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We use a fluid flow model with reactive bounds to analyse a data processing center with energy-aware servers. The servers switch between four energy states depending on the level of the buffer content and on three reactive bounds. Every state consumes different amounts of energy. We use a regenerative approach to calculate the stationary distribution of the system and the expected energy consumption.

We study the blocking probability in a Markovian bufferless queuing system with a finite number of servers when the packet arrival process is a Markov-modulated Poisson process (MMPP), a superposition of a finite number N of independent MMPPs. We present an algorithm to compute the blocking probability in the system. The algorithm is exact if some related Quasi-birth-and-death (QBD) processes are reversible. We prove that the complexity of our algorithm scales linearly with N, whereas that of the standard solution does it exponentially. We illustrate the use of our algorithm in a bufferless multi-server system receiving long-range dependent (LRD) input traffic. This problem finds applications in the study of the blocking probability in bufferless optical packet switching (OPS) and optical burst switching (OBS) networks. We emulate LRD traffic with an MMPP, a superposition of N independent ON/OFF sources, which are also MMPPs. Our algorithm is in this case approximative since the reversibility condition is not fulfilled with the proposed MMPP. An extensive numerical analysis suggests that our algorithm can accurately approximate the blocking probability in the original queueing system with LRD input traffic. We provide an insight into the reason why our approximation is accurate.

The design of OBS networks that guarantee QoS provisioning for different classes of traffic is a major topic under current research. In this work we formulate a unified framework for studying QoS in OBS networks with a GMPLS-based control plane. We use this framework in order to investigate two problems. First, the configuration of the parameters of an aggregation strategy so that a given Forwarding Equivalency Class observes its corresponding QoS requirements. Second, we address the problem of planning a whole OBS network given a series of QoS constraints for each one of the Forwarding Equivalency Classes in the network. The presented QoS framework constitutes a valuable tool for studying QoS-related issues in OBS networks.

We consider systems which exhibit a mixture of smooth behavior and occasional jumps, controlled by continuous-time Markovian processes on a finite state space, and we call these fluid queues with jumps, thereby emphasizing the fact that they constitute a generalization of fluid queues. We characterize their stationary distribution in an algorithmically tractable way by constructing an auxiliary fluid queue without jumps. We give a few examples to illustrate the procedure and we analyze in detail a buffer model where bursts of high priority traffic interrupt the transmission of low priority files.

In our Web traffic model, http session requests occur according to a Poisson process and each request induces multiple transmissions of sub-documents, called objects. We use a transient MAP process to model the epochs at which the transmissions of objects associated to a given document are initiated. The lengths of transmission of the objects are modeled as i.i.d, random variables. We analyze the distribution of the total number of objects being in transmission at any given time and determine its auto-correlation function.

Recently, new services have emerged which utilize the Internet as a delivery mechanism for multimedia content. With the advent of broadband accesses, more users are willing to download large volume content from servers, such as video files of TV shows. While some popular video services (e.g. YouTube.com) or some broadcasting companies (e.g. ABC.com) use streaming data with Flash technology, some media distributors (e.g. iTunes) offer entire TV shows for download. In this study, we investigate the performance of the German site OnlineTVRecorder.com (OTR), which acts as an online video cassette recorder (VCR) where users can program their favorite shows over a web interface and download the recorded files from a server or its mirrors. These files are offered in different file formats and can consist of several hundred megabytes up to 1 GB or more depending on the length of the TV show as well as the encoding format. OTR can, thus, be seen as an example for a server-based content distribution system with large data files.

Recent measurement studies [8] have shown that peer-to-peer (P2P) file sharing applications are the major traffic source in the Internet. P2P applications, such as eDonkey, Kazaa, or BitTorrent, form overlay networks on the application layer and offer its peers to download and share their files with other peers in a highly distributed way. As a consequence, peers act simultaneously as both clients and servers. For a comprehensive survey of P2P technology, we refer to [7].