Admission Control for IEEE 802'11e Wireless LANs

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Admission Control for IEEE 802.11e Wireless LANs

• Student Conroy Smith
• Supervisor Neco Ventura
• Department of Electrical Engineering
• University of Cape Town

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Overview

• Introduction
• IEEE 802.11e QoS Enhancement
• Proposed Problem
• Proposed Admission Control solution
• Performance Evaluation and Preliminary Results
• Conclusions
• Future Work

3
Introduction

• Wireless LANs are expected to have a major impact
  on peoples daily life styles
• Provides Cheaper Internet Connectivity
• Relatively high throughput
• Ease of Implementation
• Being endowed with roaming capabilities
• Voice enabled devices are now being equipped with
  WiFi capabilities
• This allows WiFi to compete directly with 3G
  Cellular Networks

The Internet
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Introduction

• Original 802.11 Standard Lacks QoS Support
• WLANS was traditionally a Best Effort Wireless
  Access
• IEEE 802.11e provides a QoS enhancement
• Modifications made to MAC layer
• Provides service differentiation
• QoS can only be achieved at when the network load
  is not too heavy
• Channel overloading decreases network throughput

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IEEE 802.11e QoS enhancement

• IEEE 802.11e Specifies are new Hybrid
  Co-ordination Function (HCF)
• The HCF Specifies 2 Access modes
• HCF Controlled Channel Access (HCCA)
• Enhanced Distributed Channel Access (EDCA)

MAC Layer Modification of the IEEE 802.11e
enhancement
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IEEE 802.11e EDCA

• The EDCA allow service differentiation, by
  supporting 8 different priorities
• further mapped to 4 Access Classes (ACs)
• Each AC behaves as a single enhanced DCF
  contending entity with dedicated queues

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IEEE 802.11e EDCA

• Differentiation achieved by
• AIFS
• CWmin
• CWmax
• TXOP

Queuing Architecture of EDCA
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IEEE 802.11e EDCA

• Contention in the EDCA

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Problem of overloading 802.11 channel in the EDCA

• Traffic congestion and can lead to severe overall
  network degradation.
• New flows will may not be able to achieve their
  QoS
• They may also degrade the QoS of other admitted
  flows
• The need for Admission control has become apparent

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Proposed Admission Control For IEEE 802.11e

• A measurement/model-based Admission control
• WLAN channels are modeled using the a modified
  Bianchi Model 4
• This is used to Bandwidth Estimations for each
  Virtual Station
• Each AC queue act as a Virtual Station
• Queue utilization and collision statistics are
  measured and used by the model
• Uses TSPEC to negotiate Admission control
• Flows must state their throughput requirements

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Admission Negotiation
Typical TSPEC Negotiation
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Admission Control Decisions

• A new request will demand more Throughput for its
  Virtual Station
• New flows will be Accepted ONLY if
• Achievable Bandwidth (Si) Requested
  Bandwidth For All Virtual Stations
• Achievable Bandwidth

P(C) - Probability of a collision in a slot P(I)
- Probability of an idle slot P(S) - Probability
of a successful Tx in a slot P(SVSi) -
Probability of a successful Tx on Virtual Station
i
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Admission Control Decisions Calculating the
Probabilities
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Calculating Transmission Probability for each
Virtual Station

• A modified Bianchi model is used to calculate the
  Transmission Probabilities for each Virtual
  Station

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Accuracy of Bandwidth Estimations

• Bandwidth Estimation Framework Integrated in the
  NS-2 Contributed Model from 5
• Simulation Consists of
• 1 AP
• 6 Stations, 3 have unlimited data to send and 3
  are unsaturated
• All Stations transmit at 18 Mbps (802.11a)

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Performance Evaluation of proposed admission
control solution
Accuracy of the Bandwidth Estimations
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Performance Evaluation Simulation Set up

• At time t 3 sec, each station has a TCP session
  and a voice and video flow
• A new voice and video requests are added every 2
  seconds
• Voice flows 64 Kbps
• Video flows 750 Kbps

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Preliminary Results
Performance without Admission Control (TCP
session Voice flow Video flow)
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Preliminary Results
Performance with Admission Control (TCP session
Voice flow Video flow)
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Preliminary Results
Performance without Admission Control (Total
Throughput)
Flow 16 admitted
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Preliminary Results
Performance with Admission Control (Total
Throughput)
Flow 16 rejected

• Admitted Flows
• 9 Voice
• 7 Video

Flow 18 rejected
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Conclusions

• IEEE 802.11e WLANs provides QoS Support
• EDCA Allows differentiation of 4 ACs
  Differentiated by, CW, TXOP and AIFS
• Channel overloading can lead to severe
  degradation of QoS for EDCA flows
• A measurement aided model-based admission control
  solution is proposed to protect QoS for EDCA
  flows
• The accuracy of the bandwidth estimation
  indicates that effective admission control
  decisions can be made

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Future Work

• Extend the Admission Control scheme to be
  compatible with TXOP Bursting and RTS/CTS
  handshake mechanisms
• Investigate whether acceptable delays are achieved

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References

• 1 Y. Xiao and H. Li, Evaluation of
  Distributed Admission Control for the IEEE
  802.11e EDCA, IEEE Communications Magazine, vol.
  42, no. 9, pp. S20S24 2004
• 2 D. Gu and J. Zhang, A New Measurement-based
  Admission Control Method for IEEE 802.11 Wireless
  Local Area Networks, Mitsubishi Elec. Research
  Lab, Tech. rep. TR-2003-122, Oct. 2003.
• 3 D. Pong and T. Moors, Call Admission
  Control for IEEE 802.11 ContentionAccess
  Mechanism, Proc. IEEE GLOBECOM03, vol. 1, San
  Francisco, CA, Dec. 2003, pp. 17478.
• 4 G. Bianchi, Performance Analysis of the
  IEEE 802.11 Distributed Coordination Function,
  IEEE JSAC, 18(3) 535-47, Mar. 2000.
• 5 http//yans.inria.fr/ns-2-80211/
• 6 H. Wu et. al. IEEE 802.11e Enhanced
  Distributed Channel Access (EDCA) Throughput
  Analysis
• 7 Z Kong et. al. Performance Analysis of IEEE
  802.11e Contention-Based Channel Access
• 8 J. F. Robinson and T. S. Randhawa,
  Saturation Throughput Analysis of IEEE 802.11e
  Enhanced Distributed Coordination Function

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• Questions
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