isolating physical per for smart rate selection in 802.11
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Isolating Physical PER for Smart Rate Selection in 802.11. Malik Ahmad Yar Khan and Darryl Veitch ARC Special Centre for Ultra-Broadband Information Networks (CUBIN) The University of Melbourne, Australia IEEE Infocom 2009 (acceptance rate = 19.65%). Outline. Introduction The core idea - PowerPoint PPT PresentationTRANSCRIPT
Isolating Physical PER for Isolating Physical PER for Smart Rate Selection in Smart Rate Selection in 802.11802.11
Malik Ahmad Yar Khan and Darryl VeitchMalik Ahmad Yar Khan and Darryl Veitch
ARC Special Centre for Ultra-Broadband Information NetARC Special Centre for Ultra-Broadband Information Networks (CUBIN)works (CUBIN)
The University of Melbourne, AustraliaThe University of Melbourne, Australia
IEEE Infocom 2009IEEE Infocom 2009(acceptance rate = 19.65%) (acceptance rate = 19.65%)
OutlineOutline
IntroductionIntroduction The core ideaThe core idea RCA modificationRCA modification
– Fragmentation implementationFragmentation implementation– RTS/CTS implementationRTS/CTS implementation
PerformancePerformance ConclusionConclusion
IntroductionIntroduction
Rate selection algorithms in use in 8Rate selection algorithms in use in 802.11 suffer from a fundamental pro02.11 suffer from a fundamental problemblem– Implicity or explicity make decisions baImplicity or explicity make decisions ba
ses on total Packet Error Rate (PER)ses on total Packet Error Rate (PER) False rate decision lowers the systeFalse rate decision lowers the syste
m throughputm throughput
IntroductionIntroduction
Total PER = PPER + CPERTotal PER = PPER + CPER– PPER: Physical PERPPER: Physical PER– CPER: contention PERCPER: contention PER
It is often the case CPER It is often the case CPER dominates PPERdominates PPER– Poor latency, loss and throughputPoor latency, loss and throughput
PER under a ideal PER under a ideal environmentenvironment
Goal of the paperGoal of the paper
Providing a novel way to isolate Providing a novel way to isolate the physical errorthe physical error
Providing a modular way of Providing a modular way of isolating the contention error isolating the contention error which any rate adaptation which any rate adaptation algorithm can be enhancedalgorithm can be enhanced
FragmentationFragmentation
Only consider a packet is Only consider a packet is fragmented into 2 framesfragmented into 2 frames
The fragment 2 is sent out only The fragment 2 is sent out only after an SIFS after the final ACKafter an SIFS after the final ACK– Provided there are no hidden terminalsProvided there are no hidden terminals
FragmentationFragmentation
If the first fragment is lost, for nay If the first fragment is lost, for nay reason, the second will not even reason, the second will not even be sentbe sent
Observation: the loss of a second Observation: the loss of a second fragment on the first transmission fragment on the first transmission attemptattempt– Physical errorPhysical error
RTS/CTSRTS/CTS
Once the RTS-CTS exchange is Once the RTS-CTS exchange is completed, the data packet will completed, the data packet will have the channel reserved, and have the channel reserved, and will only encounter error for will only encounter error for physical reasonsphysical reasons
Block reservation in Block reservation in 802.11e802.11e
An option in IEEE 802.11eAn option in IEEE 802.11e The second data packet of such The second data packet of such
blocks could be used to directly blocks could be used to directly measure PPERmeasure PPER
Main conceptMain concept
Not to use these methods all the Not to use these methods all the time in practicetime in practice
Only trigger their use often Only trigger their use often enough to gather good statistics enough to gather good statistics on PPERon PPER
Scatterplots of PER with nScatterplots of PER with no cross traffico cross traffic
Scatterplots of PER with CScatterplots of PER with CT and fragmentationT and fragmentation
Scatterplots of PER with CT and Scatterplots of PER with CT and fragmentation (RTS/CTS on)fragmentation (RTS/CTS on)
Rate dependence of IP Rate dependence of IP throughputthroughput
Fragmentation Fragmentation implementationimplementation Only descriptors of second fragmentOnly descriptors of second fragment
s are passed to the RCAss are passed to the RCAs A mechanism is needed to trigger thA mechanism is needed to trigger th
e fragmentation of selected packetse fragmentation of selected packets– Maintains a simple ON/OFF variableMaintains a simple ON/OFF variable
RTS/CTS RTS/CTS implementationimplementation RTS/CTS protection is switched on RTS/CTS protection is switched on
by a per-packet decisionby a per-packet decision Use Long Retry Count (LRC) to Use Long Retry Count (LRC) to
record the statistic of RTS/CST record the statistic of RTS/CST transmissiontransmission
PerformancePerformance
Two main metricsTwo main metrics– Weighted mean rate summariesWeighted mean rate summaries– IP throughputIP throughput
All experiments are run in IEEE 802.11a iAll experiments are run in IEEE 802.11a in testbedn testbed– Full rate set:{6,9,12,18,24,36,48,54}Full rate set:{6,9,12,18,24,36,48,54}– Packet size: 1500 bytesPacket size: 1500 bytes– 10 stations if no further explanation10 stations if no further explanation
The wireless testbedThe wireless testbed
St[1-13] are stations, Sniff[1-2] St[1-13] are stations, Sniff[1-2] are sniffersare sniffers
Two implementation Two implementation protocolsprotocols SampleRateSampleRate
– A MIT master thesisA MIT master thesis– Implemented on MadWifiImplemented on MadWifi
AMRRAMRR– A multi-rate algorithm also implementeA multi-rate algorithm also implemente
d on MadWifid on MadWifi
Single user with different RCAsSingle user with different RCAs
TPER for single user TPER for single user case for AMRRcase for AMRR
SampleRate with different paSampleRate with different packet sizes (1472B)cket sizes (1472B)
SampleRate with different paSampleRate with different packet sizes (716B)cket sizes (716B)
UDP upstream system UDP upstream system throughputthroughput
TCP upstream system throughputTCP upstream system throughput
ConclusionConclusion
The paper investigates two ways The paper investigates two ways to isolate Physical PERto isolate Physical PER– RTS/CTSRTS/CTS– MAC level packet fragmentationMAC level packet fragmentation
Higher channel rates were used Higher channel rates were used when PPER was in fact low, even when PPER was in fact low, even when contention is presentwhen contention is present
Thank you!!Thank you!!