The Technologies Behind the Internet Lecture 2 – April 14, 2016 “Lincoln Towers University” April 2016 Thursdays 7:30-9 pm, 150 WEA Community Room Instructor: Stephen Weinstein [email protected], (646) 267-5904 Lecture notes posting site: projectopenlincolntowers.org/lincolntowersuniversity
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The Technologies Behind the InternetLecture 2 – April 14, 2016
Pulse Code Modulation (PCM), a special example of PAM
Uses binary pulses to carry digital data coming from analog to digital (A/D) conversion of a speech signal. Invented by Alec Reeves in Paris in 1937.
PCM Examples:
64 Kbps PCM in the digital telephone network.(8000 8-bit samples/sec, 64 Kbps)
1.4 Mbps PCM used for CD audio(44.1 Kbps x 16 bits/sample x 2 stereo channels, 1.41 Mbps)Enhanced with error-correction coding
1902-1971
Alec Reeves
A/D
SIGSALY, a secret voice communication system betweenRoosevelt and Churchill in WWII, was developed by BellLabs based in part on Reeves’ work.
Bandpass
filters
Voice
in
Pitch
detector
PCM
PCM
PCM
PCM
PCM
Mux Recording of
random sequence
Modulator
Radio carrier
generator
Transmitted radio
signal
Receiving end decrypts by using
synchronized recording of
the same random sequence.
Multilevel frequency-
Shift keying
http://www.jproc.ca/crypto/sigsaly1.html
Modulation, as in SIGSALY, is often the impression of aninformation waveform (such as a sequence of modulatedpulses) on a sine wave carrier, to get through a high-frequency channel.
Example 1: AM radio
Amplitude
modulator
Analog waveform
Carrier sine wave
generator (e.g. CBS, 880 KHz)
Example 2: Quadrature amplitude modulation (QAM)
Amplitude
Modulator
sine
Amplitude
Modulator
cosine
PAM pulse train 1
PAM pulse train 2
-Modulates PAM pulse trains onto both cosine and sine carrier
waves at the desired carrier frequency.
-Widely used in cable and wireless systems for Internet data delivery
-Because cosine and sine waveforms are orthogonal (900 out of phase),
the receiver can separate the two streams.
-Doubles the data rate compared with modulating one sine wave.
SumCarrier
generator
Transmitted
signal
Engineers like to represent the cosine/sine pulse amplitude
pairs by a signal constellation.
64 QAM
Amplitude of pulse modula-
ted on the cosine carrier
Amplitude of pulse modulated
on the sine carrier
Internet downloads on your cable system are likely to use this
modulation.
1 3 5 7
3
Example: (5,3)
1
5
7
Pulse modulated on cosine carrier
5
3
Pulse modulated on sine carrier
Use of the (5,3) point in the signal constellation
Example 3: Frequency modulation (FM)
Frequency
modulator
Carrier sine wave
generator (e.g., WNYC-
93.9 MHz)
Information waveform
(e.g., pulse train)
Lower frequency
corresponds to
negative modulation
pulse
Higher frequency
corresponds to
positive modulation
pulse
Example 4: Orthogonal Frequency Division Multiplexing(OFDM)
Breaks a transmission channel into tiny subbands. Signals for these
subbands are generated by software computation (the Fast Fourier
Transform) rather than by separate electronic signal generators.
Carl Friedrich Gauss
1777-1855
Discovered FFT
in 1805
FFT
Subcarrier
frequency
f0
f1
f2
f3
f4
f5
f6
f7
t
Used in Digital Subscriber
Line, 4G cellular mobile,
digital broadcasting
applications
What is a Modem (Modulator-DEModulator)?
Definition: A network terminating device supporting data transferacross the network. Performs functions including modulation, demodulation, synchronization, channel equalization and signal detection.
Dialup Modem
Public switched telephone
network (PSTN)
InternetServiceProvider
Dialup, not so long ago ….
Copperphoneline
Usually on a cardinside the computer
ISP
Internet backboneWebhost
What’s in a simple modem?
Outgoing digitalinformation
User side
Pulse amplitudes
Modulation(e.g., QAM)
Network side
Directionalcoupler
Sync & Demodulation
Sourcecoding
Error correction,encryption
ChannelequalizerSample
DecisionDigitalinforma-tion fromother end
Control logic
Corrects distortions of channel (like variations in transmission strengthat different frequencies)
Modems for cable and optical access networks have control messaging and signaling capabilities appropriate for the spectrum assignments and access contention systems of those technologies. Example: cable modem upstream capacity reservations
Technical advances in recent decades created broadband (very high capacity) cellular mobile service
Major example: MIMO (multiple in, multiple out antennas)
Trans.Rec.
Multiple “spatially orthogonal” channels created between transmitterand receiver can increase capacity by a factor of 10!
3. Networks
Definition from lecture 1:A set of originating and terminating nodes, forwarding nodes, and the transport links connecting them, for conveying data (information) traffic.
Major network categories and examples
WiFi(IEEE 802.11)
DSL
Optical Core Network,
metropolitan & long haul
Local AreaNetworks
Cellularmobile
Cable (HFC)
Ethernet Opticalfiber
Accessnetworks
Personal AreaNetworks
CoreNetworks
Bluetooth
Infrared
Satellite
Wireless networks for Internet services: Cellular mobile, WiFi and Bluetooth
“Backhaul” network
Mobile switching
center
PSTN Internet
Web
host
Cable
or FiOS
Cable modem
or FiOS optical
termination
Wireless
router (WiFi)Ethernet
Base
station
Bluetooth
Cellular mobile, an access network
“Fronthaul” network
Radio network
controller
“Backhaul” network
Mobile switching
center
PSTN Internet
Radio processing
functions
Base
stations
Power
amplifiers
Modern structure with a Radio Network Controller supporting
multiple “bare bones” base stations
Why cellular?
Because it allows frequency reuse in non-adjacent cells. Previously,
a particular frequency channel could be used by only one call in an
entire metropolitan area.
f1
f2
f3
f4
f5
f6
f7
f1
f1f1
f1 f1
f1
Cellular mobile generations
1G: Analog “AMPS” system
2G: Digital voice (GSM in Europe, IS-95 (CDMA) & IS-136 (TDMA)
in U.S.). Minimal data capability.
3G: Digital voice and data (wideband CDMA and CDMA-2000
Bluetooth uses a frequency-hopping “spread spectrum”
scheme co-invented during WWII by Hedy LamarrRef: http://www.women-inventors.com/Hedy-Lammar.asp
Bluetooth frequency hopping
carrier freq (GHz)
time (ms).625 1.25
2.402
2.403
2.404
2.405
2.406
2.480
1.875 2.5 3.125 3.75
(Random hopping among 79 carrier frequencies)
4. Protocols
Protocol definition (from first lecture)
A formal description of the format and rules for a message exchange. Several layers of protocols are usually needed to completely specify aninformation exchange.
Protocol stack: A way of addressing complexity in large systems
-Modularizes functions.
-Facilitates interoperability between diverse equipment from
different manufacturers.
-Permits changes at a higher protocol level without changing
the functions at lower levels (“mix and match”).
ISO (International Standards Organization) referencemodel: OSI (Open Systems Interconnection)