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ECEN4533 Data Communications Lecture #1 7 January 2013 Dr. George Scheets www.okstate.edu/elec-eng/scheets/ecen4533 n Read Chapter 1.1 n Ungraded Homework.

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Presentation on theme: "ECEN4533 Data Communications Lecture #1 7 January 2013 Dr. George Scheets www.okstate.edu/elec-eng/scheets/ecen4533 n Read Chapter 1.1 n Ungraded Homework."— Presentation transcript:

1 ECEN4533 Data Communications Lecture #1 7 January 2013 Dr. George Scheets n Read Chapter 1.1 n Ungraded Homework Problems: None

2 ECEN4533 Data Communications Dr. George Scheets Lecture #29 January n Read Chapter n Problems: None n Quiz #1, Lecture 12, 4 February

3 ECEN4533 Data Communications Dr. George Scheets Lecture #311 January n Read 2.1, 2.2 n Problems n Quiz #1, Lecture 12, 4 February

4 Grading n In Class: Quizzes, Tests, Final Exam Open Book & Open Notes WARNING! Study for them like theyre closed book! n Graded Homework: Design Problems n Ungraded Homework: Assigned most every class Not collected Solutions Provided Payoff: Tests & Quizzes

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

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

7 Cheating n Dont do it! If caught, expect to get an 'F' for the course. n My idol: Judge Isaac Parker U.S. Court: Western District of Arkansas a.k.a. Hanging Judge Parker a.k.a. Hanging Judge Parker

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

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

10 Coax cable images from &

11 Fiber Optic Cable 1 1/4 inch SC

12 Channel Capacity Claude Shannon Bell Labs, MIT Ralph Hartley Bell Labs images from wikipedia.com

13 Channel Capacity (C) n C = W*Log 2 (1 + SNR) bps u W = channel bandwidth (Hz) u SNR = channel signal-to-noise ratio n Maximum bit rate that can be reliably shoved down a connection n EX) Analog Modem (30 dB SNR) C = 3500 *Log 2 ( ) = 34,885 bps n EX) 6 MHz TV RF Channel (42 dB SNR) C = 6,000,000 *Log 2 (1 + 15,849) = Mbps

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

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

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

17 Channel Capacity, Increasing SNR n C = W*Log 2 (1 + SNR) bps n Suppose at/near C limit & no extra BW available and... n Current SNR = 10 (C = W3.459) ? u Need to bump SNR up to 120 to double bps (C = W6.919) n Current SNR = 120? u Need to bump SNR up to 14,640 to double bps (C = W13.84) n Current SNR = 14,640? u Need to bump SNR up to 214.4M to double bps (C = W27.68) n To increase C by factor of 8 u Increase SNR by factor of 214,358,881 n Is increasing BW a better idea?

18 Channel Capacity, Increasing W n C = W*Log 2 (1 + SNR) bps n C = W*Log 2 (1 + [Signal Power]/[Noise Power]) bps n C = W*Log 2 (1 + [Signal Power]/[N o W]) bps n N o = Noise Power Spectral Density (watts/Hertz) n Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 u C = WLog 2 (1+10) = W3.459 n Bumping W to 8W u C = 8WLog 2 ( ) = 8W1.170 = W9.359 u Capacity increases by a factor of 9.359/3.459 = n Bumping W by 214,358,881 u C = 214,358,881W Log2( ) = 14.43W u C increases by a factor of 14.43/3.459 = (worse than SNR!)

19 Channel Capacity, Increasing Both n C = W*Log 2 (1 + SNR) bps n C = W*Log 2 (1 + [Signal Power]/[Noise Power]) bps n C = W*Log 2 (1 + [Signal Power]/[N o W]) bps n N o = Noise Power Spectral Density (watts/Hertz) n Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 u C = WLog 2 (1+10) = W3.459 n Bumping both W & Signal Power by factor of 8 yields u C = 8WLog 2 (1+10) = 8W3.459 = W27.67 u Capacity increases by a factor of 8 n Best to bump W, but also bump Signal Power

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

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

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

23 ISO OSI Seven Layer Model n Layer 7 Application User Program n Layer 6 Presentation Windows API n Layer 5 Session TCP, Windows n Layer 4 TransportTCP, Windows n Layer 3 Network IP, Windows n Layer 2 Data LinkPC NIC/CPU n Layer 1 Physical PC NIC

24 TCP/IP Model n Layer 5 Application Application n Layer 5 Presentation n Layer 4 Session Transport (TCP) n Layer 4 Transport n Layer 3 Network Internet (IP) n Layer 2 Data LinkData Link n Layer 1 Physical Physical } }

25 Typical Network: Core & Access Trunks Access Lines a b c d e i h f g

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

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

28


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