## 1 Introduction
The drawback of this scheme is that it requires communication with the controller after a link failure, i.e., a round-trip between controllers and switches, which takes more time when compared with the proactive scheme, leading to an increased network latency. This paper proposes flow-aware pro-reactive (FAPR), a scheme aimed at integrating protection with restoration mechanisms. The scheme strives to achieve faster link failure recovery speed while also ensuring the high usability and adaptability of backup paths based on flow type awareness. We assess the quality of the backup paths by measuring the interruption rate of the flows passing through the backup paths. In this paper, the interruption rate of flows refers to the ratio of the lost data packets' number (due to insufficient link bandwidth after failure recovery) to all data packets' number. Firstly, we use a method called pro-VLAN [19] to pre-deploy backup paths in switches, which is designed to quickly restore transmission after a fault based on classical protection principles. Secondly, before failures, we calculate multiple backup paths for each link in the network topology and temporarily store them in the controller. When a link failure occurs, the switch automatically switches to the pre-deployed backup path by pro-VLAN, and the notification message is sent to the controller simultaneously. After receiving the notification message, the controller extracts all the flow data and analyzes characteristics of different types of flows individually. Based on the current global network view, the controller calculates and selects the most suitable paths from the stored backup paths to allocate to different flows. After the second switch-over by the restoration mechanism, the flows can forward along the most suitable path according to actual network conditions. The main advantages and contributions of this paper are summarized as follows:1. FAPR adopts the proactive link failure recovery scheme to ensure fast recovery speed after link failures. The recovery time required by our proposed scheme is reduced by 65% compared with the purely reactive scheme. 2. FAPR uses the reactive link failure recovery scheme to promise high usability of backup paths. More specifically, it pre-calculates and stores backup paths for network links to reduce a portion of the calculation latency after link failures, and optimizes backup paths before they are dispatched to minimize unnecessary resource consumption. 3. FAPR analyzes characteristics of the affected flows and allocates suitable paths from the stored backup paths, reducing the possibility of blockage or interruption in the subsequent forwarding process. Specifically, the interruption rate of flows after failure recovery is reduced by 20% and 50% compared with the reactive and proactive schemes, respectively. As a result, this helps to improve the quality of network services. The rest of this paper is organized as follows. Section 2 introduces the related work. Section 3 illustrates the motivation of this paper with examples. Section 4 details FAPR. Section 5 presents the experimental results and provides analysis. Finally, Section 6 concludes the paper and looks forward to future work.