## 5 Evaluation
The amount of delay which packets experience due to flow entry miss deeply depends on the target network environment. It goes up if the controller is far from the switches, the network is congested, or the speeds of the devices are slow. Moreover, it can be dynamically changed when these conditions are dynamically changed. Therefore, we have shown the ratio of the number of the delayed packets, instead of the delayed time which delayed packets are experienced. As seen in the result, the flow miss rate of the SFF scheme is very low in comparison with the other schemes such as FIFO, LFU and LRU. Therefore, the message exchange and SDN controller overheads of the SFF scheme are lower than those of the other schemes. The ratio of delayed packets means the ratio of the number of the delayed packets over the number of the total packets. In the result, the legend 111 means that a packet is delayed due to flow mismatching at switch #1, #2 and #3. The legend 100 means that a packet is delayed at switch #1 only. As seen in the result, almost half of the packets experienced the delay at all switches in the FIFO, LFU and LRU scheme. However, only 7% of the packets experienced the delay in the SFF scheme. Therefore, less packets experienced delay when the SFF scheme is used. Figure 10 shows the flow miss rate and ratio of delayed packets when the flow table size of each switch is 160 entries. In the results, the flow miss rate and ratio of delayed packets are lower than those of 128 flow entries. Less flows are missed and less packets are delayed because of the large size of the flow table. In this case, the LFU scheme has the worst performance. However, the LRU and SFF schemes have good performances. Figure 9: Experiment results with 128-128-128 flow table size. Figure 11 shows the results when the flow table sizes of each switch are 160, 128 and 160 entries respectively. The flows are missed and packets are delayed the most at switch #2 because the switch has the smallest number of flow entries. In this case, the LFU scheme has the worst performance and the SFF has the best performance. Figure 12 shows the results when the flow table sizes of each switch are 160, 128 and 96 entries respectively. In this case, the flows are missed and packets are delayed the most at switch #3 because it has the smallest flow table size. In the results, the SFF scheme has the lowest flow miss rate and the number of delayed packets is also the smallest in comparison to the other schemes. As a result, the SFF scheme shows the best performance. Figure 13 shows the flow miss rate and ratio of delayed packets when the flow table sizes of each switch are 96, 128 and 160 entries respectively. In this case, the flows are missed and the packets are delayed the most at switch #1 on the contrary of the previous case. This is also because the switch has the smallest flow entries. Even in this case, the SFF scheme has the lowest flow miss rate and the number of delayed packets is the smallest too. Therefore, the SFF scheme shows the best performance even in this case. Figure 11: Experiment results with 160-128-160 flow table size. Figure 10: Experiment results with 160-160-160 flow table size.