Stephan Heckmüller

Decreasing call blocking probability of Broadband TV services by a channel access control scheme

The current trend of network convergence has been best exemplified by the recent emergence of new services such as Broadband TV (BTV) offered by Telcos around the world. A very relevant research topic is to improve the quality of experience (QoE). This paper focuses on decreasing the user call blocking probability (CBP), which is one of the most important BTV QoE metrics. At first, we analyze a currently typical BTV network architecture. And then, a state-vector-based simulation model is proposed to evaluate the CBP (on a single link). After that, we present a class-based distribution model of channel watching probabilities, and based on this distribution model, we elaborate a general TV channel access control (TCAC) scheme in order to reduce the CBP. This scheme is flexible and can be applicable in many different scenarios. Finally, a case study is carried out, and it demonstrates the potential of this TCAC scheme to improve the BTV QoE by decreasing the CBP on a single link.

Decreasing the Call Blocking Probability of Broadband IPTV Services in Stationary and Peak-hour Scenarios

In the provisioning of broadband Internet Protocol TV (IPTV) services, call blocking probability (CBP) denotes the ratio of failed user requests, which is one of the most important metrics on IPTV quality of experience (QoE). This paper aims to evaluate and further to decrease the end-to-end (E2E) CBP of IPTV services in both stationary and peak-hour scenarios. At first, we analyze a currently typical xDSL based IPTV delivery network architecture and its simplification. Then, a recently developed IPTV user behavior model is briefly presented. Next, a state-vector-based simulation model is proposed to evaluate the E2E CBP in an entire IPTV delivery network with tree topology. The simulation model is then applied to both stationary and peak-hour scenarios, and thereafter, a comparative simulation study demonstrates significant differences between the E2E CBPs evaluated in the two different scenarios. After that, we elaborate an extended TV channel admission control (TCAC) scheme to be applied in an entire IPTV delivery network. Simulation experiments illustrate the potential of our TCAC scheme to enhance the IPTV QoE by relatively decreasing the E2E CBP significantly (up to 25%), in both stationary and peak-hour scenarios.

Using Load Transformations for the Specification of Arrival Processes in Simulation and Analysis

In this paper the innovative approach of load transformation is used to derive valid load models for secondary loads in computer networks, as they can be observed at lower-layer interfaces of protocol stacks. We apply the technique of load transformation onto a load represented by batch Markovian arrival process (BMAP) models and choose as concrete load transformation the practically relevant token bucket mechanism, which is widely used in current networks. We are able to determine closed-form analytical solutions to describe the transformed load. Investigations by means of simulations of the quality of our analytical models reflecting token-bucket-based load transformations underline the high level of accuracy and validity of the predicted secondary load. We also present a tool implementing different transformation functionalities which can be used for the specification of arrival processes for simulative and analytic performance evaluation.

Reconstructing arrival processes to discrete queueing systems by inverse load transformation

In this article we propose methods to estimate the parameters of arrival processes to G/D/1 queueing systems only based on observed departures from the system. The derived estimates can be used for performance evaluation and capacity planning in cases where the arrival process is not observable directly. Instead, only the departure process modified at the (last) server needs to be observed. Concerning the arrival process we begin by focusing on the normally distributed number of arrivals per interval and on autoregressive processes. Both classes can be used to model traffic in communication networks on links with a high degree of aggregation. In the case of autoregressive processes we apply the Tobit regression model in order to derive accurate estimates of all parameters of the arrival process. We then continue by generalizing the estimation procedures to correlated arrival processes by using the Buckley–James Estimator. The results are presented for the single G/D/1 queue but are then generalized to the more realistic scenario of sequences of queues with possibly varying bottleneck capacity. The latter especially permits the modeling of effects due to interfering cross traffic. We show how the derived estimates can be used for performance evaluation or capacity planning based on effective bandwidth theory. Finally, we demonstrate that the estimation procedures can be utilized within wireless networks by means of a detailed simulation model.

Load transformation of Markovian arrival processes: methods and tool support

Loads in computer networks, i.e. sequences of requests, are modified within the protocol hierarchy of multiple nodes during the transmission process via an interconnected network such as the Internet. This alteration can be seen as a transformation which tends to be of high complexity in todays computer networks. A comprehensive knowledge of the affecting load transformation(s) can be of great help for the prediction of loads as seen at interfaces within the communication network based on information concerning load at the application layer (primary load). In the past we successfully developed realistic, analytical models for important types of load transformations. In particular we proposed load transformations for primary loads which can be validly described by BMAPs (Batch Markovian Arrival Processes). For a deeper understanding and simplified usage of these analytical transformation models the availability of a tool which allows for a systematic application of the models is highly advantageous. Accordingly this contribution presents a tool which admits the generation of process descriptions of loads which are transformed, possibly multiple times, in a simple and intuitive manner.

Lasttransformation durch Rekonstruktion von Auftragslängen anhand von Paketdaten

Zusammenfassung Die Analyse von Verkehrsmessdaten erfolgt heutzutage meist auf der Basis von Statistiken über das Verkehrsaufkommen oder die Verkehrszusammensetzung sowie aufgrund von Eigenschaften einzelner Verkehrsströme oder Pakete. Außer Acht gelassen wird dabei häufig, dass der gemessene Verkehr das Ergebnis einer Interaktion oder eines Datenaustausches auf Anwendungsschicht ist. Dabei ist in vielen Fällen nicht die Analyse des Verkehrs von eigentlichem Interesse, sondern die Untersuchung des Zustands oder des Verhaltens der Anwendung. Durch Modellierung und Transformation von Lasten ist es möglich, den Zusammenhang zwischen Ankunftsprozessen auf der Anwendungsschicht und den resultierenden Ankunftsprozessen auf der Vermittlungsschicht zu beschreiben. Der vorliegende Beitrag beschäftigt sich mit der Umkehrung dieser Transformation und ihrer praktischen Umsetzung bei der Interpretation von Verkehrsmessungen. Ziel ist es, anhand von gemessenen Paketströmen auf Eigenschaften der ursprünglichen Auftragsströme auf Anwendungsschicht schließen zu können. Dazu werden insbesondere Methoden zur Rekonstruktion von Längeneigenschaften nach der Segmentierung bzw. Fragmentierung von Aufträgen vorgestellt und bewertet.

Bereitstelhmg von Dienstgüte für aggregierte Multimedia-Ströme in lokalen ‘Broadcast’-Netzen

Mit der zunehmenden Bedeutung von echtzeitkritischen Audio- und Videoapplikationen wachst die Wichtigkeit von Dienstgutegarantien in Rechnernetzen. Als eine Moglichkeit Dienstgute zu gewahrleisten, bietet sich die Ressourcenreservierung, wobei sich eine statische Reservierung als ineffizient herausgestellt hat. In der vorgestellten Arbeit wurde ein dynamisches Reservierungssystem auf seine Eignung fur aggregierte Audio- und Videolasten untersucht. Durch analytische Untersuchungen konnte zunachst gezeigt werden, dass sich mit zunehmender Aggregation die Abschatzung der zu erwartenden Last verbessert. Hierzu wurde der bei der Lastschatzung entstehende Fehler fur reale Lasten und verschiedene stochastische Beschreibungsmethoden untersucht. Die Untersuchung des Gesamtsystems zeigte weiterhin, dass sich die Effizienz in fast alien Fallen durch Aggregation erhohen lasst.