CN_UNIT_1.pdf

DELHI TECHNICAL CAMPUS, Greater Noida DEPARTMENT OF COMPUTER APPLICATIONS Computer Networks Faculty: Dr. Archana Sharma UNIT-1 Data Communications Components The effecti...

DELHI TECHNICAL CAMPUS, Greater Noida DEPARTMENT OF COMPUTER APPLICATIONS Computer Networks Faculty: Dr. Archana Sharma UNIT-1 Data Communications Components The effectiveness of a data communications system depends on four fundamental characteristics: delivery, accuracy, timeliness, and jitter. 1. Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user. 2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable. 3. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission. 4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 30 ms (milli second). If some of the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result. A data communications system has five components: Message, Sender, Receiver, Transmission medium, Protocol 1. Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2. Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on. 3. Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on. 4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5. Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese Transmission Modes Data Flow Communication between two devices can be simplex, half-duplex, or full-duplex as shown in Figure 1. Simplex In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive (Figure a). Keyboards and traditional monitors are examples of simplex devices. 2. Half-Duplex In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa (Figure b). Walkie-talkies and CB (citizens band) radios are both half duplex systems. 3. Full-Duplex In full-duplex, both stations can transmit and receive simultaneously (Figure c). One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time. Type of connections There are two possible types of connections: point-to-point and multipoint. Point-to-Point: o A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Most point-to- point connections use an actual length of wire or cable to connect the two ends, but other options, such as microwave or satellite links, are also possible which are shown in the following figure. Multipoint: o A multipoint (also called multidrop) connection is one in which more than two specific devices share a single link as shown in the following figure. o In a multipoint environment, the capacity of the channel is shared, either spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection. Networks Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. 1. Performance: Performance can be measured in many ways, including transit time and  response time. The performance of a network depends on a number of factors, including the number of users, the type of transmission medium, the capabilities of the connected hardware, and the efficiency of the software. Performance is often evaluated by two networking metrics: throughput and delay. We often need more throughput and less delay. 2. Transit time: Transit time is the amount of time required for a message to travel from one device to another. 3. Response time: Response time is the elapsed time between an inquiry and a response. 4. Reliability: In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network's robustness in a catastrophe. 5. Security: Network security issues include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses. Definition: A network is a set of devices (often referred to as nodes) connected by communication links to share resourses. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. “Computer network’’ to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. Networks come in many sizes, shapes and forms, as we will see later. They are usually connected together to make larger networks, with the Internet being the most well-known example of a network of networks. There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent system. Usually, it has a single model or paradigm that it presents to the users. Often a layer of software on top of the operating system, called middleware, is responsible for implementing this model. A well-known example of a distributed system is the World Wide Web. It runs on top of the Internet and presents a model in which everything looks like a document. Goals of Computer Networks: The following are some important goals of computer networks: Resource Sharing – Many organization has a substantial number of computers in operations, which are located apart. Ex. A group of office workers can share a common printer, fax, modem, scanner, etc.  High Reliability – If there are alternate sources of supply, all files could be replicated on two or more machines. If one of them is not available, due to hardware failure, the other copies could be used. Inter-process Communication – Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications. Flexible access – Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another. Other goals include Distribution of processing functions, Centralized management, and allocation of network resources, Compatibility of dissimilar equipment and software, Good network performance, Scalability, Saving money, Access to remote information, Person to person communication, etc. Saving Money- The second goal of a computer network is saving money. Small computers have a much excellent value proportion than higher ones. Mainframes are approximately a method ten times quicker than the quickest single-chip microprocessors, but they cost a huge number of times more. Improve Performance- The fourth goal of a computer network is to improve accessibility and the performance of the system. A system’s performance can be improved by inserting one or more processors into it as its workload grows. Communication Medium-The computer network offers a powerful communication medium. The different user on the network can immediately identify a document that has been refreshed on a network. Uses/Application of computer network: Some of the network applications in different field are the following: Marketing and sales– Computer networks are widely used in both marketing sales firms. These are used by marketing professionals to collect, exchange, and analyzes data relating to customer requirements and product development cycles. Teleshopping is also important part of sales applications that use order-entry computers or telephones connected to an order-processing network, and on-line reservation services for hotels airline and so on. Manufacturing– Now days, computer networks are used in a several aspects of manufacturing, including the manufacturing process itself. Two applications which use a network to provide necessary services are computer-assisted manufacturing (CAM) and computer –assisted designing (CAD) both of which permit multiple users to work on a project simultaneously. Financial Services– In Present, Financial services are completely dependent on computer networks. Main applications are credit history searches, foreign exchange and investment services, and Electronic Funds Transfer (EFT) that permits a user to transfer money without going into bank. Teleconferencing– With The help of teleconferencing conferences are possible to occur without the participants being in the same place. Applications include simple text conferencing, voice conferencing, and video conferencing. Cable Television- Future Services provided by cable television network can include video on request, as well as the same information, financial and communications services currently provided by the telephone companies and computer networks.  Information Services- Network information services include bulletin boards and data banks. A World Wide Web site offering the technical specifications for a new product is an information service. Electronic Messaging– Electronic mail (e-mail) is the most widely used network application. Electronic Data Interchange (EDI)– EDI permits business information to be transferred without using paper. Directory services – By using directory services, it is possible to store the last of files in a central location to speed worldwide search operations. Cellular Telephone: – In the past, two parties desiring to use the services of the telephone company had to be linked by a fixed physical connection. But, in present cellular network make it possible to maintain wireless phone connections even while travelling over large distances. Topology of a network Topology defines the structure of the network of how all the components are interconnected to each other. There are two types of topology: physical and logical topology. Physical topology is the geometric representation of all the nodes in a network. 1. Bus Topology o The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable. o Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.  o When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not. o The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks. o The configuration of a bus topology is quite simpler as compared to other topologies. o The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations. Advantages of Bus topology: o Low-cost cable: In bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low. o Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support upto 10 Mbps. o Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available. o Limited failure: A failure in one node will not have any effect on other nodes. Disadvantages of Bus topology: o Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling. o Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes. o Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other. o Reconfiguration difficult: Adding new devices to the network would slow down the network. o Attenuation: Attenuation is a loss of signal leads to communication issues. Repeaters are used to regenerate the signal. 2 Ring Topology o Ring topology is like a bus topology, but with connected ends.  o The node that receives the message from the previous computer will retransmit to the next node. o The data flows in one direction, i.e., it is unidirectional. o The data flows in a single loop continuously known as an endless loop. o It has no terminated ends, i.e., each node is connected to other node and having no termination point. o The data in a ring topology flow in a clockwise direction. o The most common access method of the ring topology is token passing. Working of Token passing o A token moves around the network, and it is passed from computer to computer until it reaches the destination. o The sender modifies the token by putting the address along with the data. o The data is passed from one device to another device until the destination address matches. Once the token received by the destination device, then it sends the acknowledgment to the sender. o In a ring topology, a token is used as a carrier. Advantages of Ring topology: o Network Management: Faulty devices can be removed from the network without bringing the network down. o Product availability: Many hardware and software tools for network operation and monitoring are available. o Cost: Twisted pair cabling is inexpensive and easily available. Therefore, the installation cost is very low. o Reliable: It is a more reliable network because the communication system is not dependent on the single host computer. Disadvantages of Ring topology: o Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes. o Failure: The breakdown in one station leads to the failure of the overall network. o Reconfiguration difficult: Adding new devices to the network would slow down the network. o Delay: Communication delay is directly proportional to the number of nodes. Adding new devices increases the communication delay. 3 Star Topology  o Star topology is an arrangement of the network in which every node is connected to the central hub, switch or a central computer. o The central computer is known as a server, and the peripheral devices attached to the server are known as clients. o Coaxial cable or RJ-45 cables are used to connect the computers. o Hubs or Switches are mainly used as connection devices in a physical star topology. o Star topology is the most popular topology in network implementation. Advantages of Star topology o Efficient troubleshooting: Troubleshooting is quite efficient in a star topology as compared to bus topology. In a bus topology, the manager has to inspect the kilometers of cable. In a star topology, all the stations are connected to the centralized network. Therefore, the network administrator has to go to the single station to troubleshoot the problem. o Network control: Complex network control features can be easily implemented in the star topology. Any changes made in the star topology are automatically accommodated. o Limited failure: As each station is connected to the central hub with its own cable, therefore failure in one cable will not affect the entire network. o Familiar technology: Star topology is a familiar technology as its tools are cost-effective. o Easily expandable: It is easily expandable as new stations can be added to the open ports on the hub. o Cost effective: Star topology networks are cost-effective as it uses inexpensive coaxial cable. o High data speeds: It supports a bandwidth of approx 100Mbps. Ethernet 100BaseT is one of the most popular Star topology networks. Disadvantages of Star topology o A Central point of failure: If the central hub or switch goes down, then all the connected nodes will not be able to communicate with each other.  o Cable: Sometimes cable routing becomes difficult when a significant amount of routing is required. 4 Tree topology o Tree topology combines the characteristics of bus topology and star topology. o A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion. o The top-most node in tree topology is known as a root node, and all other nodes are the descendants of the root node. o There is only one path exists between two nodes for the data transmission. Thus, it forms a parent-child hierarchy. Advantages of Tree topology o Support for broadband transmission: Tree topology is mainly used to provide broadband transmission, i.e., signals are sent over long distances without being attenuated. o Easily expandable: We can add the new device to the existing network. Therefore, we can say that tree topology is easily expandable. o Easily manageable: In tree topology, the whole network is divided into segments known as star networks which can be easily managed and maintained. o Error detection: Error detection and error correction are very easy in a tree topology. o Limited failure: The breakdown in one station does not affect the entire network. o Point-to-point wiring: It has point-to-point wiring for individual segments. Disadvantages of Tree topology o Difficult troubleshooting: If any fault occurs in the node, then it becomes difficult to troubleshoot the problem. o High cost: Devices required for broadband transmission are very costly. o Failure: A tree topology mainly relies on main bus cable and failure in main bus cable will damage the overall network.  o Reconfiguration difficult: If new devices are added, then it becomes difficult to reconfigure. 5 Mesh topology o Mesh technology is an arrangement of the network in which computers are interconnected with each other through various redundant connections. o There are multiple paths from one computer to another computer. o It does not contain the switch, hub or any central computer which acts as a central point of communication. o The Internet is an example of the mesh topology. o Mesh topology is mainly used for WAN implementations where communication failures are a critical concern. o Mesh topology is mainly used for wireless networks. o Mesh topology can be formed by using the formula: Number of cables = (n*(n-1))/2; Where n is the number of nodes that represents the network. Advantages of Mesh topology: o Reliable: The mesh topology networks are very reliable as if any link breakdown will not affect the communication between connected computers. o Fast Communication: Communication is very fast between the nodes. o Easier Reconfiguration: Adding new devices would not disrupt the communication between other devices. Disadvantages of Mesh topology o Cost: A mesh topology contains a large number of connected devices such as a router and more transmission media than other topologies.  o Management: Mesh topology networks are very large and very difficult to maintain and manage. If the network is not monitored carefully, then the communication link failure goes undetected. o Efficiency: In this topology, redundant connections are high that reduces the efficiency of the network. 6 Hybrid Topology o The combination of various different topologies is known as Hybrid topology. o A Hybrid topology is a connection between different links and nodes to transfer the data. o When two or more different topologies are combined together is termed as Hybrid topology and if similar topologies are connected with each other will not result in Hybrid topology. For example, if there exist a ring topology in one branch of ICICI bank and bus topology in another branch of ICICI bank, connecting these two topologies will result in Hybrid topology. Advantages of Hybrid Topology o Reliable: If a fault occurs in any part of the network will not affect the functioning of the rest of the network. o Scalable: Size of the network can be easily expanded by adding new devices without affecting the functionality of the existing network. o Flexible: This topology is very flexible as it can be designed according to the requirements of the organization.  o Effective: Hybrid topology is very effective as it can be designed in such a way that the strength of the network is maximized and weakness of the network is minimized. Disadvantages of Hybrid topology o Complex design: The major drawback of the Hybrid topology is the design of the Hybrid network. It is very difficult to design the architecture of the Hybrid network. o Costly Hub: The Hubs used in the Hybrid topology are very expensive as these hubs are different from usual Hubs used in other topologies. o Costly infrastructure: The infrastructure cost is very high as a hybrid network requires a lot of cabling, network devices, etc. Types of computer network 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. Computer network divided into two categories called wired and wireless. Types of CN Based on Based on Based on geographical communication structure area medium Peer-2-Peer LAN Wired Client/Server MAN Wireless WAN NOTE- All the networks can be of wired and wireless type. Wired Network: As we all know, “wired” refers to any physical medium made up of cables. Copper wire, twisted pair, or fiber optic cables are all options. A wired network employs wires to link devices to the Internet or another network, such as laptops or desktop PCs. Wireless Network: “Wireless” means without wire, media that is made up of electromagnetic waves (EM Waves) or infrared waves. Antennas or sensors will be present on all wireless devices. Cellular phones, wireless sensors, TV remotes, satellite disc receivers, and laptops with WLAN cards are all examples of wireless devices. For data or voice communication, a wireless network uses radiofrequency waves rather than wires. Wired Network Wireless Network A wired network employs wires to link “Wireless” means without wire, media that devices to the Internet or another network, is made up of electromagnetic waves (EM such as laptops or desktop PCs. Waves) or infrared waves. Antennas or  sensors will be present on all wireless devices Faster transmission speed Slow transmission speed Propagation delay is Low Propagation delay is high More Secure & hence Reliable Less Secure & hence less Reliable Devices must be hard-wired Installation is Quick Less expensive device More expensive devices High installation & maintenance cost Low installation & maintenance cost Wireless routers, access points, etc. are Hub, Switch, etc. devices are used used. LAN (Local Area Network) 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. Local Area Network provides higher security. PAN (Personal Area Network) 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. Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network. Wired Personal Area Network is created by using the USB. Examples of Personal Area Network: Body Area Network: Body Area Network is a network that moves with a person. Offline Network: An offline network can be created inside the home, so it is also known as a home network. A home network is designed to integrate the devices such as printers, computer, television but they are not connected to the internet.  Small Home Office: It is used to connect a variety of devices to the internet and to a corporate network using a VPN MAN (Metropolitan Area Network) 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). 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. Examples of Wide Area Network: Mobile Broadband: A 4G network is widely used across a region or country. Last mile: A telecom company is used to provide the internet services to the customers in hundreds of cities by connecting their home with fiber. Private network: A bank provides a private network that connects the 44 offices. This network is made by using the telephone leased line provided by the telecom company. Advantages of Wide Area Network: Following are the advantages of the Wide Area Network 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: 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. 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. 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. Difference between LAN, MAN, WAN Parameter LAN MAN WAN Full Form LAN is an acronym for MAN is an acronym for WAN is an acronym for Local Area Network. Metropolitan Area Wide Area Network. Network. Definition and LAN is a network that MAN is a The WAN network spans Meaning usually connects a small comparatively wider to an even larger group of computers in a network that covers locality. It has the given geographical large regions- like capacity to connect area. towns, cities, etc. various countries together. For example, the Internet is a WAN. Network The LAN is private. The MAN can be both The WAN can also be Ownership Hospitals, homes, private or public. both private or public. schools, offices, etc., Many organizations may own it. and telecom  operators may own them. Maintenance and Very easy to design and Comparatively Very difficult to design Designing maintain. difficult to design and and maintain. maintain. Speed LAN offers a very high MAN offers a WAN offers a low Internet speed. moderate Internet Internet speed. speed. Delay in It faces a very short It faces a moderate It faces a high Propagation propagation delay. propagation delay. propagation delay. Faulty Tolerance The LAN exhibits a better The MAN exhibits a The WAN also exhibits a fault tolerance than the lesser fault tolerance. lesser fault tolerance. rest of the networks. Congestion The congestion in the It exhibits a higher It exhibits a higher network is very low. network congestion. congestion in the network. Communication LAN typically allows a MAN allows multiple A huge group of Allotment single pair of devices to computers to interact computers can easily establish a simultaneously with interact with each other communication. But it each other. using the WAN. may also support more computers. Uses Schools, homes, It basically covers a It covers an entire colleges, hospitals, city, a small town, or country, a subcontinent, offices, etc., can privately any given area with a or an equivalent area. use it. bigger radius than the LAN.  The Internet The Internet is a short form for an interconnected network. It has become a vital part of our lives, helping us connect with people worldwide. The Internet is made of a large number of independently operated networks. It is fully distributed with no central control. Each independently-operated system is motivated to ensure that there is end-to-end connectivity of every part of the network. The Internet is simply a wire that runs underground and allows two computers to communicate with each other. A server is a particular computer that is connected directly to the Internet. When we talk about specific web pages, they are simply files that are stored on the server’s hard drive. Every server has a unique protocol address or an IP address. IP addresses are essential for computers to find each other. History of the Internet The first question that pops into your mind is probably, “Who started the internet?”. The Internet was developed by Bob Kahn and Vint Cerf in the 1970s. They began the design of what we today known as the ‘internet.’ It was the result of another research experiment which was called ARPANET, which stands for Advanced Research Projects Agency Network. This was initially supposed to be a communications system for the Defense Team of the United States of America - a network that would also survive a nuclear attack. It eventually became a successful nationwide experimental packet network. But when was the first Internet started? It is believed that on 6 August 1991, when the World Wide Web opened to the public. How Does the Internet Work? Computers that we use every day are called clients because they are indirectly connected to the Internet through an internet service provider. When you open a webpage on your computer, you connect to the webpage, and then you can access it. Computers break the information into smaller pieces called packets, which are reassembled in their original order. If we put the right address on a packet and send it to any computer which is connected as part of the internet, each computer would figure out which cable to send it down next so that it would get to its destination. With several computers on a network, it may create confusion even with unique addresses. This transfer of messages is handled by the Packet Routing Network, and hence a router is required to set up. The Transfer Control Protocol is another system that makes sure no packet is lost or left behind because it might create a disrupted message at the receiving end. The below are the steps for how the message is transferred. 1. First, Computer1 sends a message by IP address to Computer2 2. The message sent by Computer1 is broken into small pieces- packets. 3. These small pieces- packets are transferred concerning Transfer Protocol so that the quality is maintained. 4. Finally, these small pieces- packets reach Computer2 and are reassembled at their IP address. Father of the Internet: Tim Berners-Lee Tim Berners-Lee was the man, who led the development of the World Wide Web, the defining of HTTP (HyperText Transfer Protocol), HTML (hypertext markup language) used to create web pages, and URLs (Universal Resource Locators). Tim Berners-Lee was born in London and he graduated in Physics from Oxford University in 1976. Currently, Tim Berners-Lee is the Director of the World Wide Web Consortium, the group that sets technical standards for the web. Evolution of the Internet Although the Internet was developed much earlier, it only became popular in households in the 1990s. The emergence of the Internet can be tracked by how many businesses and homes started changing the way they worked and started connecting their laptops and other devices to the Internet. However, the concept of hypertext transfer protocol (HTTP) as we know it today, was created only during this time. This meant that people could access the same web pages on their devices now and share information. There has been a dramatic growth in the number of internet users since its inception. As a result, the number of computer networks that are connected has grown exponentially too. It started with only connecting less than ten computers initially. Today, 440 million computers can be connected directly, making life easier for people across the globe. Sharing information and knowledge has become extremely easy for those that have access to the Internet. The country with the highest number of internet users is China, with 1.4 billion users, followed by India with 1.3 billion and the United States of America with a little over 0.3 billion users. Protocols and Standards There are several types of protocols and standards used in computer networks, including Transmission Control Protocol (TCP), Internet Protocol (IP), User Datagram Protocol (UDP) and network standards such as TCP/IP, HTTP, FTP, among others. Transmission Control Protocol (TCP) Transmission Control Protocol (TCP) is a fundamental component of computer networks, designed to ensure accurate and reliable data transmission between devices. As one of the core protocols in the Internet Protocol (IP) suite, TCP guarantees that all information packets arrive at their intended destination in the correct order and without errors. TCP's well-established rules help facilitate smooth communication across various network architectures while maintaining high standards of security and performance. For example, when downloading a large file from a website or conducting online banking transactions, TCP ensures that your connection remains stable and secure throughout the entire process. Internet Protocol (IP) Internet Protocol (IP) is a fundamental network protocol that enables data communication across the internet. It is responsible for routing and forwarding data packets from one device to another, based on their unique addressing scheme. IP addresses are used to identify devices that are connected to a network, allowing them to communicate with each other. One of the key features of IP is its ability to work in conjunction with other protocols such as TCP or UDP, forming the backbone of the internet's infrastructure. Without it, we wouldn't be able to send emails or browse web pages online. User Datagram Protocol (UDP) User Datagram Protocol (UDP) is a connectionless protocol that operates on top of the Internet Protocol (IP). It is faster than Transmission Control Protocol (TCP) because it does not guarantee the delivery of packets or in order delivery, making it less reliable. UDP is commonly used for time-sensitive applications such as online gaming, video streaming, and voice-over-IP (VoIP), where speed and efficiency are more important than reliability. It should be noted that while UDP does not provide flow control or error correction like TCP, it has several benefits. For one thing, it requires fewer resources than TCP since no state tracking is required at either end of the communication channel. Professionals who work with computer networks must understand which protocols to use for specific applications to optimize network performance effectively. Network Standards (TCP/IP, HTTP, FTP, Etc.) There are different types of network standards used in computer networks that are essential for data communication. These include − Transmission Control Protocol/Internet Protocol (TCP/IP) − TCP/IP is the most commonly used protocol and standard in computer networks. It is responsible for ensuring reliable data transmission over the internet by breaking down data into smaller packets that can be sent across different network devices. Hypertext Transfer Protocol (HTTP) − HTTP is a standard protocol used for transmitting web pages and other content on the World Wide Web. It defines how web clients such as browsers communicate with servers to retrieve information. File Transfer Protocol (FTP) − FTP is another protocol used to transfer files between devices on a network. It provides a simple way of sending and receiving files, making it an essential tool for businesses that need to transfer large amounts of data. Simple Mail Transfer Protocol (SMTP) − SMTP is a standard protocol used for sending email messages between different email clients and servers on the internet. Domain Name System (DNS) − DNS is a set of protocols that translates human-readable domain names into IP addresses used by computers to locate websites and other resources on the internet. Network Models The OSI Model  The OSI Model or the Open Systems Interconnection Model is a conceptual framework which describes the functions of a networking system. OSI describes how information from a software application in one computer moves through a physical medium to the software application in another computer. OSI consists of seven layers, and each layer performs a particular network function. OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications. OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task. Each layer is self-contained, so that task assigned to each layer can be performed independently. Functions of the OSI Layers There are the seven OSI layers. Each layer has different functions. A list of seven layers are given below: 1. Physical layer  The main functionality of the physical layer is to transmit the individual bits from one node to another node. It is the lowest layer of the OSI model. It establishes, maintains and deactivates the physical connection. It specifies the mechanical, electrical and procedural network interface specifications. Functions of a Physical layer: Line Configuration: It defines the way how two or more devices can be connected physically. Data Transmission: It defines the transmission mode whether it is simplex, half- duplex or full-duplex mode between the two devices on the network. Topology: It defines the way how network devices are arranged. Signals: It determines the type of the signal used for transmitting the information. 2. Data-Link Layer This layer is responsible for the error-free transfer of data frames. It defines the format of the data on the network.  It provides a reliable and efficient communication between two or more devices. It is mainly responsible for the unique identification of each device that resides on a local network. It contains two sub-layers: Logical Link Control Layer o It is responsible for transferring the packets to the Network layer of the receiver that is receiving. o It identifies the address of the network layer protocol from the header. o It also provides flow control. Media Access Control Layer o A Media access control layer is a link between the Logical Link Control layer and the network's physical layer. o It is used for transferring the packets over the network. Functions of the Data-link layer Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address. Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header. Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed. Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occurr, then the receiver sends the acknowledgment for the retransmission of the corrupted frames. Access Control: When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time. Feedback: after transmitting the frames, the system waits for the feedback. 3. Network Layer It is a layer 3 that manages device addressing, tracks the location of devices on the network. It determines the best path to move data from source to the destination based on the network conditions, the priority of service, and other factors. The Data link layer is responsible for routing and forwarding the packets. Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an internetwork. The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6. Functions of Network Layer: Internetworking: An internetworking is the main responsibility of the network layer. It provides a logical connection between different devices. Addressing: A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet. Routing: Routing is the major component of the network layer, and it determines the best optimal path out of the multiple paths from source to the destination. Packetizing: A Network Layer receives the packets from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP). 4 Transport Layer The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no duplication of data. The main responsibility of the transport layer is to transfer the data completely.  It receives the data from the upper layer and converts them into smaller units known as segments. This layer can be termed as an end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably. The two protocols used in this layer are: Transmission Control Protocol o It is a standard protocol that allows the systems to communicate over the internet. o It establishes and maintains a connection between hosts. o When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end. User Datagram Protocol o User Datagram Protocol is a transport layer protocol. o It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable. Functions of Transport Layer: Service-point addressing: Computers run several programs simultaneously due to this reason, the transmission of data from source to the destination not only from one computer to another computer but also from one process to another process. The transport layer adds the header that contains the address known as a service-point address or port address. The responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of the transport layer is to transmit the message to the correct process. Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers. Connection control: Transport layer provides two services Connection-oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route. Flow control: The transport layer also responsible for flow control but it is performed end- to-end rather than across a single link. Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error. 5 Session Layer It is a layer 3 in the OSI model. The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices. Functions of Session layer: Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it allows the communication between two processes which can be either half-duplex or full-duplex. Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery. 6 Presentation Layer A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems. It acts as a data translator for a network. This layer is a part of the operating system that converts the data from one presentation format to another format. The Presentation layer is also known as the syntax layer. Functions of Presentation layer: Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on. Different computers use different encoding methods, the presentation layer handles the interoperability between the different encoding methods. It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end. Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network. Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video. 7 Application Layer  An application layer serves as a window for users and application processes to access network service. It handles issues such as network transparency, resource allocation, etc. An application layer is not an application, but it performs the application layer functions. This layer provides the network services to the end-users. Functions of Application layer: File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer. Mail services: An application layer provides the facility for email forwarding and storage. Directory services: An application provides the distributed database sources and is used to provide that global information about various objects. TCP/IP Protocol Suite It was developed by the DoD (Department of Defence) in the 1960s. It is named after the two main protocols that are used in the model, namely, TCP and IP. TCP stands for "Transmission Control Protocol" and IP stands for "Internet Protocol". TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality, however, the modules are not necessarily interdependent The TCP/IP model consists of four layers: the application layer, transport layer, network layer and host to network layer. 1. Host-to- Network Layer −It is the lowest layer that is concerned with the physical transmission of data. TCP/IP does not specifically define any protocol here but supports all the standard protocols. 2. Internet Layer −It defines the protocols for logical transmission of data over the network. The main protocol in this layer is Internet Protocol (IP) and it is supported by the protocols ICMP, IGMP, RARP, and ARP. 3. Transport Layer − It is responsible for error-free end-to- end delivery of data. The protocols defined here are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). 4. Application Layer − This is the topmost layer and defines the interface of host programs with the transport layer services. This layer includes all high-level protocols like Telnet, DNS, HTTP, FTP, SMTP, etc. Functions of TCP/IP layers: Functions of each Layer 1. Host-to-network layer  It is also called a network interface layer or link layer or network access layer. The host-to-network layer is the lowest layer of the TCP/IP model and is concerned with the physical transmission of data. It can be considered as the combination of physical layer and data link layer of the OSI model. It also includes how bits should optically be signaled by hardware devices which directly interfaces with a network medium, like coaxial, optical, coaxial, fiber, or twisted-pair cables. The functions of this layer are – It defines how bits are to be encoded into optical or electrical pulses. It accepts IP packets from the network layer and encapsulates them into frames. It synchronizes the transmission of the frames as well as the bits making up the frames, between the sender and the receiver. It states the transmission mode, i.e. simplex, half duplex or full duplex It states the topology of the network, i.e. bus, star, ring etc. The protocols that this layer supports are − 1. Ethernet 2. Frame Relay 3. Token Ring 4. ATM 2. Network layer The network layer, also called the internet layer. It deals with packets and connects independent networks to transport the packets across network boundaries. The network layer protocols are IP and Internet Control Message Protocol, which is used for error reporting. The main work of this layer is to send the packets from any network, and any computer still they reach the destination irrespective of the route they take. The Internet layer offers the functional and procedural method for transferring variable length data sequences from one node to another with the help of various networks. Message delivery at the network layer does not give any guaranteed to be reliable network layer protocol. Layer-management protocols that belong to the network layer are: 1. Routing protocols 2. Multicast group management 3. Network-layer address assignment. 3. Transport Layer The transport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network.  Transport layer builds on the network layer in order to provide data transport from a process on a source system machine to a process on a destination system. It is hosted using single or multiple networks, and also maintains the quality of service functions. It determines how much data should be sent where and at what rate. This layer builds on the message which are received from the application layer. It helps ensure that data units are delivered error-free and in sequence. Transport layer helps you to control the reliability of a link through flow control, error control, and segmentation or de-segmentation. The transport layer also offers an acknowledgment of the successful data transmission and sends the next data in case no errors occurred. TCP is the best-known example of the transport layer. Important functions of Transport Layers It divides the message received from the session layer into segments and numbers them to make a sequence. Transport layer makes sure that the message is delivered to the correct process on the destination machine. It also makes sure that the entire message arrives without any error else it should be retransmitted. The two protocols used in the transport layer are: User Datagram Protocol (UDP) o It provides connectionless service and end-to-end delivery of transmission. o It is an unreliable protocol as it discovers the errors but not specify the error. o User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged. o UDP does not specify which packet is lost. UDP contains only checksum; it does not contain any ID of a data segment. Transmission Control Protocol (TCP) o It provides a full transport layer services to applications. o It creates a virtual circuit between the sender and receiver, and it is active for the duration of the transmission. o TCP is a reliable protocol as it detects the error and retransmits the damaged frames. Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed and a virtual circuit is discarded. o At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original message.  o At the receiving end, TCP collects all the segments and reorders them based on sequence numbers. 4. Application Layer An application layer is the topmost layer in the TCP/IP model. Application layer interacts with an application program, The application layer is the OSI layer, which is closest to the end-user. It is responsible for handling high-level protocols, issues of representation. When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport layer. Application layer interacts with software applications to implement a communicating component. The interpretation of data by the application program is always outside the scope of the OSI model. Example of the application layer is an application such as file transfer, email, remote login, etc. The function of the Application Layers are Application-layer helps you to identify communication partners, determining resource availability, and synchronizing communication. It allows users to log on to a remote host This layer provides various e-mail services This application offers distributed database sources and access for global information about various objects and services. There is an ambiguity occurs in the application layer. Every application cannot be placed inside the application layer except those who interact with the communication system. For example: text editor cannot be considered in application layer while web browser using HTTP protocol to interact with the network where HTTP protocol is an application layer protocol. Following are the main protocols used in the application layer: HTTP: HTTP stands for Hypertext transfer protocol. This protocol allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio, video. It is known as a Hypertext transfer protocol as it has the efficiency to use in a hypertext environment where there are rapid jumps from one document to another. SNMP: SNMP stands for Simple Network Management Protocol. It is a framework used for managing the devices on the internet by using the TCP/IP protocol suite. SMTP: SMTP stands for Simple mail transfer protocol. The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is used to send the data to another e-mail address. DNS: DNS stands for Domain Name System. An IP address is used to identify the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. Therefore, the system that maps the name to the address is known as Domain Name System.  TELNET: It is an abbreviation for Terminal Network. It establishes the connection between the local computer and remote computer in such a way that the local terminal appears to be a terminal at the remote system. FTP: FTP stands for File Transfer Protocol. FTP is a standard internet protocol used for transmitting the files from one computer to another computer. A Comparison of the OSI and TCP/IP Reference Models OSI TCP/IP OSI represents Open System TCP/IP model represents the Interconnection. Transmission Control Protocol / Internet Protocol. OSI is a generic, protocol independent TCP/IP model depends on standard standard. It is acting as an interaction protocols about which the computer gateway between the network and the network has created. It is a connection final-user. protocol that assigns the network of hosts over the internet. OSI TCP/IP The OSI model was developed first, and The protocols were created first and then then protocols were created to fit the built the TCP/IP model. network architecture’s needs. It provides quality services. It does not provide quality services. The OSI model represents defines It does not mention the services, administration, interfaces and interfaces, and protocols. conventions. It describes clearly which layer provides services. The protocols of the OSI model are better The TCP/IP model protocols are not unseen and can be returned with another hidden, and we cannot fit a new protocol appropriate protocol quickly. stack in it. It is difficult as distinguished to TCP/IP. It is simpler than OSI. It provides both connection and It provides connectionless transmission in connectionless oriented transmission in the network layer and supports connecting the network layer; however, only and connectionless-oriented transmission connection-oriented transmission in the in the transport layer. transport layer. It uses a horizontal approach. It uses a vertical approach. The smallest size of the OSI header is 5 The smallest size of the TCP/IP header is bytes. 20 bytes. Protocols are unknown in the OSI model In TCP/IP, returning protocol is not and are returned while the technology difficult. modifies. Network Standards Networking standards define the rules for data communications that are needed for interoperability of networking technologies and processes. Standards help in creating and maintaining open markets and allow different vendors to compete on the basis of the quality of their products while being compatible with existing market products. During data communication, a number of standards may be used simultaneously at the different layers. The commonly used standards at each layer are − Application layer − HTTP, HTML, POP, H.323, IMAP Transport layer − TCP, SPX Network layer −IP, IPX Data link layer − Ethernet IEEE 802.3, X.25, Frame Relay Physical layer −RS-232C (cable), V.92 (modem) Physical Layer Physical layer in the OSI model plays the role of interacting with actual hardware and signaling mechanism. Physical layer is the only layer of OSI network model which actually deals with the physical connectivity of two different stations. This layer defines the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc. Physical layer provides its services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts them to electrical pulses, which represent binary data. The binary data is then sent over the wired or wireless media. Signals Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk. Both analog and digital data can be represented in digital or analog signals. Digital Signals Digital signals are discrete in nature and represent sequence of voltage pulses. Digital signals are used within the circuitry of a computer system. Analog Signals Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves. Parameter Analog Signal Digital Signal A signal for conveying information A signal which is a discrete function Definition which is a continuous function of time is of time, i.e. non-continuous signal, known as analog signal. is known as digital signal.  Parameter Analog Signal Digital Signal An analog signal is typically represented The typical representation of a Typical by a sine wave function. There are many signal is given by a square wave representation more representations for the analog function. signals also. Analog signals use a continuous range Digital signals use discrete values of values to represent the data and (or discontinuous values), i.e. Signal values information.values to represent the data discrete 0 and 1, to represent the and information. data and information. Signal The bandwidth of an analog signal is The bandwidth of a digital signal is bandwidth low. relatively high. The analog signals are more suitable for The digital signals are suitable for transmission of audio, video and other Suitability computing and digital electronic information through the communication operations such as data storage, etc. channels. The digital signals are more stable Effect of Analog signals get affected by the and less susceptible to noise than electronic noise electronic noise easily. the analog signals. The digital signals have high Due to more susceptibility to the noise, Accuracy accuracy because they are immune the accuracy of analog signals is less. from the noise. Digital signals use less power than Power Analog signals use more power for data analog signals for conveying the consumption transmission. same amount of information. Digital circuits are required for Analog signals are processed by analog Circuit processing of digital signals whose circuits whose major components are components main circuit components are resistors, capacitors, inductors, etc. transistors, logic gates, ICs, etc. Observational The analog signals give observational The digital signals do not given errors errors. observational errors. The common examples of analog signals The common example of digital Examples are temperature, current, voltage, voice, signal is the data store in a pressure, speed, etc. computer memory.  Parameter Analog Signal Digital Signal The analog signals are used in land line The digital signals are used in Applications phones, thermometer, electric fan, computers, keyboards, digital volume knob of a radio, etc. watches, smartphones, etc. Transmission Impairment When signals travel through the medium they tend to deteriorate. This may have many reasons as given: Attenuation For the receiver to interpret the data accurately, the signal must be sufficiently strong.When the signal passes through the medium, it tends to get weaker.As it covers distance, it loses strength. Dispersion As signal travels through the media, it tends to spread and overlaps. The amount of dispersion depends upon the frequency used. Delay distortion Signals are sent over media with pre-defined speed and frequency. If the signal speed and frequency do not match, there are possibilities that signal reaches destination in arbitrary fashion. In digital media, this is very critical that some bits reach earlier than the previously sent ones. Noise Random disturbance or fluctuation in analog or digital signal is said to be Noise in signal, which may distort the actual information being carried. Noise can be characterized in one of the following class: Thermal Noise Heat agitates the electronic conductors of a medium which may introduce noise in the media. Up to a certain level, thermal noise is unavoidable. Intermodulation  When multiple frequencies share a medium, their interference can cause noise in the medium. Intermodulation noise occurs if two different frequencies are sharing a medium and one of them has excessive strength or the component itself is not functioning properly, then the resultant frequency may not be delivered as expected. Crosstalk This sort of noise happens when a foreign signal enters into the media. This is because signal in one medium affects the signal of second medium. Impulse This noise is introduced because of irregular disturbances such as lightening, electricity, short-circuit, or faulty components. Digital data is mostly affected by this sort of noise. Addressing: Four levels of addresses are used in an internet employing the TCP/IP protocols: physical (link) addresses, logical (IP) addresses, port addresses, and specific addresses 1. Physical Addresses/ MAC address The physical address, also known as the link address or MAC address. MAC stands for Media Access Control. Every node in the LAN is identified with the help of MAC address. It is unique and cannot be changed. It is the lowest-level address. This address is assigned by the manufacturer. Represented in hexadecimal The size and format of the physical addresses vary depending on the network. For example, Ethernet uses a 6-byte (48-bit) physical address that is imprinted on the network interface card (NIC). LocalTalk (Apple), however, has a I-byte dynamic address that changes each time the station comes up. 2. Logical Addresses/ IP addresses Logical addresses are necessary for universal communications that are independent of underlying physical networks. Physical addresses are not adequate in an internetwork environment where different networks can have different address formats. Logical addresses are can be changed based on the location of the device. Logical address can be assigned manually or dynamically. Currently a 32-bit address that can uniquely define a host connected to the Internet. No two publicly addressed and visible hosts on the Internet can have the same IP address. Two ways of assigning IP address. IPV4 and IPV6 Ipv4 Ipv6 Address length IPv4 is a 32-bit address IPv6 is12 a 128-bit address. Fields IPv4 is a numeric address that IPv6 is an alphanumeric address that consists of 4 fields which are consists of 8 fields, which are separated by dot (.). separated by colon. Classes IPv4 has 5 different classes of IPv6 does not contain classes of IP IP address that includes Class addresses. A, Class B, Class C, Class D, and Class E. Number of IP IPv4 has a limited number of IPv6 has a large number of IP address IP addresses. addresses. VLSM It supports VLSM (Virtual It does not support VLSM. Length Subnet Mask). Here, VLSM means that Ipv4 converts IP addresses into a subnet of different sizes. Address It supports manual and DHCP It supports manual, DHCP, auto- configuration configuration. configuration, and renumbering. Address space It generates 4 billion unique It generates 340 undecillion unique addresses addresses. End-to-end In IPv4, end-to-end In the case of IPv6, end-to-end connection connection integrity is connection integrity is achievable. integrity unachievable. Security features In IPv4, security depends on In IPv6, IPSEC is developed for the application. This IP security purposes. address is not developed in keeping the security feature in mind. Address In IPv4, the IP address is In IPv6, the representation of the IP representation represented in decimal. address in hexadecimal. Fragmentation Fragmentation is done by the Fragmentation is done by the senders senders and the forwarding only. routers. Packet flow It does not provide any It uses flow label field in the header identification mechanism for packet flow for the packet flow identification. identification. Checksum field The checksum field is The checksum field is not available in available in IPv4. IPv6. Transmission IPv4 is broadcasting. On the other hand, IPv6 is scheme multicasting, which provides efficient network operations. Encryption and It does not provide encryption It provides encryption and Authentication and authentication. authentication. Number of octets It consists of 4 octets. It consists of 8 fields, and each field contains 2 octets. Therefore, the total number of octets in IPv6 is 16.  3. Port Addresses In a node, many processes will be running. Data which are sent/received must reach the right process. Every process in a node is uniquely identified by port number. Port=communication end point Port addresses are like extensions to your IP address. For example, your computer's IP address is 192.168.11.1, while the file transfer protocol (FTP) port number is 20. 4. Specific Addresses Some applications have user-friendly addresses that are designed for that specific address. Examples include the e-mail address (for example, [email protected]) and the Universal Resource Locator (URL) (for example, www.mhhe.com). The first defines the recipient of an e-mail, the second is used to find a document on the World Wide Web Transmission Media: Guided Media, Unguided Media 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: 1. Twisted pair: 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. Types of Twisted pair: 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. 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. 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. 10.1.2 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). Coaxial cable is of two types: 1. Baseband transmission: It is defined as the process of transmitting a single signal at high speed. 2. 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. 10.1.3 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. Diagrammatic representation of fibre optic cable: 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. 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. 10.2 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: 10.2.1 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. 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. Radio waves cover a large area, and they can penetrate the walls. Radio transmission provides a higher transmission rate. 10.2.2 Microwaves Microwaves are of two types: Terrestrial microwave Satellite microwave communication. Terrestrial Microwave Transmission 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: 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. 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. Satellite Microwave Communication 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. 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. 10.2.3 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. 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. Characteristics of Infrared: 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. Review of Error Detection and Correction codes. Switching In large networks, there can be multiple paths from sender to receiver. The switching technique will decide the best route for data transmission. Switching technique is used to connect the systems for making one-to-one communication. Classification of Switching Techniques 11.1 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. Communication through circuit switching has 3 phases: Circuit establishment Data transfer Circuit Disconnect Circuit Switching can use either of the two technologies: Space Division Switches: Space Division Switching is a circuit switching technology in which a single transmission path is accomplished in a switch by using a physically separate set of crosspoints.  Space Division Switching can be achieved by using crossbar switch. A crossbar switch is a metallic crosspoint or semiconductor gate that can be enabled or disabled by a control unit. The Crossbar switch is made by using the semiconductor. For example, Xilinx crossbar switch using FPGAs. Space Division Switching has high speed, high capacity, and nonblocking switches. Advantages Of Circuit Switching: 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. 11.2 Message Switching 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. Advantages Of Message Switching Data channels are shared among the communicating devices that improve the efficiency of using available bandwidth.