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

3

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

4

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

5

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

1

Actual frames from existing VoIP flows

channel

Clock starts Clock stopsTc

Tt

Additionaly transmittable frames

2

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