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

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Presentation on theme: "Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones 1 Vishnu Navda (MSR India) Ashish Sharma (MSR India Intern/UCSB) Ram Ramjee."— Presentation transcript:

1 Cool-Tether: Energy Efficient On-the-fly WiFi Hot-spots using Mobile Smartphones 1 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 2 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 3 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 4 GPRS/ EDGE/ 3G Web WiFi WAN Client/ Laptop

5 Energy Consumption on WAN Interface communication 11s residual – tail sleep Power consumed by EVDO wireless radio Active state >5x Base High energy overhead for communication 1.Sporadic communication incurs multiple tails 2.Striping data over multiple phones incurs multiple tails

6 Wi-Fi Connectivity Options 6 OptionLaptopSmartphonePros & Cons 1Ad-hoc –Ad-hoc PSM mode not supported widely –ATIM + Beacon transmission overhead 2ClientAP–No support –Beacon transmission overhead 3APClient + Infrastructure PSM mode well supported + 2x less energy compared to Ad-hoc 3. Using reverse infrastructure mode is energy efficient

7 Energy-aware Design 1.Make communication bursty – Proxy in the cloud + Gatherer 2.Use optimal # of phones – Energy-aware Striper 3.Use reverse Infrastructure mode for WiFi 7

8 A Typical Web Browsing Session 8

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

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

11 Striping using Optimal # of Phones 11 To transfer S bits of data, given n phones, where each phone has B bps bandwidth, P Base base power drain, and E setup constant tail energy, the optimal number of phones to use is given by:

12 Cool-Tether Architecture 12 Smartphones: Byte-Exchanger + WiFi client GPRS/ EDGE/ 3G Internet Infrastructure: Proxy + Gatherer + Striper Client: WiFi AP + Assembler Additional Client(s): WiFi client WiFi 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 WAN

13 Impact of Proxy and Gatherer Single phone experiment Standard Web-access workload – sessions + think times 1.No Proxy (Baseline) – all web requests issued by laptop – separate connections for each request 2.Proxy – single TCP connection – No DNS requests 3.Proxy + Gatherer – gather and send web page with embedded objects 13 Proxy+Gatherer reduces energy consumption by 26% and workload completion times by 19% over baseline

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

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 15 1.Reverse Infrastructure achieves 50% saving over Ad-hoc 2.Cool-Tether achieves 38% to 72% savings compared to COMBINE 1.Reverse Infrastructure achieves 50% saving over Ad-hoc 2.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 16

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 17

18 Thanks 18


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