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Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones

Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones. Vishnu Navda (MSR India) Ashish Sharma (MSR India Intern/UCSB) Ram Ramjee (MSR India) Venkat Padmanabhan (MSR India) Elizabeth Belding (UCSB). Context. Trends:

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Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones

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  1. Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones Vishnu Navda (MSR India) Ashish Sharma (MSR India Intern/UCSB) Ram Ramjee (MSR India) Venkat Padmanabhan (MSR India) Elizabeth Belding (UCSB)

  2. Context • Trends: • Near-ubiquitous cellular wireless broadband (2.5/3G) • Popularity of Internet enabled smartphones • Commoditization of WiFi technology • WiFi equipped devices • Can smartphones be used as Internet gateways to devices, at home, at work and on the move? • Avoid need for separate provisioning • Opportunity to tether multiple phones

  3. Existing Tethering Mechanisms • USB cable • Multi-phone tethering not supported • Wires are inconvenient • Bluetooth • Low data rates  high energy/bit cost • WiFi Ad-hoc mode • No power-save support • Do not support multi-phone tethering • Agnostic of energy consumption

  4. Design Goals of Cool-Tether • Optimize wireless energy consumption on phones • WAN and WiFi interfaces • Support for multi-phone tethering • Efficiently stripe data over multiple phones GPRS/ EDGE/ 3G Web Client/ Laptop WAN WiFi

  5. Energy Consumption on WAN Interface communication 11s residual – “tail” High energy overhead for communication Active state >5x Base sleep Power consumed by EVDO wireless radio • Sporadic communication incurs multiple tails • Striping data over multiple phones incurs multiple tails

  6. Wi-Fi Connectivity Options 3. Using “reverse” infrastructure mode is energy efficient

  7. Energy-aware Design • Make communication bursty • Proxy in the cloud + Gatherer • Use optimal # of phones • Energy-aware Striper • Use reverse Infrastructure mode for WiFi

  8. A Typical Web Browsing Session

  9. Aggregation using Proxy Support Key idea Transform many short bursts into fewer long spurts Reduce tail overhead Proxy + Gatherer

  10. Energy-Aware Striper Key idea Choose optimal number of phones to transfer a given data chunk Energy-Aware Striper

  11. Striping using Optimal # of Phones To transfer S bits of data, given nphones, where each phone has B bps bandwidth, PBase base power drain, and Esetupconstant tail energy, the optimal number of phones to use is given by:

  12. Cool-Tether Architecture Infrastructure: Proxy + Gatherer + Striper Internet Client: WiFi AP + Assembler GPRS/ EDGE/ 3G WiFi WAN Smartphones: Byte-Exchanger + WiFi client Additional Client(s): WiFi client • Infrastructure • Web Proxy • other protocols possible • Gatherer • fetch embedded objects • Striper • stripe over multiple phones • Smartphones • Byte-Exchanger • persistent TCP connections • WiFi Client mode • Client • WiFi AP mode • Assembler • combines responses from multiple phones

  13. Impact of Proxy and Gatherer • Single phone experiment • Standard Web-access workload • sessions + think times • No Proxy (Baseline) • all web requests issued by laptop • separate connections for each request • Proxy • single TCP connection • No DNS requests • Proxy + Gatherer • gather and send web page with embedded objects Proxy+Gatherer reduces energy consumption by 26% and workload completion times by 19% over baseline

  14. Use 1 phone # of Phones to use with Different Workloads Use 2 phones Use 3 phones Use 4 phones Experimental and analytical numbers match

  15. Comparison with prior work: COMBINE • COMBINE approach • client side striping • energy agnostic • (1)Ad-hoc CAM or (2)Reverse Infrastructure PSM • (3) Cool-Tether • Proxy + Gatherer + Striper • Reverse Infrastructure PSM • Reverse Infrastructure achieves 50% saving over Ad-hoc • Cool-Tether achieves 38% to 72% savings compared to COMBINE

  16. Related Work • Mobile Wireless Access • GPRSWeb(Cambridge): proxy + caching • Multi-path striping • COMBINE(MSR): client-side striping + energy agnostic • PRISM(UMich): focuses on TCP problems • MAR(Cambridge, MSR Cambridge), PluriBus(MSR Redmond): improves download performance + energy agnostic

  17. Summary • Cool-Tether provides energy-efficient, affordable connectivity using smartphones • leverages unique characteristics of WAN link • employs cloud proxy to optimize energy drain • uses “reverse” infrastructure mode for WiFi

  18. Thanks http://research.microsoft.com/~navda

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