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Notes-Cn-Unit-1 1 UNIT – 1 INTRODUCTION OF NETWORKS Unit-01/Lecture-01 Introduction & Definition[RGPV/Dec 2010/ Jun 2014] A network is a set of devices (often referred to as nodes) connected by communication links. 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. FIGURE 1.1: NETWORK Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security. Performance Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another. Response time is the elapsed time between an inquiry and a response. 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. If we try to send more data to the network, we may increase throughput but we increase the delay because of traffic congestion in the network. 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. 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. Need and advantages of computer network [RGPV/Dec 2010] You have undoubtedly heard the the whole is greater than the sum of its parts. This phrase describes networking very well, and explains why it has become so popular. A network isn't just a bunch of computers with wires running between them. Properly implemented, a network is a system that provides its users with unique capabilities, above and beyond what the individual machines and their software applications can provide. we dont take any liability for the notes correctness. http://www.rgpvonline.com 2 Most of the benefits of networking can be divided into two generic categories: connectivity and sharing. Networks allow computers, and hence their users, to be connected together. They also allow for the easy sharing of information and resources, and cooperation between the devices in other ways. Since modern business depends so much on the intelligent flow and management of information, this tells you a lot about why networking is so valuable. Here are some of the specific advantages generally associated with networking: Connectivity and Communication Networks connect computers and the users of those computers. Individuals within a building or work group can be connected into local area networks (LANs); LANs in distant locations can be interconnected into larger wide area networks (WANs). Once connected, it is possible for network users to communicate with each other using technologies such as electronic mail. This makes the transmission of business (or non-business) information easier, more efficient and less expensive than it would be without the network. Data Sharing One of the most important uses of networking is to allow the sharing of data. Before networking was common, an accounting employee who wanted to prepare a report for her manager would have to produce it on his PC, put it on a floppy disk, and then walk it over to the manager, who would transfer the data to her PC's hard disk. True networking allows thousands of employees to share data much more easily and quickly than this. More so, it makes possible applications that rely on the ability of many people to access and share the same data, such as databases, group software development, and much more. Intranets and extranets can be used to distribute corporate information between sites and to business partners. Hardware Sharing Networks facilitate the sharing of hardware devices. For example, instead of giving each of 10 employees in a department an expensive color printer one printer can be placed on the network for everyone to share. Internet Access The Internet is itself an enormous network, so whenever you access the Internet, you are using a network. The significance of the Internet on modern society is hard to exaggerate, especially for those of us in technical fields. Internet Access Sharing Small computer networks allow multiple users to share a single Internet connection. Special hardware devices allow the bandwidth of the connection to be easily allocated to various individuals as they need it, and permit an organization to purchase one high-speed connection instead of many slower ones. Data Security and Management In a business environment, a network allows the administrators too much better manage the company's critical data. Instead of having this data spread over dozens or even hundreds of small computers in a haphazard fashion as their users create it; data can be centralized on shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information. Performance Enhancement and Balancing Under some circumstances, a network can be used to enhance the overall performance of some applications by distributing the computation tasks to various computers on the network. Entertainment Networks facilitate many types of games and entertainment. The we dont take any liability for the notes correctness. http://www.rgpvonline.com 3 Internet itself offers many sources of entertainment, of course. In addition, many multi- player games exist that operate over a local area network. Many home networks are set up for this reason, and gaming across wide area networks (including the Internet) has also become quite popular. Physical Structures Type of Connection[RGPV/ Dec 2013/ Jun 2014] A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. For visualization purposes, it is simplest to imagine any link as a line drawn between two points. For communication to occur, two devices must be connected in some way to the same link at the same time. There are two possible types of connections: point-to-point and multipoint. Point-to-Point 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. When you change television channels by infrared remote control, you are establishing a point-to-point connection between the remote control and the television's control system. FIGURE 1.2: POINT TO POINT CONNECTION Multipoint A multipoint connection is one in which more than two specific devices share a single link. 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. FIGURE 1.3: MULTIPOINT CONNECTION Physical Topology[RGPV/Jun 2009, Jun 2013] The term physical topology refers to the way in which a network is laid out physically: 1 or more devices connect to a link; two or more links form a topology. we dont take any liability for the notes correctness. http://www.rgpvonline.com 4 FIGURE 1.4: TOPOLOGY Mesh In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects. To find the number of physical links in a fully connected mesh network with n nodes, we first consider that each node must be connected to every other node. Node 1 must be connected to n - I nodes, node 2 must be connected to n – 1 nodes, and finally node n must be connected to n - 1 nodes. We need n (n - 1) physical links. However, if each physical link allows communication in both directions (duplex mode), we can divide the number of links by 2. In other words, we can say that in a mesh topology, we need N (n -1) /2 duplex-mode links. FIGURE 1.5: MESH TOPOLOGY To accommodate that many links, every device on the network must have n – 1 input/output (VO) ports to be connected to the other n - 1 station. A mesh offers several advantages over other network topologies. First, the use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems that can occur when links we dont take any liability for the notes correctness. http://www.rgpvonline.com 5 must be shared by multiple devices. Second, a mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system. Third, there is the advantage of privacy or security. When every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevent other users from gaining access to messages. Finally, point-to- point links make fault identification and fault isolation easy. Traffic can be routed to avoid links with suspected problems. This facility enables the network manager to discover the precise location of the fault and aids in finding its cause and solution. The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required.
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