Understanding link-level 802.11 behavior: replacing convention with measurement

Judd, Glenn; Steenkiste, Peter

doi:10.4108/wicon.2007.2165

Cited by 15 publications

(11 citation statements)

References 18 publications

(28 reference statements)

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“…10, we use the observed link-level behavior to analyze the performance of a production wireless network. This paper is an extended version of [5].…”

Section: Introductionmentioning

confidence: 98%

Characterizing 802.11 wireless link behavior

Judd

Steenkiste

2008

Wireless Netw

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Since wireless signals propagate through the ether, they are significantly affected by attenuation, fading, multipath, and interference. As a result, it is difficult to measure and understand fundamental wireless network behavior. This creates a challenge for both network researchers, who often rely on simulators to evaluate their work, and network managers, who need to deploy and optimize operational networks. Given the complexity of wireless networks, both communities often rely on simplifying rules, which frequently have not been validated using today's wireless radios. In this paper, we undertake a detailed characterization of 802.11 link-level behavior using commercial 802.11 cards. Our study uses a wireless testbed that provides signal propagation emulation, giving us complete control over the signal environment. In addition, we use our measurements to analyze the performance of an operational wireless network. Our work contributes to a more accurate understanding of link-level behavior and enables the development of more accurate wireless network simulators.

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“…10, we use the observed link-level behavior to analyze the performance of a production wireless network. This paper is an extended version of [5].…”

Section: Introductionmentioning

confidence: 98%

Characterizing 802.11 wireless link behavior

Judd

Steenkiste

2008

Wireless Netw

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“…A number of works have identified the channel conditions and timing under which physical layer capture occurs for pairs of nodes [1], [7], [22]. Others have proposed modifying physical layer properties to address the lack of fairness that results [23], [24].…”

Section: G Extensions and Applicationsmentioning

confidence: 98%

“…In such cases, a topological asymmetry results in a hidden node having inferior channel state information, forcing the hidden node to contend at random times guided by binary exponential backoff rather than at "idle times" driven by carrier sense. However, while the effects of information asymmetry and channel asymmetries are understood in isolation ( [2], [3], [4], [5] and [6], [7], [8], respectively), their interdependencies have thus far been ignored.…”

Section: Introductionmentioning

confidence: 98%

Coupled 802.11 Flows in Urban Channels: Model and Experimental Evaluation

Camp

Aryafar

Knightly

2010

2010 Proceedings IEEE INFOCOM

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Contending flows in multi-hop 802.11 wireless networks compete with two fundamental asymmetries: (i) channel asymmetry, in which one flow has a stronger signal, potentially yielding physical layer capture, and (ii) topological asymmetry, in which one flow has increased channel state information, potentially yielding an advantage in winning access to the channel. Prior work has considered these asymmetries independently with a highly simplified view of the other. However, in this work, we perform thousands of measurements on coupled flows in urban environments and build a simple, yet accurate model that jointly considers information and channel asymmetries. We show that if these two asymmetries are not considered jointly, throughput predictions of even two coupled flows are vastly distorted from reality when traffic characteristics are only slightly altered (e.g., changes to modulation rate, packet size, or access mechanism). These performance modes are sensitive not only to small changes in system properties, but also small-scale link fluctuations that are common in an urban mesh network. We analyze all possible capture relationships for two-flow sub-topologies and show that capture of the reverse traffic can allow a previously starving flow to compete fairly. Finally, we show how to extend and apply the model in domains such as modulation rate adaptation and understanding the interaction of control and data traffic. I. INTRODUCTIONIn urban environments, IEEE 802.11 nodes interact in many ways, e.g., within and among paths in a multi-hop network and among deployments from different domains. Competing transmitters rarely have equal link quality to a given receiver, i.e., channel asymmetries are prevalent, especially in urban channels. When packets overlap in time, even slight link quality differences have been shown to cause physical layer capture such that the packet sent over the higher quality link is received correctly but the packet sent over the weaker link is dropped [1]. Moreover, transmitters or receivers of competing flows often have unequal channel state information, a situation termed information asymmetry. In such cases, a topological asymmetry results in a hidden node having inferior channel state information, forcing the hidden node to contend at random times guided by binary exponential backoff rather than at "idle times" driven by carrier sense. However, while the effects of information asymmetry and channel asymmetries are understood in isolation ([2], [3], [4], [5] and [6], [7], [8], respectively), their interdependencies have thus far been ignored.In this paper, we jointly consider information and channel asymmetries with both analytical models and extensive, urban measurements. As in [9], we employ the two-flow enumeration technique of [4] and consider all topological couplings of paired flows. However, in contrast to [4], [9], we inform the

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“…The original goal of the wireless emulator testbed was to allow researchers to compare the performance of different wireless protocols under identical circumstances, e.g. [5,6]. However, the same properties that make the testbed an attractive platform for the research community, are also useful in an educational setting.…”

Section: Wireless Network Emulatormentioning

confidence: 99%

“…[5]. This typically involves relatively little programming and it reinforces and expands on material covered in the first half of the course.…”

Section: Projectsmentioning

confidence: 99%

The use of a controlled wireless testbed in courses

Steenkiste¹

2009

SIGCSE Bull.

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Wireless networking has become a popular topic in both undergraduate and graduate courses. However, putting together good assignments in wireless networking is difficult because the behavior of the wireless network depends strongly on the physical environment. We have used a wireless networking testbed based on signal propagation emulation in a number of wireless networking courses. The wireless emulator supports highly realistic experiments, while also offering a high degree of control and repeatability. This combination is very useful in a teaching context. In this paper we give an overview of the wireless emulator and we describe how it was used to support assignments and open-ended projects in several courses.

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Understanding link-level 802.11 behavior: replacing convention with measurement

Cited by 15 publications

References 18 publications

Characterizing 802.11 wireless link behavior

Characterizing 802.11 wireless link behavior

Coupled 802.11 Flows in Urban Channels: Model and Experimental Evaluation

The use of a controlled wireless testbed in courses

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