The past century of telecommunications has shown that failures in networks are prevalent. Although much has been done to prevent failures, network nodes and links are bound to fail eventually. Failure recovery processes are therefore needed. Failure recovery is mainly influenced by (1) detection of the failure, and (2) circumvention of the detected failure. However, especially in SDNs where controllers recompute network state reactively, this leads to high delays. Hence, next to primary rules, backup rules should be installed in the switches to quickly detour traffic once a failure occurs. In this work, we propose algorithms for computing an all-to-all primary and backup network forwarding configuration that is capable of circumventing link and node failures. Omitting the high delay invoked by controller recomputation through preconfiguration, our proposal's recovery delay is close to the detection time which is significantly below the 50 ms rule of thumb. After initial recovery, we recompute network configuration to guarantee protection from future failures. Our algorithms use packet-labeling to guarantee correct and shortest detour forwarding. The algorithms and labeling technique allow packets to return to the primary path and are able to discriminate between link and node failures. The computational complexity of our solution is comparable to that of all-to-all-shortest paths computations. Our experimental evaluation on both real and generated networks shows that network configuration complexity highly decreases compared to classic disjoint paths computations. Finally, we provide a proof-of-concept OpenFlow controller in which our proposed configuration is implemented, demonstrating that it readily can be applied in production networks.
There are also algorithms that propose protection schemes based on (un)directed disjoint trees, e.g., the Roskind-Tarjan algorithm @cite_4 or the Medard-Finn-Barry-Gallager algorithm @cite_6 . The Roskind-Tarjan algorithm finds @math all-to-all undirected min-sum disjoint trees, while the Medard-Finn-Barry-Gallager algorithm finds a pair of one-to-all directed min-sum disjoint trees that can share links in the reverse direction. Contrary to our work, their resulting end-to-end paths can often be unnecessarily long, which may lead to higher failure probabilities and higher network operation costs. A more extensive overview of disjoint paths algorithms is presented in @cite_30 .
@cite_30 @cite_4 @cite_6
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Network survivability--the ability to maintain operation when one or a few network components fail--is indispensable for present-day networks. In this paper, we characterize three main components in establishing network survivability for an existing network, namely, (1) determining network connectivity, (2) augmenting the network, and (3) finding disjoint paths. We present a concise overview of network survivability algorithms, where we focus on presenting a few polynomial-time algorithms that could be implemented by practitioners and give references to more involved algorithms. We present a new algorithm which creates redundant trees on arbitrary node-redundant or link-redundant networks. These trees are such that any node is connected to the common root of the trees by at least one of the trees in case of node or link failure. Our scheme provides rapid preplanned recovery of communications with great flexibility in the topology design. Unlike previous algorithms, our algorithm can establish two redundant trees in the case of a node failing in the network. In the case of failure of a communications link, our algorithm provides a superset of the previously known trees.