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. Overview. Introduction IEEE 802.11e QoS Enhancement Proposed Problem Proposed Admission Control solution - PowerPoint PPT PresentationTRANSCRIPT
Admission Control for IEEE 802.11e Wireless LANs
Student: Conroy Smith
Supervisor: Neco Ventura
Department of Electrical Engineering
University of Cape Town
UCT-COE Seminar000 Page 2 April 20, 2023
Overview
Introduction IEEE 802.11e QoS Enhancement Proposed Problem Proposed Admission Control solution Performance Evaluation and Preliminary Results Conclusions Future Work
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Introduction
Wireless LANs are expected to have a major impact on people’s 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 SupportWLANS was traditionally a “Best Effort” Wireless Access
IEEE 802.11e provides a QoS enhancementModifications made to MAC layerProvides service differentiation
QoS can only be achieved at when the network load is not too heavyChannel overloading decreases network throughput
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IEEE 802.11e QoS enhancement
MAC Layer Modification of the IEEE 802.11e 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)
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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:AIFSCWminCWmaxTXOP
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
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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(S|VS=i) - Probability of a successful Tx on Virtual Station i
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:
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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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- Measured Collision Probability
- Percentage of time that the Virtual station is considered to be Saturatedip
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Accuracy of Bandwidth Estimations
Bandwidth Estimation Framework Integrated in the NS-2 Contributed Model from [5]
Simulation Consists of:1 AP6 Stations, 3 have unlimited data to send and 3 are unsaturatedAll 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
Flow 18 rejected
Admitted Flows:
•9 Voice
•7 Video
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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. S20–S24 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 GLOBECOM’03, vol. 1, San Francisco, CA, Dec. 2003, pp. 174–78.
[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”
Questions
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