Frank Roijers

Analysis of flow transfer times in IEEE 802.11 wireless LANs

In this paper we present an integrated packet/flow level modelling approach for analysing flow throughputs and transfer times inieee 802.11wlans. It captures the statistical characteristics of the transmission of individual packets at themac layer and takes into account the system dynamics due to the initiation and completion of data flow transfers. In particular, at the flow level the system is modelled by a processor sharing type of queue, reflecting theieee 802.11mac design principle of distributing the transmission capacity fairly among the active flows. The integrated packet/flow level model is analytically tractable and yields a simple approximation for the throughput and flow transfer time. Extensive simulations show that the approximation is very accurate for a wide range of parameter settings. In addition, the simulation study confirms the attractive property following from our approximation that the expected flow transfer delay is insensitive to the flow size distribution (apart from its mean).RésuméNous présentons dans cet article un modèle intégrant les niveaux paquets et flux, qui permet l’analyse du débit utile des flux et de leur temps de transfert dans des réseaux locaux sans filieee 802.11. Le modèle développé prend en compte les caractéristiques statistiques de la transmission de paquets individuels au niveau de la couchemac, ainsi que la dynamique du système liée à l’initialisation et à la terminaison des transferts de flux de données. Plus précisément, au niveau des flux, le système est modélisé à l’aide d’une file d’attente à processeur partagé, refletant ainsi le partage équitable de la capacité de transmission entre les différents flux actifs, tel que réalisé par la couchemac de l’ieee 802.11. Le modèle à deux niveaux, paquets/flux, peut être résolu analytiquement et fournit une approximation simple du débit utile et du temps de transfert de flux. De nombreuses simulations ont montré que, pour une large gamme de paramètres, l’approximation est très précise. De plus, les résultats de nos simulations vérifient une propriété intéressante découlant de notre approximation à savoir que le delai de transfert moyen d’un flux est indépendant de la distribution des tailles (seule sa moyenne compte).

A performance study on service integration in IEEE 802.11E wireless LANs

Several studies in literature have investigated the performance of the proposed ieee 802.11e standard for qos differentiation in wlan, but most of them are limited both with respect to the range of the parameter settings and the considered traffic scenarios. The aim of the present study is twofold. First, we systematically investigate the differentiating capabilities of qos mechanisms. Second, we investigate how well the qos mechanisms are able to support different types of services under realistic traffic conditions. In particular, we investigate flow-level performance characteristics (e.g., file transfer times) in the situation that the number of active stations varies dynamically in time.

Performance analysis of differentiated resource-sharing in a wireless ad-hoc network

In this paper we model and analyze a relay node in a wireless ad-hoc network; the capacity available at this node is used to both transmit traffic from the source nodes (towards the relay node), and to serve traffic at the relay node (so that it can be forwarded to successor nodes). Clearly, a network node that is used more heavily than others is prone to becoming a performance bottleneck. Therefore we consider the situation that the relay node obtains a share of the capacity that is m times as large as the share that each source node receives. The main performance metrics considered are the workload at the relay node and the average overall flow transfer time, i.e., the average time required to transmit a flow from a source node via the relay node to the destination. Our aim is to find expressions for these performance metrics for a general resource-sharing ratio m, as well as a general flow-size distribution. The analysis consists of the following steps. First, for the special case of exponential flow sizes we analyze the source-node dynamics, as well as the workload at the relay node by a fluid-flow queueing model. Then we observe from extensive numerical experimentation over a broad set of parameter values that the distribution of the number of active source nodes is actually insensitive to the flow-size distribution. Using this remarkable (empirical) result as an approximation assumption, we obtain explicit expressions for both the mean workload at the relay node and the overall flow transfer time, both for general flow-size distributions.

Evaluation of qos provisioning capabilities of IEEE 802.11e wireless LANs

Several studies in literature have investigated the performance of the proposed ieee 802.11e standard for qos differentiation in wlan, but most of them are limited both with respect to the range of the parameter settings and the considered traffic scenarios.The aim of the present study is to systematically investigate (by simulations) the impact of each of the qos differentiation parameters, under more realistic traffic conditions. In particular, we investigate flow-level performance characteristics (e.g., file transfer times) in the situation that the number of active stations varies dynamically in time.