Self-Protecting Multipaths (SPM): Efficient Resilience for Transport Networks

The self-protecting multipath (SPM) is a simple and efficient endto-end protection switching mechanism for transport networks. It distributes the traffic of a demand between two nodes according to a specific load balancing function over several disjoint paths and redistributes it if one of them fails. The load balancing functions can be optimized so that backup capacity in the network is optimally shared by multiple demands in various failure scenarios. As a result, resilience against all link and node failures can be achieved with only little extra capacity and in capacitated networks more protected traffic can be carried with the SPM than with other resilience mechanisms. The SPM is rather simple which facilitates its deployment in practice. This chapter explains the SPM in detail, distinguishes it from other, similar mechanisms, shows how the load balancing functions can be optimized, and illustrates the superior performance of the SPM. 1 Structure and Operation The self-protecting multipath (SPM) has been first published in [1]. It carries a traffic demand d between two routers in a network and protects the transmission against network failures. The path layout Pd = (p0d, ...,p kd−1 d ) of the SPM for a demand d consists of kd disjoint parallel paths pid that are explicitly established between two routers as depicted in Figure 1. The traffic is distributed over them according to a load balancing function lfd that indicates the traffic fraction that should be carried over each of them. If paths fail, the source node sees a pattern fd of failed and working paths in the SPM for demand d and redistributes the traffic over the working paths according to another SPM-specific load balancing function lfd that depends on the observed failure pattern fd. Thus, the SPM redistributes traffic only when one of its partial paths is affected by a network failure. To detect a failure pattern fd, the source node must check whether each partial path within a SPM is working. This also includes partial paths that do not carry any traffic. They act as sensors in the network, give feedback about the network health, and can also trigger traffic shifts if they fail. When the traffic matrix and the link capacities are given for a network, the routing and the load balancing functions of the SPM can be configured in an optimized way so that link utilizations are low under normal conditions and in failure scenarios. This This work was funded by Siemens AG, Munich, and by the Deutsche Forschungsgemeinschaft (DFG) under grant TR257/18-2. The authors alone are responsible for the content. Chapter in “Recent Advances in Providing QoS and Reliability in the Future Internet Backbone”, Nova Science Pub., 2010 – page 1