Contributions published at Communication Systems Group (Burkhard Stiller)

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A method for configuring a plurality of service equipment elements located along a data path connecting two elements in a network, said network comprising a plurality of administration servers, each administration server being responsible for configuring a respectively different plurality of service equipment elements, said method comprising: sending a trial-balloon message along said data path, said trial-balloon message when being received by a service equipment element in said data path causing said service equipment element to contact its corresponding administration server and said trial-balloon message further being forwarded by said service equipment element by which it was received to the next service equipment element in said data path; said administration elements in response to being contacted by their respective service equipment elements configuring said service equipment elements in accordance with context information received by said administration servers.

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Publish/Subscribe is a messaging paradigm that supports dynamic many-to-many communication in a loosely coupled distributed environment. MQTT is a topic-based publish/subscribe protocol. Information producers publish topic related events to a message broker, and information consumers subscribe to some of these topics. The message broker is responsable to store the events and forward them to the information consumers. IBM implemented a publish/subscribe infrastructure consisting of a small footprint message broker and messaging clients, using the MQTT protocol. The flexible design of this implementation allows to dynamically configure protocol stacks consisting of modules that offer different services, such as reliability or segmentation and reassembly. The MQTT protocol has been designed without security in mind, but the need of a secured communication between the messaging clients and the message broker evolved. In this thesis, the design and prototypical implementation of encryption and access control modules is introduced, which are pluggable into the protocol stacks.

In the last few years wireless local area networks became more and more popular, meanwhile enabling access to the Internet and to private or company-internal networks all over the place. With the increasing amount of users sharing one and the same medium, running demanding applications with the need of exchanging larger and larger quantities of data, the necessity growed to provide an information interchange guaranteeing a high security and a satisfiable quality of service (QoS). Latter property asks among other things for a MAC protocol enabling an efficient and fair medium access for competing network participants. In this thesis different MAC schemes are investigated under the aspect of QoS, examining their efficiency and showing up their strengths and weaknesses. Further those key elements of a MAC mechanism are analyzed which influence the QoS and based on these results a new MAC classification scheme is introduced, the universal cube classification (UCC). Finally some propositions are presented, which could be implemented in a new protocol to provide a satisfying QoS. The intention of this thesis is also to help the reader get familiarized with existing MAC protocols, allow a deeper understanding of the general functionality of the medium access mechanisms and enable a certain acquirement of sensitivity in the context of recognizing MAC scheme immanent problems.

This diploma thesis aims at the design and implementation of a prototypical charging component for mobile grid services. Charging is used, to calculate the bills for customers who used services. In mobile grid services, many parameters measured, like for example the bandwidth usage, are stored in a database, which is the basis to calculate the charge. Tariff models are designed, to define how every parameter from the accounting database is charged. In mobile grid services, the charging component has to be flexible to adapt to new resource parameters. Discounts and negative prices are also necessary, to support charging services provided by the customers and to give discounts if the service quality was not sufficient. The calculations are managed completely by the tariff definition database what allows the charging component to be adaptable to changes of the measured data in the database. The implementation of the charging component is based on the requirements for mobile grid services, it is flexible, it supports charging for hierarchical sessions and discount calculations. The implementation has been performed in Java and the tariff definitions are stored as XML files. At the end of this thesis, the prototypical charging component is tested and evaluated.

Due to the advent of Web service technologies, service-oriented Architectures (SOAs) have regained importance in both research and industry in the recent past. But while service design and implementation makes is evolving at good pace, there is still a lack of methodological support for decision makers in companies. A surprising fact if one considers that they are key-persons when it comes to the initiation or denial of a SOA. The goal of this diploma thesis is assessing on a strategic level how well an IT environment is able to support a SOA. For it to be a success, a model must be created, implemented, tested, and discussed that allows for this assessment. Since the thesis is parented by the Department for Systems Architecture of the industry partner Kühne + Nagel, the implementation must be feasible for this company and any data required for the testing may be taken from its actual IT environment. However, the model is required be generally applicable. To achieve the above-stated goals, this diploma thesis introduces the Soability model, which consists of a set of measurement instructions and equations, an evaluation methodology, and a process that shows how to fill the model with data and how to interpret it. A first implementation of Soability has been done in Telelogic System Architect, which is an Enterprise Architecture tool used within Kühne + Nagel. Soability uses questionnaires to gather domain expert knowledge about applications, infrastructure, organisation units, and exogenous influences. The rules of measurement and the equations are then applied to condense the data before it may be used by the Soability evaluation methodology upport strategic decision making. For the IT environment of Kühne + Nagel, the evaluation reveals that the company is not ready for a SOA from an infrastructure and organisational point of view. In its application landscape, however, functionalities could be identified that would represent valuable services in a SOA. However, some of these functionalities are very demanding from a technical point of view, which is why their enabling should be postponed until more experience in the design and implementation of services has been gained. There was also functionality identified that will hardly ever make sense a SOA. The approach proposed by this diploma thesis is lightweight in the sense that it allows for the fast and low cost evaluation of a broad parts of an IT environment so that decisions relevant to SOA can be made with a big picture in mind. Therewith Soability addresses the lack of methodological support for decision makers in companies. However, building a model for a complex domain like SOA requires many assumptions and simplifications to be made. Due to the novelty of the approach, there was almost no experimental data to be found in the literature on which the measurement instructions could rely. Hence, first proposal have been made and argued for by this diploma thesis, but they need to be substantiated or refined by future experiments. Since the Soability model is designed for extensibility it embraces such refinement on several levels.