Ch 1. Mobile Adaptive Computing

Mobile computing?– Distributed system– Wireless communications– Mobility of communications devices

Difference between mobile computing and mobilecommunications?

– Ex. “Italian restaurant” through search engine.– Ex. Video streaming over the Internet– Limitations of mobile computing devices: energy, screen, …– Security or privacy– Middleware layer

What is Mobile Computing

2

Mobile computing?– Distributed system– Wireless communications– Mobility of communications devices

Difference between mobile computing and mobilecommunications?

– Ex. “Italian restaurant” through search engine.– Ex. Video streaming over the Internet– Limitations of mobile computing devices: energy, screen, …– Security or privacy– Middleware layer

The vision of mobile computing– Roam seamlessly with your computing devices while continuing

to perform computing and communication tasks uninterrupted.

Transparency– The ability of a system to hide some characteristics of its

underlying implementation from users– Access transparency– Location transparency: name transparency, user mobility– Failure transparency– Mobile computing: mobility transparency

Adaptability – The key to MobileComputing

3

The vision of mobile computing– Roam seamlessly with your computing devices while continuing

to perform computing and communication tasks uninterrupted.

Transparency– The ability of a system to hide some characteristics of its

underlying implementation from users– Access transparency– Location transparency: name transparency, user mobility– Failure transparency– Mobile computing: mobility transparency

Constraints of mobile computing environments– Mobile computers can be expected to be more resource-poor

than their static counterparts: e.g., battery– Mobile computers are less secure and reliable.– Mobile connectivity can be highly variable in terms of its

performance (bandwidth and latency) and reliability. Fig 1.1

4

Constraints of mobile computing environments– Mobile computers can be expected to be more resource-poor

than their static counterparts: e.g., battery– Mobile computers are less secure and reliable.– Mobile connectivity can be highly variable in terms of its

performance (bandwidth and latency) and reliability. Fig 1.1

Application-aware adaptation– Application-transparent (the system is fully responsible for

adaptation)– Laissez-faire (the system provides no support at all)– E.g., bandwidth, battery– Fig 1.2

5

Application-aware adaptation– Application-transparent (the system is fully responsible for

adaptation)– Laissez-faire (the system provides no support at all)– E.g., bandwidth, battery– Fig 1.2

What can be adapted?– The functionality and the data

How to adapt?– Client-server (CS) model

Adapting functionality– CS model– A server with soft or hard state about the clients– Coda File servers (Saty 1996a)

A few trusted servers act as the permanent safe haven of the data.A large number of un-trusted clients can efficiently and securelyaccess the data.Good performance is achieved by using techniques such as cachingand prefetching.Security of data is ensured by employing end-to-end authenticationand encrypted transmissions.

Mechanisms for Adaptation

6

What can be adapted?– The functionality and the data

How to adapt?– Client-server (CS) model

Adapting functionality– CS model– A server with soft or hard state about the clients– Coda File servers (Saty 1996a)

A few trusted servers act as the permanent safe haven of the data.A large number of un-trusted clients can efficiently and securelyaccess the data.Good performance is achieved by using techniques such as cachingand prefetching.Security of data is ensured by employing end-to-end authenticationand encrypted transmissions.

– Impact of mobility on the CS model: a resource-poor mobileclient = thin clients

Adapting data– Fidelity: the degree to which a copy of data presented for use at

the client matches the reference copy at the server.Video data – frame rate and image qualitySpatial data – minimum feature sizeTelemetry data – sampling rate and timeliness

– QoS requirementsInformation qualityPerformance

– Agility: the speed and accuracy with which an adaptiveapplication detects and responds to changes in its computingenvironments, e.g., change in resource availability.

7

– Impact of mobility on the CS model: a resource-poor mobileclient = thin clients

Adapting data– Fidelity: the degree to which a copy of data presented for use at

the client matches the reference copy at the server.Video data – frame rate and image qualitySpatial data – minimum feature sizeTelemetry data – sampling rate and timeliness

– QoS requirementsInformation qualityPerformance

– Agility: the speed and accuracy with which an adaptiveapplication detects and responds to changes in its computingenvironments, e.g., change in resource availability.

Software sensors– e.g., TCP’s congestion control

Coda (continued data availability) distributed file system– Coda client (called Venus) maintains a local cache.– Hoarding: the client prefetches files from the server to store

locally.– Emulating: read and write access to local files– Write-disconnected: whether to fetch files from the server or to

allow local access– Reintegration: the log of operation is used.

How to develop or incorporateadaptations in applications

8

Software sensors– e.g., TCP’s congestion control

Coda (continued data availability) distributed file system– Coda client (called Venus) maintains a local cache.– Hoarding: the client prefetches files from the server to store

locally.– Emulating: read and write access to local files– Write-disconnected: whether to fetch files from the server or to

allow local access– Reintegration: the log of operation is used.

– Fig 1.3

9

What can adaptations be performed?– Proxy: an intermediate software entity– Adapting to the hw/sw capabilities of the mobile device– e.g., security firewalls, NAT, transcoding proxies

10

– Fig. 1.4

11

WebExpress– Fig. 1.6

12

– Caching– Differencing: for common graphic interface processing– Protocol reduction: reduction of TCP/IP connection overhead

using virtual sockets.– Reduction of HTTP headers: e.g., MIME

13

Odyssey [Noble 1997]– Between application and the operating system in handing the

presence of wireless links– Network bandwidth drops -> Odyssey informs the video, audio,

and other applications of the change -> proper adaptations innetwork usage

– When network conditions change, the os notifies the applicationof what has happened.

Support for building adaptive mobileapplications

14

Odyssey [Noble 1997]– Between application and the operating system in handing the

presence of wireless links– Network bandwidth drops -> Odyssey informs the video, audio,

and other applications of the change -> proper adaptations innetwork usage

– When network conditions change, the os notifies the applicationof what has happened.

Rover [Joseph 1995]– Object-based sw toolkit for developing both mobility-aware and

mobility-transparent CS distributed applications– Relocatable dynamic objects(RDO): loadable dynamically from

the server to the client– Queued Remote Procedure Call (QRPC): nonblocking rpc

supporting split-phase operations– Optimize use of expensive links– Make use of asymmetric links– Stage messages near the destination

15

Rover [Joseph 1995]– Object-based sw toolkit for developing both mobility-aware and

mobility-transparent CS distributed applications– Relocatable dynamic objects(RDO): loadable dynamically from

the server to the client– Queued Remote Procedure Call (QRPC): nonblocking rpc

supporting split-phase operations– Optimize use of expensive links– Make use of asymmetric links– Stage messages near the destination