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The Challenges of Mobile Computing

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Title: The Challenges of Mobile Computing


1
The Challenges of Mobile Computing
  • George H. Forman, John Zhorjan

Alfred Park, Feb. 4, 2003
2
The Future of Computing
  • Its not just desktop computers anymore
  • Steve Jobs recently stated that 2003 would be the
    Year of the Notebook and added that we want
    to replace even more desktops with notebooks
  • Mobile computing is a building block for
    pervasive computing
  • Calm Technology Mark Weiser
  • Third Paradigm Alan Kay
  • A little history first

3
Its Been a Long Time Coming
  • The Dynabook
  • Conceived by Alan Kay, argued as the originator
    of the laptop concept
  • Handheld, wireless connectivity, full multimedia
    capabilities, support for programming
  • Circa 1972! Over 30 years ago

4
The Dynabook
A portable interactive personal computer, as
accessible as a book
5
The Vision is not a Reality Yet
  • In a recent interview, Alan Kay remarked that
    even with the advent of PDAs, small notebooks,
    etc., the Dynabook concept is not a reality.
  • Why?
  • Todays technology path is not aligned with
    original spirit of the Dynabook concept
  • Lacking technology
  • We will examine the difficulties facing mobile
    computing due to technology constraints

6
Mobile Computing ! Notebooks
  • PDAs
  • Cellular phones
  • Tablet PCs
  • Wearable computers

Apple Newton (1993)
7
Tablet PC Demo Video
  • Acer TravelMate C100 Tablet PC

8
A New Paradigm
  • tomorrows networked mobile computers are
    part of a greater computing infrastructure
  • It will revolutionize the way computers are
    used
  • Safe to say the paradigm shift has already begun

9
Mobile Computing Properties
  • Wireless Communication
  • Network connectivity is essential for mobile
    computing platforms
  • Mobility
  • Issues relating to dynamic information change
  • Portability
  • What good is a device that only lasts 5 minutes
    on battery power?

10
Wireless Communication
  • Issues
  • Lower bandwidth, higher error rates, signal path
    problems
  • Increased communication latency, retransmissions,
    and timeout delays
  • Mobility affords greater range of problems, e.g.
    moving from one coverage area to another

11
Disconnection
  • Two solution approaches
  • (1) Prevent disconnections
  • (2) Cope with disconnections
  • For mobile computers, allowing disconnections to
    happen and recovering from them is the better
    solution
  • Asynchronous operation (X11)
  • Caching and reconciliation (Coda FS)

12
Low Bandwidth
  • There is a discernible difference in bandwidth
    between wireless and wired connections
  • Two techniques to improve bandwidth
  • (1) Install more wireless cells by overlapping
    cells on different wavelengths, or
  • (2) reduce transmission ranges
  • Other techniques compression and logging
  • Available bandwidth is largely user-perceived, so
    tricks such as scheduling communication (lazy
    write-back and pre-fetching) to improve
    bandwidth utilization

13
Security Risks
  • Greater security risks than wired communication
  • Solutions
  • Hardware-based CLIPPER chip
  • Software-based Kerberos authentication services

14
Other Issues
  • High bandwidth variability
  • Applications should adapt to mobile devices
    changing from wired to wireless modes (and vice
    versa)
  • Heterogeneous networks
  • Moving from one service area to another

15
Wireless Today
  • IEEE 802.11 wireless standards
  • a, b, d, e, f, g, h, i
  • Up to 54Mbps transmission speeds (802.11a and
    802.11g), low bandwidth issue addressed with both
    solutions along with scaled bandwidth
  • GPRS (2.5G) and UMTS (3G)
  • Next generation cellular networks connecting
    cellphone users to the Internet
  • Security issues
  • WEP weak key vulnerability will be addressed in
    the 802.11i standard, which applies to the a, b,
    g physical standards

16
Mobility
  • The dynamic nature of mobile computing increases
    the volatility of information to support the
    platform
  • Caching vs. recomputation

17
Address Migration
  • Current IP addressing scheme imposes difficulties
    for dynamically changing addresses
  • Four different methods
  • Selective broadcast
  • Central services
  • Home bases
  • Forwarding Pointers

18
Location Dependent Information
  • Dynamic reconfiguration of local services and
    other location sensitive data requires the
    ability of mobile devices to reacquire this data
    that reflects the change in location
  • Privacy issues mechanisms are needed to prevent
    users from snooping potentially sensitive data
    about other mobile users

19
Mobility Today
  • IP Mobility (Mobile IP) Draft Proposal
  • Similar to the Forwarding Pointers method
  • Fixed home address and a care-of address that
    changes at each new point of attachment

20
Portability
  • Mobile devices are fundamentally different from
    stationary machines such as desktop computers
  • Must be designed with variety of constraints in
    mind, such as size and power consumption
    properties much like a wristwatch

21
Low Power
  • Tradeoff between battery weight (size) and
    battery life
  • Power consumption proportional to CV2F
  • C, Capacitance reduced by greater levels of VLSI
    and multichip modules
  • V, Voltage reduced with chips and accessories
    requiring lower voltages
  • F, Clock frequency reduced by scaling back clock
    rate when not needed
  • Software mechanisms for power conservation, such
    as turning off backlights or spinning down hard
    disks

22
Risks to Data
  • Mobile devices are more prone to complete data
    loss
  • Privacy concerns
  • Solution Encryption, but is it feasible on a
    mobile computing platform?
  • Data consistency
  • Replicated file systems Coda FS

23
Small User Interface
  • Windowing systems/managers inadequate for small
    devices
  • Favor recognition over keyboards or buttons
  • Gesture, handwriting, and voice recognition
  • Ambiguous input problematic
  • Pen-based input

24
Small Storage Capacity
  • Hard Disks are a liability, PDAs use solid-state
    memory instead
  • Use of distributed file systems and remote paging
    not applicable in most mobile computing scenarios
  • Interpreted script languages provide an
    alternative to reducing compiled object code sizes

25
Portability Today
  • Intel XScale Architecture
  • Low power consumption for amount of processing
    power provided
  • IBM Microdrives
  • Up to 4GB, low power consumption
  • Large Solid-State Memories
  • PDA, Cell phones
  • Embedded wireless functionality (IrDA, Bluetooth,
    and 802.11)

26
Relevance to Real-time Systems
  • Mobility Depending on the requirements,
    deadlines could be driven by the correctness and
    validity of address or other information required
    for proper operation of the device (e.g. systems
    implementing the 802.11e QoS standard)
  • Portability Hardware support for real-time
    operating systems in mobile computing RTOS must
    strike a balance between power consumption, ease
    of use, and features (e.g. servicing the GUI and
    the gesture / handwriting / voice recognition
    routines to provide a responsive environment)

27
Video Augmented Surfaces
  • Ubiquitous computing with mobile computers
  • Using cameras and computers in the environment
    with portable notebooks to augment surfaces
  • Jun Rekimoto of Sony CSL A Spatially Continuous
    Workspace for Hybrid Computing Environments
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