## 4 Traffic Filtering-Based Techniques
### Comparison  
We described five traffic filtering-based techniques for reducing HSR unicast traffic. QR and TC approaches remove duplicated and circulated unicast traffic from rings in HSR networks. TC removes circulated traffic from only DANH rings, while the QR removes circulated traffic from both DANH and QuadBox rings. However, both QR and TC do not prune unicast traffic for unused rings. The PL prunes unicast traffic for unused DANH rings, while the EPL prunes the traffic for both unused DANH and QuadBox rings. However, the PL and EPL do not remove circulated unicast traffic from active rings. The FHT filters unicast traffic for both unused DANH and QuadBox rings, and also remove duplicated and circulated traffic from active rings. Characteristics of these techniques are summarized in Table 2.  
To compare traffic performance of these techniques, we conducted several simulations using the OMNeT++ simulation tool [37]. We consider a sample network consisting of three QuadBox rings and eight DANH rings; each DANH ring has four DANH nodes, as shown in Figure 12. Two QuadBoxs  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Traffic Filtering Features** & **QR** & **TC** & **PL** & **EPL** & **FHT** \\ \hline Filtering traffic for DANH rings & No & No & Yes & Yes & Yes \\ Filtering traffic for QuadBox rings & No & No & No & Yes & Yes \\ Removing duplicated and circulated traffic & Yes & Yes & No & No & Yes \\ Learning MAC addresses & No & No & Yes & Yes & Yes \\ Using control messages & No & No & No & No & Yes \\ Filtered traffic & Any & Any & Unicast & Unicast & Unicast \\ Network topology & Ring & Ring & Ring & Ring \\ \hline \end{tabular}
\end{table}
Table 2: Characteristics of traffic filtering-based techniques.  
are used to prevent a single point of failure in the network. In these simulations, a source node in DANH ring 1 sends unicast frames to a destination node in DANH ring 5.  
Table 3 shows the number of network unicast frames recorded from the simulations under the standard HSR protocol, the QR approach, the PL approach, the EPL approach, and the FHT approach.  
Figure 13 shows the comparison of traffic performance of these techniques. The simulation results show that, in the sample network, the TC and QR approaches reduce network unicast traffic by 31% and 41%, respectively, compared to the standard HSR protocol. The PL approach has better traffic performance than the QR approach; it reduces network unicast traffic by 51% compared to standard HSR protocol and by about 17% compared to the QR approach. The EPL improves traffic performance for the PL approach; it reduces network unicast traffic by 61% compared to standard HSR protocol and by about 21% compared to the PL approach. FHT provides the best traffic performance. For our sample network, the FHT approach reduces network traffic by 84% compared to standard HSR protocol and by about 57% compared to the EPL approach.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Number of Sent Frames** & **HSR** & **QR** & **TC** & **PL** & **EPL** & **FHT** & **ODP** & **DVP** & **RDP** \\ \hline
10 & 1390 & 820 & 960 & 732 & 620 & 220 & 220 & 220 & 220 \\
20 & 2780 & 1640 & 1920 & 1392 & 1120 & 440 & 440 & 440 \\
30 & 4170 & 2460 & 2880 & 2052 & 1620 & 660 & 660 & 660 \\
40 & 5560 & 3280 & 3840 & 2712 & 2120 & 880 & 880 & 880 & 880 \\
50 & 6950 & 4100 & 4800 & 3372 & 2620 & 1100 & 1100 & 1100 & 1100 \\
60 & 8340 & 4920 & 5760 & 4032 & 3120 & 1320 & 1320 & 1320 & 1320 \\
70 & 9730 & 5740 & 6720 & 4692 & 3620 & 1540 & 1540 & 1540 \\
80 & 11,120 & 6560 & 7680 & 5352 & 4120 & 1760 & 1760 & 1760 & 1760 \\
90 & 12,510 & 7380 & 8640 & 6012 & 4620 & 1980 & 1980 & 1980 & 1980 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The number of network traffic frames of traffic reduction techniques.  
Figure 12: The simulation network.