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

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

3. January 8, 2002CE80N -- Winter 2002 -- 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)

4. January 8, 2002CE80N -- Winter 2002 -- 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

5. January 8, 2002CE80N -- Winter 2002 -- 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

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

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

8. January 8, 2002CE80N -- Winter 2002 -- 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.

9. January 8, 2002CE80N -- Winter 2002 -- 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)

10. January 8, 2002CE80N -- Winter 2002 -- Lecture #210 Plain Old Telephone Service (POTS) Source: Telephony Basics http://jhunix.hcf.jhu.edu/~tnaugler/770.512/Common_files/TelephonyBasics/TelephonyBas ics.htm

11. January 8, 2002CE80N -- Winter 2002 -- 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.

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

13. January 8, 2002CE80N -- Winter 2002 -- Lecture #213 Cellular Network Source: WebProForum http://www.iec.org/tutorials/cell_comm/

14. January 8, 2002CE80N -- Winter 2002 -- Lecture #214 Internet Telephony Source: WebProForum http://www.iec.org/tutorials/int_tele/index.html

15. January 8, 2002CE80N -- Winter 2002 -- Lecture #215

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

17. Its An Analog World

18. January 8, 2002CE80N -- Winter 2002 -- Lecture #218 Electromagnetic waves Frequency = Speed of Light/Wavelength f (Hz) = 3x10 8 / (meters) Source: NASA http://imagers.gsfc.nasa.gov/ems/ems.html

19. January 8, 2002CE80N -- Winter 2002 -- Lecture #219 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)

20. January 8, 2002CE80N -- Winter 2002 -- 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

21. January 8, 2002CE80N -- Winter 2002 -- 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

22. January 8, 2002CE80N -- Winter 2002 -- 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

23. January 8, 2002CE80N -- Winter 2002 -- Lecture #223 Binary Number System We have 10 fingers Computers have devices with 2 states...1000100101...10^310^210^110^0 10011the binary number 2^42^32^22^12^0place values (1 * 2^4) + (0 * 2^3) + (0 * 2^2) + (1 * 2^1) + (1 * 2^0) = 16 + 0 + 0 + 2 + 1 = 19

24. January 8, 2002CE80N -- Winter 2002 -- Lecture #224 Binary Number System Text can be represented in binary ASCII - American Standard Character Information Interchange Ascii Binary Code A 01000001 a01100001 B 01000010 b01100010 C 01000011 c01100011 D 01000100 d01100100 1 00110001 #00100011 2 00110010 $00100100 3 00110011 %00100101

25. January 8, 2002CE80N -- Winter 2002 -- 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

26. January 8, 2002CE80N -- Winter 2002 -- 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

27. January 8, 2002CE80N -- Winter 2002 -- 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

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

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

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

31. January 8, 2002CE80N -- Winter 2002 -- 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.

32. January 8, 2002CE80N -- Winter 2002 -- 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.

33. January 8, 2002CE80N -- Winter 2002 -- 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...

34. January 8, 2002CE80N -- Winter 2002 -- 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

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

36. January 8, 2002CE80N -- Winter 2002 -- 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

37. January 8, 2002CE80N -- Winter 2002 -- 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

38. January 8, 2002CE80N -- Winter 2002 -- 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

39. January 8, 2002CE80N -- Winter 2002 -- 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

40. January 8, 2002CE80N -- Winter 2002 -- 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.

41. January 8, 2002CE80N -- Winter 2002 -- 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.

42. January 8, 2002CE80N -- Winter 2002 -- 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

43. January 8, 2002CE80N -- Winter 2002 -- 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.