Automatic rate adaptation in CSMA/CA wireless networks may cause drastic throughput degradation for high speed bit rate stations (STAs). The CSMA/CA medium access method guarantees equal long-term channel access probability to all hosts when they are saturated. In previous work it has been shown that the saturation throughput of any STA is limited by the saturation throughput of the STA with the lowest bit rate in the same infrastructure. In order to overcome this problem, we first introduce in this paper a new model for finite load sources with multirate capabilities. We use our model to investigate the throughput degradation outside and inside the saturation regime. We define a new fairness index based on the channel occupation time to have more suitable definition of fairness in multirate environments. Further, we propose two simple but powerful mechanisms to partly bypass the observed decline in performance and meet the proposed fairness. Finally, we use our model for finite load sources to evaluate our proposed mechanisms in terms of total throughput and MAC layer delay for various network configurations.

Confronted with the generalization of monitoring in operational networks, researchers have proposed placement algorithms that can help ISPs deploy their monitoring infrastructure in a cost effective way, while maximizing the benefits of their infrastructure. However, a static placement of monitors cannot be optimal given the short-term and longterm variations in traffic due to re-routing events, anomalies and the normal network evolution. In addition, most ISPs already deploy router embedded monitoring functionalities. Despite some limitations (inherent to being part of a router), these monitoring tools give greater visibility on the network traffic but raise the question on how to configure a networkwide monitoring infrastructure that may contain hundreds of monitoring points.We reformulate the placement problem as follows. Given a network where all links can be monitored, which monitors should be activated and which sampling rate should be set on these monitors in order to achieve a given measurement task with high accuracy and low resource consumption? We provide a formulation of the problem, an optimal algorithm to solve it, and we study its performance on a real backbone network.

Abstract

Confronted with the generalization of monitoring in operational networks, researchers have proposed placement algorithms that can help ISPs deploy their monitoring infrastructure in a cost effective way, while maximizing the benefits of their infrastructure. However, a static placement of monitors cannot be optimal given the short-term and longterm variations in traffic due to re-routing events, anomalies and the normal network evolution. In addition, most ISPs already deploy router embedded monitoring functionalities. Despite some limitations (inherent to being part of a router), these monitoring tools give greater visibility on the network traffic but raise the question on how to configure a networkwide monitoring infrastructure that may contain hundreds of monitoring points.We reformulate the placement problem as follows. Given a network where all links can be monitored, which monitors should be activated and which sampling rate should be set on these monitors in order to achieve a given measurement task with high accuracy and low resource consumption? We provide a formulation of the problem, an optimal algorithm to solve it, and we study its performance on a real backbone network.