Transcript Cool-Tether - Microsoft Research

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
GPRS/
EDGE/
3G
Client/
Laptop
WiFi
Web
WAN
• Optimize wireless energy consumption on phones
– WAN and WiFi interfaces
• Support for multi-phone tethering
– Efficiently stripe data over multiple phones
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Active state
>5x Base
Power (mW)
Energy Consumption on WAN Interface
1200
1100
1000
900
800
700
600
500
400
300
200
communication
11s residual – “tail”
sleep
High energy
overhead for
communication
0 1 2 3 4 5 6 7 8 9 1011121314
Time (s)
Power consumed by EVDO wireless radio
1. Sporadic communication incurs multiple tails
2. Striping data over multiple phones incurs multiple tails
Wi-Fi Connectivity Options
Option
Laptop
Smartphone
Pros & Cons
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Ad-hoc
Ad-hoc
–
–
Ad-hoc PSM mode not supported widely
ATIM + Beacon transmission overhead
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Client
AP
–
–
No support
Beacon transmission overhead
3
AP
Client
+
+
Infrastructure PSM mode well supported
2x less energy compared to Ad-hoc
3. Using “reverse” infrastructure mode is energy efficient
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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
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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
– Web Proxy
• other protocols possible
Infrastructure:
Proxy +
Gatherer +
Striper
Internet
– Gatherer
• fetch embedded objects
– Striper
• stripe over multiple phones
• Smartphones
– Byte-Exchanger
Client:
WiFi AP +
Assembler
• persistent TCP connections
WiFi
– WiFi Client mode
• Client
WAN
GPRS/
EDGE/
3G
– WiFi AP mode
– Assembler
• combines responses from
multiple phones
Additional
Client(s):
WiFi client
Smartphones:
Byte-Exchanger +
WiFi client
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– 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
1000
800
600
400
200
0
No Proxy
Latency in Seconds
• Single phone experiment
• Standard Web-access workload
Energy in Joules
Impact of Proxy and Gatherer
Proxy
Proxy +
Gatherer
1000
800
600
400
200
0
No Proxy
Proxy+Gatherer reduces energy consumption by 26% and
workload completion times by 19% over baseline
Proxy
Proxy +
Gatherer
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Normalized Total Energy
1.4
# of Phones to use with
Different Workloads
Use 1 phone
1.2
1
Use 2 phones
0.8
Use 3 phones
0.6
5KB-Sessions
0.4
14KB-Sessions
0.2
Use 4 phones
40KB-Sessions
160KB-Sessions
0
1
2
3
4
Number of Phones used for Striping
Experimental and analytical numbers match
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100
90
80
70
60
50
40
30
20
10
0
• COMBINE approach
Ad-hocCOMBINE
InfrastructureCOMBINE
Cool-Tether
10
30
50
70
90
110
130
150
170
190
210
230
250
270
290
310
Total Energy Consumed in %
Comparison with prior work:
COMBINE
# Web Requests
1.
2.
– 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
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