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

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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)
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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

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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

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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
WiFi
WAN
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Energy Consumption on WAN Interface
communication
11s residual tail
High energy overhead for communication
sleep
Power consumed by EVDO wireless radio

• Sporadic communication incurs multiple tails
• Striping data over multiple phones incurs
  multiple tails

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Wi-Fi Connectivity Options
3. Using reverse infrastructure mode is energy
efficient
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Energy-aware Design

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

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A Typical Web Browsing Session
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Aggregation using Proxy Support
Key idea Transform many short bursts into fewer
long spurts Reduce tail overhead
Proxy Gatherer
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Energy-Aware Striper
Key idea Choose optimal number of phones to
transfer a given data chunk
Energy-Aware Striper
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Striping using Optimal of Phones
To transfer S bits of data, given n phones, where
each phone has B bps bandwidth, PBase base power
drain, and Esetup constant tail energy, the
optimal number of phones to use is given by
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Cool-Tether Architecture
Infrastructure Proxy Gatherer Striper

• 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

Client WiFi AP Assembler
WiFi
WAN
Smartphones Byte-Exchanger WiFi client
Additional Client(s) WiFi client
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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

ProxyGatherer reduces energy consumption by 26
and workload completion times by 19 over
baseline
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of Phones to use with Different Workloads
Experimental and analytical numbers match
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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

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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

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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

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Thanks

• http//research.microsoft.com/navda