Flow Scheduling of Service Chain Processing in a NFV-Based Network

Network Function Virtualization (NFV) is changing the way we implement the network functions from expensive hardware to software middleboxes, called Virtual Network Functions (VNFs). Flows always request to be processed by several middleboxes in a specific order, which is known as a service chain. Most researches study the middlebox placement problem and few of them pay attention to the flow scheduling of a deployed service chain, resulting in poor control of flow completion times. However, the flow completion time is an extreme metric to evaluate the performance of a network. Therefore, we focus on the service chain scheduling problem. We aim to minimize the flow completion time in two aspects: the longest completion time (makespan) and the average completion time. First, a transmission and processing delay model is proposed to formulate the communication latency behaviour of flows being processed by middleboxes. When there are only two middleboxes in the service chain, we propose one optimal solution for each aspect, respectively. For a service chain with an arbitrary length, we prove the NP-hardness of our problem in both aspects and two corresponding heuristic algorithms are designed, which are extended from our proposed optimal solutions for a service chain with a length of two. Real testbed experiments and extensive simulations are conducted to evaluate the performance of our proposed algorithms in various scenarios.