16-09-2016, 03:20 PM
1454961031-200303IEEEPerCom03MobileComputing.pdf (Size: 225.98 KB / Downloads: 7)
Abstract
Storage capacity and communication bandwidth are
two factors that significantly impact the design and
implementation of mobile systems. Furthermore, storage
density is increasing at an exponential rate faster than the
associated communication bandwidth. High-density
storage in very small form factors will enable new classes
of applications that would not be possible in systems
which rely heavily on communication. These applications,
which involve continuous capture, pre-loaded content,
and proactive data loading, will help overcome some of
the barriers presented to mobile systems. Researchers
would be prudent to recognize these trends and better
understand how technology growth will impact their
research agenda.
Factors for mobile computing
In this paper we examine two dimensions of
technology that profoundly affect the design of mobile
computing platforms: communication bandwidth and
storage density. Memory and communication can to some
extent play off against each other. If you are mobile and
have a high bandwidth connection to the Internet, then it
is less important how much data you are carrying with
you; the communication link can be used to acquire the
data on demand. On the other hand if the communication
bandwidth is small or frequently unavailable, then
carrying as much data as possible in the mobile device is
desirable, ensuring access even during communication
blackouts.
At any given time the state-of-the-art in the capability
of storage and communication bandwidth, and the relative
costs of each solution, will have considerable impact on
the design choices made for commercial mobile systems.
Already at this time a CompactFlash™ card with 1GB of
flash memory (see Figure 1) can be purchased
commercially and IBM has sold a miniature magnetic
disk in a similar package since year 2000. It is therefore instructive to look carefully at these technology trends
and try to understand their implication.
A spectrum of options
Historically, storage has been a major factor effecting
the capabilities and design of computer systems. Early
systems relied completely on local storage, while other
models used communication to access remote data
sources. It was not until the convergence of storage and
communication that the modern day Internet took off to
create computing as we know it today. Similar patterns
can be seen with consumer video consumption, through
technologies such as VCRs, broadcast TV, and Digital
Video Recorders (DVRs). Mobile systems are starting to
repeat some of the same trends as “stationary” computing;
however, mobility brings unique opportunities and
challenges which will require new solutions and open up
new application domains.
Early PC systems were isolated islands of storage:
capable of performing their self-contained tasks, but
required significant amounts of manual effort to move
things around. This model was adequate for spreadsheets
and many personal productivity applications, but did not
encompass the power of “remote” content. This scenario
is equivalent to a VCR and TV without an antenna or
cable – it would allow you to watch movies but not tap
into the dynamic nature of “live” media. Furthermore,
until recently, it has been impractical to carry all your
data with you on a mobile device; however, in the last
couple of years storage trends have enabled laptops and
PDAs to provide for most of our immediate storage
needs. In the future, increasing storage densities will
enable applications such as portable media collections, to
enable me to carry all of “my” movies, wherever I go.
The converse of local-storage systems are
communication-centric models that allow access to
remote information with a minimum of local resources.
Broadcast TV and cell-phones are two popular examples
of this technique – lots of available content with little or
no local storage. For computers, there have been many
systems that have explored computation platforms
without relying on local storage capability [4, 6, 12, 13].
The problem with these communication-centric models is
that they are dependent upon the remote source of
information, which makes it very difficult to optimize,
personalize, or sometimes just operate the system.
Without a VCR, for example, you are required to watch a
particular show when it’s on, not when you want to watch
it. The constraints of mobile devices, such as limited
battery life and varying network availability, exasperate
these problems and make local storage a very effective
means to improve device operation.
Hybrid models, which offer both the capabilities of
local storage and communication, access the best of both
worlds and provide a very compelling user experience.
Digital Video Recorders, such as TiVo, allow users to
proactively download media content to local storage and
view it whenever they want, dramatically changing their
TV viewing experience. For desktop PC systems,
combining local storage and the Internet allows us to
efficiently manage collections of personal photographs
and easily send them to friends & family. Furthermore,
local storage allows for “unseen” optimizations such as
local image caching which dramatically improves the
web-browsing experience. Mobile devices are starting to
see similar benefits from the confluence of storage and
communication technologies: laptops with wireless
connectivity, phones as PDAs, and emerging devices such
as the Apple iPod[3], and Intel’s Portable Media Player
(PMP) (see Figure 3), which will enable access to
dynamic media whenever and wherever we want it.
The Personal Server [14] (see Figure 4) is an
emerging research project that allows access to personal
content, stored on a mobile device, through any
convenient interface: accessing my address book through
your laptop, for example. By breaking down the barriers
between devices, the project aims to increase the utility of
mobile computing and bring personalization to the
environment around us.
Another focus of this project is to take advantage of
localized communication technologies, such as Bluetooth
[1], to avoid service provider costs, and some of the
bandwidth and power limitations. In this example, a
different kind of ubiquitous communication is being used,
one based on local spheres of connectivity in combination
with local storage to achieve the desired mobile result.
Internet Suspend Resume [5], on the other hand,
enables anytime/anywhere access to a familiar computing
environment by migrating a complete execution environment through the network to a local virtual
machine. By relying on local storage capacity, this
technique enables new forms of mobile computing that do
not rely on the limited capabilities of a mobile device.
Both these projects combine storage and
communication to provide unique capabilities tailored to
mobile contexts. As storage capacity and density continue
to increase, these models will allow ubiquitous access to
content without compromising accessibility, content, or
convenience.