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CSE 535

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Title: CSE 535


1
CSE 535 Mobile ComputingLecture 3 An
Overview of Mobile Computing Part II
Ubiquitous Computing, Wireless Networking
  • Sandeep K. S. Gupta
  • School of Computing and Informatics
  • Arizona State University

Based on Slides by Prof. Richard, UNO
2
Agenda
  • Introduction to Ubiquitous (Mobile) Computing
  • Vision
  • Current state-of-art
  • Wearable Computing
  • Challenges
  • Introduction to Wireless Networking
  • Wireless Characterisitcs
  • Cellular Network (UMTS)
  • IEEE 802.11
  • Bluetooth

3
Summary from Last Class
  • Fundamental to Mobile computing is various
    techniques in hardware/software to adapt to
    variation in resource availability taking into
    account contextual information including user
    preferences.
  • Wireless sensor networking is enabling technology
    for pervasive/ubiquitous computing

4
References
  • Ubiquitous Computing
  • Marc Weisers papers (see Ch1 and Ch4 references
    list in the book) to get a feel for the
    challenges/potential of mobile/pervasive
    computing
  • Chapter 1 of book
  • Chapter 4 introduction (sec 4.1)
  • WSN
  • Chapters 8-9

5
Ubiquitous, Mobile, Nomadic
  • Terminology not always consistent
  • Nomadic computing portable no mobility while
    connected
  • Mobile computing on-the-go, e.g., while
    sitting on a train possibility of network
    connections remaining open
  • Pervasive or Ubiquitous computing
  • computing everywhere OR
  • computers everywheremost of them invisible

6
Computers Everywhere
  • Marc Weiser
  • Vision of ubiquitous computing hundreds of
    computers per person, various sizes and
    capabilities
  • Tabs
  • very small--smart badge w/ user info, etc.
  • allow personalized settings to follow a user
  • leave bios behind at meetings
  • attached to virtually everything--e.g., books,
    car keys, etc.

7
Ubiquitous Computing Reality
  • Pads
  • scrap computer -- grab and use anywhere
  • arrange on a desk as you would sheets of paper
  • can project onto larger computers with a wave
    of your hand
  • Write on pad, draw on it, pull up documents
  • Liveboards
  • Larger displays whiteboard, personalized
    bulletin board, etc.

8
Reality (2)
  • Some of Weisers H/W predictions
  • Large displays, a fraction of a centimeter thick,
    powered continuously for days on a small battery
    (no, no, no!)
  • 1GHz processors (yes, yes, yes)
  • 16MB of memory on a single unit (easy, memory is
    far cheaper than we could have imagined in 1991)
  • Several GB of storage easily available (yes
    weve done better than this)
  • So, were behind in displays, batteries

9
What does Ubiquitous (Mobile) Computing Offer?
  • A choice of work environments
  • In your garden (but watch out for birds!)
  • Coffee shops
  • In the field
  • Remote access to important data
  • Clients office (no "can I borrow your
    computer")
  • Meetings (e.g., quick access to statistics,
    reports)
  • Repair manuals, books, etc.
  • Translation facilities
  • In the grocery store!

10
Offerings (2)
  • Electronic note-taking
  • While touring a new city
  • Where am I? What is this building? How do I
    get to Lane Avenue? Im hungry!
  • Diversion
  • E-books stored, downloadable
  • Games e.g., chess, solitaire, poker
  • Ubiquitous communication
  • email, Web
  • voice
  • video

11
What About the Toys?
  • A variety of computing and communication devices
    for mobile users
  • Watch-sized devices (and usually a watch!)
  • PDA (Personal Digital Assistants)
  • Multifunction cellular phones
  • Palm-sized computers
  • Wearable computers
  • Pads
  • Notebook computers

more computing power
12
Portable Information Appliances
(This slide courtesy of Sumi Helal _at_ The
University of Florida)
Car Stereo-Phone
13
Case Study Palm VII
  • Interfaces serial, IR, 8Kb/sec Mobitex wireless
  • Protocols HTTP transactions only, through
    Palm.net proxy
  • Processor 16MHz Motorola Fireball ( 68000
    video controller, etc.)
  • Memory 2/8MB
  • No expansion slots
  • Screen 160x160 pixels, monochrome
  • Built-in applications typical PDA (notes,
    calendar, etc.)
  • Simple character-based handwriting recognition
  • Runs PalmOS
  • Software development C, Java, various scripting
    languages
  • Dimensions 5.25 X 3.25 X 0.75, 6.7oz

14
Palm VII
15
Case Study Palm M515
  • Interfaces USB, IR
  • Processor Faster 33MHz
  • Networking via IR or cable to a cellular phone
  • Memory 16MB
  • Secure Digital (SD) expansion slot
  • Screen 160x160 pixels, 16bit color
  • Built-in applications typical PDA (notes,
    calendar, etc.)
  • Simple character-based handwriting recognition
  • Runs PalmOS 4.1
  • Software development C, Java, various scripting
    languages
  • Dimensions 4.5 X 3.1 X 0.5, 4.9oz

16
Palm M505
17
Palm Accessories
30/each
Memory Games Books
Wireless LAN module ()
Portable keyboards
18
Handspring Visor (Palm Derivative)
cellular
MP3 player
springboard modules for expansion
camera
voice recorder
19
Case Study Palm Tungsten T3
  • Interfaces USB, IR
  • Processor 400MHz ARM-compatible
  • Networking via IR or cable or Bluetooth to a
    cellular phone
  • Memory 64MB
  • Secure Digital (SD) expansion slot
  • Screen 320x480 pixels, color
  • Built-in applications typical PDA (notes,
    calendar, etc.)
  • Simple character-based handwriting recognition
  • Runs PalmOS 5.2.1
  • Software development C, Java, various scripting
    languages
  • Dimensions 4.3 X 3 X 0.6, 5.5oz
  • Price 399

20
Case Study HP/Compaq IPAQ
  • Interfaces USB, IR, Bluetooth, CF, Secure
    Digital, PCMCIA
  • Processor 206MHz StrongARM CPU
  • Networking via CF or PCMCIA or Bluetooth
    interfaces
  • Memory 32MB ROM 64MB RAM CF or SD expansion
  • Screen 320x240 pixels, 16bit color
  • Built-in applications typical PDA (notes,
    calendar, etc.) Pocket Word, Excel, Internet
    Explorer, etc.
  • Character-based or script handwriting recognition
  • Runs Windows CE or Linux
  • Software development VB, C, Java, various
    scripting languages
  • Dimensions 5.3" x 3.3" x .62, 6.7oz
  • Devices like this 300-1000 lots of
    expansion options

21
Case Study Sony VAIO Picturebook
733MHz Crusoe (Pentium-compatible) 256MB /
20GB 8.9 1280x600 screen Built-in digital
camera, 1394 interface ¾ size keyboard 1 PCMCIA
slot Windows/Linux, etc. 2000 when last
available
22
Tiny Computers
16MB 66MHz 486SX used as a web server
See http//wearables.stanford.edu/
23
M1/M2 Displays
320x240 (M1, 500) 800x600 (M2, 5000)
24
Wearable Computing
The inventor of wearable computing Steve Mann.
See http//wearcam.org/mann.html
25
Today
26
Batteries Suck Network Cables or Power cables?
  • And bird poop is bad.

27
Characteristics of Mobile Devices
  • Resource-poor compared to their desktop
    counterparts
  • Limited processing power
  • Limited battery life
  • Limited network connectivity
  • Poor availabilitythey sleep a lot!
  • Poor display resolution (except notebooks)
  • Tedious data input (except notebooks)

28
Characteristics (2)
  • Resource poor...
  • Not very expandable
  • Our condolences to the landfills...
  • Peripherals traded for mobility, so...
  • One device typically doesnt do it all
  • Poor compatibility between devices
  • Functionality is often duplicated
  • work belt syndrome for the mobile computing
    nerd
  • Bluetooth will help, but bandwidth limited
  • Service discovery and better device cooperation
    to overcome poverty

29
Characteristics (3)
  • Limitations are a result of tradeoffs between
    portability and horsepower
  • Very small size limits traditional I/O methods
  • New ones handwriting recognition, voice input
  • Must work well or extreme frustration...
  • Must work with other people present!!
  • Batteries weigh more than any other component in
    most mobile devices
  • Smaller batteries, less power
  • CPU speeds reduced to conserve power

30
Characteristics (4)
  • Notebook computers fare better in the comparison
    with desktops because form factor isnt so
    restrictive
  • Reasonable screen size
  • Decent keyboards
  • Mouse substitutes
  • Ample memory
  • But even a 4lb notebook is too tedious to carry
    everywhere--and too inconvenient to use quickly

31
Mobile Computing Challenges
  • Challenges in mobile computing directly related
    to the resource-poor nature of the devices
  • Mobile computing isnt a simple extension of
    distributed computing
  • Hostile environment
  • Power-poor
  • Poor (or no) network bandwidth
  • Higher error rates
  • Variable latency
  • Frequent disconnection
  • Mobility

Evil for network protocols built for traditional
wired networks
32
Challenges (2)
  • Result Must rethink many issues cant just
    plug in classic distributed systems theory
  • Disconnection ltgt Crashed!
  • Adaptability to deal with varying conditions
  • Transcoding proxies--scale content (e.g., images)
    to match available bandwidth
  • Mobile proxies to convert content (e.g.,
    Postscript ASCII)
  • Agent systems for information access
  • More clever ways of checking for data consistency
  • Application callbacks to monitor conditions
    (network, battery power, etc.)

33
Proxies, Proxies
Postscript to text proxy
Text
Postscript
34
Adaptation

system/application cooperation
none
full
level of application adaptability
application entirely responsible for
reacting (or not) to changing conditions
system entirely responsible for reacting (or not)
to changing conditions protects application
35
More Challenges
  • Cache! Cache! Cache!
  • When possible, allow the risk of inconsistent
    data
  • even if it requires human intervention to fix
  • Prevalent network protocols require work to give
    good performance for wireless
  • Schemes for mobility
  • TCP hacks
  • Schemes for intelligent handoff between network
    interfaces
  • Tradeoffs between cost, bandwidth, availability

36
Wireless Networking
  • Issues
  • Technologies
  • What makes the bits fly?
  • Can we afford it?
  • Currently, no single technology will cut it
  • Handoff seems essential
  • How do we run traditional applications over these
    technologies?
  • What works well?
  • What needs more work?
  • WAN Wide Area Network
  • MAN Metro Area Network
  • LAN Local Area Network
  • PAN Personal Area Network

37
Wireless Networking Technologies
  • Satellite (WAN)
  • Microwave (MAN)
  • Broadband Wireless (MAN)
  • Laser (MAN)
  • Cellular (WAN)
  • Bluetooth (Wireless PAN)
  • IrDA (Wireless point-to-point PAN)
  • Wireless LANs
  • 802.11 standards (e.g., Lucent WaveLAN)

38
Global Wireless Infrastructure
Slide courtesy of Sumi Helal _at_ UFL
39
Wireless Problems
  • Typically much slower than wired networks
  • State of the art wireless LAN 54Mb/sec
  • Wired LAN 10000Mb/sec
  • Higher transmission bit error rates (BER)
  • Uncontrolled population
  • Difficult to ensure Quality of Service (QoS)
  • Asymmetric bandwidth
  • Limited communication bandwidth aggravates the
    problem of limited battery life

40
Satellite
  • GEO (Geosynchronous/Geostationary)
  • Remains "stationary" relative to equator
  • Deployed _at_ 36,000 kmrequires a big rocket!
  • Need only 3 to cover earth
  • High latency (1/4 sec or so round trip)
  • Need high-power transmitter to reach satellite
  • Arthur C. Clarke 'How I lost a billion dollars
    in my spare time
  • XM Satellite radio uses GEOs (only 2, tho)

41
Satellite (2)
  • LEO (Low Earth Orbit)
  • Much lower orbitsless than 1000 km
  • Must have handoff mechanismdon't appear
    stationary to earthbound base stations
  • Lower power transmitter than GEO
  • Lower latency, but handoff delay
  • Space junk!
  • MEO (Middle Earth Orbit)
  • 10,000 km

42
Satellite DirecPC/DirecWAY
  • 400Kb/sec downlink from GEO
  • Previously, modem uplink, but now 2-way
  • Dish must see the sky (typical of satellite)
  • Blech169MB (1-4 hours) threshold (at last
    check??)
  • HUGE latency compared to DSL or cable modems
  • Last resort only!

43
Microwave
  • Range 20 miles or more, typically less
  • Line of sight only, point to point
  • Rain causes problems, because rain absorbs
    microwave energy
  • Ethernet speeds
  • Ducks won't fry

44
Laser
  • High-speed systems exist 155Mb/sec
  • Line of sight only, 300m for Jolt
  • Relatively high cost
  • (One complete 155Mb/sec system for 24K, last
    time I checked)

45
Brief Survey of "Cellular"
  • CDPD Cellular Digital Packet Data
  • Transmit digital data over existing cellular
    network
  • 19.2Kb/sec
  • Uses idle channels in the cellular network
  • Mobitex Ericsson technology
  • 8Kb/sec, fairly high latency (4-8s RTT!)
  • Systems exist in US, Europe but Palm VII is
    US-only
  • Migrating to 19.2Kb?
  • GSM
  • Most European
  • 9600bps
  • Limited coverage in U.S.

46
UMTS
  • Universal Mobile Telecom System
  • International
  • Initially up to 2Mb/sec
  • Support for IP
  • Quality of Service (QoS) guarantees
  • Enables mobile multimedia, other
    bandwidth-intensive applications
  • Widespread deployment by 2005
  • See http//www.umts-forum.org for more info

47
Dont Throw Away Your DSL Yet!
  • Bandwidth is shared by users within a particular
    cell (1-4 miles across)
  • For Sprint, Im currently getting 90Kb/sec.
  • Cost?
  • Depends on who you talk to and if the rules hold
    up
  • 30-100 per month for unlimited data

48
128Kb "Everywhere" Metricom
  • Ricochet by Metricom
  • 128Kb/sec service in select areas
  • In practice, 70Kb ?
  • Frequency-hopping system
  • Shoebox-sized units mounted on street lights
  • Draws power from light
  • One pole-mounted unit every ¼ to ½ mile,
    checkerboard pattern
  • Rest In Peace (RIP) in 2001 but now its back
  • 75/month flat during initial lifetime, now
    24.95/month flat
  • Modem is now free
  • Ricochet purchased by Aerie networks, now YDI?
  • Network is mostly dark, but alive again in Denver
    and San Diego
  • Cost has decreased substantially, but limited
    availability
  • 7000 customers in 2004

49
Wireless LANs
  • One example IEEE 802.11 standard
  • CSMA/CA instead of CSMA/CD, as in Ethernet
  • Ethernet detect collision during transmission
  • Wireless impossible can only hear own signal
    during transmission
  • Current speeds 1Mb/sec 54Mb/sec
  • Access point / NIC prices have recently dropped
    substantially
  • 802.11b 2-11Mb/sec (we have this) in 2GHz range
  • 802.11a 54Mb/sec in 5GHz range (incompatible
    with 802.11b, very dependent on line of sight)
  • 802.11g 20Mb/sec, compatible with 802.11b

50
802.11 Details
  • Medium-range wireless local area network
    technology
  • 2.45GHz Industrial, Scientific, Medical (ISM)
    Band
  • Old 1Mb/sec , now 2 - 54Mb/sec transmission
    speeds
  • Older 1Mb/sec spec used Frequency Hopping Spread
    Spectrum (FHSS)
  • Units change frequency rapidly according to an
    agreed channel hopping sequence
  • Helps to reduce interference
  • Higher data rates use Direct Sequence Spread
    Spectrum (DSSS) Radio
  • Units broadcast a broad, redundant signal that is
    resistant to interference
  • US 11 distinct channels (partially overlapping)
  • Three channels (1, 6, 11) do not overlap at all

51
Representative Products
  • Orinico (Lucent) Silver cards
  • lt 100
  • Orinoco (Lucent) Access Point
  • 300-700 per AP
  • Residential wireless routers w/o bridging
  • Under 100
  • No roaming, for single AP (e.g., home) deployment
  • Apple Airport products
  • Under 150
  • Newest supports streaming audio

52
802.11 The Big Picture
53
OrAd-hoc Mode
54
How Far? 802.11b Wavelan Specs
Environment 11Mb/sec 5.5Mb/sec
2Mb/sec
Completely Open Environment 525 ft 885 ft 1300 ft
Semi-open Environment 165 ft 230 ft 300 ft
Closed (floor-to-ceiling brick) 80 ft 115 ft 130 ft
55
Card/Access Point Communication Joining a BSS
Passive
Beacons from AP (periodic synchronization
transmission, contains info to synchronize
clocks, supported data rates, Traffic
Indication Map TIM)
Probe Request (request for synchronization
information for a desired ESS identifier)
Active
Probe Response (response with synchronization
information)
56
Authentication/Association
Authentication Always allow or
challenge/response and/or is your MAC address
OK? (security issues later) Association
Request/Response negotiation to allow a mobile
host to join an access point Reassociation
disassociates with current access point and
moves to another (allows roaming) Card can
listen for beacons from other access points to
determine stronger signals
57
Moving Packets
Access points act as bridges that serve their set
of mobile hosts
If packet is addressed to a mobile host that is
served by this access point, then broadcast
it. Otherwise, drop it on the distribution
system network for delivery to another
access point or another destination.
58
Distributed Coordination Function
  • Ethernet uses CSMA/CD (Carrier Detect Multiple
    Access/Collision Detection)
  • Listen to medium
  • If quiet, begin transmission, but listen
  • If transmission is garbled, backoff and retry
  • Not feasible with wireless
  • Not all stations can hear each other!
  • Transmission drowns out signal of other radios

59
Distributed Coordination Function (2)
  • 802.11 uses CSMA/CA (Carrier Detect Multiple
    Access/Collision Avoidance)
  • Wait, then listen to medium
  • If quiet for specified duration, begin
    transmission, otherwise wait again
  • After transmission, wait for explicit ACK, if no
    response, wait, retransmit
  • Can also use RTS/CTS to combat hidden terminal
    problem
  • RTS contains source, destination, duration info
  • Request To Send reserves near sender, Clear To
    Send reserves medium near receiver
  • RTS/CTS functionality rarely used in production
    systems

60
802.11 Future
  • Revisions to standards for security
  • 802.1X / 802.11i (later)
  • We were looking at 802.11b
  • 802.11a 54Mb/sec, 5GHz
  • 802.11g 20Mb/sec, compatible w/ 802.11b
  • 802.11a has more non-overlapping channels than
    802.11b
  • 802.11b 3 non-overlapping channels
  • 802.11a channels do not overlap

61
Hiperlan
  • European standard Hiperlan/2
  • Operates in 5GHz range of 802.11a
  • Problem 5GHz currently reserved for Hiperlan
  • Same access point-oriented topology as 802.11
  • 30-50m (90-150ft) range
  • 25Mb/sec peak data rate
  • Connection orientedAP governs data rates, etc.
    so QoS guarantees can be made (unlike 802.11)
  • DES/Triple DES encryption
  • Supports digital certificates for authentication
  • Time Division Multiple Access (TDMA)units
    transmit in certain slots
  • Info source Hiperlan/2 Forum Whitepaper
    HiperLAN/2 The Broadband Radio Transmission
    Technology Operating in the 5 GHz Frequency Band

62
802.11a, 802.11b, Hiperlan
  • Does it matter for a particular user?
  • A bit.
  • For general purpose computing, user would need
    cards for any wireless network she is likely to
    encounter
  • At worst
  • 802.11a/b/g card for US
  • Many laptops now have integrated a/b/g
  • In US, 802.11b is currently the most important
    802.11 protocol your devices should support
  • Hiperlan for Europe??
  • Other differences affect applications
  • E.g., no QoS in 802.11, but do have it in Hiperlan

63
Bluetooth Goals
  • Provide small, inexpensive, power-conscious radio
    system
  • Short range
  • Bluetooth says, cables! Bah!
  • Personal (short-range) ad-hoc networks
  • Device communication and cooperation
  • Not really intended as a wireless LAN technology,
    but its being used as such

64
Who is Bluetooth?
  • Danish king Bluetooth II (940-981)
  • Lived to a ripe old age ( 70 years)
  • First baptized Danish king
  • Significance in this context?
  • The "Blue" in IBM?
  • Deep Blue
  • Deeper Blue
  • Big Blue
  • The Ericsson Scandinavian connection?

65
Bluetooth Hardware
  • Predicted long term cost lt 5/unit
  • (in the short term, more)

66
Bluetooth Hardware
  • Low-cost radio operates in the 2.4GHz band
  • Maximizes international acceptance
  • except in France?! Well
  • Bluetooth 1Mb/sec over several meters
  • Range can be extended with an external power
    amplifier
  • Up to 7 simultaneous links
  • 75 hours voice 3 months standby w/ 600mAh
    battery

67
Bluetooth Protocol Stack
   
 
 
 
TCS
vCard, etc.
SDP
OBEX
RFCOMM
LMP
L2CAP
Audio
Baseband
Radio
68
The Cordless Desktop
!!!!
Ummm..no.
69
Goodbye CablesHello Cooperation
X
X
Joe 555-1287
X
Gotta remember to tell the pager Joes number
changed...
70
Send and Forget...
71
"Last hop" Network Access
TDK's 8 node Bluetooth Access Point
72
Piconets / Scatternets
piconet B
piconet A
Max eight active devices per piconetone
master Parking allows more devices to be addressed
73
Bluetooth Kills Trees...
  • 200 for a paper copy 50 shipping
  • 1500 pages!
  • Quite readable, but loooooooooong!

74
Aside Bluetooth vs. IrDA
  • IrDA Line of sight vs. omnidirectional BT
  • IrDA has advantages and disadvantages
  • Low-tech security for data transfer
  • E.g., business cards
  • Inconvenient for Internet bridge solutions
  • Connected IrDA devices must remain relatively
    stationary
  • Higher bandwidth than Bluetooth (4-16Mb/sec)
  • Similar high-level standards (e.g., OBEX)
  • But Bluetooth supports multipoint communication
  • Current costs for deployment of IrDA are much
    cheaper (lt 2/unit)

75
Bluetooth Device Connection States
  • Standby waiting to join a piconet
  • Inquire looking for other Bluetooth devices
  • Page connecting to a specific device
  • Connected actively involved in a piconet
  • Hold power conservation state
  • Internal timer runs, connection maintained
  • Park power conservation state
  • Connection "broken" forgets member address, but
    can be reactivated

76
Bluetooth States
Standby
idle
Inquiry
Page
Connected
Transmit
Park
Hold
power conservation
77
Bluetooth Security
  • Authentication
  • Prevents unauthorized access to data on a
    Bluetooth device
  • Encryption
  • Secure transfers, prevent eavesdropping
  • Frequency Hopping
  • Makes snooping more difficult...
  • Limited Range
  • Makes snooping more obvious!

78
Bluetooth Security (2)
  • Each Bluetooth device
  • 48 bit 802-style unique identifier
  • 128 bit private authentication keys
  • 8 to128 bit private encryption keys (configurable
    in hardware)
  • 128 bit random number per transaction
  • Radios negotiate encryption strength
  • No governmental restrictions on authentication
  • Encryption is a different story
  • Link-level security in Bluetooth authenticates
    the device, not the user

79
Bluetooth Security (3)
  • Pairing installs a common secret key for
    authentication
  • Assumes access to both devices at the same time
  • Can also enter PIN at connection setup
  • Challenge/response for authentication
  • Encryption keys generated from authentication
    keys

80
Bluetooth Concerns
  • Frequencies overlap 802.11 standard
  • "Always on" may cause problems, worries FAA
  • (Take the train!)
  • Definitely need integration with software, not
    just hardware compatibility
  • 1Mb/sec isn't fast enough for some applications
  • and it definitely isnt enough to replace all
    cables (monitor, USB, SCSI, etc.)
  • But next generation spec may hit 2-20Mb/sec
  • Bluetooth SDP (Bluetooths service discovery
    protocol) isnt very sophisticated

81
Next Class
  • Wireless Networking
  • Mobile IP
  • TCP
  • Mobile Adaptive Apps
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