Klaus-Tycho Foerster

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We study consistent migration of flows, with special focus on software defined networks. Given a current and a desired network flow configuration, we give the first polynomial-time algorithm to decide if a congestion-free migration is possible. However, if all flows must be integer or are unsplittable, this is NP-hard to decide. A similar problem is(More)
We consider the problem of finding efficient methods to update forwarding rules in Software Defined Networks (SDNs). While the original and updated set of rules might both be consistent, disseminating the rule updates is an inherently asynchronous process, resulting in potentially inconsistent states. We highlight the inherent trade-off between the strength(More)
Computer networks have become a critical infrastructure. Designing dependable computer networks however is challenging, as such networks should not only meet strict requirements in terms of correctness, availability, and performance, but they should also be flexible enough to support fast updates, e.g., due to a change in the security policy, an increasing(More)
Updating network flows in a real-world setting is a nascent research area, especially with the recent rise of Software Defined Networks. While augmenting <i>s-t</i> flows of a single commodity is a well-understood concept, we study updating flows in a multi-commodity setting: Given a directed network with flows of different commodities, how can the capacity(More)
We study complexity and algorithms for network updates in the setting of Software Defined Networks. Our focus lies on consistent updates for the case of updating forwarding rules in a loop free manner and the migration of flows without congestion. In both cases, we study how the power of two affects the respective problem setting. For loop freedom, we show(More)
We study deterministic leader election in multi-hop radio networks in the beeping model. More specifically, we address explicit leader election: One node is elected as the leader, the other nodes know its identifier, and the algorithm terminates at some point with the network being quiescent. No initial knowledge of the network is assumed, i.e., nodes know(More)
Because diet is a key issue in the treatment of diabetes mellitus, it is assumed that these patients are prone to eating disorders. In a multicenter study, we have therefore assessed the prevalence of eating disorders in 662 patients with insulin dependent diabetes mellitus (IDDM) (n = 340) and non-insulin-dependent diabetes mellitus (NIDDM) (n = 322). A(More)
We study the problem of exploring all nodes of an unknown directed graph. A searcher has to construct a tour that visits all nodes, but only has information about the parts of the graph it already visited. The goal is to minimize the cost of such a tour. In this paper, we present upper and lower bounds for both the deterministic and the randomized online(More)
In this work we study local checkability of network properties like <i>s-t</i> reachability, or whether the network is acyclic or contains a cycle. A structural property <i>S</i> of a graph <i>G</i> is <i>locally checkable</i>, if there is a prover-and-verifier pair (<i>P, V</i>) as follows. The <i>prover P</i> assigns a label to each node in graphs(More)
In the classical game of Cops and Robbers on graphs, the capture time is defined by the least number of moves needed to catch all robbers with the smallest amount of cops that suffice. While the case of one cop and one robber is well understood, it is an open question how long it takes for multiple cops to catch multiple robbers. We show that capturing ` ∈(More)