PESCAPE: SLA-Preserving Escape Routes for Service Function Chains

Abstract

Service Function Chains (SFCs) in Network Function Virtualization (NFV) and Software Defined Networking (SDN) environments must satisfy end-to-end Service Level Agreements (SLAs) while surviving link failures. Existing protection mechanisms either provision redundant Virtual Network Functions (VNFs), incurring additional compute cost, or rely on service-chain-agnostic IP fast reroute. This work introduces PESCAPE, a method that plans escape paths jointly with the placement process. The approach is encoded as a single CP-SAT model in OR-Tools that determines VNF placement, primary routing, and a link-disjoint escape jointly under shared delay, bandwidth, and compute constraints, with dataplane failover checked on Mininet. Across a 6-node ring-plus-chord topology (5 chains) and the unmodified Topology Zoo Geant2012 40-node European National Research and Education Network (NREN) backbone (50 chains, loose and tight SLAs, averaged over five workload seeds), PESCAPE drives the failure-time SLA-violation rate to 0% by construction. The tight-SLA regime exposes the delay-acceptance trade-off: PESCAPE accepts 45% of requests at zero violations; greedy admits 85% but 62% of (request, primary-edge) pairs violate the SLA at failure; sequential CP-SAT collapses to 13% acceptance with 98% violation. Solver time stays under 10 s for 50 requests on the 40-node backbone, and pre-installed escape rules enable failover without recomputation.