MPLS Traffic Engineering in OSPF Networks - a combined Approach

One of the main reasons for the development of MPLS was the need for flexible Traffic Engineering (TE) in IP networks ([8], [1]). Additionally a lot of IP service providers have found that Traffic Engineering of their networks can have a tactical and strategic value [2]. The first part of the paper introduces a linear optimization approach for Traffic Engineering in MPLS networks. Most remarkable on the presented approach is the additive objective function, which optimizes both the maximum utilization as well as the average utilization. In practice, most of the existing OSPF or IS-IS networks will have a transition phase between the pure IGP routing and the MPLS driven approach. Thus, we extend our optimization approach from a regular IGP network to a mixed IGP-MPLS environment. To avoid configuration complexity and state space explosion in MPLS devices, it could also make sense to start with a MPLS environment and take advantage of the configuration simplicity and the state space reduction capability of IGP protocols. In addition the paper includes a performance comparison between default configured OSPF, weight optimized OSPF and pure MPLS networks and show the benefit of OSPF optimization and MPLS Traffic Engineering. Based on this comparison we can offer some valuable clues to decide in favor of a local or global TE system

Leistungsbewertung Strukturierter Overlay Netze

Overlay networks establish logical connections between users on top of the physical network. While randomly connected overlay networks provide only a best effort service, a new generation of structured overlay systems based on Distributed Hash Tables (DHTs) was proposed by the research community. However, there is still a lack of understanding the performance of such DHTs. Additionally, those architectures are highly distributed and therefore appear as a black box to the operator. Yet an operator does not want to lose control over his system and needs to be able to continuously observe and examine its current state at runtime. This work addresses both problems and shows how the solutions can be combined into a more self-organizing overlay concept. At first, we evaluate the performance of structured overlay networks under different aspects and thereby illuminate in how far such architectures are able to support carrier-grade applications. Secondly, to enable operators to monitor and understand their deployed system in more detail, we introduce both active as well as passive methods to gather information about the current state of the overlay network.Unter einem Overlay Netz versteht man den Zusammenschluss mehrerer Komponenten zu einer logischen Topologie, die auf einer existierenden physikalischen Infrastruktur aufsetzt. Da zufällige Verbindungen zwischen den einzelnen Teilnehmern aber sehr ineffizient sind, wurden strukturierte Overlay Netze entworfen, bei denen die Beziehungen zwischen den einzelnen Teilnehmern fest vorgeschrieben sind. Solche strukturierten Mechanismen versprechen zwar ein großes Potential, dieses wurde aber noch nicht ausreichend untersucht bzw. wissenschaftlich nachgewiesen. In dieser Arbeit wird mit mathematischen Methoden und ereignisorientierter Simulation die Leistungsfähigkeit von strukturierten Overlay Netzen untersucht. Da diese stark von der aktuellen Situation im Overlay abhängt, entwickeln wir Methoden, mit denen sich sowohl passiv, als auch aktiv, wichtige Systemparameter zur Laufzeit abschätzen bzw. messen lassen. Zusammen führen die vorgeschlagenen Methoden zu selbstorganisierenden Mechanismen, die den aktuellen Zustand des Overlays überwachen, diesen bewerten und sich gegebenenfalls automatisch an die aktuellen Verhältnisse anpasse

Autonomically Improving the Security and Robustness of Structured P2P Overlays

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Estimating the size of a Chord ring

The Chord system is a decentralized peer-to-peer mechanism designed to store and search key/value pairs. The peers in a Chord overlay network are represented on a circle, whereas each peer has to maintain log 2(n) neighbors to guarantee a stable overlay structure in the presence of high churn rates. A single peer, however, does not know the current size n of the Chord ring. Choosing a constant value for the number of neighbors does not scale to large networks and involves unnecessary overhead in small networks. In this paper we therefore introduce an estimator for the current size of the Chord ring based on a peer’s neighbor- and fingerlists. To be able to rate the goodness of the estimator we show how to calculate the corresponding confidence intervals.

Source Models for Speech Traffic Revisited

uni-wuerzburg.de In this paper, we analyze output traces of different voice codecs and present analytical models to describe them by stochastic processes. Both the G.711 and the G.729.1 codec yield constant bit rate traffic, the G.723.1 as well as the iLBC codec use silence detection leading to an on/off process, and the GSM AMR and the iSAC codec produce variable bit rate (VBR) traffic. We apply all codecs to a large set of typical speech samples and provide quantitative models that are based on standard and modified on/off processes as well as memory Markov chains. Our models are in good accordance with the original traces as they capture the complementary cumulative distribution function (CCDF) of the on/off phase durations and the packet sizes, the autocorrelation function (ACF) of consecutive packet sizes, and the queuing properties of the original traces. In addition, they are rather simple which makes them especially useful for application in analytical and simulative studies. The durations of the on/off phases in our model are an order of magnitude larger than those found by previous work and to the best of our knowledge this is the first paper presenting a model for VBR voice.

Source Traffic Characterization for Thin Client Based Office Applications

A thin client is a small network computer which is used as a remote screen visualizing the output of software applications running on a central server. To provide a seamless service to thin client users the network connection between the client and the server must be dimensioned properly. In this paper we therefore characterize the traffic generated by different types of thin client users when working with popular office applications like Microsoft Word, Excel, or PowerPoint. We analyze the traffic patterns measured in our testbed environment and thus provide a basis for subsequent research studies as well as for administrators to estimate the amount and the characteristics of user generated traffic.