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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). Context. Trends:

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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
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
existing tethering mechanisms
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
design goals of cool tether
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

energy consumption on wan interface
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
wi fi connectivity options
Wi-Fi Connectivity Options

3. Using “reverse” infrastructure mode is energy efficient

energy aware design
Energy-aware Design
  • Make communication bursty
    • Proxy in the cloud + Gatherer
  • Use optimal # of phones
    • Energy-aware Striper
  • Use reverse Infrastructure mode for WiFi
aggregation using proxy support
Aggregation using Proxy Support

Key idea

Transform many short bursts into fewer long spurts

Reduce tail overhead

Proxy +

Gatherer

energy aware striper
Energy-Aware Striper

Key idea

Choose optimal number of phones to transfer a given data chunk

Energy-Aware Striper

striping using optimal of phones
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:

cool tether architecture
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
impact of proxy and gatherer
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

of phones to use with different workloads

Use 1 phone

# of Phones to use with Different Workloads

Use 2 phones

Use 3 phones

Use 4 phones

Experimental and analytical numbers match

comparison with prior work combine
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
related work
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
summary
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
thanks
Thanks

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