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OdysseyAgile, Application-Aware Adaptation for Mobility

Kip Walker

some slides “borrowed” from Satya

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A Glimpse of the Future

Imagine you are a tourist in Paris

with a wearable computer

wireless access to remote services

unobtrusive heads-up display, microphone, earphones

speech for computer interactions

online language translation

Let’s go . . . . . .

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What Makes This Science Fiction?

Lack of hardware?

NO! We have what we need.

Lack of applications?

Nope - we have those too.

Need a system capable of coping with the problems of mobility

Odyssey to the rescue...

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Problems with MobilityMobile elements are resource-poor

relative to static elements of same era weight, power, size constraints

Mobility leads to communication uncertainty enormous variation in bandwidth & latency intermittent connectivity

Power management is a concern actions may have to be slowed or deferred communication costs energy

need to rely on resources of remote servers,

but may not be able to reach them!

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Adaptation

Make mobile clients more robust by offering adaptation rely on servers when possible function autonomously if needed monitor and adjust to current conditions

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Adaptive Applications

applications consume resources

network bandwidth, CPU cycles, battery power, disk space, $$$

resources are variable

…so…

applications adapt use of resources as resource quality changes

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Goals

Support variety of applications and data types

Concurrent applications

Quick adaptation

Simple programming model

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Who Controls Adaptation

The Operating System?

Individual applications?

Both!

… Application-Aware Adaptation

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What Knobs Do We Have?

Where work gets done

let powerful remote servers do the work

How snazzy the data is: “Fidelity”

degrade data meaningfully before giving to mobile host

has many dimensions

one is universal: consistency

others depend on data typemovies: frame rate, frame qualitygeographical databases: feature set, minimum feature size

tradeoffs are application-dependent

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Cutting to the chase…

We built a prototype

runs on several UN*X platforms

logically an OS extension

provides a small API to applications

Implementation follows directly from the high-level design

need data type aware components to offer fidelity choices

need a central piece to watch the resources (network, etc.)

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Viceroy and Wardens

System-level data differentiation through wardens specialized code components (a la device drivers) provides system-level support to manage a data type trusted entities (unlike applications)

Wardens subordinate to viceroy single, central component type-independent, system-level support responsible for all resource allocation, arbitration central point of authority and control for Odyssey

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Client Structure

Interceptor

Application

Odyssey

NetBSDOS Kernel

Warden2

Warden3

Vic

ero

y

Warden1

Odyssey callsUpcallAll system calls

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Resource Negotiation

Applications give viceroy a window of tolerance for some resource viceroy monitors resource availability if it leaves window, notifies application via upcall

Our architecture supports many resources we currently focus only on network bandwidth

Available bandwidth

Fid. 1 Fid. 2 Fid. 3 Fid. 4

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Applications

Video

server offers movie at several levels of fidelity

application plays the track that the current bandwidth can support

xanim: split into client and server

WWW

“distillation server” degrades data before shipping to client

images can be compressed

HTML can be summarized

Netscape: client-side proxy + remote distillation server

Speech Recognition

local/remote/hybrid execution

Janus: support remote recognition method, hybrid

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Evaluation (don’t blink…)

Application-aware adaptation is superior to static strategies

applications are able to attain desired “performance”

movie doesn’t drop frames

web delays are masked by compression

speech recognition always available

Centralized resource management outperforms alternatives

all applications come closer to meeting performance goals

Agility needs improvement

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Future WorkShort term

adaptation for Web objects other than images improving agility on bandwidth drops support for unified cache managment

Medium term explore integration of Odyssey in other operating systems broaden number of managed resources enlarge range of supported applications ...

Long term deploy Odyssey for real use dynamic function vs. data shipping as in speech ...

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Conclusion

Need for adaptation in mobile systems is widely recognized

Application-aware adaptation

offers most general and effective approach to adaptation

collaborative partnership between system and application

previous approaches are limiting cases of this approach

Odyssey prototype provides initial validation of concept

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Contributors to Odyssey

Primary contributors Jason Flinn Dushyanth Narayanan Brian Noble M. Satyanarayanan Eric Tilton Kip Walker

Numerous secondary contributors involved in Coda Janus NetBSD Trace Modulation etc., etc., etc.