136 lines
5.3 KiB
Plaintext
136 lines
5.3 KiB
Plaintext
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\ / |_
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/ \ e n o n | o u n d a t i o n
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presents:
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\ /
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*------ the \ /
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/ \ files ------*
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/ \
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Fall/1993 Issue: 6
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INTRODUCTION TO BASIC DIGITAL TECHNOLOGY
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Written by: Erik Turbo
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File: 6 of 6
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6. Multiplexing and Fiber Optics
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6.1 Space Division Multiplexing (SDM)
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Space Division Multiplexing is the bunding of many physically seperate trans-
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mission paths into a common path. The channels are to be seperated in space.
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6.2 Frequency Division Multiplexing (FDM)
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Frequency Division Multiplexing is the combination of many individual
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channels on a common facility. Each individual channel is placed on a
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common facility at a different "carrier frequency." The individual
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channels are said to be separated in frequency.
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6.3 Digital Facility with Multiplexers
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______ ___ ___ ______
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<--->| | | | | | | |<--->
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<--->| CHAN |--->| | | |--->| CHAN |<--->
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<--->| | | | | | | |<--->
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| | | M | | M | | |
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<--->| BANK |<---| U | _________________ | U |<---| BANK |<--->
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<--->| | | X | | | | X | | |<--->
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<--->|______| | | | DIGITAL | | | |______|<--->
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| / |--->| TRANSMISSION |--->| / |
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| |<---| SYSTEM |<---| | ______
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______ | D | | | | D | | |<--->
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<--->| | | E | | | | E | | CHAN |<--->
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<--->| CHAN |--->| M | |_________________| | M |--->| |<--->
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<--->| | | U | | U | | |
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| | | X | | X | | |
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<--->| BANK |<---| | | |<---| BANK |<--->
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<--->| | | | | | | |<--->
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<--->|______| |___| |___| |______|<--->
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---> high speed ---> low speed
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<--- low speed <--- high speed
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The function of a Multiplexer is to combine two or more lower rate bit streams
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into one high rate bit stream. At the other end of teh transmission system a
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Demultiplexer is needed to seperate the single high rate bit stream into
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two or more lower rate bit streams.
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Generally, multiplexers, or Muldems, are required whenever the digital
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transmission system operates at a rate other than DS1.
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6.7 Fiber Optic Systems
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___________ ______________ _____________
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|Electrical | | | | |
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Input | to | | Transmission | | Optical to | Output
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-------> | Optical |---| Medium |---| Electrical |---------->
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| Transducer| | | | Transducer |
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|___________| |______________| |_____________|
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Basic Fiber Optic System
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Components
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A basic fiber optic system consists of an optical transmitter, a fiber optic
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channel, and an optical receiver. The input is usually DS1, DS1C, DS2, or
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DS3 electrical signals multiplexed in the optical transmission system.
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A transducer converts the electrical pulses into light pulses. The light
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sources include LASER, Light Amplification by Stimulated Emission of
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Radiation, and LEDS, Light Emitting Diodes. Most systems generate a
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signel frequency of light operating upwards in the 1500 nanometers range.
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The light source is turned on and off at a fixed pulse rate. The order
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of the "on" and "off" signals follow the bit pattern of the incoming
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electrical signals.
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The optical fiber are pure glass which provide a low loss transmission path
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for the lightwave signals.
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The optical fiber are pure glass which provide a low loss transmission path
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for the lightwave signals.
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Fiber systems used bny Telephone Companies are produced by NEC, Rockwell,
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AT&T, and Northern Telecom.
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6.5 Fiber
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Typical Fibers
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The fiber consists of a core, cladding, and protective coating.
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> The core is made from germanium-doped silica glass and provides the medium
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for the digital optical signal.
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> The cladding which surrounds the core is also made of silica glass, but has
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different transmission characteristics that bend (refracts) the signal to
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stay within the core.
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Advantages of Lightguide
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1. The large bandwidth allows much higher channel carrying capacities.
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2. Less attenuation allows longer distances between regenerators, ranging
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from 35 to 50 miles.
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3. The small size eases installation and allows mutliple use of conduit by
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using innerduct.
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------------------------------------------------------------------------------
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EOF ---------------- Xenon Foundation Productions 1993 -------------------EOF
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------------------------------------------------------------------------------
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