In this paper we present an integrated packet/flow level modelling approach for analysing flow throughputs and transfer times in 802.11 s. The packet level model captures the statistical characteristics of the transmission of individual packets at the layer, while the flow level model takes into account the system dynamics due to the initiation and completion of data flow transfers. The latter model is a processor sharing type of queueing model reflecting the 802.11 design principle of distributing the transmission capacity fairly among the active flows. The resulting 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).

Abstract-In this paper we consider the general problem of resource provisioning within cloud computing. We analyze the problem of how to allocate resources to different clients such that the service level agreements (SLAs) for all of these clients are met. A model with multiple service request classes generated by different clients is proposed to evaluate the performance of a cloud computing center when multiple SLAs are negotiated between the service provider and its customers. For each class, the SLA is specified by the request rejection probabilities of the clients in that class. The proposed solution supports cloud service providers in the decision making about 1) defining realistic SLAs, 2) the dimensioning of data centers, 3) whether to accept new clients, and 4) the amount of resources to be reserved for high priority clients. We illustrate the potential of the solution by a number of experiments conducted for a large and therefore realistic number of resources.

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We study a telecommunications network integrating prioritized stream calls and delay tolerant elastic calls that are served with the remaining (varying) service capacity according to a processor sharing discipline. The remarkable observation is presented and analytically supported that the expected elastic call holding time is decreasing in the variability of the elastic call size distribution. As a consequence, network planning guidelines or admission control schemes that are developed based on deterministic or lightly variable elastic call sizes are likely to be conservative and inefficient, given the commonly acknowledged property of e.g. www documents to be heavy tailed. Application areas of the model and results include fixed ip or atm networks and mobile cellular gsm/gprs and umts networks.