dumas_ch01 - Chapter 1 Introduction andCommunications M...

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Chapter 1: Introduction Principles of Computer Networks  Principles of Computer Networks  and Communications and Communications M. Barry Dumas and Morris Schwartz M. Barry Dumas and Morris Schwartz
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Chapter 1 Principles of Computer Networks and Communications 2 Objectives Describe evolving role of communications Describe wiring dilemma of connecting phones Provide historical perspective on voice and data communications Differentiate between types of signaling and identify the role of bandwidth in communications Describe differences in standards and architecture models in design of networks
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Chapter 1 Principles of Computer Networks and Communications 3 Overview Communication is at the heart of humankind’s ability to Disseminate ideas and information Coordinate complex tasks Build cohesive societies “Communication provides both the fundamental underpinnings of civilization and an important mechanism for its growth and development.”
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Chapter 1 Principles of Computer Networks and Communications 4 Communications between People Voice (within hearing distance) Writing, fixed location Writing over distance (via postal) Voice, fixed location (electromechanical) Voice over distance (electromagnetic waves) Voice over distance (optical)
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Chapter 1 Principles of Computer Networks and Communications 5 Historical Perspective of Communications—Timeline 1844 Telegraph begins operating 1876 Telephone is invented 1880 30,000 telephones in United States 1891 Electromechanical switchboard (Strowger patents to thwart competitor’s wife) 1938 Bell crossbar switch (faster, more reliable, less noise) 1958 AT&T develops modem here 1969 ARPANET begins as first packet-switched network 1970s Data networks separate from the voice network 1980s Optical fiber transmissions actively deployed Internet available to general public 1990s Convergence of voice and data networks 2000s Emergence of wireless
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Chapter 1 Principles of Computer Networks and Communications 6 Communication Technology and the Electromagnetic Spectrum Category Frequencies Wavelengths Infrared To 4 x 10 14 Hz 0.0000007 meters Microwaves To 3 x 10 11 Hz 0.004 meters Radio waves Below 3 x 10 9 Hz 0.100 meters [See http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ]
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Chapter 1 Principles of Computer Networks and Communications 7 Wire Pairs for Full Interconnection Number of wire pairs [N is number of phones] (N) * (N – 1) --------------- 2 e.g., 4 phones (4) * (4 – 1) ---------------- = 6 pairs 2
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Chapter 1 Principles of Computer Networks and Communications 8 Wire Pairs for Full Interconnection Using wire pairs, 1,000 phones would require 499,500 connections ! Calculation : (1,000) x (999) ------------------ = 499,500 2
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Chapter 1 Principles of Computer Networks and Communications 9 Alternative to Paired Wires between Every Telephone Subscribers [customer] Switchboard at central office (phone company) Each subscriber phone is terminated at a switchboard Operator uses a patch cord to connect between subscriber phones
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Chapter 1
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