Transcript Wireless Wakeups revisited : Mobisys

Wireless Wakeups Revisited:
Energy Management for VoIP
over Wi-Fi Smartphones
Yuvraj Agarwal
(University of California, San Diego)
Ranveer Chandra, Victor Bahl, Alec Wolman (Microsoft Research),
Kevin Chin (Windows CE), Rajesh Gupta (UC San Diego)
Motivation
• VoIP is increasingly popular (esp. in enterprises)
– Low cost of deployment, manageability
– Increased functionality over PSTN
• VoIP over Wi-Fi adds support for mobility
• VoIP over a Wi-Fi enabled Smartphone is compelling
– Smartphone (PDA + Cell-phone) gaining popularity
 Support multiple radio interfaces (Wi-Fi, BT, Cellular)
– Single device for all communication needs (Cellular + VoIP)
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Enterprise VoIP Deployments
Wi-Fi
Access Point
VoIP phone
Internet
PSTN
Enterprise
Network
LAN
ATA
VoIP proxy
Smartphone
(Wi-Fi + Cellular)
Wi-Fi Interface
Cellular Interface
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Problem Statement
Wi-Fi has to be ON to receive incoming calls
• Wi-Fi power consumption is high even when idle
• Reduces battery lifetime
• Cingular 2125 : GSM (6.25days), Wi-Fi (9Hrs) !
Turn Wi-Fi ON only when needed!
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Possible Approach: Wireless Wakeups
• Wake-On-Wireless [MobiCom’02]
– Multiple radio solution
 High power Wi-Fi radio in OFF state
 Wi-Fi turned on by signal on a custom low-power radio
– Barriers to deployment:
 Additional Infrastructure, additional radios
 Short range radios : Dense deployment required
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Our Approach: Cell2Notify
• Key insights : Cellular Interfaces (GSM/CDMA)
– Ubiquitous connectivity
– Usually always turned ON
– Consumes less power than Wi-Fi when “idle”
• How to signal an incoming VoIP call ?
– Send a “ring” over the cellular interface
– Encode “wake-up” call using a specific Caller-ID !
Analogy:
“Turn your Wi-Fi ON as soon as I call you from this number.
Turn Wi-Fi OFF after the call had ended”
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Smartphone Power Consumption
Power Consumption
(mW)
1200
1000
800
600
400
200
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• Cellular voice radio (GSM) highly optimized for low idle power
– Cingular 2125: GSM radio consumes 38 times less power than Wi-Fi
!
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Cell2Notify Protocol
IP Phone
Soft Phone
Network
CompleteEnterprise
call setup
over Wi-Fi
Access
Point
Internet
Smart Phone
LAN
ATA
Incoming
PSTN VoIP call
Disable
Enable Wi-Fi
Wi-Fi
SIP Proxy
Match
VoIP
to GSM number
Call
GSM
number
Register GSM number
Wi-Fi interface
GSM interface
ATA = Analog Telephony Adapter
GSM Network
Base Station
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Handling Calling Scenarios
• Clients may move in and out of WiFi/Cellular coverage
1.
2.
3.
4.
Within both Wi-Fi and cellular coverage (default)
Out of both Wi-Fi and cellular coverage (unreachable)
Out of Wi-Fi, in cellular coverage
In Wi-Fi, out of cellular coverage
• Robustness: required to handle these scenarios
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Scenario: Within Cellular, out of Wi-Fi range
SIP Proxy
Call on GSM
Caller ID = UID
Smartphone
Turn on Wi-Fi
Wait for timeout
Scan
Forward call on GSM
Caller ID = Normal
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Scenario: In Wi-Fi, out of cellular coverage
SIP Proxy
Out of Cellular coverage
Smart Phone
Turn on Wi-Fi,Auth,
Associate, Get IP address
(Use 802.11 PSM)
Incoming Call
Back in cellular coverage
Turn off Wi-Fi
Use Cell2Notify
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Cell2Notify : Implementation
• Design goals:
– Easy and incrementally deployable
– No additional hardware, infrastructure
• Cell2Notify :
– Modifications at the VoIP proxy
– Modifications to the Smartphone clients
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Cell2Notify: Modifications at the VoIP Proxy
• No changes to the VoIP protocol itself (SIP)
• Add “call-handling rules” for each VoIP extension
• Incrementally deployable
Send Ring Notification to Caller
– Configuration changes only
Set outbound Caller-ID
– Allows a mix of participating and non-participating clients
Dial the GSM number of the
Smartphone
Wait for 2 seconds
Dial SIP extension 8 times, with
a 1s interval between re-tries
Send invalid greeting to caller
Disconnect call
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Cell2Notify : Modifications on the Clients
• Only software modifications on Smartphone:
– As a user-level service (daemon) on the client
– No kernel modifications
• Functionality:
–
–
–
–
–
Distinguish between wake-up and regular cellular call
Ability to power its Wi-Fi interface ON/OFF
Scan for APs. Authenticate and Associate with a particular AP
Bring up a VoIP softphone user interface
Detect end of VoIP call
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Cell2Notify : Prototype Client Device
• Cell phones relatively closed platforms
• Emulated a Smartphone  off-the-shelf (cellphone + laptop)
• Utilize Bluetooth “Headset Profile” to pair them !
Signal over
Bluetooth
W810i
WinXP Laptop +
Wi-Fi + SIP Client
Emulated Smartphone
• Is our prototype realistic ?
• Latency overhead in an integrated solution will be lower
• Need to modify connection manager (Windows-CE)
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System Evaluation
• Goal: estimate increase in battery lifetime for a
Smartphone device
• Methodology :
– Measure power consumption of a Smartphone for various states
 Instrument Smartphone to measure accurate power
– Collect typical usage patterns
 Gather call logs for enterprise users
 Maintain call durations and call time
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Call logs : Usage Patterns
Call Log : James
60
Duration of Calls
(Minutes)
50
40
30
20
10
0
1
3
5
7
9
11
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15
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21
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Duration of Calls (Minutes)
Call Log: John
60
50
40
30
20
10
0
1
Hour of the Day
3
5
7
9
11 13 15 17 19 21 23
Hour of the Day
Call Log: Beth
James and John are real enterprise users
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Duration of Calls
(Minutes)
50
40
Beth is a hypothetical user with a very
heavy usage pattern (15min per hour)
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20
10
0
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3
5
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15
17
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Hour of the Day
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Power Consumption of a Smartphone
Cingular 2125
Scenario
Power (mW)
All Radios Off
(Flight mode)
15.688
GSM Idle
27.38
Wi-Fi (searching)
1042.44
Wi-Fi (Connected)
441.82
Wi-Fi (send/recv)
1113.811
• Used to estimate energy savings for the Smartphone
• Using real usage patterns from 3 different enterprise users
• Lifetime based on the integrated 1150mAH @ 3.7V Li-ion battery
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Lifetime (Hours of Usage)
Battery Lifetime : Smartphone
70
60
Using WiFi
Using Cell2Notify
540%
50
40
230%
30
20
70%
10
0
Beth
John
James
• Substantial increase in battery lifetime depending on usage!
• John: 230% improvement, James : 540%
• Beth improves lifetime by 70% despite very heavy usage
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Latency Tradeoff
• Wi-Fi interface switched OFF : added latency to receive a
VoIP call
Steps
Latency
(prototype)
1.
Call on cellular interface
3.6 s
2.
Enable Wi-Fi interface
1.4 s
3.
Connect to Wi-Fi AP
0.17 s
4.
Enable VoIP Client + Get IP address
4.65 s
5.
SIP Notifications (Register, Subscribe)
0.52 s
Total Latency
• 10s of Latency

10.34 s
2 rings
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Reducing Latencies
• Call on Cellular interface
– Use ATA rather than external VoIP gateway (2.5s vs 3.6s)
• Enable Wi-Fi interface
– Windows XP takes 1.4s, better in Win-CE
– Disable Zero-Conf, wrote specific utility to enable/disable card
• Connect to Access Point (Scan, Authenticate, Associate)
– Cache known/seen APs and try them first
• Obtain IP address using DHCP
– Cache DHCP lease parameters
Expected Latency in a Smartphone implementation : 7s
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Alternative: VoIP over Cellular Data Network?
• VoIP over cellular data network (1xEvDO,GPRS/EDGE)
Power Consumption (Watts)
– Expensive: requires subscription to data plan
– Poor performance: Cellular data networks not optimized for VoIP
– Greater power consumption than Wi-Fi for VoIP traffic !
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1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Verizon V620
(1xEVDO)
SE-GC83
Netgear WAG511
(GPRS/EDGE)
(Wi-Fi)
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Conclusions
• Cell2Notify
– Specific application : VoIP over Wi-Fi Smartphones
– Significantly lower bar for deployment
 Cellular : Leverage near ubiquitous coverage
 No additional hardware infrastructure needed
– Leverage the diversity of multiple radio interfaces
– Extends battery lifetime significantly : 1.7 to 6.4 times
– End-to-end latency increase : Maximum of 2 additional rings
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Cell2Notify: (August/2007 Update!)
• We now have an implementation for a Windows Mobile Smartphone
– Any Windows Mobile 6 based smartphone with WiFi can use Cell2Notify!
• Demo at Mobisys 2007
• Poster and Demo at the UCSD/School of Engineering Research Expo
 Cell2Notify won 1st Prize!
• Video of Cell2Notify in action can be seen at:
http://mesl.ucsd.edu/yuvraj/research/cell2notify.html
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Questions ?
Website : http://mesl.ucsd.edu/yuvraj
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Backup Slides !
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Discussion: Modifying the Caller-ID
• Cell2Notify: Needs a unique-ID sent as Caller-ID
– Distinguish between a regular and wake-up call
• Using a static caller-IDs can be exploited
– Attackers can also spoof caller-ID
– Solution: Caller-ID changes every time
– S/KEY system (shared keys), Caller-ID is a one way hash
• Is modifying the Caller-ID legal ?
– Done commonly by enterprise PBXs
– No law in the US that prevents it for “legitimate use”
– Commercial services employing spoofing [spooftel, spoofcard]
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Alternative to VoIP over Wi-Fi
• VoIP over cellular data network (1xEvDO,GPRS/EDGE)
– Expensive: requires subscription to data plan
– Performance : Cellular data networks not optimized for VoIP
– Greater power consumption than Wi-Fi for VoIP traffic !
2
Verizon V620 (1xEVDO)
Power (Watts)
SE-GC83 (GPRS/EDGE)
1.5
Netgear WAG511 (Wi-Fi)
1
0.5
0
Not Connected
Connected and Idle
Connected and Active
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Questions ?
QUESTIONS
Website : http://mesl.ucsd.edu/yuvraj
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