CSE 535 Mobile Computing Lecture 6: Adaptive App.

1
CSE 535 Mobile ComputingLecture 6 Adaptive
App.

• Sandeep K. S. Gupta
• School of Computing and Informatics
• Arizona State University

Based on Slides by Prof. Richard, UNO
2
Adaptation
3
Adaptation

• Mobile applications must adapt to changing
  resource levels to provide an acceptable
  computing experience to users
• Can
• Adapt functionality
• Adapt data

4
Functional Adaptation

• Change the way the application operates as
  resources change
• Use cached copies of data instead of making
  remote procedure calls against a server
• Render low resolution images rather than relying
  on an (unreachable) rendering farm

5
Data Adaptation

• Change the quality or timeliness of data streams
• Higher or lower resolution video
• Change bitrate of streaming audio
• Use out-of-date temperature or stock market data
  rather than current values when disconnected

6
Adaptation

Odyssey is one point on this spectrum
none
full
level of application adaptability
application entirely responsible for
reacting (or not) to changing conditions
system entirely responsible for reacting (or not)
to changing conditions protects application
7
Application-Aware Adaptation

• In most cases, adaptation is application-specific
• e.g., if network bandwidth becomes scarce, need
  to do different things for applications dealing
  with
• Video
• Audio
• Still images
• Stock quotes
• individual applications (data type etc.)

8
Application-Aware (2)

• Applications are in better position to perform
  needed adaptations
• In client/server scenarios, may need to adapt at
  both the client and server ends
• Possible approaches
• Purely internal to application
• Layer under application
• Using special OS features and/or libraries
• Use application-specific (but general purpose?)
  proxies
• Web browsers can use last approach
• Can have any sort of adaptation as long as an
  appropriate proxy exists

9
"Agile Application-Aware "

• Paper
• "Agile Application-Aware Adaptation for Mobility"
  
• Seehttp//www.cs.uno.edu/golden/6990MC/MobilePa
  pers/satya3.ps
• Describes the Odyssey system
• Prototype that allows mobile applications to
  adapt to changing conditions
• Network bandwidth
• Battery / CPU power, etc.

10
"Fidelity"

• Mobile clients may access a number of data stores
• Databases
• WWW
• Files
• Ideally, want data accessed by mobile host to be
  identical to "reference" copy
• Might be unrealistic
• Fidelity measures degree to which copies match

11
"Fidelity" (2)

• Odyssey provides a framework for developing
  diverse fidelity guarantees
• Largely depends on type of data
• Video
• Color depth, resolution, frames per second
• Audio
• of bits per sample, encoding scheme
• Web data
• Age latest copy of page vs. a slightly older one
• Generally, must also depend on application
• Different applications may choose different
  tradeoffs

12
"Concurrency"

• Palm pilots typically execute only one
  application at a time
• Likely that users of more powerful mobile
  computers (IPAQs, laptops) will want to run
  multiple applications
• Background monitoring applications
• Means OS must manage network resources, battery
  power, cache space,
• All resources are not just for you!

13
"Agility"

• System should react quickly and accurately to
  changes in availability of resources
• Changes may result because of a physical reason
• Battery is draining
• Network access is curtailed because of
  interference
• or because of increased application demands
• Additional applications are now running

14
Odyssey Goals

• Allow application-aware adaptation
• Each application will decide how to adapt to
  changing conditions
• Can register its interest in various resource
  levels
• System informs applications when resource levels
  deviate from certain tolerances
• Support application diversity and concurrency
• Applications decide how resource level map to
  fidelity levels
• Odyssey controls resource monitoring
• Application can either adapt functionality or
  data quality
• Odyssey examples concentrate on data adaptation

15
Application Aware Adaptation

• Wardens support type-awareness
• Supporting a new type involves writing a warden
• Viceroy is responsible for centralized resource
  management

video warden
viceroy
application
battery warden

16
Application Aware Adaptation (2)

• Applications access resources through Odyssey
• All data to and from server flows through Odyssey
• Wardens communicate with data servers, handle
  caching
• Applications never contact wardens directly
• request() system call allows applications to
  express windows of tolerance
• Viceroy uses an upcall callback to notify
  application that resource level has strayed
• Application then adjust expectations, does
  another request()

17
Adaptation Example

• Video application requests enough bandwidth to
  receive high resolution,15fps in color
• Odyssey says Umm, no.
• Application drops requirements to low resolution,
  10fps in black and white
• Specifies both min and max bandwidth
• Scenario 1
• Bandwidth drops
• Odyssey informs application that bandwidth has
  fallen below specified limit
• Application makes another request (e.g., 3fps or
  still images) or decides video isnt feasible and
  informs the user

18
Adaptation Example (2)

• Scenario 2
• Bandwidth increases substantially
• Odyssey informs application that bandwidth has
  risen above upper limit
• Application makes another attempt 15fps color

19
Odyssey Architecture (from paper)
20
"Fidelity"

• Mobile clients may access a number of data stores
• Databases
• WWW
• Files
• Ideally, want data accessed by mobile host to be
  identical to "reference" copy
• Might be unrealistic
• Fidelity measures degree to which copies match

21
Sample Applications (1)

• Video Player Xanim
• For evaluation, split into client/server
• Store three formats at server high quality, low
  quality, black and white
• Not too much magic application calculates
  bandwidth requirement
• Registers requirement,asks for a change
  informat if bandwidthchanges

22
Sample Applications (2)

• Netscape
• More challenging, source code is not available
• Solution uses Netscape proxy facility
• Proxy interfaces with Odyssey and selects
  fidelity
• Web warden chooses image quality
• Multiple image formats stored on a server

Handles different image formats
23
Odyssey Evaluation

• Experiments help determine
• How agile is Odyssey in the face of changing
  network bandwidth?
• How beneficial is it for (some) applications to
  exploit the adaptation that Odyssey offers?
• Bandwidth is controlled by modifying network stack

24
"Waveforms"
Increase in bandwidth
Decrease in bandwidth
Brief, sharp increase in bandwidth Brief, sharp
decrease in bandwidth
25
Agility Measurements (1)
26
Agility Measurements (2)
27
Agility Measurements (3)
28
Agility Measurements (4)
29
Evaluation of Adaptation (1)

• How much does it help?
• Table below summarizes for video player
• Bandwidth is always sufficient for B/W frames
• Interested in lowest drop rates _at_ highest fidelity

static strategies
(Numbers in parentheses are standard deviations)
30
Evaluation of Adaptation (2)

• Table below summarizes for web browser
• Experiment repeatedly retrieves the same image
  until time is up
• Interested in best fidelity within twice
  Ethernet's load time

fooled
static strategies
(Numbers in parentheses are standard deviations)
31
More on Adaptation

• Odyssey allows applications to register interest
  in resource levels and adapt accordingly
• For multitasking operating systems, need more
• When multiple applications compete for resources
• Need prioritization of applications
• Prioritization will likely require interaction w/
  user
• Middleware might learn whats important?
• Adaptation interface should allow applications to
  know about existence of other competing
  applications

32
Final Word on Adaptation

• Although proxies can be used, Odyssey really
  aimed at systems for which source code is
  available
• Other systems geared toward applications which
  cant easily be modified
• e.g., Puppeteer targets applications which
  provide a data manipulation API
• (That is, some way to feed data to an
  application programmatically)

33
Final Picture on Adaptation