1. Realizing the Full Potential of PSM using Proxying
Ning Ding
Abhinav Pathak
Y. Charlie Hu
Clay Shepard
Lin Zhong
Dimitrios Koutsonikolas

2. Smartphone is Energy Constrained
Battery capacity only doubles in last 15 years
3G/4G
GPS
CPU
Screen
WiFi
Camera

3. WiFi Energy Consumption
Data AP … …
Phone
Data
Idle
Even in idle, WNIC drains out battery in 6-10 hrs!
Send
WiFi NIC Power
(mW)
Recv
1000mW
Idle Listen
765mW
650mW
Time (ms)

4. Modes of WiFi NIC Constant Awake Mode (CAM) Power Saving Mode (PSM)
Send, Recv, Idle Listen
High power
Power Saving Mode (PSM)
Cannot send/recv/idle listen
Very little power

5. WiFi: Power Saving Mode
Beacon
Beacon
Beacon
Beacon AP
100ms
100ms
100ms
Beacon
Phone
WiFi NIC Power
(mW)
Time (ms)

6. WiFi: Power Saving Mode (cont’d)
Server
Data
PSM Wake-up Delay
PSM does not come for free!
Beacon AP
Phone
WNIC in PSM, cannot recv
WNIC switch to CAM
WiFi NIC Power
(mW)
Time (ms)

7. PSM Energy - performance trade off Two implementations of PSM
Static PSM
Dynamic PSM

8. Static PSM Server AP Phone Static PSM WiFi NIC Power Flow Time: 300ms
Data
SYNACK
Wake-up Delay
Wake-up Delay
Wake-up Delay
ACK
SYNACK AP
Beacon
SYN
Req
Phone
Static PSM
Flow Time: 300ms
Energy:
3 μAh
WiFi NIC Power
(mW)
Already in PSM
Time (ms)

9. Dynamic PSM Server AP Phone Static PSM Flow Time: 300ms Energy: 3 μAh
Data
SYN
ACK
ACK AP
Beacon
SYN
Req
Phone
PSM Timeout
Static PSM
Flow Time: 300ms
Energy:
3 μAh
Dynamic PSM
Flow Time: 90ms
Energy:
10 μAh
WiFi NIC Power
(mW)
Time (ms)

10. Motivation
Performance
Energy
Static PSM
Dynamic PSM
Can we make it ?

11. Understand Dynamic PSM
Server AP
Phone
RTT
Phone
PSM Timeout
Nokia N900
200ms
HTC Nexus One
iPhone 4
95ms
PSM Timeout
Key: PSM Timeout > RTT

12. Percy: Design 1. 2. AP Split-TCP Proxy AP PSM Timeout 200ms/95ms

13. Percy: Short Flows Server AP+Proxy Phone Static PSM Flow Time: 300ms
Data
Server
SYN
Data
SYN
ACK
Req
ACK
Req
AP+Proxy
Beacon
SYN
Phone
Static PSM
Flow Time: 300ms
Energy:
3 μAh
Dynamic PSM
Flow Time: 90ms
Energy:
10 μAh
Percy
Flow Time: 110ms
Energy:
4 μAh
WiFi NIC Power
(mW)
Time (ms)

14. Percy: Long Flows Periodical Flush WiFi NIC Power (mW) Time (ms) SYN
Data
Req
SYN
ACK
ACK
SYN
Req
Beacon
Periodical
Flush
WiFi NIC Power
(mW)
Time (ms)

15. Evaluation Trace-driven experiment PSM configurations
10-phone 1-week trace
38,069 HTTP flows
PSM configurations
Percy
Static PSM
Dynamic PSM:
Nokia
N900
HTC Nexus One
iPhone 4

16. Result – Energy Consumption
67%
44%
Total energy consumption for different PSM schemes

17. Result – Network Performance
Time (ms)
CDF of flow time difference compared to Android PSM configuration

18. Conclusion Existing PSMs have inherent problems A simple system: Percy
improve the energy savings
maintain good performance
Percy saves 44-67% energy while incur minimal flow time elongation