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-In this work, we measure Wireless Local Area Network (WLAN) voice performance and capacity. While most WLAN applications today are data centric, the growing popularity of Voice over IP (VoIP) applications and the trend towards convergence with cellular networks will catalyze increased voice traffic. Since voice applications compete not only with each other, but also with data applications for WLAN bandwidth, quantifying voice performance and capacity in the presence of simultaneous data traffic is an important issue. We offer a practical investigation of the 802.11b MAC layer's ability to support simultaneous voice and data applications. We quantify VoIP capacity for standard WLAN networks, indicative of those already in the field, as well as evaluate the practical benefits of implementing backoff control and priority queuing at the access point. Conclusions are drawn based on an extensive set of real-world measurements conducted using off-theshelf equipment in an experimental testbed. I INTRODUCTIONOnce only seen within the enterprise, Wireless Local Area Networks (WLANs) are increasingly making their way into residential, commercial, industrial and public areas. Examples of such environments are hotels, airports and coffee shops, which typically have a floating end user population. University campuses and conference settings also benefit from WLANs since they provide flexible connectivity and network access at reduced costs. While the majority of traffic in WLAN deployments is data, we expect that voice will be an increasingly important application and a significant driver for WLAN adoption and integration, particularly as voice over IP (VoIP) applications flourish. Additionally, voice will be especially important in vertical industries such as construction, healthcare, and banking, etc. Therefore it is crucial to understand voice performance in WLANs. Furthermore, since WLAN endpoints share a common transmission medium, voice applications must compete with data applications for access and bandwidth. As such, voice quality and capacity can be significantly affected by the simultaneous transmission of data traffic in these networks. So it is also critical to understand the effects of data transmissions on voice performance and capacity.We focus exclusively on IEEE 802.11b [1], the most popular and prominently deployed WLAN standard. We measure the achievable voice performance and capacity using an experimental testbed consisting of commercially available, off-the-shelf components indicative of those that have already been deployed. With such a large legacy base for 802.11b equipment, especially among residential and enterprise customers, we believe that this approach provides the most immediately relevant results.In addition to standard 802.11b, we investigate MAClayer and queuing mechanisms , which can be easily implemented and can improve voice performance. Specifically, we measure the effects of backoff control and priority queuing (BC-PQ), as provided by [2]. Using both the standard and additional...

The problem of fair bandwidth sharing among adaptive (TCP) and non-adaptive (i.e. CBR-UDP) flows at an Internet gateway is considered. An algorithm that drops packet preventively, an an attempt to actively penalize the non-adaptive traffic that attempts to "steal" buffer space, and therefore bandwidth f r o m the adaptive trafic flows, is presented. The algorithm maintains minimal Bow state information and is therefore scalable. The performance of the algorithm is compared with other gateway algorithms and it is shown that, in the presence of non-adaptive traffic, at achieves a more balanced bandwidth allocation among the different flows. The behavior of a flow subjected to the given algorithm has also been analysed in detail.

We consider ad hoc networks with multiple, mobile intruders. We investigate the placement of the intrusion detection modules for misuse-based detection strategy. Our goal is to maximize the detection rate subject to limited availability of communication and computational resources. We mathematically formulate this problem, and show that computing the optimal solution is NP-hard. Thereafter, we propose two approximation algorithms that approximate the optimal solution within a constant factor, and prove that they attain the best possible approximation ratios. The approximation algorithms though require recomputation every time the topology changes. Thereafter, we modify these algorithms to adapt seamlessly to topological changes. We obtain analytical expressions to quantify the resource consumption versus detection rate tradeoffs for different algorithms. Using analysis and simulation, we evaluate these algorithms, and identify the appropriate algorithms for different detection rate and resource consumption tradeoffs.Abstract-We consider ad hoc networks with multiple, mobile intruders. We investigate the placement of the intrusion detection modules for misuse-based detection strategy. Our goal is to maximize the detection rate subject to limited availability of communication and computational resources. We mathematically formulate this problem, and show that computing the optimal solution is NP-hard. Thereafter, we propose two approximation algorithms that approximate the optimal solution within a constant factor, and prove that they attain the best possible approximation ratios. The approximation algorithms though require recomputation every time the topology changes. Thereafter, we modify these algorithms to adapt seamlessly to topological changes. We obtain analytical expressions to quantify the resource consumption versus detection rate tradeoffs for different algorithms. Using analysis and simulation, we evaluate these algorithms, and identify the appropriate algorithms for different detection rate and resource consumption tradeoffs.

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