# Enhanced Effective Filtering Approach (eEFA) for Improving HSR Network Performance in Smart Grids  
[PERSON]  
1 Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea; [EMAIL_ADDRESS] or [EMAIL_ADDRESS] (N.X.T. ); [EMAIL_ADDRESS] (J.M.R.) [PERSON]  
1 Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea; [EMAIL_ADDRESS] or [EMAIL_ADDRESS] (N.X.T. ); [EMAIL_ADDRESS] (J.M.R.) [PERSON]  
2 Department of Electronic Engineering, Myongthe first received copy before passing the copy to its upper layers, and discards the duplicate. If a failure (e.g., link failure or node failure) occurs, only one path between the source and the destination is interrupted and the other path can still be used to deliver the frame to the destination. Therefore, HSR can provide seamless communications with zero recovery time for Ethernet rings. For more complex ring topologies, quadruple port devices (QuadBoxes) are used to interconnect DANH rings. A connected-ring HSR network consists of DANH rings and QuadBox rings. HSR works very well in single-ring HSR networks; however, it generates a lot of redundant traffic in connected-ring HSR networks. This drawback is caused by the following issues:  
1. Issue 1: Duplicating and circulating frames in all the rings, except the destination DANH ring;
2. Issue 2: Forwarding unicast frames into all DANH rings; and
3. Issue 3: Forwarding unicast frames into all QuadBox rings. This problem causes high consumption of network bandwidth and may degrade the network traffic performance in HSR networks. Several approaches have been proposed to solve this problem that is faced in the standard HSR protocol. Two main types of traffic reduction approaches are available: the traffic filtering-based approach and the dual paths-based approach [6]. In the former, redundant unicast traffic in HSR networks is reduced by filtering the traffic for rings and/or by preventing the traffic from being duplicated and circulated in rings. In the latter, unicast frames are forwarded from a source to a destination through two separate paths that are pre-established between the source and the destination. Traffic filtering-based techniques can be classified into single-filtering techniques, including the quick removing (QR) technique [7], the traffic control (TC) technique [8], the port locking (PL) technique [9], and combined-filtering techniques, including the hybrid QR and PL approach (QRPL) [10], the enhanced port locking (EPL) technique [11], the filtering HSR traffic (FHT) technique [12], and the effectively filtering approach (EFA) [13]. Most of the filtering-based techniques (QR, TC, PL, QRPL, and EPL) do not solve all the HSR issues. FHT and EFA are techniques that solve all the issues. However, FHT generates additional control overhead in HSR networks, whereas EFA still forwards the first sent frame to all DANH rings, including nondestination DANH rings. Several dual paths-based techniques have been proposed to reduce redundant unicast traffic in HSR networks based on pre-established paths. These techniques discover and establish dual paths between a source and a destination in an HSR network before forwarding unicast traffic frames from the source to the destination through the dual paths. Dual paths-based techniques include the dual virtual paths (DVP) [14] technique, which was then extended as extended dual virtual paths (EDVP) [15], the ring-based dual paths (RDP) [16] technique, and the dual separate paths (DSP) [17] technique. These dual paths-based techniques significantly reduce redundant unicast traffic in HSR networks. The main drawback of the techniques, however, is to generate additional control overhead in the networks because they exchange control messages to discover and establish dual paths.