16-05-2012, 04:24 PM
Fundamental Challenges in Mobile Computing
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Introduction
• Mobility is inherently hazardous.
A Wall Street stockbroker is more likely to be
What is really different about mobile computing? The mugged on the streets of Manhattan and have his
computers are smaller and bits travel by wireless rather laptop stolen than to have his workstation in a
than Ethernet. How can this possibly make any difference? locked office be physically subverted. In addition to
Isn’t a mobile system merely a special case of a distributed security concerns, portable computers are more
system? Are there any new and deep issues to be vulnerable to loss or damage.
investigated, or is mobile computing just the latest fad? • Mobile connectivity is highly variable in
This paper is my attempt to answer these questions. The performance and reliability.
paper is in three parts: a characterization of the essence of Some buildings may offer reliable, high-bandwidth
mobile computing; a brief summary of results obtained by wireless connectivity while others may only offer
my research group in the context of the Coda and Odyssey low-bandwidth connectivity. Outdoors, a mobile
systems; and a guided tour of fertile research topics client may have to rely on a low-bandwidth wireless
awaiting investigation. Think of this paper as a report from network with gaps in coverage.
the front by an implementor of mobile information systems • Mobile elements rely on a finite energy source.
to more theoretically-inclined computers scientists. While battery technology will undoubtedly improve
over time, the need to be sensitive to power
Constraints of Mobility
consumption will not diminish. Concern for power
Mobile computing is characterized by four constraints: consumption must span many levels of hardware
• Mobile elements are resource-poor relative to static and software to be fully effective.
elements. These constraints are not artifacts of current technology,
For a given cost and level of technology, but are intrinsic to mobility. Together, they complicate the
considerations of weight, power, size and design of mobile information systems and require us to
ergonomics will exact a penalty in computational rethink traditional approaches to information access.
resources such as processor speed, memory size,
and disk capacity. While mobile elements will
The Need for Adaptation
improve in absolute ability, they will always be
resource-poor relative to static elements. Mobility exacerbates the tension between autonomy and
interdependence that is characteristic of all distributed
systems. The relative resource poverty of mobile elements
This research was supported by the Air Force Materiel Command as well as their lower trust and robustness argues for
(AFMC) and ARPA under contract number F196828-93-C-0193. reliance on static servers. But the need to cope with
Additional support was provided by the IBM Corp. and Intel Corp. The
views and conclusions contained here are those of the authors and should unreliable and low-performance networks, as well as the
not be interpreted as necessarily representing the official policies or need to be sensitive to power consumption argues for selfendorsements,
either express or implied, of AFMC, ARPA, IBM, Intel, reliance.
Taxonomy of Adaptation Strategies
The range of strategies for adaptation is delimited by two
extremes, as shown in Figure 1. At one extreme,
adaptation is entirely the responsibility of individual
applications. While this laissez-faire approach avoids the
need for system support, it lacks a central arbitrator to
resolve incompatible resource demands of different