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.
IBSDN @cite_7 achieves robustness through running a centralized controller in parallel with a distributed routing protocol. Initially, all traffic is forwarded according to the controller's configuration. Switches revert to the path determined by the traditional routing protocol once a link is detected to be down. The authors omit crankback paths through crankback detection using a custom local monitoring agent. The proposed system is both elegant and simple, though does require customized hardware, since switches need to connect to a central controller, run a routing protocol, and implement a local agent to perform crankback detection. Moreover, the time it takes the routing protocol to converge to the post-failure situation may be long and cannot outpace a preconfigured backup plan.
@cite_7
1561042325 2110916358 2009508457 2089422736
A reliable and scalable mechanism to provide protection against a link or node failure has additional requirements in the context of SDN and OpenFlow. Not only it has to minimize the load on the controller, but it must be able to react even when the controller is unreachable. In this paper we present a protection scheme based on precomputed backup paths and inspired by MPLS “crankback” routing, that guarantees instantaneous recovery times and aims at zero packet-loss after failure detection, regardless of controller reachability, even when OpenFlow's “fast-failover” feature cannot be used. The proposed mechanism is based on OpenState, an OpenFlow extension that allows a programmer to specify how forwarding rules should autonomously adapt in a stateful fashion, reducing the need to rely on remote controllers. We present the scheme as well as two different formulations for the computation of backup paths. Dealing with network failures effectively is a major operational challenge for Internet service providers. Commonly deployed link state routing protocols such as OSPF react to link failures through global (i.e., network-wide) link state advertisements and routing table recomputations, causing significant forwarding discontinuity after a failure. The drawback with these protocols is that they need to trade off routing stability and forwarding continuity. To improve failure resiliency without jeopardizing routing stability, we propose a proactive local rerouting based approach called failure insensitive routing (FIR). The proposed approach prepares for failures using interface-specific forwarding, and upon a failure, suppresses the link state advertisement and instead triggers local rerouting using a backwarding table. In this paper, we prove that when no more than one link failure notification is suppressed, FIR always finds a loop-free path to a destination if one such path exists. We also formally analyze routing stability and network availability under both proactive and reactive approaches, and show that FIR provides better stability and availability than OSPF. One of the main concerns on SDN is relative to its ability to quickly react to network failures, while limiting both the control-plane overhead and the additional forwarding state kept by data-plane devices. Despite its practical importance, this concern is often overlooked in OpenFlow-based proposals. In this paper, we propose a new architecture, called IBSDN, in which a distributed routing protocol flanks OpenFlow to improve network robustness, reaction to failures, and controller scalability. In deeply exploring this idea, we complement our architecture with data-plane triggered mechanisms that improve its efficiency. We prove that the resulting solution ensures robustness for any combination of topological failures, and quickly reduces the path stretch. Finally, experimenting with a prototype implementation, we show that our approach is practical and overcomes the main limitations of previous work. We develop a robust plume tracking strategy using mobile sensor networks in three dimensional (3D) fields. Inspired by the plume tracking behavior of blue crabs, we propose a stochastic model of plume spikes detected by sensing agents based on the Poisson counting process, which enables us to transform the turbulent plume field detected by sensing agents to a continuously-differential field, the minimum of which is considered as a source in the field, and shares the same location with the plume source. The transformation allows us to design and analyze source-seeking algorithms in smooth fields instead of in turbulent fields with higher fluctuation spatially and temporally. Inspired by fish schools that seek darker (shaded) regions in environments with complex lighting variations, we develop a distributed source-seeking algorithm using mobile sensor networks without explicit gradient estimation. The velocity of each agent is designed using only the measurements taken by the agent and the relative positions to its neighboring agents. We prove that, using this design, the moving direction of a three-agent group will converge to the opposite gradient direction of the field, thus, the group moves towards a source in the field. We also prove that the tracking system is input-to-state stable (ISS), indicating that the system is robust to disturbances. We then generalize the design to N-agent groups, and demonstrate the strategy in both smooth fields and turbulent fields in simulations.