Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT
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Transcript of Call Admission Control in IEEE 802.11 Wireless Networks using QP-CAT
Call Admission Control in Call Admission Control in IEEE 802.11 Wireless IEEE 802.11 Wireless Networks using QP-CATNetworks using QP-CAT
Sangho ShinHenning Schulzrinne
Department of Computer ScienceColumbia University
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Call Admission Control (CAC) Call Admission Control (CAC) in IEEE 802.11 Wireless in IEEE 802.11 Wireless NetworksNetworks
QoS
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
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Call Admission Control (CAC) Call Admission Control (CAC) in IEEE 802.11 Wireless in IEEE 802.11 Wireless NetworksNetworks
WIFI
WIFI
WIFI WIFI
WIFI
WIFI
QoS
CAC
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Framework of CACFramework of CAC
IEEE 802.11e Admission Control
ADDTS RequestCategoryTSpec
ADDTS Response
CategoryTSpecStatus
?Min/Max MSDUMin/Max Service IntervalMin/Avg/Max Data Rate
WIFI
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OutlineOutline CAC in 802.11 Wireless Networks Related work QP-CAT Simulation results Experimental results Extension of QP-CAT Conclusion
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CAC in 802.11 Wireless CAC in 802.11 Wireless NetworksNetworks
Problems Difficult to estimate QoS of VoIP traffic from
the channel status Difficult to predict the impact of new VoIP
calls Keys
Accurate metric for QoS Need to represent delay not throughput
Prediction algorithm Need to accurately predict the impact of new calls
on QoS of existing calls
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Related workRelated work Model based
Build a theoretical model Compute available bandwidth or delay
Monitoring based Monitor the current transmissions Compute a metric (channel usage ratio etc.)
Probing based Metric: delay and packet loss Used for wired networks Very accurate and simple Waste a certain amount of bandwidth
Virtual Probing based QP-CAT
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QoS Metric in QP-CATQoS Metric in QP-CAT Metric: Queue size of the AP
Strong correlation b/w the queue size of the AP and delay
D=(Q+1)DT
D=downlink delayDT=TX time of a VoIP frame
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QoS Metric in QP-CATQoS Metric in QP-CATEstimation error
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Emulate newVoIP traffic
Packets from a virtual new flow
QP-CAT Algorithm QP-CAT Algorithm (1/5)(1/5)
Basic flow of QP-CAT
Compute Additional Transmission
channel
Actual packets
Additional transmission
Decrease the queue size
Predict the future queue size
+
current packets
additional packets
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QP-CAT Algorithm QP-CAT Algorithm (2/5)(2/5)
Emulation of VoIP flows Two counters: DnCounter, UpCounter Follow the same behavior of new VoIP flows Increase the counters every packetization
interval of the flows
Decrement the counters alternatively
20ms time
DnCounter++UpCounter++
DnCounter++UpCounter++
DnCounter++UpCounter++
20ms
Example : 20ms packetization interval
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QP-CAT Algorithm QP-CAT Algorithm (3/5)(3/5)
Computation of Additional Transmission
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Actual frames from existing VoIP flows
channel
Clock starts Clock stopsTc
Tt
Additionaly transmittable frames
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DIFSbackoff
Tv
SIFSACK frame
VoIP packet
TbTACK
Tt
t
cp T
Tn
Handling Tr
Virtual Collision
Tt Tt-Tr
Tc1
DnCounter--
Tt
Tr<Tb
UpCounter--
Tc2DIFS
additional
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QP-CAT Algorithm QP-CAT Algorithm (4/5)(4/5)
Tt
Tc
DnCounter--
2Tt
Tt Tt-Tb
UpCounter--Tr=TDIFS+Tb
TbTr
DnCounter++(due to collision)
DnCounter--
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QP-CAT Algorithm QP-CAT Algorithm (5/5)(5/5)
np= Tc / Tt
Tr= Tc – Tt∙np
Tr>0
N
Tc=Tc+Tr-TDIFS
Y Tr=Tb+TDIFS
DnCounter++N
Y
Handling the remaining time
Basic CAT
Collision detection
Collision handling
DnCounter –= np /2UpCounter –= np /2Qp=QA+DnCounter
Queue size Prediction (QP)
Measure Tc
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QP-CATQP-CAT
16 calls (actual)
17 calls + 1 virtual call(predicted by QP-CAT)
16 calls + 1 virtual call(predicted by QP-CAT)
17 calls (actual)
17th call is admitted
17 calls + 1 virtual call(predicted by QP-CAT)
16 calls + 1 virtual call(predicted by QP-CAT)
18th call starts17 calls (actual)
18 calls (actual)
Simulation results
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ExperimentsExperiments Linux, MadWifi,
Atheros ORBIT test-bed in
Rutgers University
Experimental setup Ethernet-to-
Wireless 11Mb/s data rate
client
client clientclient client
clientclientclient
clients clientAPclient
client clientclientclient
IEEE 802.11b
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QP-CATQP-CAT Experimental results (64kb/s 20ms PI)
11Mb/s 1 node - 2Mb/s
2 nodes - 2Mb/s 3 nodes - 2Mb/s
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Multiple execution of QP-Multiple execution of QP-CATCAT Parallel execution
Need to test various types of VoIP traffic Run multiple QP-CAT using each type
simultaneously Serial execution
The longer we monitor, the better decision
Takes time for accurate decision Run two QP-CAT serially
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QP-CATeQP-CATe QP-CAT with 802.11e Emulate the transmission during
TXOP
D D D TCP
TXOP
D D D TCP
Tc
D D D
TXOP
CAC
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ConclusionConclusion QP-CAT uses the queue size of the
AP as the metric for QoS of VoIP traffic
QP-CAT can accurately predict the impact of new VoIP calls using CAT
We can run QP-CAT in parallel or serially to handle multiple new VoIP flows
QP-CAT can handle background traffic in 802.11e using QP-CATe
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Thank you
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QP-CAT Algorithm QP-CAT Algorithm (4/8)(4/8)
Computation of Additional Transmission
Tc = Tc2 + Tr - TDIFS
Tr > Tb
Tr < Tb
1 2 Tr
1 2 Tr
1 2 Tr
tpcr TnTT
Tc2
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802.11 Frame 802.11 Frame TransmissionTransmission
DIFS
DataSIFS
ACK
DIFSData
SIFS
ACKNode A
Node B
Defer
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QP-CAT Algorithm QP-CAT Algorithm (5/8)(5/8)
Handling Tr : Tr > Tb
Tt
Emulation of actual transmission
CAT
Tc1 Tt-TrDIFS
DnCounter-- UpCounter--
Tt
backoff
Additional frames
Actual frames
DnCounter--
Tc2
DIFS
additional
additional DIFS
Tr
Additional frame is transmitted first
Actual frame is transmitted later
>Tb
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QP-CAT Algorithm QP-CAT Algorithm (6/8)(6/8)
Handling Tr : Tr < Tb
Tt Tt-Tr
Emulation of actual transmission
CAT
Tc1
DnCounter--
Tt
Tr<Tb
Additional frames
Actual frames
UpCounter--
Tc2
Additional frame is transmitted later
Actual frame is transmitted first
DIFSadditional
additional DIFS
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QP-CAT Algorithm QP-CAT Algorithm (7/8)(7/8)
Tt
Emulation of transmission
CAT
Tc
DnCounter--
Additional frames
Actual frames
2Tt
Tt Tt-Tb
UpCounter--Tr=TDIFS+Tb
TbTr
Collision
Retransmissions
DnCounter++(due to collision)
DnCounter--
Virtual collision
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ImplementationImplementation Environment
Linux, MadWifi driver, Atheros chipset Monitoring
Atheros chipset notifies RX timestamp in microsecond and TX timestamp in millisecond
Additional wireless card as monitor mode at the AP
Computing TC
TC = RX2 – RX1 - TT
RX1 RX2
TC
TT
Up Dn
RX TX
TC
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Related work Related work (3/3)(3/3)
ComparisonApproaches Metric Assumption Adapts to
channelWaste of BW Extensibility
Theoreticalapproaches
CW/TXOPComputed bandwidth
Saturated channel
No Low Good
CUE/CBR CUECBR
Max CU/CB(Measured in advance)
No(Fixed Max CU)
Middle(Reserved BW for collisions)
Good
Actual Probing
Delaypacket loss
No Yes High(Probing flow)
Bad
QP-CAT Queue size of the AP
No Yes Low Good