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8/3/2019 (12)PSM Throttling
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ICNP07, Beijing, China 1
PSM-throttling: Minimizing Energy
Consumption for Bulk DataCommunications in WLANs
Xiaodong ZhangOhio State University
in Collaborations withEnhua Tan, Ohio StateLei Guo, Yahoo!
Songqing Chen, George Mason University
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What is Going on in Internet?
Wireless accesses to Internet are very pervasive:
Everywhere: campus, offices, home, public utilities
Most are supported by Wireless LANs Media content is heavily delivered in Internet:
Streaming: Real or Window media (> 80% in TCP)
HTTP-based streaming: YouTube, Google Video (TCP)
TCP downloading: web sites (traditional or web 2.0)
Mobile devices are increasingly diverse and portable: Laptop, PDA, iPhone, WiFi phone
Challenge: mobile devices can easily exhaust theirbatteries by viewing streaming media.
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Limited Power in Mobile Devices
WLAN
InternetAccess Point(AP)
WiFi
PhoneLaptop
PDA
YouTubeServers
Windows/RealMedia Server
Wireless Network
Interfaceis a major powerconsuming source!
Web Server
Question: Can we minimize WNI (WirelessNetwork Interface) power consumption whilesatisfying the QoS requirement?
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802.11 Power Saving Mode (PSM)and Its Variant
802.11 Power Saving Mode (PSM):
Wakeup every 100ms via PS poll Limits:
Buffered packets lead to delayed TCP acknowledgements
Increase round trip time estimation at the sender side May degrade the TCP throughput
PSM adaptive (PSM-A): Widely used in commercial products
Only sleep when no packet receives for a while (e.g. 75ms)
Offer less power saving, but retain TCP performance
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Ideal Power Saving Condition:
Sleep Well and Work Energetically If the media traffic can form a predictable pattern:
periodic bursts Client WNI can sleep/work periodically
Transmitting: 1.346W, receiving: 0.9W, idle: 0.741W
Sleep: 0.048W
Receiving Packets
Time
Sleeping
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Forming Ideal Condition by Proxy
Buffer and shape media traffic into periodical bursts
A proxy between mobile devices and media servers Devices can predict packet arrival time, safely sleeping
minimizing power consumption without performance loss
Limits: modified client
Proxy needs to handle diverse communication protocols
Needs a dedicated and expensive infrastructure
Reference: Chandra & Vahdat, USENIX02
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Problem Statement
Can we minimize mobile devices power
consumption while satisfying the QoSrequirement, without using a dedicated proxy?
Internet
Server
WirelessDevice
Proxy
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Outline
Problem Statement
Motivation and Overview Design
Internet Experiments on Bandwidth Throttling
PSM-throttling Design Evaluation
Summary
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Conventional TCP Throughput Control
Internet
Server
Client
Full-Speed Transmission
TCP
CongestionControl
TCPCongestion
Control
Works well for lowvolume ofsimultaneousrequests
Large volume ofsimultaneousrequests makeservers be thebottleneck
TCP congestioncontrol cannot welladdress serverbottleneck problem
B d id h Th li S L
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Bandwidth Throttling: Serve LargeVolume of Requests Simultaneously
Internet
Client 1
Media
Server
Client 2
Bandwidth Throttling:
Server sends packets at alimited constant rate (lowerthan end-to-end bandwidth)
More Simultaneousrequests will be served
Underutilizedbandwidth
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Bandwidth Throttled TCP Transmission
Server
Client WNI
Win =256 K
Receiving
Window size defaults to 256K
ACK every two data packets
Transfer rate throttled by the server in a constant rate
WNI is busy receiving, no time to sleep
PSM th ttli A Cli t hi t d M h i t C t
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PSM-throttling: A Client-hinted Mechanism to CreateBursts for Power Saving
20 K burst 20 K burst 20 K burstServer
Client WNI
Win =20 K
Win = 0
recv sleep
Flow burst period
Win =20 K
Win = 0
recv sleep
Flow burst period
Win =20 K
Burst tput
E2Ebandwidth
Average throughput =Normal
Streaming/Transfer Rate
No proxy needed
Application independent and client-centric: onlyadd a new function in client WNI driver
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Related Technical Issues
How can a server recognize client hints?
Utilizing TCP flow control mechanism: placing hints inreceive window fieldin the TCP header
No change to servers
An ACK packet during sleep consumes trivial power
For a given flow burst period (T), E2E bandwidth, and
average throughput (r), (win size = T r) burstand sleeptimes are determined
to sufficiently sleep, T should be larger than 2
RTT
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Bandwidth Throttling Detection in
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Bandwidth Throttling Detection inTCP-based Media Transmissions
Major media servers, such as Windows/Real Media servers,and lighttpd server (used by YouTube), have build-inbandwidth throttling
We confirm this by detecting server-side throttling:
Choke the transmission for 200 ms at client side: Win = 0
Unchoke: Win = Original
If resulting traffic bursts and the TCP throughput is remainedthe same server is using bandwidth throttling
We analyze the burst patterns and throughputs of Internet
traffics to verify our detection methods
Real Media Server: A Sequence
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Real Media Server: A Sequencewithout Choke/Unchoke
Packets are continuouslyDelivered: Tput = 350Kbps
Real Media Server: the Sequence
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Real Media Server: the Sequencewith Periodical Choking
Bursty and keeps the TCPThroughput: Tput = 350Kbps
Windows Media Server: a Sequence
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Windows Media Server: a Sequencewithout Choke/Unchoke
Windows Media Server: the
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Windows Media Server: theSequence with Periodical Choking
Bursty and keeps the TCPthroughput
YouTube Server: a Sequence without
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YouTube Server: a Sequence withoutchoke/unchoke
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Linux File Server: a Sequence
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Linux File Server: a Sequencewithout choke/unchoke
Linux File Server: the Sequence with
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Linux File Server: the Sequence withPeriodical Choking
TCP throughput reduced! No throttling at theserver side
PSM-throttling Design:
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PSM throttling Design:Bandwidth Throttling Detection
Measure the stable flow rate rfor a specificduration T
0
Creating bursts by choking the connection forhalf of the time
Measure the flow burst rate r
If r2r, server is engaging bandwidth
throttling, which can be used for power savingin PSM-throttling
PSM throttling Design
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PSM-throttling Design:
Further Increase Traffic Burst
sleepsleep sleep
AP
client
packertarrival
sleep sleep
flow burst period
active active active
recvpoll
If the burst rate is not high enough (not fully utilizing thewireless channel):
Client waits for about 20 ms so that there are enough packets
buffered at the AP PS Poll to receive the buffered packets More bursty!
P t t I l t ti
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Prototype Implementation
Add a new function to client WNI driver:
D-Link DWL-G520 wireless card (Atheros chipset) Madwifi 0.9.2 driver under Linux 2.6.18
Comparing with 4 other schemes CAM: Continually Aware Mode (no power saving)
CC: Client-Centric (IWQoS04) PSM: Power Saving Mode (IEEE standard)
PSM-A: PSM Adaptive (focus on comparing with)
P f E l ti
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Performance Evaluation
Lab and Internet Experiments:
P f E l ti R lt
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Performance Evaluation Results
-50%
-75%
Windows and Real media streaming
Performance Evaluation Results
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(cont.)
-75%
-58%
YouTube pseudo streaming; HTTP downloading
Summary
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Summary
Internet bandwidth is no longer critical bottleneck, but serversdue to increasingly high volume of simultaneous requests
Conventional traffic smoothing methods are no longer useful
Bandwidth throttling addresses this problem We take this unique opportunity to design and implement PSM-
throttling to create receive/sleep periods for power saving on WNI
PSM-throttling has the merits of: No additional infrastructure support
Application independent and client-centric
Save up to 75% of the power and keep the TCP throughput Applicable for cellular networks and WiMax networks
Hints from applications can further improve PSM-throttling
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Thank you!
Enhua Tan: [email protected]://www.cse.ohio-state.edu/hpcs/
PSM-throttling: Adaptation to Server
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g pTransmission Rate
Dynamically adjust the
receive window size If the throughput is not
decreasing, increase
the recv wnd size
If sleep time falls below
a RTT, decrease therecv wnd size
clientserver
RTT
recv
sleep
flow burst
period
win = 13.5 KRTT
win = 15 K
13.5 K
15 K
sleep time
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g pto Server Transmission Fluctuations
As title