Bruno Müller-Clostermann

Modeling and analysis of communication systems based on computational methods for Markov chains

The authors describe a computational approach for modeling and analyzing modern communication systems based on numerical methods for Markov chains. Advanced direct and iterative procedures for the calculation of the stationary distribution of a homogeneous discrete- or continuous-time Markov chain with finite state space are presented. They are implemented in a convenient software tool called MACOM for interactive modeling and performance evaluation of communication systems. MACOM provides the user with a predefined markovian model world describing modern telecommunication networks with adaptive routing schemes and advanced congestion-control mechanisms. The versatility of these algorithms is illustrated by their application to Markovian queuing models derived from telecommunications networks. >

Performance engineering of SDL/MSC systems

The paper addresses issues related to the performance of systems specified with SDL and MSC and describes how performance aspects can be integrated with the SDL/MSC method. We identify the aspects that are relevant to performance evaluation and performance tuning. Afterwards we introduce basic performance modelling techniques and survey approaches that integrate performance evaluation into the context of SDL and MSC.

Performance Evaluation of SDL Systems Adjunct by Queueing Models

Designing complex systems requires formal methods supporting validation and performance evaluation before implementation. Here we introduce a method based on the adjunction of queueing stations to SDL-specifications. The resulting integrated model combines functional and non-functional properties, in particular it is assessable by quantitative evaluation techniques. As a consequence SDL-specifications may serve as a basis for performance evaluations of systems during the design phase. Here we present the basic concepts of this approach, propose a syntax for attaching performance submodels to SDL-specifications and sketch a tool that employs our approach. The scope of the proposed method is illustrated by an example from the telecommunication area.

The QUEST-approach for the performance evaluation of SDL-systems

Designing complex systems requires formal methods supporting validation and performance evaluation before implementation. We present an approach based on the adjunction of queueing stations and traffic sources to SDL-systems yielding integrated models assessable by quantitative evaluation. As a consequence SDL-specifications may be used as a basis for performance evaluations of systems during the design phase. Apart from the underlying concept we introduce the language QSDL (Queuing SDL), and the QUEST tool that implement our approach. As an example we show how the performance of an SDL specified communication protocol may be investigated by employing QSDL and QUEST.

MACOM - A TOOL FOR THE MARKOVIAN ANALYSIS OF COMMUNICATION SYSTEMS

MACOM is a tool for the performance analysis of communication systems. Based on queueing network concepts the MACOM model world additionally comprises features which are necessary to describe and investigate phenomena typically arising in communication systems. The graphical specifications of a model is transformed automatically into a Markov chain which is analyzed by numerical methods. Both stationary and transient performance measures can be calculated. Models with up to 100000 states can be solved. The numerical procedures include direct as well as iterative techniques. Iterations can be speeded up by relaxation or aggregation/disaggregation techniques. In addition to the graphical user interface, MACOM also supports the management of models, the specification of experiments and the representation of results. The implementation takes full advantage of modern workstation technology yielding an easy to use and very efficient tool. The versatility of the tool is demonstrated by its application to two models derived from teletraffic theory.

An approximate product form for a class of degradable queueing networks

Abstract An approximate product form for a class of degradable queueing networks (DQNs) is presented. DQNs emerge from a synthesis of the well-known separable queueing networks (BCMP networks) and the classical machine-repair-man model. Under the assumption that failure and repair events which change the level of performance are much less frequent compared with the service completions of tasks moving through the network, the presented product from approximates the exact probability distribution very closely. Because DQNs are nearcompletely decomposable, the error of approximation depends on the degree of coupling between the different modes of degraded performance. In accordance with the theory of nearcomplete decomposability, a numerical example shows that the approximation error is proportional to the degree of coupling.

A simulation framework for the evaluation of scenarios and algorithms for common radio resource management

We present a simulation framework based on a systematic view on Common Radio Resource Management (CRRM). It enables a cost-benefit investigation of different CRRM algorithms and architectures. Different scenarios, centralized as well as decentralized ones, can be clearly defined based on five standard components, namely the radio access system, the environment, the user equipment, the CRRM information manager, and the CRRM decider. The costs and time consumption of CRRM operations are taken into account via chargeable messages. The clarity of the model enables an efficient investigation of CRRM algorithms based on optimization theory, game theory, physical models and other methods. The resulting framework has been implemented as a hybrid simulation model using OMNeT++. A convenient and straightforward integration of different wireless network technologies and user service demands is also supported; models for UMTS and GSM/EGPRS are already integrated. The scope of the proposed framework is demonstrated by the evaluation of realistic scenarios.

Applying techniques and tools for the performance engineering of SDL systems

Abstract The integration of performance evaluation techniques into the SDL method is an important task. In particular in the area of telecommunications and distributed systems where product families have to be maintained for many years, performance should be considered from the very beginning of system design. This paper demonstrates how performance engineering can be successfully applied. Firstly, an SDL specification of TCP/IP is used to derive a performance model that includes the original SDL system as well as additional constructs describing the consumption of time and resources. Different implementation variants have been evaluated in experimental scenarios. Secondly, the application of a specification-driven monitoring technique to the same SDL specification of TCP/IP is described. The case study shows how the functional and temporal behaviour of an implementation derived from an SDL specification can be analysed and improved by monitoring the running system. The two approaches, modelling and monitoring, are supplementary to each other. This paper provides arguments that the systematic application of specification-driven performance engineering will result in major savings of time and money in later development phases and for later system releases.

Synchronized Queueing Networks: Concepts, Examples and Evaluation Techniques

Synchronized queueing networks (SQN) are a new type of models, which allow the analysis of queueing systems subject to synchronization constraints. SQN-models originate from traditional queueing networks which have been enlarged by a new type of nodes. These nodes, called counters, can be viewed as synchronization primitives, which are used by the tasks moving through the network. Due to this combination of synchronization and queueing features SQN-models are a new approach towards the unified representation of areas which have been studied separately for a long time.

A hybrid simulation framework for the evaluation of common radio resource management scenarios

We present a hybrid modeling framework with interacting simulative and analytic submodels for the efficient evaluation of common radio resource management (CRRM). It enables a cost–benefit investigation of different CRRM algorithms and architectures. Centralized as well as decentralized scenarios can be clearly defined by five standard components, namely the radio access system, the environment, the user equipment, the CRRM information manager, and the CRRM decider. The costs and time consumption of CRRM operations are taken into account via chargeable messages. The clarity of the model enables an efficient investigation of CRRM algorithms based on optimization theory, game theory, physical models, and other methods. The resulting framework has been implemented as a hybrid simulation model using the discrete event simulation system OMNeT++. A convenient and straightforward integration of different wireless network technologies and user service demands is also supported; models for the universal mobile telecommunications system (UMTS) and the global system for mobile communications/enhanced general packet radio service (GSM/EGPRS) are already integrated. The scope of the proposed framework is demonstrated by the evaluation of realistic scenarios.