Sistema De Ipv6

A Measurement-Based Approach to Modeling Link
Capacity in 802.11-Based Wireless Networks
Anand Kashyap

Samrat Ganguly

Samir R. Das

Computer Science Dept.
Stony Brook University
Stony Brook, NY, USA

NEC Laboratories America
Princeton, NJ, USA

Computer Science Dept.
Stony Brook University
Stony Brook, NY, USA

samrat@nec-labs.com

anand@cs.sunysb.edu

samir@cs.sunysb.eduABSTRACT
We present a practical, measurement-based model that captures the effect of interference in 802.11-based wireless LAN
or mesh networks. The goal is to model capacity of any
given link in the presence of any given number of interferers
in a deployed network, carrying any specified amount of offered load. Central to our modeling approach is a MAC-layer
model for 802.11 that is fed byPHY-layer models for deferral and packet capture behaviors, which in turn are profiled
based on measurements. The target network to be evaluated
needs only O(N ) measurement steps to gather metrics for
individual links that seed the models. We provide two solution approaches – one based on direct simulation (slow, but
accurate) and the other based on analytical methods (faster,
butapproximate). We present elaborate validation results
for a 12 node 802.11b mesh network using upto 5 interfering
transmissions. We demonstrate, using as comparison points
three simpler modeling approaches, that the accuracy of our
approach is much better, predicting link capacities with errors within 10% of the base channel datarate for about 90%
of the cases.

Categories and Subject DescriptorsC.4 [Performance of Systems]: Measurement techniques,
Modeling techniques; C.2.1 [Network Architecture and
Design]: Wireless communication.

General Terms
Experimentation, Measurement.

Keywords
Wireless network capacity, wireless interference, 802.11.

1.

INTRODUCTION

Practical models for predicting the wireless link capacity are crucial to an efficient operation and deployment ofwireless network. The performance of network protocols

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Figure 1: Example of problem.
and algorithms such as QoS routing, load balancing, admission control and channel assignment can be significantly
improved with an accurate model of link capacity. Capacity modelsare also required as analysis tools to efficiently
explore a gamut of network configurations and traffic load
scenarios for performance evaluation.
Recently, the proliferation of 802.11 based wireless LAN
and mesh networks has lead to several research efforts focussing on predicting the capacity of an 802.11-specific wireless link [19, 20]. What makes the accurate estimation of
802.11 link capacityan inherently challenging task is that
the link capacity is an ensemble effect of physical layer behavior, complex CSMA-based MAC layer interaction, and
interference effect from multiple active sources.
The objective of our work is to characterize and model the
impact of interference caused by active traffic from multiple
surrounding nodes on the link capacity. For example, referring to Figure 1,consider a set of active links (CA, BD and
EF) with specified amounts of offered traffic loads (in Mbps,
for example). Our goal is to create a model that can predict
the throughput capacity of any given link (e.g., BC or AB),
i.e., the maximum amount of traffic (in Mbps) that the link
can carry. Unlike the plethora of modeling work in existing
literature [5, 11, 17] that uses purely analytical...