1
Realizing the Full Potential of PSM using Proxying
Ning DingAbhinav PathakY. Charlie Hu
Dimitrios KoutsonikolasClay ShepardLin Zhong
2
Smartphone is Energy Constrained
CPU
Screen
3G/4G
WiFi
GPS
Camera
Battery capacity only doubles in
last 15 years
3
WiFi Energy Consumption
Send
Recv
Idle Listen1000mW
765mW650mW
Time (ms)
WiFi NIC Power(mW)
… …
Phone
AP
Data
Data
Idle
Even in idle, WNIC drains out battery
in 6-10 hrs!
4
Modes of WiFi NIC
• Constant Awake Mode (CAM)– Send, Recv, Idle Listen– High power
• Power Saving Mode (PSM)– Cannot send/recv/idle listen– Very little power
5
WiFi: Power Saving Mode
100ms 100ms 100ms
Beacon
Phone
APBeacon Beacon Beacon
Time (ms)
WiFi NIC Power(mW)
Beacon
6
WiFi: Power Saving Mode (cont’d)
Beacon
Phone
AP
Data
WNIC in PSM, cannot recv
WNIC switch to CAM
PSM Wake-up Delay
PSM does not come for free!
Server
Time (ms)
WiFi NIC Power(mW)
7
PSM
• Energy - performance trade off
• Two implementations of PSM– Static PSM– Dynamic PSM
8
Static PSM
Phone
APSYN
ServerSYNACK
SYNACK
Req
Wake-up Delay
Wake-up Delay
Wake-up Delay
Already in PSM
Time (ms)
WiFi NIC Power(mW)
Static PSM
Flow Time: 300ms
Energy:3 μAh
Data
ACK
Beacon
9
Dynamic PSM
WiFi NIC Power(mW)
Phone
APSYN
ServerSYNACK
Req
PSM Timeout Dynamic PSM
Flow Time: 90ms
Energy:10 μAh
Static PSM
Flow Time: 300ms
Energy:3 μAh
Data
ACK
Beacon
Time (ms)
10
Motivation
Performance Energy
Static PSM
Dynamic PSM
Can we make it ?
11
Understand Dynamic PSM
Phone
AP
Server
RTT
PSM Timeout
Key: PSM Timeout > RTT
Phone PSM TimeoutNokia N900 200ms
HTC Nexus One 200ms
iPhone 4 95ms
12
Percy: Design
AP AP Split-TCP Proxy
PSM Timeout200ms/95ms
PSM Timeout30ms
1.
2.
13
Data
ACK
Beacon
Percy: Short Flows
Phone
AP+Proxy SYN
Server
Req
DataSYN
SYNACK Req
Percy
Flow Time: 110ms
Energy:4 μAh
Static PSM
Flow Time: 300ms
Energy:3 μAh
Dynamic PSM
Flow Time: 90ms
Energy:10 μAh
Time (ms)
WiFi NIC Power(mW)
Percy: Long Flows
14
SYNReq
SYN
SYNACK
Req
Periodical Flush
Time (ms)
WiFi NIC Power(mW)
Data
ACK
Beacon
15
Evaluation
• Trace-driven experiment– 10-phone 1-week trace– 38,069 HTTP flows
• PSM configurations– Percy– Static PSM– Dynamic PSM:
NokiaN900 iPhone 4
HTC Nexus One
16
Result – Energy Consumption
Total energy consumption for different PSM schemes
67%
44%
17
Result – Network Performance
CDF of flow time difference compared to Android PSM configuration
Time (ms)
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