ECE155ALecture4

ECE155ALecture4 - Computer Networks Lecture 4 Professor...

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1 Computer Networks Lecture 4 Professor Louise E. Moser Winter 2010
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2 Public Switched Telephone System Structure of the telephone system Local loop: Modems, DSL, and wireless Trunks and multiplexing Switching
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3 Structure of the Telephone System Major Telephone System Components Local loops - Analog twisted pairs going to homes and businesses Trunks - Digital fiber optics connecting the switching offices Switching offices - Where calls are moved from one trunk to another A Typical Circuit Route for a Medium-Distance Call
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4 Local Loop: Modems, DSL, Wireless Use of both analog and digital transmission for a computer-to-computer call Conversion is done by modems and codecs Transmission lines suffer from attenuation, delay, distortion, and noise
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5 Modems (a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation Modem – Device used between digital computer and analog telephone system to convert digital bit stream into modulated analog signal and vice versa Codec – Device used to convert analog speech signal into a digital bit stream and vice versa
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6 Digital Subscriber Lines (DSL) Twisted pair, designed for digital as well as analog DSL 100,000 bits/sec – 1,000,000 bits/sec If you live more than 5 miles from the telephone exchange, you probably can’t get DSL Currently, Verizon is installing fiber because it’s faster Higher DSL speed => smaller serviceable area Bandwidth vs. distance over category 3 UTP for DSL
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7 Digital Subscriber Lines Typical DSL Equipment Configuration NID – Network Interface Device Splitter – Analog filter that separates voice from data ADSL – A standard, 80-90% of bandwidth is downstream, rest is upstream DSLAM – DSL Access Module
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8 Wireless Local Loops Local Multipoint Distribution Service IEEE 802.16 WiMax Wireless MAN
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9 Transmission and Multiplexing Idea: Multiplex many conversations over a single physical channel with high bandwidth FDM – Frequency Division Multiplexing Frequency spectrum divided into logical channels Each user has exclusive use of its own frequency band WDM – Wavelength Division Multiplexing – Variation of FDM for fiber optic channels TDM – Time Division Multiplexing Time divided into slots Each user has its own time slot Users take turns in round-robin fashion
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10 Frequency Division Multiplexing (a) Original bandwidths (b) Bandwidths raised in frequency (c) Multiplexed channel
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11 Wavelength Division Multiplexing
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