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CompSci notes - Computer Science 7 September 2011 Networks...

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Computer Science 7 September 2011 Networks Computer network: collection of computing devices that are connected various ways to communicate and share resources. Share intangible: files, music, etc…or they can share tangible resources: printers, scanners, etc… Can have physical or wireless networks Each device on a network is called a node Main issue with networking is the data transfer rate, or the speed that data is moved from one place on a network to another. This data transfer rate is referred to as the band width of a network. Bandwidth vs Throughput These are two concepts that are commonly misunderstood Bandwidth is the maximum rate at which data can be moved over a given link or circuit. Defined as the amount of data that can flow through a network at any given time. So, if we upgrade the modem or increase the bandwidth, we should get a higher data transfer rate…but this isn’t always true Throughput: we find that the actual network speeds are much lower. Throughput is the actual bandwidth, as opposed to the theoretical bandwidth. High number of users accessing the network or hardware isn’t capable of using the full bandwidth,… or the network topology. Types of Networks LAN (Local Area Network): connects network devices over a short distance: offices, schools, or homes. These are typically owned, controlled, and managed by a single or organization. Topologies (configurations) Ring topology: connects all nodes in a closed loop where messages travel in one direction until they reach the destination. Star toplogy: centers on one node to which all other nodes are connected. This center node sends all messages. Bus topology: all nodes are connected to a single line that carries messages in both directions. Nodes connected to the bus can read all messages, but ignores what isn’t addressed to them. (Ethernet) Before any device can send a packet, devices on the bus determined that no other device is sending a packet on the cable. When a device sends a packet on the bus, all nodes can see it. If two nodes “talk” at the same time, a collision happens (BE ABLE TO DRAW THIS FOR THE TEST!) WAN (Wide Area Network): spans a large physical distance. The internet is the largest WAN, spanning the earth. Network of LANs. A device called a router connects LANs to WANs. Gateway: used so different LANs can communicate with each other. One node is designated as the “gateway” to handle communication. MAN (Metropolitan area Network): networks spanning a physical area bigger than a LAN but smaller that a WAN, such as a city. A MAN is typically owned by a single entity like the govt or large corporation.
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LAN vs WAN: Most WANs are not owned by any one organization. People can employ one LAN and connect to the Internet WAN via an internet service provider (ISP) using a modem.
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