Ein Jahr auf Oesel : Beiträge zum System Ludendorff

http://www.ester.ee/record=b1456550*es

Performance of middleware based architectures: a quantitative approach

Most of today's E-business applications on the Internet are built upon middleware-based architectures. For service providers offering these applications performance is essential: less-than-acceptable performance levels may lead to customer churn, and thus loss of revenue, and as such directly affect the company's competitive edge. This raises the critical need for service providers to be able to predict and control performance. In this paper we demonstrate the usefulness of a quantitative modeling approach to analyze and predict the performance of middleware-based applications. To this end, we develop a quantitative performance model of middleware architectures based on CORBA, the de-facto standard for object middleware. A particular feature of the model is that it explicitly takes into account priority mechanisms that handle the access to the processors among the different threads. To validate the model we have compared performance predictions from simulation runs with results from lab experiments for a variety of parameter settings. The results show that (1) the inclusion of priority mechanisms in the model leads to a significant improvement of the accuracy of the performance predictions based on the model, and (2) a quantitative modeling approach to assess and predict the performance of middleware-based applications is very promising

A Global Reference Model of the DNS

The Domain Name System (DNS) is a crucial component of today’s Internet. At this point in time the DNS is facing major changes such as the introduction of DNSSEC and Internationalized Domain Name extensions (IDNs), the adoption of IPv6 and the upcoming extension of new generic Top-Level Domains. These changes can have impact on the behaviour of the DNS. In this paper we present a first global DNS reference model with the aim to predict the DNS traffic behaviour under specific conditions. In fact, this quantitative model is intended to be used for analyzing what-if scenarios. For example, how will DNS query rates at the recursive and authoritative name servers increase in case DNSSEC validation errors lead to sending more Servfail responses towards DNS clients? The DNS reference model takes into account all relevant components present in the DNS architecture. To characterize the system variables describing the query behaviour at each of these independent system components, we statistically analyze real world data from recursive resolvers. In addition, we use experimental results that characterize DNS client behaviour and data from the literature to characterize the behaviour of authoritative name servers. In order to validate our reference model we compare the model predictions to the real world data. The validation results show that the model predictions are rather accurate. At the end of the paper we present a specific what-if scenario to demonstrate the applicability of the model