CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002

January 8, 2002CE80N -- Winter Lecture #22 Reading Chapter 3, Telephones Everywhere Chapter 4, The World Was Once Analog, Chapter 5, The Once and Future Digital Network;

January 8, 2002CE80N -- Winter Lecture #23 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)

January 8, 2002CE80N -- Winter Lecture #24 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

January 8, 2002CE80N -- Winter Lecture #25 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

January 8, 2002CE80N -- Winter Lecture #26 Telephone is pervasive

January 8, 2002CE80N -- Winter Lecture #27 The Telephone Network Provides Universal Service –Any individual user may call up any other user. Ubiquitous

January 8, 2002CE80N -- Winter Lecture #28 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.

January 8, 2002CE80N -- Winter Lecture #29 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)

January 8, 2002CE80N -- Winter Lecture #210 Plain Old Telephone Service (POTS) Source: Telephony Basics ics.htm

January 8, 2002CE80N -- Winter Lecture #211 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.

January 8, 2002CE80N -- Winter Lecture #212 Inter-Exchange Carrier

January 8, 2002CE80N -- Winter Lecture #213 Cellular Network Source: WebProForum

January 8, 2002CE80N -- Winter Lecture #214 Internet Telephony Source: WebProForum

January 8, 2002CE80N -- Winter Lecture #215

January 8, 2002CE80N -- Winter Lecture #216 Phone-to-phone conversations

Its An Analog World

January 8, 2002CE80N -- Winter Lecture #218 Electromagnetic waves Frequency = Speed of Light/Wavelength f (Hz) = 3x10 8 / (meters) Source: NASA

January 8, 2002CE80N -- Winter Lecture #219 EM Spectrum AM radio ( kHz) FM radio (88 – 108 MHz) TV (52-88 MHz, MHz, MHz) Satellite (GHz) Infrared ( THz)

January 8, 2002CE80N -- Winter Lecture #220 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

January 8, 2002CE80N -- Winter Lecture #221 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

January 8, 2002CE80N -- Winter Lecture #222 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

January 8, 2002CE80N -- Winter Lecture #223 Binary Number System We have 10 fingers Computers have devices with 2 states ^310^210^110^ the binary number 2^42^32^22^12^0place values (1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = = 19

January 8, 2002CE80N -- Winter Lecture #224 Binary Number System Text can be represented in binary ASCII - American Standard Character Information Interchange Ascii Binary Code A a B b C c D d # $ %

January 8, 2002CE80N -- Winter Lecture #225 Sampling – A Moving Snapshot Recording of voltage levels at prescribed time intervals. –Nyquists 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

January 8, 2002CE80N -- Winter Lecture #226 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

January 8, 2002CE80N -- Winter Lecture #227 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. Quantization

January 8, 2002CE80N -- Winter Lecture #228 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

January 8, 2002CE80N -- Winter Lecture #229 Sampled Music -- CDs Sample music signal 44,100 times/second –Music signal is bandlimited to 22 kHz

January 8, 2002CE80N -- Winter Lecture #230 Days of Future Past Digital and back again –Smoke signals –Drums –Flashlights –Telegraph Morse Code (encoding system)

January 8, 2002CE80N -- Winter Lecture #231 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.

January 8, 2002CE80N -- Winter Lecture #232 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.

January 8, 2002CE80N -- Winter Lecture #233 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...

January 8, 2002CE80N -- Winter Lecture #234 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

January 8, 2002CE80N -- Winter Lecture #235 Digital Signaling (DS) Hierarchy:

January 8, 2002CE80N -- Winter Lecture #236 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

January 8, 2002CE80N -- Winter Lecture #237 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

January 8, 2002CE80N -- Winter Lecture #238 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

January 8, 2002CE80N -- Winter Lecture #239 Compare and Contrast 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 Internet packet-switching connectionless dumb network intelligent end-systems unreliable connection designed for data no quality-of-service

January 8, 2002CE80N -- Winter Lecture #240 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.

January 8, 2002CE80N -- Winter Lecture #241 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.

January 8, 2002CE80N -- Winter Lecture #242 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

January 8, 2002CE80N -- Winter Lecture #243 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.