Packet dispersion in ieee 802 11 wireless networks
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Packet Dispersion in IEEE 802.11 Wireless Networks. Mingzhe Li, Mark Claypool and Bob Kinicki WPI Computer Science Department Worcester, MA 01609 [email protected] Second International Workshop on Performance and Management of Wireless Local Area Networks (P2MNet)

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Packet dispersion in ieee 802 11 wireless networks l.jpg

Packet Dispersion inIEEE 802.11Wireless Networks

Mingzhe Li, Mark Claypool and

Bob Kinicki

WPI Computer Science Department

Worcester, MA 01609

[email protected]

Second International Workshop on Performance and Management of Wireless Local Area Networks (P2MNet)

Tampa, Florida, November 14, 2006


Outline l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Introduction l.jpg
Introduction

  • Bandwidth estimation techniques focus on network capacity or available bandwidth.

  • Most bandwidth estimation has involved only wired networks.

  • This paper focuses on packet dispersion in wireless LANs (WLANs).

P2MNet Workshop November 14, 2006


Outline4 l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Packet dispersion techniques l.jpg
Packet Dispersion Techniques

  • Packet pair dispersion

    • two equal-sized packets are sent back-to-back through the network.

  • Packet train dispersion

    • multiple back-to-back probe packets are sent through the network.

P2MNet Workshop November 14, 2006


Packet pair dispersion l.jpg
Packet Pair Dispersion

narrow link

P2MNet Workshop November 14, 2006


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NS-2 Additionsto Model WLANs

  • Receiver Based Auto Rate (RBAR) module was re-implemented in NS 2.27 to model 802.11 dynamic rate adaptation [ Sadeghi et al.]

  • An NS-2 extension to model Rayleigh fading was implemented [Ratish et al.]

P2MNet Workshop November 14, 2006


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Wireless Rate Adaptationunder Rayleigh Fading

NS-2 simulation results

P2MNet Workshop November 14, 2006


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Wireless Traffic Classification

  • Probing traffic

    • Packet pairs or trains sent downstream through the AP to the wireless client.

  • Crossing traffic

    • Downstream traffic going through the AP to other wireless clients.

  • Contending traffic

    • Upstream traffic that accesses the shard wireless channel and competes with probe packets on the estimated path.

P2MNet Workshop November 14, 2006


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Wireless Traffic Classification

P2MNet Workshop November 14, 2006


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WLAN Packet Dispersion Issues

  • Wireless frame retries

    • increase the packet delay variance that produce packet dispersion inconsistencies.

  • Dynamic Rate Adaptation

  • Fading channel

  • Noisy wireless channel - BER

  • Contending Traffic

P2MNet Workshop November 14, 2006


Simulated wireless effects on bandwidth estimation l.jpg
Simulated Wireless Effects on Bandwidth Estimation

  • CDF represents 1000

  • packet-pair estimates

  • 1000-byte probe packets

  • and CBR contending packets

  • Contending traffic = 1Mbps

  • upstream flow

P2MNet Workshop November 14, 2006


Outline13 l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Wlan packet dispersion model l.jpg
WLAN Packet Dispersion Model

Assumptions

Bottleneck link is the WLAN last hop.

No crossing traffic.

  • Dispersion, T, between two packets in a packet pair is characterized in terms of E[T] and V[T] for a WLAN that includes: packet size, link data rate, BER and access methods (base or RTS/CTS).

  • While wireless channel conditions can be characterized by received signal strength indicator (RSSI), SNR and BER, our simplified model assumes these other factors impact BER.

    • The impact of channel conditions on bandwidth estimation is evaluated via V[T], the packet dispersion variance.

P2MNet Workshop November 14, 2006


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WLAN Packet Dispersion Model

  • From previous 802.11 models, we build a new model for wireless packet dispersion where dispersion is defined as the delay between the arrival times of the first and second packets in the packet pair.

  • Thus, the model must include the delay before the transmission of the second packet, E[D], and the time to transmit it, Ts, and dispersion is:

    E[T] = E[D] + Ts

P2MNet Workshop November 14, 2006


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WLAN Packet Dispersion Model

  • Since E[D] depends on the wireless link rate, Cl , the average packet size, L and the number of nodes in the contention domain, n, we have

    E[D] = d (Cl, L, n)

  • Similarly, for the transmission time,

    Ts = ts (Cl, L)

P2MNet Workshop November 14, 2006


Bandwidth estimate l.jpg
Bandwidth Estimate

  • Defining, Cest, as the bandwidth estimate based on the wireless packet pair dispersion model, our model is defined by:

P2MNet Workshop November 14, 2006


Outline18 l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Model validation l.jpg
Model Validation

  • Validation results include an ideal WLAN and a scenario with contention and BER.

  • Ideal validation includes NS-2 simulations, analytic model and actual measurements.

P2MNet Workshop November 14, 2006


Ideal wlan scenario l.jpg
Ideal WLAN Scenario

The ideal scenario consists

of an AP with a single

wireless client for both

basic (BAS) and RTS/CTS

access methods.

Simulations: 500 pairs

Measurements: 100 pairs

P2MNet Workshop November 14, 2006


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Model Validation

Random Model

Simulation Parameters

Topology

P2MNet Workshop November 14, 2006


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Models with Contention and Wireless Transmission Errors

Errors in the Bandwidth Estimation Model

Compared with Simulations

Error Free BER = 10-5

P2MNet Workshop November 14, 2006


Outline23 l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Model analysis l.jpg
Model Analysis

  • In a non-saturated WLAN with low BER, low contention, packet-pair dispersion estimates the maximal channel capacity, effective capacity, Ce .

  • With considerable contending traffic and/or BER, the dispersion metric is referred to as the achievable throughput, At , for the current level of contending traffic.

P2MNet Workshop November 14, 2006


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Model Analysis

  • Effective Capacity

  • Achievable Bandwidth

  • Relationship with Available Bandwidth

P2MNet Workshop November 14, 2006


Achievable throughput l.jpg
Achievable Throughput

P2MNet Workshop November 14, 2006


Impact of channel rate on effective capacity l.jpg
Impact of Channel Rateon Effective Capacity

P2MNet Workshop November 14, 2006


Impact of ber on achievable throughput l.jpg
Impact of BER on Achievable Throughput

Five node, BAS wireless

network with 1500-byte

packets

no achievable throughput

P2MNet Workshop November 14, 2006


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Impact of RTS/CTSon Achievable Throughput

Model Results for Wireless Networks with 1500 Byte Packets

P2MNet Workshop November 14, 2006


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Standard Deviation of Achievable Throughput

P2MNet Workshop November 14, 2006


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Packet Size Effect onStandard Deviation ofBandwidth Estimations

Five node, BAS wireless

network with 1500-byte

packets

P2MNet Workshop November 14, 2006


Impact of channel rate on standard deviation of bandwidth estimations l.jpg
Impact of Channel Rateon Standard Deviation of Bandwidth Estimations

P2MNet Workshop November 14, 2006


Impact of ber on standard deviation of bandwidth estimations l.jpg
Impact of BER on Standard Deviation of Bandwidth Estimations

P2MNet Workshop November 14, 2006


Outline34 l.jpg
Outline

  • Introduction

  • Packet Dispersion in WLANs

  • WLAN Packet Dispersion Model

  • Model Validation

  • Model Analysis

  • Conclusions

P2MNet Workshop November 14, 2006


Conclusions l.jpg
Conclusions

  • Packet dispersion measures the effective capacity and the achievable throughput of a wireless network instead of the capacity as in a wired network.

  • Wireless channel conditions, such as BER and RTS/CTS access method impact the bandwidth estimation results and the variance of the results.

P2MNet Workshop November 14, 2006


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Thank You !!

Packet Dispersion inIEEE 802.11Wireless Networks

Mingzhe Li, Mark Claypool and Bob Kinicki

WPI Computer Science Department

Worcester, MA 01609

[email protected]

http://web.cs.wpi.edu/~rek/

Second International Workshop on Performance and Management of Wireless Local Area Networks (P2MNet)

Tampa, Florida, November 14, 2006



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