SRLG-disjoint multi-path protection: When LP meets ILP

Abstract

Multi-Path Routing routes the upcoming demand over multiple paths. This is feasible in networks where the demand can be split into multiple parallel flows, i.e., the network is capable to perform inverse multiplexing (e.g., ngSDH and OTN via Veat) and where the connectivity of the topology also allows it.We propose LP (Linear Programming) formulation of the MPP (Multi-Path Protection) problem, where the demand is not only routed, but also protected using multiple parallel paths. Instead of the simplest edge-disjointness we generalise our method to the general SRLG-disjointness that includes node-disjointness as well (SRLG: Shared Risk Link Group).We give a Linear Programming (LP) formulation of the problem that finds the globally optimal solution. The main features of our approach are threefold.First, we use LP with real variables that is solvable in polynomial time instead of Integer LP (ILP) and still we are able to avoid branching of the flows in nodes different than the source and the target of the considered demand.Second, we present our network transformation model which helps to handle a part of SRLG scenarios in the LP without integer variables.Finally, we generalise and reuse the idea that was developed for MPP, for dedicated path protection (DPP) and show that LP can be used in practice to achieve disjointness of paths. Even if disjointness is not guaranteed, it is achieved with high probability.

Path‐based Multipath Protection: resilience using multiple paths

“…In addition, the methods are capable to protect the demand only partially by setting an appropriate factor into the constraint. We note that the IMPP method can be used in case of shared risk link groups as well; for further details, we refer to [18]. Finally, in the case of MPP, the working and protection resources are allocated on the basis of separate variables.…”

“…We compare the PMPP method with several resilience schemes on the basis of different properties in this section. The examined methods are the following: DPP -Dedicated Path Protection with double Dijkstra method ILP -Dedicated two-path protection with integer linear programme MPP -Multipath Protection [1] MPP+CE -Multipath Protection with edgetest and lower-bound constraint [18] IMPP -Improved Multipath Protection [18] IMPP+CE -Improved Multipath Protection with edgetest and lower-bound constraint [18] PMPP-5 -Path-based Multipath Protection with 5 as maximal length of paths PMPP-10 -Path-based Multipath Protection with 10 as maximal length of paths In Figure 11, we show the normalized reserved capacities and the blocking ratios of these eight resilience schemes. The PMPP-5 method has the highest blocking ratio; thus, it has the lowest capacity reservation.…”

“…Gyarmati et al present the Improved Multipath Protection (IMPP) scheme, which has an improved LP formula , where every edge has only one variable for the flows. Two methods are proposed to control the number of the used paths; the IMPP method can be extended to handle a group of shared risk link groups.…”

“…We formalized the original and the improved version of the MPP algorithm as a linear programme . The LP formulation is one of the key properties of the MPP schemes that we want to preserve.…”

“…Contrary to these methods, we formulate the PMPP method by using the link–path formulation model where every single path between the source and the target has an LP variable. In , we described two methods that can help control the number of parallel paths used by the demand. We use these techniques in the PMPP scheme as well.…”