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CS680: Wireless Networks and Applications

William RegliDepartment of Computer Science

Drexel University

Lecture Outline

• Course Description and Policies• Project Discussion• History and current state of wireless

technologies

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Source Materials for Lectures

• These lectures stand on ‘the shoulders of giants’• Acknowledgements

– Many sources were used to create these lecture materials

– These materials are used under several rights• GNU Free Documentation License• Creative Commons• Fair Use: http://fairuse.stanford.edu/

• Where appropriate and possible, credits are given to original source

Course Objectives

• Understand wireless networks from a computer science perspective

• Technical writing intensive course– Give your self time to write and rewrite– Give yourself time to read and digest materials

• Use and understanding of 802.11 tools• Build 802.11 tools, design experiments, and

create useful demos/data

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Course Outline

• History of Wireless Networks• Details of 802.11• Mobile, Ad hoc, Wireless Networks

– Routing, security, QoS, …• Vulnerability• Other wireless applications

– SDR, Sensor networks, etc• What CS folks need to know about ECE topics

like power, antenna, etc.

Approach to Subject Matter

• Software-based and Systems Engineering for wireless networked systems and applications

• This is not a signal processing class– Meant to compliment existing ECE/CS offerings

• We will– not build whole networks, antennas, etc– use low level tools to explore new mobile and

untethered applications– Connect different systems, components and software

to perform analysis

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Expectations

• This is a seminar-like course• Class participation is important• Curiosity is critical

– The subject area is just too vast, you’ll need to read beyond what is assigned

• Projects should be demos or systems with lasting value – something you can put up on the net for download– A paper, report or web site

Projects• Project is the major part of your grade• Projects can be team projects

– but work scales at least linearly with the size of the team– Teams should be multi-disciplinary (ECE/CS)

• Topics can be– Those suggested by the instructor– Proposed by student or student team

• Any legitimate topic!!

• Proposals will be a formal process• Work will constitute the principle activity of weeks 4-11 of

the course (no final exam)– Scale of Project: 40+ hours of direct labor per person– (I.e. 6+ hours per week, minimum, on average)

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Project Proposals• Version 1: due on or before the 5th week• Version 2: due on or before the 6th week• Proposal Content

– Title– Problem Statement– Motivation– Background study, including citations and literature

review– Experimental study design– Empirical analysis– Conclusions

Grading

• 2-3 written assignments 40%– Essay, report, Q&A

• Class participation 10%• Project 50%

• A project review period may be scheduled for during finals week in lieu of an exam

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Disclaimers

• Lectures will only be able to touch the surface– Students will need to pursue extra reading

• Students should – Ask lots of questions– Make extensive use of the email list– Set up meetings with the instructor– Experiment

Ethics

• The wireless technology we are studying embodies many ethical issues– Privacy, big brother, malicious users,

eavesdropping, etc.• This is not a moral philosophy class, but it

could be

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Ethical Question #1

• You are playing with Ethereal• You find an unencrypted wireless base

station with users• Is it OK to record their traffic and re-

construct transactions for a learning exercise?

Ethical Question #2

• You are playing with Ethereal• You find an encrypted wireless base

station with users• Is it OK to record their traffic and re-

construct transactions for a learning exercise?

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Ethical Question #3

• Is it OK to launch a DoS attack on Dragonfly users in the Hagerty Library?

Ethical Question #4

• You set up a laptop, A, is a mock base station emitting packets

• You set up a second laptop, B, to receive these packets

• Is it OK to perform a DoS attack on B?

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Ethical Answers (if any)

• Technology is power• Power compels responsibility• You must understand these technologies

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Where are we today?

• Use of wireless is booming– Cellular is the prime example

• 3d world networks will likely be entirely wireless• As the “edge nodes” get richer and more

powerful, what will be the killer applications?• Societal Implications are enormous

– New modalities for work and social interaction– Privacy concerns– Security and information assurance concerns

Application of Wireless Networks

• Killer applications are beginning to emerge– Voice (phone) service– Email

• Blackberry– Pictures and photography– Instant Messaging

• Not quite – Internet browsing (on small devices)– GPS & Personalized, location-based, services

• Just over the horizon– Situation awareness, intelligent assistants

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Example: Battlefield Communications

Example Application: VoIP

1. Replace your cell phone with an IP-based phone on your PDA

2. Replace your walkie-talkie with an IP-based application on your PDA/laptop

Issues:– QoS, latency, handoff, security, …

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Example Application:Healthcare

• Handling informationoverload for doctorsand medicalprofessionals

• Access to medical sensors, records

• Entry mechanisms for reporting

Example Application: Personalized+Localized Information

• Your cell-phone, PDA, etc knows where you are• Information can be custom tailored to your place

and current activities– Restaurant recommendations– Concerts/films– Digitally augmented tourism– Real estate shopping– Emergency response

• Issues:– Privacy, anonymity

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Example Application: First Responders

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Mobility, Mobility, Mobility

• Mobility is what distinguishes wireless applications from “traditional” ones

• This entails– Highly variable operating environments– Dynamic network connectivity and bandwidth

conditions– Every node is an edge node– Power is now key– Nodes may have limited computing resources– Handoffs and mobility support

Implications for Applications

• All of the system layers interact!– Power affects networking, etc

• Software developers for wireless applications need to now worry about these interactions– Christmas lights

• Applications need to adapt to these environments

• Developers need to understand these interactions

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How did we get here?

• Physics– Electro-magnetism

• Engineering– Radio pioneers

• Media and entertainment– RCA/Victor Company, NBC

• Military

History of Wireless• 1896: Marconi’s Wireless Telegraph• 1920s/30s: Mobile Police Radio• 1935: FM Radio (Armstrong)• 1949: FCC recognizes mobile radio• 1979: NTT/Japan deploys cellular communication system• 1989: Groupe Spècial Mobile defines European digital

cellular standard, GSM• 1991: US Digital Cellular phone system introduced• 1993: IS-95 code-division multiple-access (CDMA)

spread- spectrum digital cellular system deployed in US

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History of Wireless Part II

• Wireless, until recently, has been either– Radio/TV industries– “Phone” companies– Military

• The convergence of digital technologies with radio (starting with cellular) has changed the use of the medium

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History of Military Wireless Networking

• Ethernet (Metcalf) 1976• DARPA Packet Radio Program 1978• Survivable Radio Networks 1987• Single Channel Ground-Airborne Radio

System (SINCGARS) 80s

ALOHAnet

• 1970’s effort to network the Hawaiian islands with a packet radio network– Paralleled the ARPANet effort

• Everyone was using the same frequency– Protocol to avoid collisions:

• If you have data to send, send the data• If the message collides, try resending later

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History of Wireless Internet: 802.11

• 1997– IEEE 802.11 working group developed standard for inter-working

wireless LAN products for 1 and 2 Mbps data rates in 2.4 GHz ISM(industrial, scientific, and medical) band (2400-2483 MHz)

– Required that mobile station should communicate with any wired or mobile station transparently (802.11 should appear like any other 802 LAN above MAC layer), so 802.11 MAC layer attempts to hide nature of wireless layer (eg, responsible for data retransmission)

• 1999– IEEE 802.11a amendment for 5 GHz band operation and 802.11b

amendment to support up to 11 Mbps data rate at 24 GHz– MAC sub layer uses CSMA/CA (carrier sense multiple access with

collision avoidance)• Hardware appeared in 1999

– Apple, Lucent, …

Other Forms of Wireless Network

• Cellular• Satellite• Bluetooth• Ultra Wide Band• Microwave• Optical• …

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How Regular Networks Work

• Physical Wires are the shared medium– Fiber optic, twisted pair, coax

• Host send carrier signals down wires

• Protocols (Ethernet, ATM, etc) coordinate messages to avoid collisions

• Routers act as repeaters, hosts are “leaves”

How Wireless Networks Work

• Medium is the electro-magnetic spectrum• Radio is used to signal in this medium

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The Physics and Technologies of the Physical and MAC Layers• The Electromagnetic Spectrum• Carrier-Sense Multiple Access (CSMA)• Spread Spectrum• Orthogonal Frequency-Division

Multiplexing (OFDM)

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The Electro-Magnetic Spectrum

Nomenclature

< 1 mmAbove 300 GHzduckySuper high frequency

10 mm – 1 mm30–300 GHz11EHFExtremely high frequency

100 mm – 10 mm3–30 GHz10SHFSuper high frequency

1 m – 100 mm300–3000 MHz9UHFUltra high frequency

10 m – 1 m30–300 MHz8VHFVery high frequency

100 m – 10 m3–30 MHz7HFHigh frequency

1 km – 100 m300–3000 kHz6MFMedium frequency

10 km – 1 km30–300 kHz5LFLow frequency

100 km – 10 km3–30 kHz4VLFVery low frequency

1000 km – 100 km300–3000 Hz3ULFUltra low frequency

10,000 km – 1000 km30–300 Hz2SLFSuper low frequency

100,000 km – 10,000 km3–30 Hz1ELFExtremely low frequency

> 100,000 km< 3 Hz

WavelengthFrequencyITU bandAbbrBand name

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What goes Where?• aircraft band (108~136 MHz), for air traffic

control• FM broadcast band (88~108 MHz, except 76~90

in Japan)• AM broadcast band (530~1610kHz, to 1700 in

the Americas)• upper VHF TV band (174~216 MHz in the

Americas)• L band (1452~1492 MHz) for digital radio (DAB)

outside the US• industrial, scientific, and medical (ISM)

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Sidebar: Cellular Systems

• CDMA• GSM• Old

– Analog– TDMA

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Sidebar: Satellite Systems

• L-band– 950 to 2200 MHz– GPS

• C-band– 3.4Ghz to 6.7Ghz.

• K-band– Ka-band, 27Ghz to 40Ghz– Ku-band, generally from 10.7Ghz to 18.4Ghz– Direct TV, DSS (Digital Satellite System)

ISM Bands

• industrial, scientific, and medical (ISM)– 900 MHz band (33.3 cm wavelength)– 2.4 GHz band (12.2 cm wavelength)– 5.8 GHz band (5.2 cm wavelength)

• IEEE 802.11b/g wireless Ethernet: 2.4 GHz• IEEE 802.11a wireless Ethernet: 5 GHz

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CSMA/CD (Ethernet)• Carrier-Sense Multiple Access with Collision Detection

– non-deterministic Media Access Control (MAC) protocol– node verifies the absence of other traffic before transmitting on a

shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum.

• Carrier Sense: transmitter listens for carrier wave before trying to send

• Multiple Access: multiple nodes may concurrently send and receive on the medium

• Concurrent transmission may result in frame collisions

CSMA/CA

• Carrier Sense Multiple Access with Collision Avoidance – network control protocol in which:

• a carrier sensing scheme is used,• a data station that intends to transmit sends a jam signal• after waiting a sufficient time for all stations to receive the

jam signal, the data station transmits a frame• while transmitting, if the data station detects a jam signal

from another station, it stops transmitting for a random time and then tries again.

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Hedy Lamarr, Inventor of Spread Spectrum

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Lamarr & Antheil’s Patent• Patent No. 2,292,387,

"SECRET COMMUNICATION SYSTEM," filed June 10, 1941

Spread Spectrum: Basic Idea

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Spread Spectrum• Basic Idea: Modulate signals

over a wide frequency spectra– Use RF swath much larger than

needed• DSSS (802.11b/g)

– Modulation of an RF carrier signal– high-speed, client/server

applications where radio interference is minimal

• FHSS– Hops around frequencies and

encodes signal in the frequency hopping pattern and rate.

– suited to environments where interference is high and amount of data to be transmitted is low

DSSS

FHSS

Orthogonal Frequency-Division Multiplexing (OFDM)

• Used in 802.11a, WiMAX, 802.16• Signal is split into several narrowband

channels at different frequencies.• reduces the amount of crosstalk in signal

transmissions, resilient to multi-path

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Challenges in Wireless Networks

• Every node is an edge node– Everyone is outside the firewall

• Medium is variable and dynamic– Rainy day vs clear day

• Disruption filled, limited bandwidth• Mobility => portable => batteries + power• EM spectrum is prone to interference, fading,

multi-path, Doppler shift, etc– Self interference

Etc… and the list goes on…

OSI + TCP/IP Models

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Computer Science Perspectives

• Stick to the network-layer and above– But we need to understand constraints posed

by the lower layers• Many algorithmic / AI issues

– Routing, decision making, optimality, etc• New application development framework

– Building wireless distributed and mobile application software systems

Challenges for Wireless Applications

• Good news: – many new possibilities

• Bad news: – Many new application development issues– These span the OSI stack– Security and survivability is a huge issue

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Future of Wireless Networks

• Ubiquitous, untethered computing and communications

• Situation-aware applications• Seamless connectivity across multiple

providers (like cellular today)• Some kind of charge or billing mechanisms• Interaction with sensor networks• Connectivity to traditional, centralized,

applications

Tools for this class…

• Much open source– Check out the pages for WarDriving

• Suggestions:– Use tools to deepen your understanding of

the technologies and systems – Use GPL and open source tools as the basis

for project ideas and extensions

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Network Stumbler

Ethereal

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End

OSI Reference Model

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TCP/IP Protocol Stack

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