QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer.

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QoS Guarantees QoS Guarantees for Real Time for Real Time Applications in Applications in 802.11 WLANs 802.11 WLANs Kiran P Diwakar Kiran P Diwakar Guide: Guide: Prof. Sridhar Prof. Sridhar Iyer Iyer

description

IEEE e  Proposed Variant to provide QoS in  Overcomes the ‘flat’ nature of legacy  Introduces new differentiating parameters  AIFS, variable CW.  Two methods of Channel Access  EDCF  HCF

Transcript of QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer.

Page 1: QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer.

QoS Guarantees QoS Guarantees for Real Time Applications in for Real Time Applications in

802.11 WLANs802.11 WLANs

Kiran P DiwakarKiran P Diwakar

Guide:Guide:Prof. Sridhar IyerProf. Sridhar Iyer

Page 2: QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer.

OutlineOutline

802.11e 802.11e MotivationMotivation GoalsGoals Proposed Scheme : DTMAProposed Scheme : DTMA Functional Description of DTMA EntitiesFunctional Description of DTMA Entities Handling IssuesHandling Issues ResultsResults

Page 3: QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer.

IEEE 802.11 eIEEE 802.11 e

Proposed Variant to provide QoS in 802.11.Proposed Variant to provide QoS in 802.11. Overcomes the ‘flat’ nature of legacy Overcomes the ‘flat’ nature of legacy

802.11.802.11. Introduces new differentiating parameters Introduces new differentiating parameters

AIFS, variable CW.AIFS, variable CW. Two methods of Channel AccessTwo methods of Channel Access

EDCFEDCFHCFHCF

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EDCFEDCF EDCF – Enhanced Co-ordination FunctionEDCF – Enhanced Co-ordination Function Part of HCFPart of HCF Supports upto Supports upto

8 traffic classes.8 traffic classes. Uses Backoffs Uses Backoffs and AIFS for and AIFS for

classification.classification.

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HCFHCF

HCF – Hybrid Co-ordination FunctionHCF – Hybrid Co-ordination FunctionHybrid Co-ordinator, collocated at AP.Hybrid Co-ordinator, collocated at AP.Allocates TXOPs to WSTAs.Allocates TXOPs to WSTAs.TXOP allocated during both CP and CFPTXOP allocated during both CP and CFPSeveral CAPs defined in one CP.Several CAPs defined in one CP.

CPCFP

CAP

CAP

CP

CP

CP

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Motivation Motivation Most works propose enhancements to DCF.Most works propose enhancements to DCF. PCF not fully optimized.PCF not fully optimized. Poll / Acks huge overhead when the number of Poll / Acks huge overhead when the number of

stations is high.stations is high. Transmission Times : Transmission Times :

Data (512 bytes) : 90 microsecData (512 bytes) : 90 microsec Poll / Acknowledgement : 40 microsecPoll / Acknowledgement : 40 microsec

Doing away with the individual polls / acks => Doing away with the individual polls / acks => more time for data transmission => more more time for data transmission => more throughput and less delay => better QoS.throughput and less delay => better QoS.

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GoalsGoals Theoretically Analyze 802.11e.Theoretically Analyze 802.11e. Have a more intelligent Access Point. Have a more intelligent Access Point. Add more determinism.Add more determinism. AP has all the required info from node and AP has all the required info from node and

hence can schedule better and QoS.hence can schedule better and QoS. Reduce the average delay.Reduce the average delay. Optimize the overall throughput of the Optimize the overall throughput of the

network.network. Prove that the proposed scheme has stricter Prove that the proposed scheme has stricter

and lesser delays than existing ones.and lesser delays than existing ones.

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DMTA : Dynamic Time Division DMTA : Dynamic Time Division Multiple AccessMultiple Access

Adorns the PCF part of IEEE 802.11Adorns the PCF part of IEEE 802.11 Dynamically allots transmission slots.Dynamically allots transmission slots. Explicit control information annulled.Explicit control information annulled. No Polls / Acknowledgements required.No Polls / Acknowledgements required. Privileged nodes get explicit channel access in Privileged nodes get explicit channel access in

PCF.PCF. In DCF, privileged nodes compete with lesser In DCF, privileged nodes compete with lesser

backoffs and AIFS.backoffs and AIFS. Gives lesser delays for nodes associated as Gives lesser delays for nodes associated as

‘high priority’. ‘high priority’.

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DTMA SuperframeDTMA Superframe

Beacon

New Beacon = Beacon + Cumm. Ack New Beacon = Beacon + Cumm. Ack + + Ordered Privileged List Ordered Privileged List + Time for each slot+ Time for each slot

Cumm. Ack

DTMA EDCFAll Nodes CompetePrivileged Nodes

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Functional Description of Access Functional Description of Access PointPoint

On reception of the Association / Dissociation On reception of the Association / Dissociation request, manipulate the privileged / non-request, manipulate the privileged / non-privileged list based on the bit set.privileged list based on the bit set.

On the receipt of Data from node, add the On the receipt of Data from node, add the node id to the cummulative ack-list.node id to the cummulative ack-list.

At the end of slotted-CFP, send the At the end of slotted-CFP, send the cummulative ack-list.cummulative ack-list.

Calculate the slot-size.Calculate the slot-size.

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Functional Description of Access Functional Description of Access PointPoint

On receipt of request_to_join from an out of list On receipt of request_to_join from an out of list node, reset the the not_to_schedule_flag, so node, reset the the not_to_schedule_flag, so from the next round, node will get slot.from the next round, node will get slot.

If the AP and node both have data for each If the AP and node both have data for each other, the AP schedules the node such that other, the AP schedules the node such that they transmit in alternate rounds.they transmit in alternate rounds.

On receipt of ‘Null frame’, pin node as On receipt of ‘Null frame’, pin node as mark_dont_schedule mark_dont_schedule

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Beacon

Access Point

STAId=5

STAId=4

Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3

STAId=1

PSTAId=2

PSTAId=3

PDATADATADATA

Cumm. Ack1,2 ,#

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #DCF

ON

BO=7DATA

DATA BO=9BO=4

BO=2

ACKACK

BO=4 DATABO=2BO=7BO=5 BO=2BO=9 BO=3 BO=5

ACK

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Beacon

Access Point

STAId=5

STAId=4

Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3Beacon 1-2-3

STAId=1

PSTAId=2

PSTAId=3

PDATADATADATA

Cumm. Ack1,2 ,#

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #

C_Ack

1, 2, #

BO=7DATA

DATA BO=9BO=4

BO=2

ACKACK

BO=4 DATABO=2BO=7BO=5 BO=2BO=9 BO=3 BO=5

ACK

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Handling IssuesHandling Issues

Beacon gets garbled.Beacon gets garbled. Ack_list gets garbled.Ack_list gets garbled. Node with multiple real-time flows.Node with multiple real-time flows. Node off the list wants to get back on the list.Node off the list wants to get back on the list. Synchronization issue.Synchronization issue.

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Results Results Average Delay Average Delay

ComparisonComparison Throughput Throughput

ComparisonComparison

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Optimal Beacon IntervalOptimal Beacon Interval Average DelayAverage Delay ComparisonComparison

ThroughputThroughput ComparisonComparison

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Thank You !!!!Thank You !!!!