Arne Ludwig

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Networks are critical for the security of many computer systems. However, their complex and asynchronous nature often renders it difficult to formally reason about network behavior. Accordingly, it is challenging to provide correctness guarantees, especially during network updates. This paper studies how to update networks while maintaining a most basic(More)
We consider the problem of updating arbitrary routes in a software-defined network in a (transiently) loop-free manner. We are interested in fast network updates, i.e., in schedules which minimize the number of interactions (i.e., rounds) between the controller and the network nodes. We first prove that this problem is difficult in general: The problem of(More)
—The virtualization trend in today's Internet decou-ples services from the constraints of the underlying physical infrastructure. This decoupling has the potential to facilitate more flexible and efficient resource allocations: the service can be realized at any place in the substrate network which fulfills the service specification requirements. This paper(More)
Computer networks have become a critical infrastructure. Especially in shared environments such as datacenters it is important that a correct, consistent and secure network operation is guaranteed at any time, even during routing policy updates. In particular, at no point in time should it be possible for packets to bypass security critical waypoints~(such(More)
The software-defined networking paradigm introduces interesting opportunities to operate networks in a more flexible, optimized, yet formally verifiable manner. Despite the logically centralized control, however, a Software-Defined Network (SDN) is still a distributed system, with inherent delays between the switches and the controller. Especially the(More)
—The virtualization trend in today's Internet decou-ples services from the constraints of the underlying physical infrastructure. This decoupling facilitates more flexible and efficient resource allocations: the service can be realized at any place in the substrate network which fulfills the service specification requirements. This paper studies such(More)
Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by(More)
—Cloud computing heralded an era where resources can be scaled up and down elastically and in an on-line manner. This paper initiates the study of cost-effective cloud resource allocation algorithms under price discounts, using a competitive analysis approach. We show that for a single resource, the online resource renting problem can be seen as a(More)
Developing a quantum photonics network requires a source of very-high-fidelity single photons. An outstanding challenge is to produce a transform-limited single-photon emitter to guarantee that single photons emitted far apart in the time domain are truly indistinguishable. This is particularly difficult in the solid-state as the complex environment is the(More)