Dietmar Weber

Traffic models for large ISDN-PABX's

Abstract A traffic model is a collection of data characterizing the traffic to be handled by an exchange. This paper deals with a traffic model for large-scale ISDN-PABXs. It concerns the telephone, teletex, facsimile, interactive videotex and data dialog services. Based on measurement results or - if none were available - on general reflections and assumptions, these ISDN services are described by their call mixes and by the mean holding times of the terminals involved. The volume of ISDN traffic anticipated for the future in the Federal Republic of Germany is taken as an example so as to extend the traffic model shown to an overall traffic model for complete ISDN-PABXs. In this way the model helps to formulate traffic design 7objectives for new ISDN-PABXs in the F.R. Germany.

Admission control for realtime traffic: improving performance of mobile networks by operating on actual throughput

The deployment of realtime services will be important for the economic success of the 3GPP packet domain. Within this paper, a simple approach for admission control of realtime traffic is introduced, which makes its decisions on the basis of actual throughput. We present a fluid flow model, which allows us to calculate the key performance indicators regarding packet loss, session request denial and plannable throughput. The formalism can be applied with good numerical accuracy and performance within the large range of traffic aggregation, which is characteristic of a mobile network. As an example, we apply the formalism to the traffic characteristics of voice over IP and push to talk and show in principle that our approach is promising in particular for push to talk with its high percentage of idle times.

Overload Control in ISDN PABXs

Abstract Overload control mechanisms are integral part of modern telecommunications switching systems or networks. The effectiveness of such mechanisms depends strongly on the statistical structure of the event stream generated by the periphery. In the paper, so-called load profiles for typical call types in ISDN-PABXs are analyzed. From this analysis and from the typical environment parameters under which ISDN-PABXs are operating, it can be seen that the processor load indicator is an appropriate choice for controlling overload situations. The paper gives simulation results for quota and non-quota based call rejection algorithms and checks its effectiveness in terms of general quality criteria including those proposed by CCITT.

Correlated Arrival Processes in Switching Systems and some Applications

Abstract Due to the specific interface between user and system, correlated arrival processes are the natural input stream offered to switching systems. As various publications in the past have shown, these correlations cannot be neglected when performance characteristics have to be computed. In our paper we derive - motivated by the description of so-called load profiles in switching systems - a second moment calculation for special correlated input streams and their superpositions. These type of processes can be used for better accuracy in approximations of system characteristics in switching systems. An example in the area of overload control performance is given.

Techniken zur Leistungsanalyse von Kommunikationssystemen — Kurzfassung —

Der vorliegende Aufsatz beschreibt Techniken zur Leistungsanalyse von Kommunikationssystemen, wie sie bei der Hicom®-Systemfamilie erfolgreich eingesetzt werden. Ein wesentliches Kriterium fur die Beurteilung der Leistungsfahigkeit eines derartigen Systems sind die sogenannten Reaktionszeiten. Hierbei handelt es sich um Zeiten, die das System braucht, um auf gewisse Anreize von ausen in vorgegebener Art und Weise zu reagieren. Zur Bestimmung dieser Zeiten haben wir Simulationsmodelle fUr die wesentlichen Systemkomponenten (Teilnehmerverhalten, Kommunikationsrechner) entwik-kelt. Diese Simulationsmodelle sind in der Simulationssprache GPSS (General Purpose Simulation System) geschrieben. Sie sind abgestimmt auf eine spezielle Mesmethodik zur Bestimmung von Programmlaufzeiten in Kommunikationsrechnern.