applied sciences Article
Enhanced Effective Filtering Approach (eEFA) for Improving HSR Network Performance in Smart Grids Nguyen Xuan Tien 1 1 2
*
ID
, Jong Myung Rhee 1 and Sang Yoon Park 2, *
ID
Department of Information and Communications Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea;
[email protected] or
[email protected] (N.X.T.);
[email protected] (J.M.R.) Department of Electronic Engineering, Myongji University, 116 Myongji-ro, Yongin, Gyeonggi 17058, Korea Correspondence:
[email protected]; Tel.: +82-31-330-6751
Received: 3 January 2018; Accepted: 22 January 2018; Published: 23 January 2018
Abstract: The effective filtering approach (EFA) is one of the most effective approaches for improving the network traffic performance of high-availability seamless redundancy (HSR) networks. However, because EFA uses port locking (PL) for detecting nondestination doubly-attached nodes with HSR protocol (DANH) rings in HSR networks, it forwards the first sent frame to all DANH rings in the network. In addition, it uses a control message for discovering passive QuadBox rings in both unidirectional and bidirectional communications. In this study, we propose an enhanced version of EFA called enhanced-EFA (eEFA) that does not forward unicast frames to nondestination DANH rings. eEFA does not use any control message to discover passive QuadBox rings in bidirectional communications. eEFA thus reduces the network traffic in HSR networks compared with EFA. Analytical and simulation results for a sample network show that the traffic reduction of eEFA was 4–26% and 2–20% for unidirectional and bidirectional communications, respectively, compared to EFA. eEFA, thus, clearly saves network bandwidth and improves the network performance. Keywords: smart grid; high-availability seamless redundancy (HSR); effective filtering approach (EFA); enhanced EFA (eEFA); substation automation system (SAS)
1. Introduction A smart grid is an evolving grid that uses advanced automation, control, information technology (IT), and Internet of things (IoT) systems to enable real-time monitoring and control of power flow from generation to end users. The smart grid is a new kind of electrical grid where the power system and the IT system are tightly coupled with each other [1]. It is a next-generation power distribution grid. To realize smart grid technology, substation automation systems (SASs) have been designed and used to improve the efficiency of control and communication schemes [2]. Redundancy protocols are used to provide fault-tolerant communications for SASs and, thereby, ensure their operation [3]. High-availability seamless redundancy (HSR) is one type of redundancy protocol used for providing seamless and fault-tolerant communication for SASs [4]. HSR is standardized under IEC 62439-3 [5]. It provides fault-tolerant communications for ring-based Ethernet networks by forwarding and circulating frames in all network rings. End nodes in HSR networks, called doubly-attached nodes with HSR protocol (DANH), have two HSR-enabled ports. A single-ring HSR network consists of DANHs interconnected by full-duplex links. To forward a unicast frame to a destination DANH in a single-ring network, a source DANH inserts an HSR tag into an Ethernet frame passed from its upper layers and sends the tagged frame over two of its ports. Two copies of the frame are forwarded to the destination DANH through two directions of the ring. In other words, the frame is delivered from the source to the destination through two separate paths in the ring. The destination receives two identical copies of the frame, removes the HSR tag from
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the 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. 2. 3.
Issue 1: Duplicating and circulating frames in all the rings, except the destination DANH ring; Issue 2: Forwarding unicast frames into all DANH rings; and 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. In addition, there are other techniques for reducing redundant traffic in HSR networks, including the HSR SwitchBox technique [18], the integration of HSR and OpenFlow (HSE + OF) [19], the reducing multicast traffic (RMT) [20], the cost-effective topology design for HSR resilient mesh networks [21], and the latency and traffic reduction technique for process-level network [22]. The HSR SwitchBox technique defines a new switching node in HSR networks that forwards HSR frames based on looking up of media access control (MAC) tables instead of flooding the frames. The HSE + OF approach aims to manage HSR networks by means of the software-defined networking (SDN) paradigm. The approach defines new HSE + OF nodes whose control plane is managed by an OpenFlow controller. In other words, this approach is an implementation of HSR in SDN. The RMT technique was proposed to reduce multicast traffic in HSR networks by limiting the spreading of the multicast traffic to only the rings that have members associated with that traffic instead of spreading the traffic into all the network parts. The study of traffic reduction for process-level networks [22] presented two enhanced solutions and fully implemented QR to HSR for improving the latency and reducing the traffic volume in a process-level network. The main idea of these two enhanced solutions is to reduce the minimum
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the traffic volume in a process-level network. The main idea of these two enhanced solutions is to reduce the minimum number of hops required for the delivery of messages to destinations for number of hops required for the delivery of messages to destinations for reducing the maximum reducing the maximum end-to-end latency. end-to-end latency. EFA is one of the most effective filtering techniques. EFA reduces redundant unicast traffic in EFA is one of the most effective filtering techniques. EFA reduces redundant unicast traffic in HSR HSR networks by solving all issues faced in HSR [13]. EFA uses the PL and FQR techniques for networks by solving all issues faced in HSR [13]. EFA uses the PL and FQR techniques for filtering filtering unicast traffic for nondestination DANH rings and passive QuadBox rings, respectively. In unicast traffic for nondestination DANH rings and passive QuadBox rings, respectively. In addition, addition, EFA uses QR in HSR networks to prevent traffic frames from being duplicated and EFA uses QR in HSR networks to prevent traffic frames from being duplicated and circulated in rings. circulated in rings. However, EFA has to forward the first sent frame to all DANH rings to check However, EFA has to forward the first sent frame to all DANH rings to check nondestination DANH nondestination DANH rings. Additionally, EFA uses FQR to discover passive QuadBox rings by rings. Additionally, EFA uses FQR to discover passive QuadBox rings by broadcasting a control broadcasting a control message. In this paper, we propose an enhanced version of EFA, called message. In this paper, we propose an enhanced version of EFA, called enhanced-EFA (eEFA), to enhanced-EFA (eEFA), to overcome these two issues. The main purpose of eEFA is to reduce more overcome these two issues. The main purpose of eEFA is to reduce more redundant unicast traffic redundant unicast traffic compared to EFA by filtering the first sent frame for nondestination DANH compared to EFA by filtering the first sent frame for nondestination DANH rings and by avoiding rings and by avoiding using a control message to discover passive QuadBox rings for bidirectional using a control message to discover passive QuadBox rings for bidirectional communications, thus communications, thus saving network bandwidth and improving the network performance. saving network bandwidth and improving the network performance. The remainder of this paper is organized as follows: In Section 2, we briefly introduce EFA. The remainder of this paper is organized as follows: In Section 2, we briefly introduce EFA. In Section 3, we describe eEFA. The traffic performance of eEFA is analyzed in Section 4. Several In Section 3, we describe eEFA. The traffic performance of eEFA is analyzed in Section 4. Several simulations are conducted, and their results are presented in Section 5. Finally, Section 6 presents the simulations are conducted, and their results are presented in Section 5. Finally, Section 6 presents the conclusions of this study. conclusions of this study. 2. Effective Filtering Approach (EFA) 2. Effective Filtering Approach (EFA) To significantly reduce redundant unicast traffic in HSR networks, EFA performs traffic filtering To significantly reduce redundant unicast traffic in HSR networks, EFA performs traffic filtering for all unused rings, including nondestination DANH rings and passive QuadBox rings. for all unused rings, including nondestination DANH rings and passive QuadBox rings. 1. Filter traffic for nondestination DANH rings by using PL; and 1. Filter traffic for nondestination DANH rings by using PL; and 2. Filter traffic for passive QuadBox rings by using FQR. 2. Filter traffic for passive QuadBox rings by using FQR. In this study, for the purposes of operational descriptions, performance analysis, and simulations, In this study, for the purposes of operational descriptions, performance analysis, and simulations, we consider a sample HSR network that consists of eight DANH rings interconnected by QuadBoxes, we consider a sample HSR network that consists of eight DANH rings interconnected by QuadBoxes, as shown in Figure 1. In communication scenarios, source DANH 1 sends unicast frames to as shown in Figure 1. In communication scenarios, source DANH 1 sends unicast frames to destination destination DANH 10. DANH 10.
Figure high-availability seamless redundancy; DANH: doubly-attached doubly-attached Figure 1. Sample HSR network. HSR: high-availability nodes with HSR protocol.
2.1. Filtering Unicast Traffic in DANH Rings EFA uses PL for filtering unicast frames for nondestination DANH rings. Nondestination DANH rings are those DANH rings that do not contain the destination DANH. In the sample network
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EFA uses PL for filtering unicast frames for nondestination DANH rings. Nondestination DANH rings are those DANH rings that do not contain the destination DANH. In the sample shown inshown Figurein 1, Figure DANH1,ring 3 is the DANH ring, whereas other the DANH are network DANH ringdestination 3 is the destination DANH ring, the whereas otherrings DANH nondestination DANH rings. rings are nondestination DANH rings. uses the thefirst firstframe framesent sentby bythe thesource sourceDANH DANH detect nondestination DANH rings. When PL uses toto detect nondestination DANH rings. When the the source DANH sends frame destinationDANH DANHininan anHSR HSRnetwork, network, the the frame frame is source DANH sends thethe firstfirst frame to to thethe destination forwarded to all DANH rings of the network. The frame is then circulated in all DANH rings except checking the circulation circulation of the first frame, PL the destination DANH ring, as shown in Figure 2. By checking nondestinationDANH DANHrings. rings.PLPL then locks nondestination DANH rings to prevent the discovers nondestination then locks nondestination DANH rings to prevent the next next frames being forwarded to the DANH rings. From secondframe frameonward, onward,EFA EFA does does not frames fromfrom being forwarded to the DANH rings. From thethe second forward the unicast frame to nondestination DANH rings [13]. 2.2. Filtering Filtering Unicast Unicast Traffic Traffic for 2.2. for QuadBox QuadBox Rings Rings EFA uses Nondestination DANH DANH EFA uses PL PL for for filtering filtering unicast unicast frames frames for for nondestination nondestination DANH DANH rings. rings. Nondestination rings are those DANH rings that do not contain the destination DANH. In the sample network rings are those DANH rings that do not contain the destination DANH. In the sample network shown shown in Figure 1, DANH 3 is the destination DANH ring, whereas theother otherDANH DANH rings rings are are in Figure 1, DANH ring 3ring is the destination DANH ring, whereas the nondestination DANH nondestination DANH rings. rings. PL uses the PL uses the first first frame frame sent sent by by the the source source DANH DANH to to detect detect nondestination nondestination DANH DANH rings. rings. When When the source source DANH sends the the first first frame in an the frame is the DANH sends frame to to the the destination destination DANH DANH in an HSR HSR network, network, the frame is forwarded to all DANH rings of the network. The frame is then circulated in all DANH rings except forwarded to all DANH rings of the network. The frame is then circulated in all DANH rings except the destination DANH ring, ring, as as shown shown in in Figure Figure 2. 2. By By checking checking the the circulation circulation of of the the first first frame, frame, PL PL the destination DANH discovers nondestination PL then then locks locks the the nondestination nondestination DANH DANH rings rings to to prevent prevent the the discovers nondestination DANH DANH rings. rings. PL next frames from being forwarded to the DANH rings. From the second frame onward, EFA does not next frames from being forwarded to the DANH rings. From the second frame onward, EFA does forward the unicast frame to nondestination DANH ringsrings [13].[13]. not forward the unicast frame to nondestination DANH
Figure 2. Flooding the first frame to discover nondestination DANH rings in EFA. EFA: effectively Figure 2. Flooding the first frame to discover nondestination DANH rings in EFA. EFA: effectively filtering approach. filtering approach.
2.3. Forwarding Unicast Frames 2.3. Forwarding Unicast Frames 1. First frame 1. First frame When the first frame is sent from the source DANH to the destination DANH, it is forwarded When the first sent from the source DANH the as destination it is forwarded and and circulated in allframe ringsisexcept the destination DANHtoring, shown inDANH, Figure 2. circulated alldestination rings exceptDANH the destination DANH as shown in Figure 2. message called the Wheninthe receives the first ring, sent frame, it sends a control When the destination receivesas the first sent frame,3.itUpon sendsreceiving a controlthe message the locking message back to theDANH source DANH, shown in Figure controlcalled message, lockingQuadBoxes message back to the source DANH, as shown in Figure 3. Upon the control trunk check whether the QuadBox rings to which theyreceiving are connecting aremessage, passive trunk QuadBoxes check the QuadBox rings to which theyDANH are connecting are passiveDANH QuadBox QuadBox rings. For the whether communication session between source 1 and destination 10, rings. For ring the communication session ring, between source DANH rings 1 and1destination DANH 10, QuadBox QuadBox 3 is a passive QuadBox whereas QuadBox and 2 are active QuadBox rings. ring 3 is a passive QuadBox ring, whereas QuadBox rings 1 and 2 are active QuadBox rings.
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From second frame of the communication session, EFA does not forward the frame to 2. kththe frame ( ≥ unicast 2) From the second unicast frame of the communication session, EFA does not forward the frame nondestination DANH rings and passive QuadBox rings, as shown in Figure 4. In addition, EFA uses to nondestination DANH rings and of passive QuadBox rings, as shown Figure In addition, EFA From the second unicast frame the communication session, EFAindoes not4.forward the frame QR for removing the circulated traffic from rings. uses QR for removing the circulated trafficthe from the rings. to nondestination DANH rings and passive QuadBox rings, as shown in Figure 4. In addition, EFA uses QR for removing the circulated traffic from the rings.
Figure 3. Using the locking message to discover passive QuadBox rings in EFA.
Figure 3. Using the locking message to discover passive QuadBox rings in EFA. Figure 3. Using the locking message to discover passive QuadBox rings in EFA.
Figure 4. Forwarding a unicast frame in EFA. Figure 4. Forwarding a unicast frame in EFA.
Figure 4. Forwarding a unicast frame in EFA. 2.4. Issues in EFA 2.4. Issues in EFA EFA is one of the best traffic reduction techniques for HSR networks. However, it has the 2.4. Issues in EFA following drawbacks: EFA is one of the best traffic reduction techniques for HSR networks. However, it has the following drawbacks: EFA is one of the best reduction forand HSR networks. However, it has the following 1. It still forwards thetraffic first frame to all techniques DANH rings; drawbacks: 2. It uses a control message discover rings in both unidirectional and bidirectional 1. still forwards the first to frame to allpassive DANHQuadBox rings; and communications. 2. It uses a control message to discover passive QuadBox rings in both unidirectional and bidirectional 1. It still forwards the first frame to all DANH rings; and communications. These cause additional redundant trafficQuadBox and controlrings overheads in HSR networks. In and 2. It uses a drawbacks control message to discover passive in both unidirectional this study, eEFA is proposed to solve these two problems, thereby improving the network traffic These drawbacks cause additional redundant traffic and control overheads in HSR networks. In bidirectional communications. performance of HSR networks. this study, eEFA is proposed to solve these two problems, thereby improving the network traffic performance of HSRcause networks. These drawbacks additional redundant traffic and control overheads in HSR networks. 3. study, Proposed eEFA In this eEFA is Approach proposed to solve these two problems, thereby improving the network traffic 3. Proposed eEFA Approach performance of HSR eEFA networks. We propose to solve the following issues of EFA networks: We propose eEFA to solve the following issues of EFA networks: 1. eEFA does not forward unicast frames, including the first sent frame, to nondestination DANH 3. Proposed eEFA Approach rings; does and not forward unicast frames, including the first sent frame, to nondestination DANH 1. eEFA We propose eEFA to solve the following issues of EFA networks: rings; and
1.
eEFA does not forward unicast frames, including the first sent frame, to nondestination DANH rings; and
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eEFA does not use any control message to detect passive QuadBox rings for bidirectional eEFA use any control message to detect passive QuadBox rings for bidirectional Appl. Sci.does 2018, 8,not x 6 of 15 communications. communications. 2.
eEFA does not use any control message to detect passive QuadBox rings for bidirectional
3.1. Filtering Unicast Frames in in DANH DANH Rings Rings 3.1. Filtering Unicast Frames communications.
As specified specified in in the the standard standard HSR HSR protocol, protocol, each each DANH DANH periodically periodically multicasts multicasts aa supervision supervision As 3.1. Filtering Unicast Frames in DANH Rings frame called called HSR_Supervision HSR_Supervision with with an an interval interval called called LifeCheckInterval LifeCheckInterval [5]. [5]. Upon receiving an an frame Upon receiving As specified in theeach standard HSR protocol,learns each DANH periodically multicasts a supervision HSR_Supervision frame, access QuadBox the MAC addresses of DANHs in its DANH HSR_Supervision frame, each access QuadBox learns the MAC addresses of DANHs in its DANH framestores calledthese HSR_Supervision withcalled an interval called LifeCheckInterval [5]. Upon receiving an ring and and inaaMAC MACtable table NodesTable. Supervision frames allow NodesTable ring stores these in called NodesTable. Supervision frames allow thethe NodesTable of HSR_Supervision frame, each access QuadBox learns the MAC addresses of DANHs in its DANH of access QuadBoxes to keep track of the presence of DANH nodes in their DANH rings. When accessring QuadBoxes keepintrack of the of DANH nodes in their DANH rings. When a DANHa and storestothese a MAC tablepresence called NodesTable. Supervision frames allow the NodesTable DANH does not send an HSR_Supervision frame within a given timeout called NodeForgetTime, its does of notaccess sendQuadBoxes an HSR_Supervision frame a given timeout called NodeForgetTime, its address to keep track of thewithin presence of DANH nodes in their DANH rings. When a address is removed from NodesTable. is removed NodesTable. DANHfrom does not send an HSR_Supervision frame within a given timeout called NodeForgetTime, its Instead of using PL for filtering for nondestination DANH rings, eEFA looks-up Instead using PLfrom for filtering traffictraffic for nondestination DANH rings, eEFA looks-up NodesTable address of is removed NodesTable. NodesTable to make forwarding decisions. When an access QuadBox receives an HSR unicast Instead of decisions. using PL for filtering traffic for nondestination rings, frame, eEFA itlooks-up to make forwarding When an access QuadBox receives an DANH HSR unicast looksframe, up its it looks up and its NodesTable andthere checks whether there is QuadBox an matching the destination MAC NodesTable to makewhether forwarding decisions. Whenmatching an access receives an HSR unicast NodesTable checks is an entry the entry destination MAC address offrame, the frame. it looks up its NodesTable and checks whether there is an entry matching the destination MAC address of the frame. If so, it means that the DANH ring of the QuadBox contains the destination If so, it means that the DANH ring of the QuadBox contains the destination DANH; the QuadBox then address of the frame. If so, it meansthe that the DANH ring of the QuadBox contains theQuadBox destinationsends DANH; the then forwards frame its DANH rings. If not, access forwards theQuadBox frame to its DANH rings. If not, thetoaccess QuadBox sends thethe frame over the other port DANH; the QuadBox then forwards the frame to its DANH rings. If not, the access QuadBox sendsto its the frame over the other port connecting to its QuadBox ring and does not send the connecting to its QuadBox ring and does not send the frame to its DANH ring. Figure 5frame shows the the frame over the other port connecting to its QuadBox ring and does not send the frame to its DANH ring. Figure 5 shows theframe process forwarding a unicast frame at access QuadBoxes in eEFA. process of forwarding a unicast at of access QuadBoxes in eEFA. DANH ring. Figure 5 shows the process of forwarding a unicast frame at access QuadBoxes in eEFA.
Figure 5. Process forwardinga aunicast unicast frame frame in in in eEFA. eEFA: Enhanced Figure 5. Process of of forwarding in access accessQuadBoxes QuadBoxes eEFA. eEFA: Enhanced Figure 5. Process of forwarding effectively filtering approach. a unicast frame in access QuadBoxes in eEFA. eEFA: Enhanced effectively filtering approach. effectively filtering approach. By looking up the NodesTable, eEFA avoids forwarding HSR frames, including the first sent By looking up eEFA avoids HSR frame, to nondestination DANH rings, as shown Figure 6. By looking up the the NodesTable, NodesTable, eEFA avoidsinforwarding forwarding HSR frames, frames, including including the the first first sent sent
frame, frame, to to nondestination nondestination DANH DANH rings, rings, as as shown shown in in Figure Figure 6. 6.
Figure 6. Forwarding the first sent frame in eEFA.
Figure 6. Forwarding the first sent frame in eEFA. Figure 6. Forwarding the first sent frame in eEFA.
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3.2. Discovering Passive QuadBox Rings In eEFA, eEFA, communications communications are are classified classified into into two two types: types: unidirectional unidirectional and and bidirectional. bidirectional. In a unidirectional a source toto a unidirectional communication, communication,unicast unicastframes framesare arepropagated propagatedininonly onlyone onedirection directionfrom from a source destination. In In a bidirectional communication, unicast frames are are exchanged between the source and a destination. a bidirectional communication, unicast frames exchanged between the source the In other words, in bidirectional communication, if the destination receives a framea anddestination. the destination. In other words, in bidirectional communication, if the destination receives sent bysent the by source, it will reply sending a framea back toback the source. frame the source, it willby reply by sending frame to the source. 3.2.1. 3.2.1. Unidirectional Unidirectional Communication Communication For eEFA uses uses the same for discovering passive QuadBox For unidirectional unidirectionalcommunications, communications, eEFA the process same process for discovering passive rings as EFA. In other words, eEFA uses the locking message sent by the destination DANH to discover QuadBox rings as EFA. In other words, eEFA uses the locking message sent by the destination DANH and lock passive QuadBox rings, as shown in as Figure 3. in Figure 3. to discover and lock passive QuadBox rings, shown 3.2.2. 3.2.2. Bidirectional Bidirectional Communications Communications In unlike in in the the case case of of EFA, EFA, eEFA In bidirectional bidirectional communications, communications, unlike eEFA does does not not use use any any control control message Instead, eEFA eEFA uses message to to detect detect and and lock lock passive passive QuadBox QuadBox rings. rings. Instead, uses the the first first replied replied frame frame sent sent by by the the destination destination DANH DANH to to discover discover passive passive QuadBox QuadBox rings. rings. When When the the destination destination DANH DANH receives receives the the first first sent sent frame, frame, it it replies replies by by sending sending aa unicast unicast frame frame back to the source. Upon receiving the first replied frame, trunk QuadBoxes detect passive back to the source. Upon receiving the first replied frame, trunk QuadBoxes detect passive QuadBox QuadBox rings, rings, as as shown shown in in Figure Figure 7. 7.
Figure 7. Using the first replied frame to discover passive QuadBox rings in eEFA. Figure 7. Using the first replied frame to discover passive QuadBox rings in eEFA.
Figure 8a,b show the processes of forwarding unicast frames between the source DANH and the Figure 8a,b show of respectively. forwarding unicast frames between the source DANH and the destination DANH in the EFAprocesses and eEFA, destination DANH in EFA and eEFA, respectively. 3.3. Forwarding Unicast Frames 3.3. Forwarding Unicast Frames Unlike EFA, which forwards the first sent frame to all DANH rings, eEFA does not send the first Unlike EFA, which forwards the first sent frame to all DANH rings, eEFA does not send the first sent frame and other traffic frames to nondestination DANH rings by looking up the NodesTable. sent frame and other traffic frames to nondestination DANH rings by looking up the NodesTable. Like EFA, eEFA does not forward the ( ≥ 2) frame to passive QuadBox rings. Figure 9 shows Like EFA, eEFA does not forward the kth (k ≥ 2) frame to passive QuadBox rings. Figure 9 shows the the process of forwarding the ( ≥ 2) traffic frame in eEFA. process of forwarding the kth (k ≥ 2) traffic frame in eEFA.
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(a) In EFA (b) In eEFA (a) In EFA (b) In eEFA Figure 8. Process of forwarding frames between the source and the destination. Figure 8. Process of forwarding frames between the source and the destination. Figure 8. Process of forwarding frames between the source and the destination.
Figure 9. Forwarding the ℎ ( ≥ 2) frame in eEFA. Figure 9. Forwarding the ℎ ( ≥ 2) frame in eEFA. Figure 9. Forwarding the kth (k ≥ 2) frame in eEFA.
4. Traffic Performance Analysis 4. Traffic Performance Analysis 4. Traffic Analysis This Performance section analyzes, evaluates, and compares the network traffic performance of EFA and This section analyzes, evaluates, and compares the network traffic performance of EFA and eEFA.This Wesection consider the sample HSRand network withthe data communication sessions of between analyzes, evaluates, compares network traffic performance EFA andsource eEFA. eEFA. We consider the sample HSR network with data communication sessions between source DANH 1 andthe destination DANH 10, as with shown in Figure 1. We consider sample HSR network data communication sessions between source DANH 1 DANH and destination DANH are 10, as shown in Figure 1. The1 following two scenarios considered: and destination DANH 10, as shown in Figure 1. The following two scenarios are considered: The following two scenarios arebetween considered: • Unidirectional communication the source and the destination; and • Unidirectional communication between the source and the destination; and • Bidirectional communication between the source and the destination. Unidirectionalcommunication communicationbetween betweenthe thesource sourceand andthe thedestination. destination; and •• Bidirectional • Bidirectional communication between the source and the destination. 4.1. Unidirectional Communication 4.1. Unidirectional Communication 4.1.1. In EFA 4.1.1. In EFA In EFA, the first sent frame is forwarded and circulated in all DANH and QuadBox rings except In EFA, the first sentring. frameThe is forwarded andnetwork circulated in all DANH andin QuadBox rings except the destination DANH number of frames generated the network upon the destination DANH ring. The number of network frames generated in the network upon delivering the sent first frame, denoted by , is calculated as: delivering the sent first frame, denoted by , is calculated as: = 2 − (1) = ∈ 2 − (1) ∈
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4.1. Unidirectional Communication 4.1.1. In EFA In EFA, the first sent frame is forwarded and circulated in all DANH and QuadBox rings except the destination DANH ring. The number of network frames generated in the network upon delivering 1 , is calculated as: the sent first frame, denoted by n f EFA 1 n f EFA =
∑
2ni − nd
(1)
i ∈ NR
where NR is the set of all rings in the network; nd , the number of nodes in the destination DANH ring; and ni , the number of nodes in the ith ring. When the destination receives the first sent frame, it sends a Locking message back to the source to discover passive QuadBox rings in the network. The Locking message is forwarded to the destination DANH ring and active QuadBox rings. The number of network frames generated by the locking lock , is calculated as: message, denoted by n f EFA
∑
lock n f EFA = nd +
ni
(2)
i ∈ AQR
where AQR is the set of all active QuadBox rings. For the kth(k ≥ 2) frame, EFA does not forward the frame to nondestination DANH ring and passive QuadBox rings. The number of network frames generated by the kth frame (k ≥ 2), denoted by k , is calculated as: n f EFA k n f EFA = n s + n d + ∑ ni (3) i ∈ AQR
where ns is the number of nodes in the source DANH ring. Generally, the number of network frames when the source sends N unicast frames to the uni , is calculated as: destination in unidirectional communication in EFA, denoted by n f EFA uni 1 lock k n f EFA = n f EFA + n f EFA + ( N − 1)n f EFA
(4)
1 , n f lock , and n f k , n f uni can be calculated as: By substituting n f EFA EFA EFA EFA uni n f EFA =
∑
2ni + ( N − 1)(ns + nd ) + N
i ∈ NR
∑
ni
(5)
i ∈ AQR
4.1.2. In eEFA In eEFA, the first sent frame is not forwarded to nondestination DANH rings. Instead, it is forwarded to the destination DANH ring and all QuadBox rings. The number of network frames 1 generated by the first sent frame, denoted by n f eEFA , is calculated as: 1 n f eEFA = nd +
∑
ni
(6)
i ∈ QR
where QR is the set of all QuadBox rings in the network. For unidirectional communication, eEFA also uses the Locking message to discover passive lock , QuadBox rings. The number of network frames generated by the Locking message, denoted by n f eEFA is calculated as: lock n f eEFA = n d + ∑ ni (7) i ∈ AQR
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Like EFA, eEFA does not forward the kth(k ≥ 2) frame to nondestination DANH ring and passive k QuadBox rings. The number of network frames generated by the kth frame (k ≥ 2), denoted by n f eEFA , is calculated as: k n f eEFA = n s + n d + ∑ ni (8) i ∈ AQR
Generally, the number of network frames generated in the network when the source sends N uni , is unicast frames to the destination in unidirectional communication in eEFA, denoted by n f eEFA calculated as: uni 1 lock k n f eEFA = n f eEFA + n f eEFA + ( N − 1)n f eEFA (9) 1 lock , and n f k uni By substituting n f eEFA , n f eEFA eEFA , n f eEFA can be calculated as: uni n f eEFA =
∑
ni + 2nd + ( N − 1)(ns + nd ) + N
i ∈ QR
∑
ni
(10)
i ∈ AQR
4.2. Bidirectional Communication 4.2.1. In EFA The number of network frames generated in the network when the source sends the first frame to 1,send the destination, denoted by n f EFA , is calculated as: 1,send n f EFA =
∑
2ni − nd
(11)
i ∈ NR
The number of network frames generated in the network by the Locking message, denoted by lock , is calculated as: n f EFA lock n f EFA = n d + ∑ ni (12) i ∈ AQR
After sending the Locking message, the destination DANH sends the first replied frame to the source DANH. The number of network frames generated in the network when the destination sends 1,reply the first replied frame, denoted by n f EFA , is calculated as: 1,reply
n f EFA
= nd +
∑
ni + n s
(13)
i ∈ AQR
The number of network frames generated in the network by sending the kth frame (k ≥ 2), denoted k, send by n f EFA , is calculated as: k, send n f EFA = n s + ∑ ni + n d (14) i ∈ AQR
The number of network frames generated in the network by replying to the kth frame (k ≥ 2), k, reply denoted by n f EFA , is calculated as: k, reply
n f EFA
= nd +
∑
ni + n s
(15)
i ∈ AQR
Generally, the number of network frames generated in the network when the source sends bi , is N unicast frames to the destination in bidirectional communication in EFA, denoted by n f EFA calculated as: 1,reply k, reply 1,send k, send bi lock n f EFA = n f EFA + n f EFA + n f EFA + ( N − 1) n f EFA + n f EFA (16)
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bi is calculated as: Therefore, n f EFA bi n f EFA
=
∑
! 2ni + ns + nd
+ 2( N − 1)(ns + nd ) + 2N
i ∈ NR
∑
ni
(17)
i ∈ AQR
4.2.2. In eEFA The number of network frames generated in the network by the first sent frame, denoted by 1,send n f eEFA , is calculated as: 1,send n f eEFA = n d + ∑ ni (18) i ∈ QR
When the destination receives the first sent frame, it sends the first replied frame back to the source. The number of network frames generated in the network by the first replied frame, denoted by 1,reply n f eEFA , is calculated as: 1,reply
n f eEFA = nd +
∑
ni
(19)
i ∈ AQR
The number of network frames generated in the network by sending the kth frame (k ≥ 2), denoted k, send by n f eEFA , is calculated as: k, send n f eEFA = n S + ∑ ni + n d (20) i ∈ AQR
The number of network frames generated in the network by replying to the kth frame (k ≥ 2), k, reply denoted by n f eEFA , is calculated as: k, reply
n f eEFA
= nd +
∑
ni + n s
(21)
i ∈ AR
Generally, the number of network frames generated in the network when the source sends N bi unicast frames to the destination in bidirectional communication in eEFA, denoted by n f eEFA , is calculated as: 1,reply k, reply k, send bi n f eEFA = nt1,send (22) eEFA + nteEFA + ( N − 1) nteEFA + nteEFA bi Therefore, n f eEFA is calculated as: bi n f eEFA =
∑
ni + 2nd +
i ∈ QR
∑
! ni
i ∈ AQR
+ 2( N − 1) n s + n d +
∑
! ni
(23)
i ∈ AQR
5. Simulations and Discussion Several simulations have been conducted to validate the performance analysis performed in Section 4. The network simulator OMNeT++ (Version 4.6, Andras Varga, https://www.omnetpp.org/ andras/, Budapest, Hungary, 2014) [23] was used to conduct these simulations. 5.1. Simulation Description In the simulations, we considered the sample HSR network shown in Figure 1. Two simulations were conducted to validate, evaluate, and compare the network performance for both unidirectional and bidirectional communication. In both types of communication, the source and destination DANH are DANH 1 and DANH 10, respectively. 5.1.1. Simulation 1: Unidirectional Communication In this simulation, the communication between the source and destination DANH was unidirectional. The source DANH sent N ( N = 10, 20, . . . , 100) unicast frames to the destination DANH. Network
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frames (including network traffic frames and control frames) were recorded to validate and compare the network performance. 5.1.2. Simulation 2: Bidirectional Communication In this simulation, the communication between the source and destination DANH was bidirectional. the destination DANH receives a unicast frame sent by the source DANH, it replies Appl. Sci. 2018, 8,When x 12 of 15 Appl. Sci. 2018, 8, x of 15 by sending a unicast frame back to the source DANH. The source DANH sent N ( N = 10, 20, . . . 12 , 100 ) unicast framesittocan thebe destination Network (including network traffic frames and control Overall, seen fromDANH. the graphs aboveframes that eEFA reduced the number of network frames Overall, it can be seen from the graphs above that eEFA reduced the number of network frames frames) were recorded and compare and the network performance. compared with EFA to in validate both unidirectional bidirectional communication. While EFA still compared with EFA in both unidirectional and bidirectional communication. While EFA still forwards the first sent frame to all DANH rings, eEFA filters the first sent frame for nondestination forwards the sent frame to all DANH rings, eEFA filters the first sent frame for nondestination 5.2. Results andfirst Discussion DANH rings. In addition, unlike EFA that uses the Locking message to discover passive QuadBox DANH rings. In addition, unlike EFA that uses the Locking message to discover passive QuadBox ringsFigures for both andresults bidirectional communications, eEFA does not control 10 unidirectional and 11 show the of simulations 1 and 2, respectively. Theuse lineany graphs in rings for both unidirectional and bidirectional communications, eEFA does not use any control message to detect the passive QuadBox rings for bidirectional communications. Therefore, eEFA Figures 10 and 11 show comparisons of the number of network frames generated in the network when message to detect the passive QuadBox rings for bidirectional communications. Therefore, eEFA saves the network bandwidth improves the network performance. the source DANH sent unicast and frames to the destination in EFA and eEFA. saves the network bandwidth and improves the networkDANH performance.
Figure 10. Result Result of Simulation Simulation 1. Figure Figure 10. 10. Result of of Simulation 1. 1.
Figure 11. Result of Simulation 2. Figure 11. 11. Result Result of of Simulation Simulation 2. 2. Figure
Figure 12 shows the percentage traffic reduction of eEFA compared to EFA. This graph clearly Figure 12 shows the percentage traffic reduction of eEFA compared to EFA. This graph clearly shows that the amount of traffic reduction decreased with an increase in the number of traffic frames shows that the amount of traffic reduction decreased with an increase in the number of traffic frames sent in the communication. When the source DANH sent 10 frames to the destination DANH, the sent in the communication. When the source DANH sent 10 frames to the destination DANH, the traffic reduction for unidirectional and bidirectional communication showed the maximum value of traffic reduction for unidirectional and bidirectional communication showed the maximum value of 26.21% and 19.65%, respectively. The traffic reduction rate decreased with a further increase in the number 26.21% and 19.65%, respectively. The traffic reduction rate decreased with a further increase in the number of sent frames, ultimately reaching values of 3.68% and 2.37% for unidirectional and bidirectional of sent frames, ultimately reaching values of 3.68% and 2.37% for unidirectional and bidirectional
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Overall, it can be seen from the graphs above that eEFA reduced the number of network frames compared with EFA in both unidirectional and bidirectional communication. While EFA still forwards the first sent frame to all DANH rings, eEFA filters the first sent frame for nondestination DANH rings. In addition, unlike EFA that uses the Locking message to discover passive QuadBox rings for both unidirectional and bidirectional communications, eEFA does not use any control message to detect the passive QuadBox rings for bidirectional communications. Therefore, eEFA saves the network bandwidth and improves the network performance. Figure 12 shows the percentage traffic reduction of eEFA compared to EFA. This graph clearly shows that the amount of traffic reduction decreased with an increase in the number of traffic frames sent in the communication. When the source DANH sent 10 frames to the destination DANH, the traffic reduction for unidirectional and bidirectional communication showed the maximum value of 26.21% and 19.65%, respectively. The traffic reduction rate decreased with a further increase in the number of sent Appl. Sci.frames, 2018, 8, x ultimately reaching values of 3.68% and 2.37% for unidirectional and bidirectional 13 of 15 communication, respectively. The The main main contributions contributions of of the the proposed proposedeEFA eEFAapproach approachare areas asfollows: follows:
•• ••
eEFA eEFAfilters filtersall allHSR HSRframes framesfor fornondestination nondestinationDANH DANHrings, rings,even eventhe thefirst firstsent sentframe. frame. eEFA eEFA does does not not use use any any control control message message to to discover discover passive passive QuadBox QuadBox rings rings for for bidirectional bidirectional communications. communications.
By solving solving these these issues, issues, eEFA eEFA reduces reduces more more redundant redundant unicast unicast traffic traffic than than EFA, EFA, thus thus saving saving the the By network bandwidth bandwidth and and improving improvingthe thenetwork networkperformance performancein inHSR HSRnetworks. networks. network
Figure 12. 12. Traffic Traffic reduction reduction (%) (%) of of eEFA eEFAcompared compared to to EFA EFAfor forboth bothbidirectional bidirectional and and unidirectional unidirectional Figure communications. communications.
6. Conclusions Conclusions 6. In this version of EFA called enhanced-EFA (eEFA). eEFAeEFA uses In this study, study, we weproposed proposedananenhanced enhanced version of EFA called enhanced-EFA (eEFA). existing MAC tables called NodesTable to forward HSR unicast frames to DANH rings instead of uses existing MAC tables called NodesTable to forward HSR unicast frames to DANH rings instead using PL,PL, as in of EFA. By looking up NodesTable, eEFA avoids forwarding any HSR unicast of using asthe in case the case of EFA. By looking up NodesTable, eEFA avoids forwarding any HSR frames, including the first sent frame, to nondestination DANH rings. In addition, eEFA does not use unicast frames, including the first sent frame, to nondestination DANH rings. In addition, eEFA any control to discover andtolock passive QuadBox rings for bidirectional does not usemessage any control message discover and lock passive QuadBox rings communications. for bidirectional Therefore, eEFA reduces the number of network frames sent in both unidirectional and bidirectional communications. Therefore, eEFA reduces the number of network frames sent in both unidirectional communications compared to EFA. For the sample HSR network considered in this study, the traffic and bidirectional communications compared to EFA. For the sample HSR network considered in reduction of eEFA 4–26%ofand 2–20% for unidirectional and bidirectionaland communication, this study, the trafficwas reduction eEFA was 4–26% and 2–20% for unidirectional bidirectional respectively, compared to EFA.compared eEFA thustoclearly network traffic performance HSR communication, respectively, EFA. improved eEFA thusthe clearly improved the networkof traffic networks. Our future work will develop and implement the proposed approach in hardware devices. Acknowledgments: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (grant number: 2017R1A2B4003964), and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant number: 2016R1D1A1B03933315).
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performance of HSR networks. Our future work will develop and implement the proposed approach in hardware devices. Acknowledgments: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (grant number: 2017R1A2B4003964), and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant number: 2016R1D1A1B03933315). Author Contributions: Authors Nguyen Xuan Tien, Jong Myung Rhee, and Sang Yoon Park conceived and developed the ideas behind the research. Nguyen Xuan Tien carried out the performance analysis and simulations, and wrote the paper under supervision of Jong Myung Rhee. Jong Myung Rhee and Sang Yoon Park finalized the paper. Conflicts of Interest: The authors declare no conflict of interest.
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