The pseudo-self-similar traffic model: application and validation

Since the early 1990¿s, a variety of studies has shown that network traffic, both for local- and wide-area networks, has self-similar properties. This led to new approaches in network traffic modelling because most traditional traffic approaches result in the underestimation of performance measures of interest. Instead of developing completely new traffic models, a number of researchers have proposed to adapt traditional traffic modelling approaches to incorporate aspects of self-similarity. The motivation for doing so is the hope to be able to reuse techniques and tools that have been developed in the past and with which experience has been gained. One such approach for a traffic model that incorporates aspects of self-similarity is the so-called pseudo self-similar traffic model. This model is appealing, as it is easy to understand and easily embedded in Markovian performance evaluation studies. In applying this model in a number of cases, we have perceived various problems which we initially thought were particular to these specific cases. However, we recently have been able to show that these problems are fundamental to the pseudo self-similar traffic model. In this paper we review the pseudo self-similar traffic model and discuss its fundamental shortcomings. As far as we know, this is the first paper that discusses these shortcomings formally. We also report on ongoing work to overcome some of these problems

Infrastructure Networks in Central Europe and EU Enlargement

This paper draws attention to the spatial dimension of sustainability, where spatial self-defence is an important part of control over local assets that have to be preserved. It should be added that well-structured local networks constitute an important requirement for effective spatial self-defence. In the existing European Union, where the national infrastructure networks have been relatively developed, the formation of a single market called first for concentration of efforts on the overlapping or inter-regional backbone level of networks. In the area now acceding to the EU, it is important to note that this programme cannot be applied with unchanged priorities in regions still lacking appropriate local networks, where great attention needs devoting to internal networks. In the integration process, the transition countries have to understand the importance of a multilayered network and pay equal attention to every layer of the transport network. The other issue that has been criticized is the structure of the backbone network. While the development of the trans-European networks in western Europe was governed by internal considerations – the intention of connecting national networks, the starting point in the eastern half of Europe was the external consideration of extending Trans-European Networks (TEN) to the transition countries. Even the backbone elements of the Transport Infrastructure Needs Assessment (TINA) network, which enjoy priority today, still reflect this approach. The danger remains that the additions expressing the needs of candidate countries will become lost in the process. Turning to Hungary, the paper gives a brief account of how an overcentralized transport network developed over the last century and the process by which a new road-transport layer was being created. The country today faces a similar process, as the new layer is developed into the new structure. Nonetheless, the existing and emerging structure is mistaken. An effort to reorient the conception is being made by defining the networkdevelopment criteria for a long-term inter-regional road network offering a structure separate from the traditional network of trunk roads, by developing an open grid that ensures minimum disturbance from transit traffic

Performance evaluation of an enhanced distributed channel access protocol under heterogeneous traffic

Recently there have been considerable interests focusing on the performance evaluation of IEEE 802.11e Medium Access Control (MAC) protocols, which were proposed for supporting Quality of Services (QoS) in Wireless Local Area Networks (WLANs). Different from most existing work, this study has conducted comprehensive performance evaluation and analysis of the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol in the presence of heterogeneous network traffic including non-bursty Poisson, bursty ON/OFF, and self-similar traffic generated by wireless multimedia applications. The performance results on throughput, access delay and medium utilization have demonstrated that the protocol is able to achieve satisfying QoS differentiation for heterogeneous multimedia traffic. On the other hand the results have showed that IEEE 802.11e EDCA suffering from the low medium utilization due to the overhead generated by transmission collisions and back-off processes. 1

Role of Transport Networks in Supporting the Spatial Dimension of Sustainability

The main messages of the contribution in five points are the following: (1) Besides temporal relations of sustainability, we also have to underline the importance of the spatial context of it. (2) It is the internal network of a region that helps to preserve the structure and the existing connections within the region. (3) The proper external connections of the region are also very important, but their positive effects can reach the given region only if the internal transmitter elements are existing and the region is able to adapt these effects. (4) There is no such rule that the more transit (through traffic) would be better. The transport that exceeds the region’s adaptive capacity is harmful for the local economy, society and environment alike. (5) A newer and also important function of the transport management is to bypass those areas where the extensive traffic would be harmful

Performance analysis of MANET routing protocols in the presence of self-similar traffic

A number of measurement studies have convincingly demonstrated that network traffic can exhibit a noticeable self-similar nature, which has a considerable impact on queuing performance. However, many routing protocols developed for MANETs over the past few years have been primarily designed and analyzed under the assumptions of either CBR or Poisson traffic models, which are inherently unable to capture traffic self-similarity. It is crucial to re-examine the performance properties of MANETs in the context of more realistic traffic models before practical implementation show their potential performance limitations. In an effort towards this end, this paper evaluates the performance of three well-known and widely investigated MANET routing protocols, notably DSR, AODV and OLSR, in the presence of the bursty self-similar traffic. Different performance aspects are investigated including, delivery ratio, routing overhead, throughput and end-to-end delay. Our simulation results indicate that DSR routing protocol performs well with bursty traffic models compared to AODV and OLSR in terms of delivery ratio, throughput and end-to-end delay. On the other hand, OLSR performed poorly in the presence of self-similar traffic at high mobility especially in terms of data packet delivery ratio, routing overhead and delay. As for AODV routing protocol, the results show an average performance, yet a remarkably low and stable end-to-end delay

On the nature and impact of self-similarity in real-time systems

In real-time systems with highly variable task execution times simplistic task models are insufficient to accurately model and to analyze the system. Variability can be tackled using distributions rather than a single value, but the proper charac- terization depends on the degree of variability. Self-similarity is one of the deep- est kinds of variability. It characterizes the fact that a workload is not only highly variable, but it is also bursty on many time-scales. This paper identifies in which situations this source of indeterminism can appear in a real-time system: the com- bination of variability in task inter-arrival times and execution times. Although self- similarity is not a claim for all systems with variable execution times, it is not unusual in some applications with real-time requirements, like video processing, networking and gaming. The paper shows how to properly model and to analyze self-similar task sets and how improper modeling can mask deadline misses. 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