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Note for Network Theory - NT By Subham Cool

  • Network Theory - NT
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Subham Cool
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Computer Network - Types and Topologies A computer network is a group of computers that are connected to each other for the purpose of communication. It is a combination of hardware and software resources which allows computers to communicate with many computers and share information between computing devices. Components of Network    Server - The computers that provide shared resources to network users. Receiver - The computers that access the shared resources provided by server. Medium - The wires which makes the physical connections. TYPES OF COMPUTER NETWORKS (1) Local Area Network (LAN) - It is a computer network that covers a small geographical area like home,office or small group of buildings.  It is small in size and generally owned by private body.  It covers maximum ratings of 10 km. Data transfer rates are high.  Two or more computing devices are connected by physical media such as transmission cable  LAN is based on Ethernet Technique.  (2) Wide Area Network (WAN) - It is a computer network that may covers geographical area of a country or continent. It is use to connect LANs and other types of network together so that users of different locations connect with each other,  Data transfer rate is relatively slower than LAN.  WANs are often built using switched circuits. The device which connects WAN with several LANs is called router.  (3) Metropolitan Area Network (MAN) - It is a computer network that usually spans a city or large campus. It covers maximum radius of 50 km.   It usually interconnects a number of LANs into a large network.  It may be a single network such as Cable TV network, spread over a city.

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NETWORK TOPOLOGIES Network Topologies describes the physical layout i.e. how cables, nodes and connection devices are linked or organised together. (1) Bus Network Topology - It is network topology in which set of nodes are connected by a single communication line, called a bus.  It is simplest way to connect multiple nodes  At one time only one node can send data across the network  The failure of one device does not affect the others. (2) Star Network Topology - In this, all the computers are connected to the central device called Hub.Node send electronics signal to the hub, and then to the remaining computers on the network. If Hub will fail then all other computer networks will also fail.   If only one computer will fail, then it will not affect the other networks. It is not so expensive as it requires only one cable to connect more host. 

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(3) Mesh Network Topology - In this, each node in the network has a connection with other node in the network.  The cost of this network is high as it requires large amount of cables and each node require hub. It is more reliable as there is more than one path between a source and  a destination in the network. (4) Ring Network Topology - It is a network topology each node connects to exactly two other nodes forming a single continuous pathway for signals through each node like a ring. The failure of any node may result in failure of the whole ring network.  Some Network Related Terms    Protocol - It is set of rules and standards which is used by computers to exchange data or information with each other across a network. Nodes - It is a connect point where either data transmission ends or redistribution of data starts. Hosts - It is computer or other devices connected to a computer network

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Some basics about virus:What is a VIRUS? It is actually a program, created by people who have knowledge to write software programs. In proper terms, it is called an ‘executable program’, with bad intentions! Viruses are a type of malware, i.e., it is malicious software. How does it work? (Or, how does it make out lives difficult!) A come attached with another program, and once it is in our system and we execute our program- we run the virus too! The virus replicates itself; that is multiplies when has attached itself to a computer through an infected program. So, suppose we download an mp3 song from some suspicious looking website, and we do not have anti-virus software on our PC, in such a case a virus may get downloaded along with the mp3. Once, the virus is in our computer, it then starts making copies of itself on our computer. So, you can imagine, once it replicates, it must need space, thus a virus uses up the hard disk space and that makes our PC/system slow and makes it hang or crash! What other damages does it do? (-apart from crashing our PC and frustrating us?) Depending on what the intention of the person programming the virus was, a virus can do many different types of damages, like : (i) modification of data (Transformers movie anyone?) (ii) files maybe overwritten with false information (iii) files maybe damaged, so you can not open them anymore or work on them (iv) it may even wipe out an entire drive! (v) it may make your system to re-boot again and again (vi) high threat viruses which target databases of big organizations and MNCs may even leak top security information of the companies… A Virus can be programmed to do anything, so its threat can be anything; it’s a creepy virtual world out there!

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