23-04-2011, 09:31 AM
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The Challenges of Mobile Computing
The Future of Computing
It’s 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…
It’s 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…
The Dynabook
The Vision is not a Reality… Yet
In a recent interview, Alan Kay remarked that even with the advent of PDA’s, small notebooks, etc., the Dynabook concept is not a reality.
Why?
Today’s 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
Mobile Computing != Notebooks
PDAs
Cellular phones
Tablet PCs
Wearable computers
Tablet PC Demo Video
Acer TravelMate C100 Tablet PC
A New Paradigm
``… tomorrow’s 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
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?
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
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)
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
Security Risks
Greater security risks than wired communication
Solutions
Hardware-based: CLIPPER chip
Software-based: Kerberos authentication services
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
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
Mobility
The dynamic nature of mobile computing increases the volatility of information to support the platform
Caching vs. recomputation
Address Migration
Current IP addressing scheme imposes difficulties for dynamically changing addresses
Four different methods
Selective broadcast
Central services
Home bases
Forwarding Pointers