Efficient%20and%20Transparent%20Dynamic%20Content%20Updates%20for%20Mobile%20Clients

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Efficient and Transparent Dynamic Content Updates
for Mobile Clients

• Trevor Armstrong, Olivier Trescases, Cristiana
  Amza, Eyal de Lara
• University of Toronto,
• Canada

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Typical Mobile Browsing Scenario
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Mobile Browsing Problems

• Current web browsing is poll based
• Inconvenient, requires users attention
• Browser caches ineffective for rapidly changing
  dynamic content
• Wastes battery and money

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Key Observation

• Two main types of content changes
• Irrelevant
• Pertinent
• More irrelevant than pertinent changes
• Pertinent vs irrelevant content depends on user

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Our Approach

• Allow user to distinguish pertinent from
  irrelevant
• Download page only when pertinent information
  changes
• Reduce wireless communication
• Reduce battery consumption

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How It Works
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Edge Proxy

• Monitors state of all web sites in profile
• Batches cache updates in a single transfer
• Prefetches all items in a new request

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Client

• Wrapper around Pocket Internet Explorer
• Select areas of interest within a web page
• Select thresholds of change for numerical values
• Client profile
• Used by the edge proxy when updating cache
• Stored as tree structure

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Client Profile Example
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Cache Updates

• Polling
• Mobile proxy explicitly requests cache updates
• Push Based
• Mobile proxy listens on a specific port for
  incoming updates
• Hybrid SMS
• Edge proxy sends a SMS message to client when
  updates are available
• Includes update batch size

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Poll Based Updates
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Push Based Updates
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Hybrid SMS Updates
WiFi or GPRS
Message Structure
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Experiment

• Keep track of four dynamic content web sites
• Weather (weather.cnn.com)
• Currency (www.xe.com)
• Stock Values (finance.yahoo.com)
• Online Auction (www.ebay.ca)
• Evaluation Criteria
• Data transfers to and from mobile device
• Energy consumption

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Real World Traces

• Three hour traces, played back for experiments
• eBay auction
• 732 visits to page
• 377 page changes 52
• 6 bid changes 0.8
• Currency value (XE.com)
• 733 visits to page
• 732 page changes 100
• 365 Euro changes 50

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Experimental Setup

• Edge Server
• Desktop PC running Redhat 9
• Dual Athlon 2600 processors
• 2 GB Ram
• 100 MBit Ethernet connection
• Mobile Device
• HP iPAQ 6325 running Windows Mobile 2003
• 168 MHz processor
• 64 MB Ram, 64 MB Rom
• Built in WiFi and GSM/GPRS

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Wireless Communication Tradeoffs

• WiFi (802.11)
• High bandwidth and low latency
• Power hungry
• Cellular data communication (GPRS)
• Lower power consumption
• Reduced bandwidth and high latency

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Proxy Configurations

• Without proxy
• Simple proxy
• Updates whenever there is a change to the page
• Intelligent proxy
• Updates when pertinent information changes
• Threshold proxy
• Updates when pertinent information changes by a
  user specified amount

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Data Received by Mobile Device
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Data Sent by Mobile Device
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Average Energy Consumption
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Hybrid SMS

• Experimentally determined the data size where
  downloading over WiFi is cheaper than GPRS
• Mobile proxy uses this threshold to make an
  informed choice about downloading updates

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Hybrid SMS Transition Point
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Hybrid SMS Energy Consumption
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Cold Visit

• Loaded a site the device hadnt seen before
• Proxy cache and browser cache totally empty
• Web site details
• 51 total objects
• 185 KB all together

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Cold Visit Energy Consumption
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Cold Visit - GPRS Current
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Related Work

• Proxy based systems (PAWP, WebExpress)
• Not user-centric
• SMS based services (Google SMS)
• Monetary cost
• Restricted to the data that vendor provides
• Proprietary push technologies (Blackberry)
• Restricted to the hardware of that manufacturer
• Restricted to the data that vendor provides

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Conclusions

• Most changes are irrelevant to the user
• Allow user to specify their areas of interest
• Proxy system updates client based on profile
• Our system shows data and battery savings over
  both GPRS and WiFi
• Seamless notifications even when disconnected

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Thank YouQuestions?
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System Architecture
Mobile Device
Edge Server
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Cold Visit - WiFi Current