PLUS-DAC:An Admission Control Scheme in IEEE 802.11e Wireless

65 Pages·2005·0.44 MB·English

PLUS-DAC:An Admission Control Scheme in
IEEE 802.11e Wireless LANs.
M. Tech. Project Dissertation
Submitted in partial fulfillment of the requirements
for the degree of
Master of Technology
by
Kiran Kumar Gavini
Roll No: 03329020
under the guidance of
Prof. Varsha Apte
and
Prof. Sridhar Iyer
Kanwal Rekhi School of Information Technology
Indian Institute of Technology, Bombay
2005

Dedicated to my mother

Abstract
With increasing demand of support for realtime applications, there is a compelling need for
Qualityof Service (QoS) in present day wireless LANs. IEEE 802.11 MediumAccess Control
(MAC) has become a defacto standard for wireless LANs, but there are many inherent QoS
limitationsin thebasestandard, as itwas basicallydevelopedforbest effortdataservices.
TheIEEE802.11TaskGroupE(TGe),isabouttoratifyaQoSextensiontothebase802.11
standard namely IEEE 802.11e. The IEEE 802.11e standard provides many mechanisms for
QoS support at the MAC layer level. However, even the service differentiation provided in
IEEE 802.11e is not enough to meet the QoS requirements of time bounded multimediatraffic
at high load. These can be better satisfied, if we employ Admission Control and Bandwidth
Reservationmechanisms.
Another important concern in WLANs is channel utilization. Generally, partitioning based
reservation schemes do static division of bandwidth. When bandwidth is divided statically,
often, more bandwidth can get allocated to a category which is currently not offering much
traffic to the network, resultingin under-utilizationof the bandwidthresources. More over, the
bandwidthpartitioningshouldnotbepurely basedon thepriorityofthetraffic.
We propose a measurement based distributed admission control mechanism, for the IEEE
802.11eWirelessLocalAreaNetwork(WLAN)functioningininfrastructuremode. Wecallthe
scheme PLUS-DAC (Priority, Load and Utilization based Scheme for Distributed Admission
Control). PLUS-DACmeasurestheloadandutilizationintheBSSandadaptstheTransmission
Opportunity (TXOP) reservation dynamically. Our results show that, PLUS-DAC can achieve
quasi-optimalutilizationand continuetosatisfyQoSguarantees givento multimediaflows.

Acknowledgements
I like to take this opportunity to express my deep sense of gratitude for Prof. Varsha Apte
and Prof. Sridhar Iyer, for providing excellent guidance and support. It is because of their
constantinterestandassistancethatthisprojecthasbeensuccessful. Iwouldliketothankallthe
membersofthePerfNetGroupatCSEDepartment,IITBombay,fortheirvaluablesuggestions
and helpfuldiscussions.
I would also like to thank every member of KReSIT family who have been a source of
encouragement andinspirationthroughoutthedurationofthisproject.
I would like to thank Pierre Ansel, Qiang Ni and Thierry Turletti for making their FHCF
Implementationinns-2 available,whichwehaveextendedinourSimulations.
FinallyIwouldbethankfultomyfamilyandfriendswhohavegivenmeemotionalsupport
throughoutthedurationoftheproject.
KiranKumarGavini
IIT Bomay
iii

Contents
Abstract i
Acknowledgements iii
Listoffigures vii
Listoftables ix
1 Introduction 1
1.1 Wirelessand Convergence-TheFuture . . . . . . . . . . . . . . . . . . . . . 1
1.2 Challengesin WirelessNetworks . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Need forQualityofService . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 QoSinIEEE 802.11WLANs . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 ProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.6 Thesisoutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 IEEE 802.11WLAN Standard 7
2.1 SystemArchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 DCF: DistributedCoordinationFunction . . . . . . . . . . . . . . . . . . . . . 8
2.3 PCF:Point CoordinationFunction . . . . . . . . . . . . . . . . . . . . . . . . 10
3 OverviewofIEEE 802.11eQoSStandard 13
3.1 HCFContentionbased Channel Access:EDCA . . . . . . . . . . . . . . . . . 14
3.2 HCFControlledChannel Access (HCCA) . . . . . . . . . . . . . . . . . . . . 17
3.3 QoSControl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4 TrafficSpecification (TSPEC) element . . . . . . . . . . . . . . . . . . . . . . 19
3.5 EnhancementstoIEEE 802.11e . . . . . . . . . . . . . . . . . . . . . . . . . 20
v
4 Related Work 23
4.1 Need forAdmissioncontrol . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2 AdmissionControl basedon AchievableThroughput . . . . . . . . . . . . . . 23
4.3 AdmissionControl basedon EstimatedService Rate . . . . . . . . . . . . . . 24
4.4 HARMONICA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.5 PartitioningBased DistributedAdmissionControl . . . . . . . . . . . . . . . . 25
5 PLUS-DAC:Proposed Scheme 27
5.1 TXOP Partitioningand Reservation . . . . . . . . . . . . . . . . . . . . . . . 28
5.2 DistributedAdmissionControl at each QSTA . . . . . . . . . . . . . . . . . . 30
5.3 Proposed Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.4 ImplementationDetails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4.1 ImportantChanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6 Simulationand Results 35
6.1 SimulationSetup andTrafficDescription . . . . . . . . . . . . . . . . . . . . . 35
6.2 Performance Metrics Considered . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3 High PriorityScenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.4 Low priorityscenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7 Conclusionand Future Research 47
Bibliography 48