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