication.

SYSTEM DOCUMETATION System documentation is information about built solution and acts as a reference for future maintenance or update efforts. A description of a program after it has been developed. It is organized based on system functionality rather than when changes were made to the system, making it easier for people who maintain the solution to find the information they need quickly. It includes wide range of technical and non-technical manuals, books, diagrams and descriptions relating to the use and operation of the developed system. System documentation represents documents that describe the system itself and its parts. It includes requirements documents, design decisions, architecture descriptions, program source code, and FAQs Features of Effective System Documentation: Effective system documentation should possess the following characteristics: i. It must be clearly stated in the language that is easily understood. ii. It should be possible to refer to other documents. iii. It should contain everything needed, so that those who are reading it carefully understand the system. iv. It should be accessible to those for whom it is intended. v. When the system gets modified it should be easy to update the documentation. Purpose of System Documentation: The formal system documentation fulfills the following objectives: i. To provide the necessary information to develop training programme for operators and users. ii. To create a vehicle of information to provide evidence of progress in the development process and to monitor the process i.e. it guides the development team on various stages of SDLC iii. To make conversion of a system from one machine to another machine easier. iv. To make system modification and implementation easier. v. To narrow down the communication gaps among users, designers and management. vi. To provide a means to determine in advance what will occur and when. vii. It can be used as a backup to recover the system should anything happen during implementation viii. It can be effectively used to provide a checklist of items to be covered during subsequent audit. Contents of System Documentation: The report on the system design should contain the following elements: i. An overview of the entire project describing the general purpose of the system with the relevant information. ii. Documentation for every input and output used in the system. Each document should accompany each design and explain the purpose and use of each form. iii. Documentation of every file of the system, creating and update sequences of the file should be there. iv. System flowchart describing the series of steps used in the processing of data. v. A financial analysis of the proposed and existing systems, providing present and future costs with potential cost savings. vi. A description of the computer system and its peripheral equipment’s. Levels of System Documentation: Levels of documentation mean the persons or positions in the managerial hierarchy for whom or to whom document is useful for operation purposes. These levels are: ➢ Documentation for users – To guide users on how to use the system ➢ Documentation for management – Use documents from the past projects to plan and understand the current project. ➢ Documentation for data processing department (System Developers) – Depends on the document from the previous life cycle stages to guide in future modification and maintenance of the system. 1. Documentation for User: For the smooth operation of the system, it is essential that the users understand the system fully, and are aware of that is expected of him to make it work successfully. a) The documentation should include a sample of each input document and instructions for using it. b) It should also indicate operating schedules. c) User’s documentation should cover files layout and file relation details. d) The documentation for user should explain in non-technical terms all aspects of the system from users’ point of view. e) It should also explain how the system will operate once it is fully installed. f) It should include a sample of each output report with necessary explanation. g) It should state the input document coding procedure, and also the coding structure for various fields and related tables. h) Limitations of system should also be highlighted. 2. Documentation for Management: It includes systems’ proposals covering the followings: a) Functional Design—Functional requirements. b) Resources required. c) Cost benefits analysis. d) Development schedule. e) Concepts, architectural design. 3. Documentation for Data Processing Department: This has been divided into following three categories: ➢ Documentation for system’s designers. ➢ Documentation for operations personnel. ➢ Documentation for programmers. A. Documentation for System’s Designers: It includes: i. Layouts of master files ii. Layouts of intermediate files iii. Controls iv. I/O schedules v. Output report layout vi. System flow chart vii. Implementation plan viii. Copy of program specification ix. Input from layouts. B. Documentation for operations personnel: This has three sub-groups: 1. Machine operations—this should include: i. Detailed instructions for each step. ii. File retention schedules. iii. Interrupt/Restart procedures. iv. Systems flow. 2. Data preparations: The documentations should provide samples of all input documents, card layouts, record layouts, special instrument for data preparations, retention schedules for data. 3. I/O control: i. Quality control checking procedures for each step. ii. Dispatching (reports) details iii. Processing schedules iv. Document receipt details. C. Documentation for Programmers: For each program there should be a program folder covering the followings: i. Source program listing. ii. Development of system test run. iii. Program specifications I/O layouts. iv. Usage of any special technique v. Test results vi. Test data listing vii. Program logic flowchart. viii. Changes in specifications during program.