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CE80N Introduction to Networks & The Internet. Dr. Chane L. Fullmer UCSC Winter 2002. Reading. Chapter 3, Telephones Everywhere Chapter 4, The World Was Once Analog, Chapter 5, The Once and Future Digital Network; . Telephone Network. Telephone analogy for development of the Internet
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CE80N Introduction to Networks&The Internet Dr. Chane L. Fullmer UCSC Winter 2002
Reading • Chapter 3, Telephones Everywhere • Chapter 4, The World Was Once Analog, • Chapter 5, The Once and Future Digital Network; CE80N -- Winter 2002 -- Lecture #2
Telephone Network • Telephone analogy for development of the Internet • Getting going (one person with the “only” phone does not gain much) • Early phone development was fragmented: • Each town/locale/region had independent phone system • No hardware standards (especially international) • Connections made manually (human operators) CE80N -- Winter 2002 -- Lecture #2
History of the Telephone • 1876: Alexander Graham Bell obtains patent for the telephone • 1877: The first commercial telephone service, Bell Telephone, is in operation • 1881: The first long-distance line for public use opens between Boston and Providence • 1891: The first automatic dial system is patented • 1900: Loading coil, a device which significantly reduces the tendency of a telephonic signal to grow weaker over distance, is developed CE80N -- Winter 2002 -- Lecture #2
History of the Telephone • 1915: Formal opening of line between New York and San Francisco • 1927: Commercial telephone service by radio between New York and London opens for the first time • 1947: Onset of use of microwave radio, later to become dominant carrier for long-distance telephony in U.S. • 1965: Onset of the use of an electronic switching system with the first commercial electric central office • 1988: Use of first trans-Atlantic fiber-optic cable for telephone CE80N -- Winter 2002 -- Lecture #2
Telephone is pervasive CE80N -- Winter 2002 -- Lecture #2
The Telephone Network • Provides Universal Service • Any individual user may call up any other user. • Ubiquitous CE80N -- Winter 2002 -- Lecture #2
A Necessary Perspective • Today (and for a bit longer?) two network “types”: voice, data. • Both use telephone company (telco) services -- and sometimes other services. • Need to understand basic telco to understand the Internet. CE80N -- Winter 2002 -- Lecture #2
Telephone Network • Interconnects billions of phones world-wide • Designed specifically for voice: • two-way conversations • small end-to-end delays • dedicated circuit is set up between two endpoints • Telephone handset: • carbon microphone, sound pressure changes resistance. (constant voltage). Current becomes “analog” of sound • Earphone turns current into sound pressure (moves diaphragm to move air, create sound pressure) CE80N -- Winter 2002 -- Lecture #2
Plain Old Telephone Service (POTS) Source: Telephony Basics http://jhunix.hcf.jhu.edu/~tnaugler/770.512/Common_files/TelephonyBasics/TelephonyBasics.htm CE80N -- Winter 2002 -- Lecture #2
Local Exchange Carrier • Local Loop – The connection between the central office (CO) and your home. • Local Loop Bypass – Replacing the wired connection from the CO with a wireless link. CE80N -- Winter 2002 -- Lecture #2
Inter-Exchange Carrier CE80N -- Winter 2002 -- Lecture #2
Cellular Network Source: WebProForum http://www.iec.org/tutorials/cell_comm/ CE80N -- Winter 2002 -- Lecture #2
Internet Telephony Source: WebProForum http://www.iec.org/tutorials/int_tele/index.html CE80N -- Winter 2002 -- Lecture #2
Phone-to-phone conversations CE80N -- Winter 2002 -- Lecture #2
Electromagnetic waves • Frequency = Speed of Light/Wavelength • f (Hz) = 3x108/l(meters) Source: NASA http://imagers.gsfc.nasa.gov/ems/ems.html CE80N -- Winter 2002 -- Lecture #2
EM Spectrum • AM radio (550-1600 kHz) • FM radio (88 – 108 MHz) • TV (52-88 MHz, 174-216 MHz, 470-900 MHz) • Satellite (GHz) • Infrared (200-300 THz) CE80N -- Winter 2002 -- Lecture #2
The Analog World • Analog devices • An analog device maintains an exact physical analog of information. • Phonograph – Physical image (grooves) • Tape recorder/player – Magnetic image • Early telephone handset – mic./speaker • Not Perfect – • Prone to distortion • Hiss, cracks, pops • High/Low end roll-off CE80N -- Winter 2002 -- Lecture #2
Digital and Analog • Digital signals can be any one of a finite number of discrete values • Grades, digital watch, day of the year, letters in the alphabet, integers • Analog signals can be any one of an infinite number of values • Voice signal into a microphone, analog watch, real numbers, electromagnetic wave CE80N -- Winter 2002 -- Lecture #2
Digital versus Analog • Digital generally has better performance • Regenerative repeaters • Analog - distortion and noise cumulative • Digital - true regeneration • Analog simpler (lower cost) • High installed analog base • Cost of digital circuitry now decreasing CE80N -- Winter 2002 -- Lecture #2
Binary Number System • We have 10 fingers • Computers have devices with 2 states ... 1000 100 10 1 ... 10^310^210^110^0 10011 the binary number 2^42^32^22^12^0 place values (1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = 16 + 0 + 0 + 2 + 1 = 19 CE80N -- Winter 2002 -- Lecture #2
Binary Number System • Text can be represented in binary • ASCII - American Standard Character Information Interchange Ascii Binary CodeA 01000001 a 01100001B 01000010 b 01100010C 01000011 c 01100011D 01000100 d 011001001 00110001 # 001000112 00110010 $ 001001003 00110011 % 00100101 CE80N -- Winter 2002 -- Lecture #2
Sampling – A Moving Snapshot • Recording of voltage levels at prescribed time intervals. • Nyquist’s Theorem: If an analog signal is sampled at 2x(highest frequency), we can adequately reproduce the signal. • Highest frequency in voice is 4000 Hz. Sample at 8000 Hz (disconnect/connect 8000 times per second) • Analogy – movie frames CE80N -- Winter 2002 -- Lecture #2
Quantization • Round up the voltage level to the nearest of 256 predetermined levels • Quantizing error (difference between actual level and level the voltage was rounded to) • AKA lossiness • Low amplitude signals more affected - add more quantizing levels CE80N -- Winter 2002 -- Lecture #2
Quantization • Convert the 256 quantization levels to an 8-bit code • PCM code • Every sound over the telephone is one of 256 unique pitches and volumes. CE80N -- Winter 2002 -- Lecture #2
Sampled Voice • Sample voice signal 8000 times/second • voice signal is bandlimited to 3.4 kHz (filter at 4 kHz) • Quantize samples to 256 quantization levels • logarithmic spacing gives better resolution at the low signal levels • Each sample is represented by 8 bits • Basic rate for voice is 64 Kbps CE80N -- Winter 2002 -- Lecture #2
Sampled Music -- CDs • Sample music signal 44,100 times/second • Music signal is bandlimited to 22 kHz CE80N -- Winter 2002 -- Lecture #2
Days of Future Past • Digital and back again • Smoke signals • Drums • Flashlights • Telegraph • Morse Code (encoding system) CE80N -- Winter 2002 -- Lecture #2
Days of Future Past • Telegraph • Users did not have to deal with the Morse Code directly • Instant communication – (office to office) • The Telephone System began as analog, but has now transformed over time to a digital network. CE80N -- Winter 2002 -- Lecture #2
The Digital Network • The Internet is digital – so are the computers that you use…. • Uses a binary encoding system • Two symbols – 0 or 1 • Again, users do not need to be aware of the encoding system used in the Internet. CE80N -- Winter 2002 -- Lecture #2
Time-Division Multiplexing • Carry many voice conversations on one link • Significant cost savings • One single line instead of 24 separate lines • Example: Freight Transportation • Freight cars (from 5 companies) • 5 separate locomotives, 5 lines • 5 separate trains, 1 line • Join all boxcars together to single engine, single track • Co A + Co B + Co C + Co A + Co B + Co C ... CE80N -- Winter 2002 -- Lecture #2
Time Division Multiplexing • Carry many voice conversations on one link • Example: 24-to-1 multiplexer • Samples 24 voice links 24 times as fast as the input rate • 24 samples constitute a frame • Multiplexed links can be multiplexed further CE80N -- Winter 2002 -- Lecture #2
Digital Signaling (DS) Hierarchy: CE80N -- Winter 2002 -- Lecture #2
Circuit Switching • Network consists of switches • Each user is connected to a switch • To connect two users, a circuit must be established through the network • Switch consists of: • switching hardware => data plane • switch controller => control plane CE80N -- Winter 2002 -- Lecture #2
Signaling • Mechanism to set up and tear down circuits • Performed by switch controllers • Establishment of a telephone call: • handset goes off-hook • user dials numbers • switch controller: • interprets tones and determines destination • sets up a circuit to the remote-end system • rings the remote end-system • remote user picks up phone CE80N -- Winter 2002 -- Lecture #2
Issues in the Telephone Network • Circuit switching: • circuit is limited to 64 kbps • wasteful of bandwidth when the circuit is idle • unsuitable for multimedia services • Infrastructure: • huge investment in existing equipment • demand for new services CE80N -- Winter 2002 -- Lecture #2
Compare and Contrast • Internet • packet-switching • connectionless • dumb network • intelligent end-systems • unreliable connection • designed for data • no quality-of-service • Telephone Network • circuit-switching • connection-oriented • intelligent network • dumb end-systems • reliable connection • designed for voice • quality-of-service • idle time wasted • bandwidth granularity problem CE80N -- Winter 2002 -- Lecture #2
The Digital Network • Summary • The telephone system is pervasive, ubiquitous, and provides universal service. • Digital vs Analog • Sampling and quantization to convert analog signals • The telephone network is now digital too. CE80N -- Winter 2002 -- Lecture #2
Glossary • Analog • Any representation of information in which the amount of a substance or signal is proportional to the information represented • A-to-D converter • Abbreviation for Analog-to-Digital converter. CE80N -- Winter 2002 -- Lecture #2
Glossary • Binary • Any number system that uses two values. • Binary digit (bit) • Either a 0 or 1. • Nibble – 4 bits (half a byte) • Byte -- 8 bits CE80N -- Winter 2002 -- Lecture #2
Glossary • Digital • Any technology that uses numbers to represent information. • Distortion • Input signals that are changed in unintended ways. • Integrated circuit • A small complex electronic device that contains many transistors. CE80N -- Winter 2002 -- Lecture #2