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Wireless Wakeups Revisited: Energy Management for VoIP over Wi-Fi Smartphones

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Title: Wireless Wakeups revisited : Mobisys Author: Yuvraj Agarwal Last modified by: Yuvraj Agarwal Created Date: 6/29/2006 5:47:52 PM Document presentation format – PowerPoint PPT presentation

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Title: Wireless Wakeups Revisited: Energy Management for VoIP over Wi-Fi Smartphones


1
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)

2
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)

3
Enterprise VoIP Deployments
VoIP phone
Wi-Fi Access Point
Enterprise Network
Internet
LAN
VoIP proxy
Smartphone (Wi-Fi Cellular)
Wi-Fi Interface
Cellular Interface
4
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!
5
Possible Approach Wireless Wakeups
  • Wake-On-Wireless MobiCom02
  • 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

6
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

7
Smartphone Power Consumption
  • Cellular voice radio (GSM) highly optimized for
    low idle power
  • Cingular 2125 GSM radio consumes 38 times less
    power than Wi-Fi !

8
Cell2Notify Protocol
IP Phone
Soft Phone
Enterprise Network
Complete call setup over Wi-Fi
Disable Wi-Fi
Enable Wi-Fi
Access
Point
Smart Phone
Internet
LAN
ATA
SIP Proxy
Match VoIP to GSM number
Incoming VoIP call
Call GSM number
PSTN
Register GSM number
GSM Network
Wi
-
Fi interface
GSM interface
Base Station
ATA Analog Telephony Adapter
9
Handling Calling Scenarios
  • Clients may move in and out of WiFi/Cellular
    coverage
  • 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

10
Scenario Within Cellular, out of Wi-Fi range
SIP Proxy
Smartphone
Call on GSM
Caller ID UID
Turn on Wi-Fi
Wait for timeout
Scan
Forward call on GSM
Caller ID Normal
11
Scenario In Wi-Fi, out of cellular coverage
Smart Phone
Out of Cellular coverage
SIP Proxy
Turn on Wi-Fi,Auth, Associate, Get IP address
(Use 802.11 PSM)
SIP Register
Call on Wi-Fi
Incoming Call
12
Cell2Notify Implementation
  • Design goals
  • Easy and incrementally deployable
  • No additional hardware, infrastructure
  • Cell2Notify
  • Modifications at the VoIP proxy
  • Modifications to the Smartphone clients

13
Cell2Notify Modifications at the VoIP Proxy
  • No changes to the VoIP protocol itself (SIP)
  • Add call-handling rules for each VoIP
    extension
  • Incrementally deployable
  • Configuration changes only
  • Allows a mix of participating and
    non-participating clients

Send Ring Notification to Caller
Set outbound Caller-ID
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
14
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

15
Cell2Notify Prototype Client Device
  • Cell phones relatively closed platforms
  • Emulated a Smartphone ? off-the-shelf (cellphone
    laptop)
  • Utilize Bluetooth Headset Profile to pair them
    !
  • Is our prototype realistic ?
  • Latency overhead in an integrated solution will
    be lower
  • Need to modify connection manager (Windows-CE)

16
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

17
Call logs Usage Patterns
Call Log James
James and John are real enterprise users Beth is
a hypothetical user with a very heavy usage
pattern (15min per hour)
18
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 _at_
    3.7V Li-ion battery

19
Battery Lifetime Smartphone
540
230
70
  • Substantial increase in battery lifetime
    depending on usage!
  • John 230 improvement, James 540
  • Beth improves lifetime by 70 despite very
    heavy usage

20
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 10.34 s
  • 10s of Latency ? 2 rings

21
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
22
Alternative VoIP over Cellular Data Network?
  • VoIP over cellular data network
    (1xEvDO,GPRS/EDGE)
  • Expensive requires subscription to data plan
  • Poor performance Cellular data networks not
    optimized for VoIP
  • Greater power consumption than Wi-Fi for VoIP
    traffic !

23
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

24
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.h
    tml

25
Questions ?
  • Website http//mesl.ucsd.edu/yuvraj

26
Backup Slides !
27
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

28
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 !

29
Questions ?
QUESTIONS
  • Website http//mesl.ucsd.edu/yuvraj
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