Transcript ppt
ECEN4533 Data Communications Lecture #1 7 January 2013 Dr. George Scheets www.okstate.edu/elec-eng/scheets/ecen4533 Read Chapter 1.1 Ungraded Homework Problems: None ECEN4533 Data Communications Dr. George Scheets Lecture #2 9 January 2013 www.okstate.edu/elec-engr/scheets/ecen4533/ Read Chapter 1.2 - 1.4 Problems: None Quiz #1, Lecture 12, 4 February ECEN4533 Data Communications Dr. George Scheets Lecture #3 11 January 2013 www.okstate.edu/elec-engr/scheets/ecen4533/ Read 2.1, 2.2 Problems 1.1 - 1.3 Quiz #1, Lecture 12, 4 February Grading In Class: Quizzes, Tests, Final Exam Open Book & Open Notes WARNING! Study for them like they’re closed book! Graded Homework: Design Problems Ungraded Homework: Assigned most every class Not collected Solutions Provided Payoff: Tests & Quizzes 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 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 LAMENT If you put in the time You should do fine. If you don't, You likely won't. Cheating Don’t do it! If caught, expect to get an 'F' for the course. My idol: Judge Isaac Parker U.S. Court: Western District of Arkansas 1875-1896 a.k.a. “Hanging Judge Parker” General Comments Pre/Co-requisites Knowledge of probability & statistics Knowledge of Excel, MatLab, MathCad or something similar General Format Lecture Feel free to interrupt at will Goal Understand data networks Design data networks Twisted Pair Cables LAN cables are attached to RJ-45 connection. Coax cable images from www.computingsolutions.ca & www.air802.com Fiber Optic Cable 1 1/4 inch SC Channel Capacity Claude Shannon 1916-2001 Bell Labs, MIT Ralph Hartley 1888-1970 Bell Labs images from wikipedia.com 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 Channel Capacity (C) Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log2(1 + SNR) bps Bandwidth sets the maximum baud rate symbols/second = baud If bandwidth = W Hertz, In theory, can move 2W symbols/sec In practice, can move closer to W symbols/sec 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 Binary +.447 4-Ary -1 -1.342 Mathematically, 4-Ary symbols are closer together. 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 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) ? Current SNR = 120? Need to bump SNR up to 214.4M to double bps (C = W27.68) To increase C by factor of 8 Need to bump SNR up to 14,640 to double bps (C = W13.84) Current SNR = 14,640? Need to bump SNR up to 120 to double bps (C = W6.919) Increase SNR by factor of 214,358,881 Is increasing BW a better idea? 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 Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 No = Noise Power Spectral Density (watts/Hertz) 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!) 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 Suppose at/near C limit, want to increase C by factor of 8, current SNR = 10 No = Noise Power Spectral Density (watts/Hertz) 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 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 Modem Protocol Digital Bit Stream (1's & 0's) 64 Kbps Modem Protocol Fine print indicates Uses Acceleration (compression) Some material won't be compressed Actual data transmission rates = standard dial up rates Bogus Channel Capacity Claims Silk Road (Summer 1999) Claim: Gbps in 64 KHz Stock Analyst: 70% success Claim: > Tbps over Power Lines Step Down Transformers = LP Filter Untwisted Pair = Antenna Exceeding Channel Capacity? Same impact as exceeding Speed of Light ISO OSI Seven Layer Model Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical User Program Windows API TCP, Windows TCP, Windows IP, Windows PC NIC/CPU PC NIC TCP/IP Model Layer 5 Layer 5 Layer 4 Layer 4 Layer 3 Layer 2 Layer 1 Application } Presentation Session } Transport Network Data Link Physical Application Transport (TCP) Internet (IP) Data Link Physical Typical Network: Core & Access a b 2 i 1 h c d 3 4 g e f 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 Modem Protocol Digital TDM (1's & 0's) 64 Kbps Modem Protocol PSTN Connectivity via BRI ISDN Copper Local Loop CO Copper Local Loop Fiber Optic Trunk CO Server PC Digital 64 or 128 Kbps