Thomas Renger

Fair queueing wireless ATM MAC protocols

Wireless ATM networks, which are currently under investigation, promise to support future multimedia applications. The medium access control (MAC) protocol of such systems plays a key role in providing differentiated quality of service (QoS). A variety of proposed MAC protocols use a centrally controlled flexible allocation of time slots. In order to support differentiated QoS the base station scheduler must allow a fair sharing of the available resources depending on the requested QoS. Moreover it should be insensitive against partially outdated status information of the mobile station queues. Our proposed scheme is able to support these properties and is simple to implement.

Performance Modelling of an Adaptive CAC Strategy for ATM Networks

Abstract The Asynchronous Transfer Mode (ATM) requires adequate traffic control schemes to meet the quality of service (QOS) requirements of the evolving broadband services and applications. Connection admission control (CAC) plays a key role within this traffic control framework, because it prevents a QOS degradation of existing connections by a blocking of excessive connection requests. This paper proposes an adaptive CAC strategy which is based on a monitoring of the network load and the resulting cell loss performance. A hybrid approach, combining simulation and analysis, will be developed for the performance modelling and evaluation of this concept. A comprehensive performance study taking into account various traffic load scenarios and parameter settings validates this CAC and monitoring scheme.

Simulative Comparison of the Waiting Time Distributions in Cyclic Polling Systems with Different Service Strategies

Abstract Single server polling systems often serve as models for parts of communication systems, e.g., multiplexers or Local Area Networks with a single token passing medium access protocol. Simple polling systems can be tracted analytically while certain service disciplines and many asymmetric systems can only be analyzed via simulation. Simulations also allow to obtain the distributions and quantiles of the waiting times and other characteristic values, whereas most analyses only provide the first and second moments. This paper first describes the simulated polling systems. Then it introduces the principle of measurement of distributions and quantiles in a simulation and concludes with results comparing the waiting time distributions and quantiles in systems with different service strategies and asymmetric load. Furthermore, formulae for the throughput of symmetric systems under overload are derived.

Switching block studies, network performance evaluation and traffic engineering for ATM

This paper summarizes the work done in RACE project 1022 “Technology for ATD” on performance studies of ATM switching block architectures and the studies on network performance within a small ATM network, the so called RACE ATD Technology Testbed (RATT). The aim of the studies was to investigate the behaviour of a typical ATM network under nominal load. By using the tromboning links in the RATT we were also able to study long distance connections even in the limited size of the RATT network. Special attention has been given to define a traffic scenario which can also be set up for the planned experiments. The goal of the planned experiments is to validate the performance results predicted in our studies.

Management von ATM-Netzen

Dr.-Ing. Hans Kröner wurde 1995 an der Universität Stuttgart promoviert. Von 1987 bis 1989 war er am AEG-Forschungslabor in Ulm mit dem Entwurf und der Implementierung von kohärenten optischen Kommunikationssystemen befaßt, und war anschließend als wissenschaftlicher Mitarbeiter am Institut für Nachrichtenvermittlung und Datenverarbeitung der Universität Stuttgart tätig. Seit 1994 ist er bei Leuze electronic in Owen beschäftigt, wo er an der Entwicklung von drahtlosen optischen Kommunikationssystemen arbeitet.

Impact of wireless access on traffic management in ATM networks

Traffic management plays an important role in providing differentiated quality of service and supporting the integration of a variety of broadband services within a common ATM network. Wireless ATM access networks are under definition in standards bodies as well as subject of various research activities and first field trials. The nature of the wireless medium requires new protocols that are able to cope with multiple access, error prone wireless channels, and user mobility. When attaching a wireless ATM network to a fixed ATM network proper interaction of traffic and resource management functions throughout both networks is necessary to achieve stringent QoS objectives. In this paper the relation between mobile specific protocols and traffic management functions as well as their mutual impacts are discussed. Three key areas to enable seamless traffic management integration are identified and possible solutions are outlined.

Experimental validation of an ATM traffic control framework in the EXPLOIT testbed

This paper deals with the experimental investigation of a preventive traffic control framework for ATM networks as implemented in the EXPLOIT Testbed. This framework comprises a Usage Parameter Control (UPC) function and a Connection Admission Control (CAC) function. The obtained measurement results are complemented and compared with simulation studies and analytical results. For several On/Off traffic types it is shown that the implemented UPC function enforces both the Peak Cell Rate (PCR) and the Sustainable Cell Rate (SCR) simultaneously. By measuring the cell loss ratio as a function of the number of multiplexed sources, admission boundaries for a given network performance objective can be found and compared with the implemented CAC function based on the convolution algorithm. It appears that network performance objectives can be guaranteed, while exploiting most of the possible multiplexing gain in a network with small buffers like the EXPLOIT Testbed. Finally, it is shown that the two co-operating functions constitute a traffic control framework which is robust against traffic contract violations as well as worst case traffic utilising the contracted UPC function tolerances maximally at both the cell level and the burst level.