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

CE80N CE80N Introduction to NetworksIntroduction to Networks

&&The InternetThe Internet

Dr. Chane L. Fullmer

UCSC

Winter 2002

January 8, 2002 CE80N -- Winter 2002 -- Lecture #2

2

ReadingReading

Chapter 3, Telephones Everywhere Chapter 4, The World Was Once Analog, Chapter 5, The Once and Future Digital

Network;


3

Telephone NetworkTelephone 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)


4

History of the TelephoneHistory 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


5

History of the TelephoneHistory 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


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Telephone is pervasiveTelephone is pervasive


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The Telephone NetworkThe Telephone Network

Provides Universal Service– Any individual user may call up any

other user.Ubiquitous


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A Necessary PerspectiveA 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.


9

Telephone NetworkTelephone 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)


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Plain Old Telephone Service (POTS)Plain Old Telephone Service (POTS)

Source: Telephony Basicshttp://jhunix.hcf.jhu.edu/~tnaugler/770.512/Common_files/TelephonyBasics/TelephonyBasics.htm


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Local Exchange CarrierLocal 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.


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Inter-Exchange CarrierInter-Exchange Carrier


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Cellular NetworkCellular Network

Source: WebProForumhttp://www.iec.org/tutorials/cell_comm/


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Internet TelephonyInternet Telephony

Source: WebProForumhttp://www.iec.org/tutorials/int_tele/index.html


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Phone-to-phone conversationsPhone-to-phone conversations

It’s An Analog WorldIt’s An Analog World


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Electromagnetic wavesElectromagnetic waves

Frequency = Speed of Light/Wavelength f (Hz) = 3x108/(meters)

Source: NASAhttp://imagers.gsfc.nasa.gov/ems/ems.html


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EM SpectrumEM 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)


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The Analog WorldThe 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


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Digital and AnalogDigital 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


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Digital versus AnalogDigital 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


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Binary Number SystemBinary Number SystemWe have 10 fingers

Computers have devices with 2 states

... 1000 100 10 1

... 10^3 10^2 10^1 10^0

1 0 0 1 1 the binary number

2^4 2^3 2^2 2^1 2^0 place values

(1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0)

= 16 + 0 + 0 + 2 + 1 = 19


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Binary Number SystemBinary Number System

Text can be represented in binaryASCII - 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


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Sampling – A Moving SnapshotSampling – 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


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QuantizationQuantization

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


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Convert the 256 quantization levels to an 8-bit code

PCM codeEvery sound over the telephone is

one of 256 unique pitches and volumes.

QuantizationQuantization


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Sampled VoiceSampled 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


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Sampled Music -- CDsSampled Music -- CDs

Sample music signal 44,100 times/second– Music signal is bandlimited to 22 kHz


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Days of Future PastDays of Future Past

Digital and back again– Smoke signals– Drums– Flashlights– Telegraph

• Morse Code (encoding system)


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Days of Future PastDays 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.


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The Digital NetworkThe 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.


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Time-Division MultiplexingTime-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 ...


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Time Division MultiplexingTime 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


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Digital Signaling (DS) Digital Signaling (DS) Hierarchy:Hierarchy:

DS # Voice Circuits BandwidthDS0 1 64 kbpsDS1 24 1.544 MbpsDS2 96 6.312 MbpsDS3 672 44.736 Mbps


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Circuit SwitchingCircuit 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


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SignalingSignaling

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


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Issues in the Telephone NetworkIssues 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


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Compare and ContrastCompare and ContrastTelephone

Network– circuit-switching– connection-oriented– intelligent network– dumb end-systems– reliable connection– designed for voice– quality-of-service– idle time wasted– bandwidth granularity

problem

•Internetpacket-switchingconnectionlessdumb networkintelligent end-systemsunreliable connectiondesigned for datano quality-of-service


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The Digital NetworkThe 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.


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GlossaryGlossary

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.


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GlossaryGlossary

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


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GlossaryGlossary

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

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