The Technologies Behind the InternetLecture 2 – April 14, 2016

“Lincoln Towers University”April 2016

Thursdays 7:30-9 pm, 150 WEA Community Room

Instructor: Stephen Weinstein

s.weinstein@ieee.org, (646) 267-5904

Lecture notes posting site:

projectopenlincolntowers.org/lincolntowersuniversity

Goals of this course (as presented in lecture 1)

1. Provide an intuitive explanation, not requiring an

engineering or computer science background, of

-Internet history

-The technical foundations of the Internet

-Relevant basic concepts of communications and

information technology

(Internet history, some basic information technology concepts, and

analog to digital conversion were covered in Lecture 1)

2. Answer your questions. Don’t be afraid to ask!

Lecture 2 (today): Communications

I will explain:

-Basic terms: Frequency, wavelength, spectrum, bandwidthand data rate.

-Modulation, modems, wireless

-Personal, local and access networks

-Protocol stacks.

Lecture 3 (April 21): Internet architecture & technologies

-Packet switching and Internet architecture (routers and routing algorithms, DNS, root servers, …).

-Connection-oriented service vs. connectionless (datagram).

-Important protocols:IPv4 and IPv6, TCP and UDP, OSPF, DHCP.

-Avoiding address depletion (local addresses and IPv6).

Lecture 4 (April 28): Internet applications

-The original application level protocols: ftp, smtp, telnet

-The World Wide Web: History, browsers, and web pages

-Audio and video streaming, VoIP (e.g., Skype).

-Virtual private networks (secure tunnels).

-Cloud computing.

-Security attacks (e.g., denial of service) and defenses.

-The Internet of Things.

Lecture 2: Communications

The Internet physically transfers digital information by sending

communication signals through communication networks. This

lecture examines digital signaling and communication networks,

beginning with definitions of waveform, cosine/sine wave,

frequency, frequency spectrum, wavelength, bandwidth and data

rate.

Physical channel (fiber optic

cable, copper wire, radio

channel through space)

Waveform: The change in amplitude of a signal overa period of time

Time (sec)

In this course, the waveform will usually be electrical (voltage or current)

Amplitude (volts or amperes)

… can be represented by a weighted combination of sinusoidal waveforms of different frequencies and phases(defined in the next slide).

Any waveform, as Fourier discovered long ago, …

Jean Baptiste Joseph Fourier

French mathematician

(1768-1830)

0 Tc 2Tc 3Tc

t

cos(2πfct)

-Tc

π/4 radians (450) phase advance

t

cos(2πfct + π/4)

1 cycle

Cosine wave and phase angle

(Sine wave looks the same as a cosine wave, with a 900 phase lag)

Frequency is the number of cycles per second of a sine wave.(unit: Hertz or Hz. 1000 Hz = 1 KHz; 1 million Hz = 1 MHz;1 billion Hz = 1 GHz)

1857-1894

Named for Heinrich Hertz who discovered radio waves and verified

Maxwell’s equations of electromagnetism.

The period T of a sine wave is the time it takes to run throughone cycle. T = 1/frequency (unit: seconds)

http://onlinetonegenerator.com/tuning.html

Example: A above middle C Frequency = 440 Hz (cycles per second)

0 time

(sec)

-1/440 2/440 3/4401/440

Period

Frequency spectrum – distribution of signalenergy over frequency – is the engineeringequivalent of the original waveform over time

0

Frequency (Hz)

440

Middle C (440 Hz)

0Time (sec)

-1/440 2/440 3/4401/440

Waveform over time

Frequency spectrum

[Mathematically, the spectrum has a matching spike at -440Hz

that we will ignore here for simplicity.]

Waveform over time, and frequency spectrum, for a 497 Hz violin tone

Frequency

(KHz)

harmonics

http://www.ccp14.ac.uk/ccp/web-mirrors/isotropy/~stokesh/violin.html

Time (ms)

Fundamental (497 Hz)

10

Waveform

over time

Frequency

spectrum

Frequency spectrum vs. time of a sad trombone

https://academo.org/demos/spectrum-analyzer/

The range of sinusoidal frequencies contributing toa waveform is the bandwidth of that waveform.

Bandwidth - the total span of frequencies in a signal

Usually an approximation, ignoring frequencies whose energy

contribution is too small.

30 dB

30 dB bandwidth is approx. 3600 Hz

Frequency

(KHz)

Wavelength - the length of one sinusoidal cycle as ittravels through air (for sound) or space (for an electromagnetic signal)

497Hz wave traveling through air

2.266 ft

Relationship between frequency and wavelength

fλ=v where

f=frequency (Hz)

λ=wavelength (meters)

v=wave velocity (meters/sec)

Radio transmission bands are usually described by frequency

1900 MHz 4G cellular band (λ = 0.158m, about 6.2 inches)

Optical transmission bands are usually described by wavelength

Infrared light: λ = 1550 nanometers (f = 0.194 x 1015 Hz)

Aside: Propagation time of a signal can be significant

Sound in air: v=343.2 meters/sec (about 1100 ft/sec)

Electromagnetic wave (radio or light) in a vacuum:

v (or c as in E=mc2) =300 million meters/sec

Geostationary satellites not used much for voice because it takes

about ¼ second for a radio signal to go up and down.

Distance (ft) = 1100 x seconds between flash and thunder

Data rate – what is it, and how is it different frombandwidth?

Data rate is the quantity of digital data (in bits or bytes*) transmitted

through a channel per second. Digital data is conventionally carried

on a series of pulses.

*One byte equals eight bits.

Channel

Example 1: Two-level pulses. Since each pulse level is defined by a single bit, each pulse carries

one bit of information. With square pulses, the data rate in bits/sec

and the bandwidth in Hz are approximately equal.

Time (sec)

1 0 1 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1

-1

Example 2: Four-level pulses. Since each level is identified by a pair of bits, each pulse carries two

bits of information, identifying four levels. With the same pulse shape

as before, the bandwidth is the same, so the data rate is now

approximately twice the bandwidth.

Time (sec)

11 01 00 00 10 01 11 10 01 11 00 10 01 10 01 00 11 3

1

-1

-3

Noise, and a maximum transmitter power, limit how many levels (and

thus how high a data rate) can be supported.

The rectangular pulse is not favored because it requires more bandwidth than other pulse shapes

It is possible to design pulses that smear over several pulse intervals

but nevertheless do not interfere with one another.

-0.5/T 0.5/T

f (Hz) t (sec)

T

1

-T T

Nyquist pulseFrequency spectrum of

Nyquist pulse

Nyquist pulse offers the fastest pulsing rate in a fixed bandwidth without interference among adjacent pulses

Pulse is zero at centers of neighboring pulses!

1889-1976

Harry Nyquist

Date rate: 1/T pulses/sec in bandwidth 0.5/T Hz

2. Modulation, modems, wireless

Modulation definition:

Impressing an information signal on a carrier waveform for transmission or storage purposes.

You already saw data impressed on a series of pulses. This

is Pulse Amplitude Modulation (PAM)

Time (sec)

11 01 00 00 10 01 11 10 01 11 00 10 01 10 01 00 11 3

1

-1

-3

Example: 4-level PAM

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

Cable ModemTerminationSystem

Requests

Managementmessage

Allocation for cable modem A

Allocation for cable modem B

Other control info

Slots previouslymapped

Requestcontentionarea

A A A A BB B B

Cable modem transmitopportunities

Mainten-ance

Slots not yet mapped

Grants:

http://www.cablelabs.com/specs/specification-search/?cat=docsis

Wireless – Radio and free-space optical

Both use electromagnetic waves to carry information through space

Electric Field

Early innovators of radio and free-space optical

https://en.wikipedia.org/wiki/Photophone

A.G. Bell’s Photophone

1880

Marconi with spark-gap

transmitter 1905http://www.astrosurf.com/luxorion/

Radio/marconi-spark-gap.jpg

https://www.nde-ed.org/EducationResources/CommunityCollege/RadiationSafety/

theory/nature.htm

Electromagnetic spectrumCell phone here

International agreements allocate portions of the frequency

spectrum to different services (broadcasting, cellular mobile,

various private applications, aviation, medical, emergency services,

amateur radio, military, ……).

Administered in the U.S. by the Federal Communications

Commission.

Communications spectrum includes licensed and unlicensed

portions. Licensed spectrum – auctioned by the FCC – gives an

operator exclusive use and is favored by cellular operators.

Unlicensed spectrum is shared without restriction and is used for

WiFi and Bluetooth.

Spectrum Allocation

https://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf

Spectrum used for cellular mobile and WiFi

.698

https://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf

http://www.radio-electronics.com/info/wireless/wi-fi/80211-channels-number-

frequencies-bandwidth.php

.806

.901

.902

.930

.931

1.35

1.395

1.432

1.5361.67

1.675

1.71

2.0

2.022.155

2.2

2.3

2.305

2.39

2.46

2.483.5

2.52.69

2.4 2.5

5.7255.875

Cellular WiFi

WiFi

GHz

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

systems). Rates 2 Mbps indoor, 384 Kbps outdoor pedestrian,

64 Kbps in rapidly moving vehicle.

4G: High speed digital capabilities (LTE-A). MIMO, CoMP, OFDM

and other advanced techniques. Verizon suggests download speeds

between 5 and 12 Mbps and upload speeds between 2 and 5 Mbps,

with peak download speeds approaching 50 Mbps.

5G: Standards expected 2020. Use of millimicrowave bands (50 GHz

and above), up to Gbps rates.

Current and projected worldwide mobile subscribers

gsmamobileeconomy.com/GSMA_Global_Mobile_Economy_Report_2015.pdf

Millions

https://www.wilsonamplifiers.com/frequencies-by-provider

Ethernet

Wired network using coaxial cable. Rates to 100 Gbps (and faster

coming). Used to use a collision detection system for multiple

access, but most Ethernet today is switched. Not further discussed

today.

WiFi

Wireless in unlicensed bands, rates to 1.3 Gbps in newest version

(IEEE 802.11ac). Dozens of channels to minimize interference.

Not further discussed today.intel.com/content/www/us/en/support/network-and-i-o/wireless-networking/000005725.html

Bluetooth

Low power, 2-3 Mbps personal area communications.

Discussed in next few slides.

Local and Personal Area Networks

Bluetooth

-A personal-area, low power wireless standard for moving data over

short distances among fixed and portable devices.

-Uses the unlicensed 2.4 GHz band.

-Has a maximum range of about 30 feet.

Example: Bluetooth earpiece leaving hands free during phone

calls.

http://www.slideshare.net/mnsh01987/bluetooth-technology

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)

Physical: Electrical, Mechanical & functional interfaces

Link or MAC: Ordered data flow on links, access arbitration

Network: Routing, message or packet structure

Transport: End-to-end (system, application) info transfer

Session: Control of dialog between processes (e.g. object exch.)

Presentation: Data formats, representations, and displays

Application: Application-dependent services & procedures

1

2

3

4

5

6

7

Internet defined by protocol stack

Applications

RTP, RTSP

Network level (e.g. IP, Routing protocols, DiffServ)

Medium Access Control (MAC) or Link layer

Physical networking (Wired and wireless signaling, data framing, modulation, etc.)

Transport level (e.g. MPEG, TCP, UDP)

Internet

HTML

Session level HTTP

Independent of all beneath this line

invoke transport service

Application

Transport

Network

Link, Phys

invoke media access, framing, & line signaling

Application

Transport

Network

Link, Phys

Packet transfer

Transport data package transfer

Information unit transfer

invoke internetworking service

Physical network

Protocol layers offer services to higher layers and interactacross networks

Interfaces

physical interface

This concludes lecture 2. See you next week whenwe focus on Internet structure and protocols.