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Network 1. What is a network? 2. How are networks classified? 3. What is a network topology? Can you find the word? (bus, topology, optical fibres, infrared) 1. A flexible transparent fiber of extremely pure glass or plastic, generally between 10 and 200 micrometers in diameter, used especially to carry light signals for telecommunication purposes. _________________ 2. Electromagnetic radiation having a wavelength just greater than that of red light but less than that of microwaves. __________ 3. 4. The arrangement in which the nodes of a LAN are connected to each other. _______________ A parallel circuit that connects the major components of a computer, allowing the transfer of electric impulses from one connected component to any other. ______________ Translate the following definition into English. Ένα δίκτυο είναι μια συλλογή υπολογιστών και συσκευών που συνδέονται μεταξύ τους. Το δίκτυο επιτρέπει στους υπολογιστές να επικοινωνούν μεταξύ τους και να μοιράζονται πόρους και πληροφορίες. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… …………………………………. Computer networks can also be classified according to: a. the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fibre, Ethernet, wireless LAN, HomePNA, or Power line communication. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers. Wireless technology is designed to connect devices without wiring. These devises use radio waves or infrared signals as a transmission medium. b. their scale as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area Network (CAN), Storage Area Network (SAN), etc. c. the functional relationships which exist among the elements of the network, e.g. active networking, Client-server and Peer-to-peer (groupwork) architecture. Network topology Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network, star-bus network, tree or hierarchical topology network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term “logical” here is significant. That is, network topology is independent of the “physical” layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a star topology, rather than a bus topology. In this regard, the visual and operational characteristics of a network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data; these include digital and analogue networks. Network configurations. Complete the paragraphs with the words below terminals – remote – central – directly - configuration Star: In the star configuration, the ____________ computer performs all processing and control functions. All ___________ are connected to a central computer, controller or hub. The star _______________ has two limitations; it is sensitive to failure and the ___________ devices are not able to communicate ____________; they communicate via the central computer only. Ring: In a ring communications system including a plurality of the concentrations that are connected in the form of a ring and the terminal stations connected to the line concentrators are connected to the main ring via ring subsidiaries. Devices may send information only when they are in control of the “token”, which is a package of data which indicates the device that has control. avoidance – clients – transmit – communications Bus: It is a network architecture in which a set of clients are connected via a shared _______________ line, called a bus. They are the simplest way to connect multiple __________________, but may have problems when two clients want to ______________ at the same time on the same bus. Thus systems which are bus network architecture normally have some scheme of collision handling or collision _________________ for communication on the bus. Match the phrases in the columns according to the text 1. 2. 3. 4. Wireless connection Infrared signal Ethernet Network topology a. b. c. d. Independent of the physical layout Transmission medium Physical wiring Radio waves The columns below describe characteristics of the bus, star and ring configurations. Which column refers to which configuration? A …………………….. B. ………………………… C. …………………… Simple multi-connection The device having control Control by the central computer Clients connected in a line A network in the shape of a loop Easy to fail Collision problems Only one device may send data at No direct communication a given moment Which configuration is presented in each picture? Vocabulary Avoidance = αποφυγή Classify = ταξινομώ Collision = σύγκρουση Configuration = διάταξη, δομή Convey = μεταφέρω Deploy = αναπτύσσω Hub = κεντρικός κόμβος Indicate = δείχνω, δηλώνω Layout = στήσιμο, διαρρύθμιση Limitation = περιορισμός Router = δρομολογητής Switch = μεταγωγέας Sensitive = ευαίσθητος Significant = σημαντικός Signify = υποδηλώνω Transmit = στέλλω Wiring =καλωδίωση Below is a list of the most common types of computer networks. Can you identify their name? A ___________ is a computer network used for communication among computer devices close to one person. Some examples of the devices that are used are printers, fax machines, telephones and scanners. The reach of the network is very short. A ___________ is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. A ___________ is a computer network made up of an interconnection of local area networks within a limited geographical area. It can be considered one form of a metropolitan area network, specific to an academic setting. A ___________ is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create this network. A ___________ is a computer network that covers a broad area, uses routers and public communication links. The largest and most well-known is the Internet. It is a data communications network that covers a relatively broad geographic area (i.e. one city to another, one country to another) and that often uses transmission facilities provided by common carriers, such as telephone companies.