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11agn 21 introduc8on to computer networks signals 22

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Unformatted text preview: s that carry bits of informa8on •  We’ll look at some common types: –  Wires » –  Fiber (fiber op8c cables) » –  Wireless » 14 7 10/6/13 Wires – Twisted Pair •  Very common; used in LANs and telephone lines –  Twists reduce radiated signal Category 5 UTP cable with four twisted pairs 15 Wires – Coaxial Cable •  Also common. BeQer shielding for beQer performance •  Other kinds of wires too: e.g., electrical power 16 8 10/6/13 Fiber •  Long, thin, pure strands of glass –  Enormous bandwidth over long distances Op8cal fiber Light source (LED, laser) Light trapped by total internal reflec8on Photo- detector 17 Fiber (2) •  Two varie8es: mul8- mode (shorter links, cheaper) and single- mode (up to ~100 km) One fiber Fiber bundle in a cable 18 9 10/6/13 Wireless •  Sender radiates signal over a region –  In many direc8ons, unlike a wire, to poten8ally many receivers –  Nearby signals (same freq.) interfere at a receiver; need to coordinate use 19 WiFi WiFi 20 10 10/6/13 Wireless (2) •  Microwave, e.g., 3G, and unlicensed (ISM) frequencies, e.g., WiFi, are widely used for computer networking 802.11 b/g/n 802.11a/g/n 21 Introduc8on to Computer Networks Signals (§2.2) Computer Science & Engineering 11 10/6/13 Topic •  Analog signals encode digital bits. We want to know what happens as signals propagate over media Signal 10110… …10110 23 Frequency Representa8on = Signal over 8me amplitude •  A signal over 8me can be represented by its frequen...
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