Evaluation and Optimization of Connectivity-Based Stability- and "Quality of Service"-Metrics in Overlay Networks

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In network engineering, the creation of logical communication networks on top of underlying transport networks is a well-established concept. It is used in diverse application scenarios such as peer-to-peer networks, data center architectures, configuration of virtual private networks, the design of WDM-networks, the smart grid and in multiple visions of the future internet. In particular, all these applications feature a structural division into underlay (the transport network), overlay (the logical network) and an edge mapping, returning an underlay transport path for each logical connection in the overlay.Due to their indispensable role in present-day IT infrastructures, it is necessary to adopt overlay networks that are both failure- and attack-resistant. However, currently applied structural optimizations in overlay networks rather focus on improving communication efficiency or finding a local backup path for each overlay connection. Consequently, the removal or exhaustion of few underlay edges can effect a large number of overlay connections. Hence, the overlay's quality-of-service and availability parameters may decisively degrade.Determining such critical structures and studying realistic attack approaches are preconditions for the qualitative estimation of an overlay network's resiliency. Furthermore, they provide the basis for optimizations, since identified weaknesses may be resolved by an adaption of overlay structure or edge mapping.However, when compared with classical networks, the relevant graph measures exhibit substantially different properties. Due to dependencies between underlay and overlay connections, the MaxFlow-MinCut theorem is no longer valid. Measures of graph connectivity that are equivalent in classical networks may differ. This results in multiple available generalizations of graph connectivity, with different computational properties.Furthermore, the interactions between overlay and underlay affect load-dependent quality-of-service parameters, such as flow rates, jitter and delays. In the presence of a disadvantageous edge mapping, small deviations in the bandwidth of underlay connections can lead to considerable decrease in the overlay's quality-of-service.Based on these observation, the proposed project aims at the maximization of connectivity-based stability and quality-of-service measures in overlay networks. In particular, the following objectives shall be pursued:1. Investigation and refinement of attacker models in overlay scenarios2. Improvement of analysis methods of connectivity-based stability and quality-of-service measures in overlay networks with underlay changes3. Application of analysis methods on representative overlay networks4. Stability optimizations of overlay and edge mapping