Minimizing Transmission and Processing Delay in a NFV-based Network

Software middleboxes, also called Virtual Network Functions (VNFs), are replacing expensive traditional hardwares in implementing network services. Multiple middleboxes processing flows in a specific order form a service chain. Current works mostly focus on the service chain deployment problem and pay little attention to the flow scheduling of a deployed service chain, resulting in a poor control of the flow completion times. However, a high performance network always has a strict requirement of the flow completion time. In this paper, we build a transmission and processing delay model to formulate the communication latency behavior of flows being processed by middleboxes. We aim to minimize the flow completion time in two aspects: the longest completion time (makespan) and the average completion time. We propose an optimal solution for each aspect when there are only two middleboxes in the service chain. With a service chain with an arbitrary length, we first prove the NP-hardness of our problem in both aspects and then design two corresponding heuristic algorithms, which are extended from our proposed optimal solutions for a service chain with a length of two. Extensive simulations are conducted to evaluate the performance of our algorithms in various scenarios.