Placement of Highly Available Virtual Network Functions Through Local Rerouting

The recent development of network function virtualization decouples network functions from dedicated hardware. Thus, virtual network functions (VNFs) can be distributed onto shared and virtualized platforms held by multiple data centers in various network locations. The architecture of the distributed VNFs interconnected by virtual links is denoted as the Service Function Chain (SFC). SFC has the potential to significantly reduce the opening and operating cost of the network services while improving the flexibility. However, the availability of SFC on chained up data centers is always inferior to that of network functions running on a single data center because the failure in any data center on the chain may affect its availability. To improve the availabilities of SFCs, in this paper we propose a local rerouting strategy to bypass the failed data centers on SFCs using locally rerouted paths (LRPs). Furthermore, we formulate an optimization model to minimize the maximum load on links while deploying SFCs and LRPs into the network. Thus, we reduce the potential risk of congested links caused by the local rerouting strategy. We then propose a randomized rounding approximation algorithm to solve the optimization problem, preserving the competitive ratio of O(logn) for the model. We also propose a fast heuristic algorithm to improve the efficiency. Our extensive simulation results show that the proposed algorithms can provide highly available SFCs with more balanced link load.