123f11_Lec3

123f11_Lec3 - Lecture 3: Signaling and Clock Recovery CSE...

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Lecture 3: Signaling and Clock Recovery CSE 123: Computer Networks Stefan Savage
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Last time z Protocols and layering z Layer encapsulation via packet headers Application Presentation Session Transport Network Datalink Physical Application Network Transport Datalink Physical IP Hdr Payload (Web object) TCP Hdr HTTP Hdr Ethernet Hdr datalink network transport application
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Today z How to send data from point A to point B over some link?
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Copper 4 z Typical examples ± Category 5 Twisted Pair 10-1Gbps 50-100m ± Coaxial Cable 10-100Mbps 200m twisted pair copper core insulation braided outer conductor outer insulation coaxial cable (coax)
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Fiber Optics 5 z Typical examples ± Multimode Fiber 10Gbps 300m ± Single Mode Fiber 100Gbps 25km Cheaper to drive (LED vs laser) & terminate Longer distance (low attenuation) Higher data rates (low dispersion)
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Wireless z Widely varying channel bandwidths/distances z Extremely vulnerable to noise and interference 6 Freq (Hz) 10 4 10 6 10 8 10 10 10 12 10 14 AM Coax Microwave Satellite Fiber FM Twisted Pair TV Radio UV Microwave IR Light
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Aside: Wireless spectrum z Shared medium -> regulated use z Wireless frequency allocations
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Spectrum Allocation 8 Time (min) Frequency (Hz) ± Policy approach forces spectrum to be allocated like a fixed spatial resource (e.g. land, disk space, etc) ± Reality is that spectrum is time and power shared ± Measurements show that fixed allocations are poorly utilized 0 Whitespaces?
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9 Overview for today z Digital Signaling ± Why? ± Shannon’s Law and Nyquist Limit z Encoding schemes ± Clock recovery ± Manchester, NRZ, NRZI, etc. z A lot of this material is not in the book z Caveat : I am not an EE Professor
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Signals: 10,000 foot review of digital vs analog z Data can be represented continuously as an analog wave z Or as a series of discrete digital symbols z Why is the digital representation so powerful? ± Noise resistance: has to be a 0 or 1 ± Storage/reproducibility: analog waves can be converted to digital for storage and then back to analog (think about CDs) 0 0 1 0 1 1 1 0 0 0 1
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Overall Goal: Send bits z A three-step process ± Take an input stream of bits (digital data) ± Modulate some physical media to send data (analog) ± Demodulate the signal to retrieve bits (digital again) ± Anybody heard of a modem ( Mod ulator- dem odulator)?
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This note was uploaded on 11/30/2011 for the course CSE cse123 taught by Professor Stefansavage during the Fall '11 term at UCSD.

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123f11_Lec3 - Lecture 3: Signaling and Clock Recovery CSE...

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