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Data Communications Lecture: Understanding Data Networks

This lecture provides an introduction to data communications and covers topics such as twisted pair cables, coaxial cables, fiber optic cables, and channel capacity. The lecture also emphasizes the importance of self-discipline, studying, and avoiding cheating.

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Data Communications Lecture: Understanding Data Networks

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  1. ECEN4533 Data CommunicationsLecture #1 7 January 2013Dr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen4533 • Read Chapter 1.1 • Ungraded Homework Problems: None

  2. ECEN4533 Data CommunicationsDr. George ScheetsLecture #2 9 January 2013www.okstate.edu/elec-engr/scheets/ecen4533/ Read Chapter 1.2 - 1.4 Problems: None Quiz #1, Lecture 12, 4 February

  3. ECEN4533 Data CommunicationsDr. George ScheetsLecture #3 11 January 2013www.okstate.edu/elec-engr/scheets/ecen4533/ Read 2.1, 2.2 Problems 1.1 - 1.3 Quiz #1, Lecture 12, 4 February

  4. Grading • In Class: Quizzes, Tests, Final ExamOpen Book & Open NotesWARNING! Study for them like they’re closed book! • Graded Homework: Design Problems • Ungraded Homework: Assigned most every classNot collectedSolutions ProvidedPayoff: Tests & Quizzes

  5. Why work the ungraded Homework problems? • An Analogy: Data Com vs. Football • Reading the text = Reading a playbook • Looking at the problem solutions = watching a scrimmage • Working the problems = practicing or playing in a scrimmage • Quiz = Exhibition Game • Test = Big Game

  6. To succeed in this class... • Show some self-discipline!! Important!!For every hour of class... ... put in 1-2 hours of your own effort. • PROFESSOR'S LAMENTIf you put in the timeYou should do fine.If you don't,You likely won't.

  7. Cheating • Don’t do it!If caught, expect to get an 'F' for the course. • My idol:Judge Isaac ParkerU.S. Court: Western District of Arkansas1875-1896 • a.k.a. “Hanging Judge Parker”

  8. General Comments • Pre/Co-requisites • Knowledge of probability & statistics • Knowledge of Excel, MatLab, MathCad or something similar • General FormatLecture • Feel free to interrupt at will • Goal • Understand data networks • Design data networks

  9. Twisted Pair Cables LAN cables are attached to RJ-45 connection.

  10. Coax cable images from www.computingsolutions.ca & www.air802.com

  11. Fiber Optic Cable 1 1/4 inch SC

  12. Channel Capacity Claude Shannon 1916-2001 Bell Labs, MIT Ralph Hartley 1888-1970 Bell Labs images from wikipedia.com

  13. Channel Capacity (C) • C = W*Log2(1 + SNR) bps • W = channel bandwidth (Hz) • SNR = channel signal-to-noise ratio • Maximum bit rate that can be reliably shoved down a connection • EX) Analog Modem (30 dB SNR)C = 3500 *Log2(1 + 1000) = 34,885 bps • EX) 6 MHz TV RF Channel (42 dB SNR)C = 6,000,000 *Log2(1 + 15,849) = 83.71 Mbps

  14. Channel Capacity (C) • Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log2(1 + SNR) bps • If bandwidth = W Hertz, • In theory, can move 2W symbols/sec • In practice, can move closer to W symbols/sec Bandwidth sets the maximum baud ratesymbols/second = baud

  15. Channel Capacity (C) • Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log2(1 + SNR) bps SNR sets the maximum number of bits/symbol 2 bits/symbol (1 or 0) a.k.a. Binary signaling Log2M bits/symbol a.k.a. M-Ary signaling +1 +.447 Binary 4-Ary -1 -1.342 Mathematically, 4-Ary symbols are closer together.

  16. M-Ary Signaling • Used when bandwidth is tight & SNR is decent • Baud rates same? Symbol shapes similar? If yes.. • Bandwidth required is similar • M-Ary signaling allows increased bit rate • Symbols get closer together if Power fixed • Receiver detection errors more likely

  17. Channel Capacity, Increasing SNR • C = W*Log2(1 + SNR) bps • Suppose at/near C limit & no extra BW available and... • Current SNR = 10 (C = W3.459) ? • Need to bump SNR up to 120 to double bps (C = W6.919) • Current SNR = 120? • Need to bump SNR up to 14,640 to double bps (C = W13.84) • Current SNR = 14,640? • Need to bump SNR up to 214.4M to double bps (C = W27.68) • To increase C by factor of 8 • Increase SNR by factor of 214,358,881 • Is increasing BW a better idea?

  18. Channel Capacity, Increasing W • C = W*Log2(1 + SNR) bps • C = W*Log2(1 + [Signal Power]/[Noise Power]) bps • C = W*Log2(1 + [Signal Power]/[NoW]) bps • No = Noise Power Spectral Density (watts/Hertz) • Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 • C = WLog2(1+10) = W3.459 • Bumping W to 8W • C = 8WLog2(1+1.125) = 8W1.170 = W9.359 • Capacity increases by a factor of 9.359/3.459 = 2.706 • Bumping W by 214,358,881 • C = 214,358,881W Log2(1.00000004665) = 14.43W • C increases by a factor of 14.43/3.459 = 4.172 (worse than SNR!)

  19. Channel Capacity, Increasing Both • C = W*Log2(1 + SNR) bps • C = W*Log2(1 + [Signal Power]/[Noise Power]) bps • C = W*Log2(1 + [Signal Power]/[NoW]) bps • No = Noise Power Spectral Density (watts/Hertz) • Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 • C = WLog2(1+10) = W3.459 • Bumping both W & Signal Power by factor of 8 yields • C = 8WLog2(1+10) = 8W3.459 = W27.67 • Capacity increases by a factor of 8 • Best to bump W, but also bump Signal Power

  20. 33.6 Kbps Dial-Up Modem • CO Input Line Card Low Pass Filter limits BW (3.5 KHz) • M-Ary Signaling (256 QAM or something even more complex) • Channel Capacity says max transfer is around 34 - 35 Kbps • 1960's: 300 bps using binary signaling @ 300 symbols/second • 1980's: 14,400 bps using 128-Ary signaling @ 2400 symbols/second • 1996: 33,600 bps using 1664-Ary signaling @ 3429 symbols/second CO CO PC PC Digital Bit Stream (1's & 0's) 64 Kbps Modem Protocol Modem Protocol

  21. Fine print indicates Uses Acceleration (compression) Some material won't be compressed Actual data transmission rates = standard dial up rates

  22. Bogus Channel Capacity Claims • Silk Road (Summer 1999)Claim: Gbps in 64 KHz • Stock Analyst: 70% success • Claim: > Tbps over Power LinesStep Down Transformers = LP FilterUntwisted Pair = Antenna • Exceeding Channel Capacity?Same impact as exceeding Speed of Light

  23. ISO OSI Seven Layer Model • Layer 7 ApplicationUser Program • Layer 6 Presentation Windows API • Layer 5 SessionTCP, Windows • Layer 4 Transport TCP, Windows • Layer 3 NetworkIP, Windows • Layer 2 Data Link PC NIC/CPU • Layer 1 Physical PC NIC

  24. TCP/IP Model } • Layer 5 Application Application • Layer 5 Presentation • Layer 4 SessionTransport (TCP) • Layer 4 Transport • Layer 3 Network Internet (IP) • Layer 2 Data Link Data Link • Layer 1 Physical Physical }

  25. Typical Network: Core & Access a b 2 i 1 h Trunks c Access Lines 4 d 3 g e f

  26. PSTN: Wired Dial-up Modem • Access Line (twisted pair) is expecting analog voice • Modem maps PC digital signal to a signal with voice spectral characteristics • Trunks are digital CO CO PC PC Digital TDM (1's & 0's) 64 Kbps Modem Protocol Modem Protocol

  27. PSTN Connectivity via BRI ISDN Copper Local Loop Copper Local Loop Fiber Optic Trunk CO CO Server PC Digital 64 or 128 Kbps

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