## Fachbereich Informatik

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- Formalization of Network Quality-of-Service Requirements (2007)
- The provision of network Quality-of-Service (network QoS) in wireless (ad-hoc) networks is a major challenge in the development of future communication systems. Before designing and implementing these systems, the network QoS requirements are to be specified. Existing approaches to the specification of network QoS requirements are mainly focused on specific domains or individual system layers. In this paper, we present a holistic, comprehensive formalization of network QoS requirements, across layers. QoS requirements are specified on each layer by defining QoS domain, consisting of QoS performance, reliability, and guarantee, and QoS scalability, with utility and cost functions. Furthermore, we derive preorders on multi-dimensional QoS domains, and present criteria to reduce these domains, leading to a manageable subset of QoS values that is sufficient for system design and implementation. We illustrate our approach by examples from the case study Wireless Video Transmission.

- Mapping of formal Network Quality-of-Service Requirements (2007)
- The provision of network Quality-of-Service (network QoS) in wireless (ad-hoc) networks is a major challenge in the development of future communication systems. Before designing and implementing these systems, the network QoS requirements are to be specified. Since QoS functionalities are integrated across layers and hence QoS specifications exist on different system layers, a QoS mapping technique is needed to translate the specifications into each other. In this paper, we formalize the relationship between layers. Based on a comprehensive and holistic formalization of network QoS requirements, we define two kinds of QoS mappings. QoS domain mappings associate QoS domains of two abstraction levels. QoS scalability mappings associate utility and cost functions of two abstraction levels. We illustrate our approach by examples from the case study Wireless Video Transmission.

- Ein fexibles, selbst rekonfigurierbares Rechnersystem zur Untersuchung von Selbstorganisation in verteilten Systemen (2006)
- Selbstorganisation ist eine interessante und vielversprechende Möglichkeit, um die Komplexität verteilter Systeme beherrschbar zu machen. In diesem Beitrag schlagen wir ein leistungsfähiges Rechnersystem auf Basis von rekonfigurierbarer Hardware vor, welches aufgrund seiner Flexibilität in vielen Bereichen eingesetzt werden kann. Es wird die geplante Systemarchitektur und Systemsoftware beschrieben und ein intelligentes, verteiltes Kamerasystem vorgestellt, welches wir als Anwendung mit dem vorgeschlagenen System realisieren wollen, um Selbstorganisation in verteilten Systemen näher zu untersuchen.

- On the Complexity of the Uncapacitated Single Allocation p-Hub Median Problem with Equal Weights (2007)
- The Super-Peer Selection Problem is an optimization problem in network topology construction. It may be cast as a special case of a Hub Location Problem, more exactly an Uncapacitated Single Allocation p-Hub Median Problem with equal weights. We show that this problem is still NP-hard by reduction from Max Clique.

- On Translation Validation for System Abstractions (2007)
- Abstraction is intensively used in the verification of large, complex or infinite-state systems. With abstractions getting more complex it is often difficult to see whether they are valid. However, for using abstraction in model checking it has to be ensured that properties are preserved. In this paper, we use a translation validation approach to verify property preservation of system abstractions. We formulate a correctness criterion based on simulation between concrete and abstract system for a property to be verified. For each distinct run of the abstraction procedure the correctness is verified in the theorem prover Isabelle/HOL. This technique is applied in the verification of embedded adaptive systems. This paper is an extended version a previously published work.

- On Certifying Code Generation (2007)
- Guaranteeing correctness of compilation is a ma jor precondition for correct software. Code generation can be one of the most error-prone tasks in a compiler. One way to achieve trusted compilation is certifying compilation. A certifying compiler generates for each run a proof that it has performed the compilation run correctly. The proof is checked in a separate theorem prover. If the theorem prover is content with the proof, one can be sure that the compiler produced correct code. This paper presents a certifying code generation phase for a compiler translating an intermediate language into assembler code. The time spent for checking the proofs is the bottleneck of certifying compilation. We exhibit an improved framework for certifying compilation and considerable advances to overcome this bottleneck. We compare our implementation featuring the Coq theorem prover to an older implementation. Our current implementation is feasible for medium to large sized programs.

- On Abstract Shapes of RNA (2008)
- As any RNA sequence can be folded in many different ways, there are lots of different possible secondary structures for a given sequence. Most computational prediction methods based on free energy minimization compute a number of suboptimal foldings and we have to identify the native structures among all these possible secondary structures. For this reason, much effort has been made to develop approaches for identifying good predictions of RNA secondary structure. Using the abstract shapes approach as introduced by Giegerich et al., each class of similar secondary structures is represented by one shape and the native structures can be found among the top shape representatives. In this article, we derive some interesting results answering enumeration problems for abstract shapes and secondary structures of RNA. We start by computing symptotical representations for the number of shape representations of length n. Our main goal is to find out how much the search space can be reduced by using the concept of abstract shapes. To reach this goal, we analyze the number of secondary structures and shapes compatible with an RNA sequence of length n under the assumption that base pairing is allowed between arbitrary pairs of bases analytically and compare their exponential growths. Additionally, we analyze the number of secondary structures compatible with an RNA sequence of length n under the assumptions that base pairing is allowed only between certain pairs of bases and that the structures meet some appropriate conditions. The exponential growth factors of the resulting asymptotics are compared to the corresponding experimentally obtained value as given by Giegerich et al.

- On the Expected Free Energy of RNA Molecules (2008)
- This article focuses on the analytical analysis of the free energy in a realistic model for RNA secondary structures. In fact, the free energy in a stochastic model derived from a database of small and large subunit ribosomal RNA (SSU and LSU rRNA) data is studied. A common thermody-namic model for computing the free energy of a given RNA secondary structure, as well as stochastic context-free grammars and generating functions are used to derive the desired results. These results include asymptotics for the expected free energy and for the corresponding variance of a random RNA secondary structure. The quality of our model is judged by comparing the derived results to the used database of SSU and LSU rRNA data. At the end of this article, it is discussed how our results could be used to help on identifying good predictions of RNA secondary structure.

- QoS Routing Protocols for Mobile Ad-hoc Networks - A Survey (2007)
- The provision of quality-of-service (QoS) on the network layer is a major challenge in communication networks. This applies particularly to mobile ad-hoc networks (MANETs) in the area of Ambient Intelligence (AmI), especially with the increasing use of delay and bandwidth sensitive applications. The focus of this survey lies on the classification and analysis of selected QoS routing protocols in the domain of mobile ad-hoc networks. Each protocol is briefly described and assessed, and the results are summarized in multiple tables.

- ChordNet: Protocol Specification and Analysis (2009)
- This work specifies and analyzes the ChordNet protocol. ChordNet is able to connect huge numbers of nodes in an efficient peer-to-peer network.