# Performance Evaluation of MPTCP on Simultaneous Use of 5G and 4G Networks
## 4 Performance Evaluation
### Performance Evaluations of MPTCP Schedulers When the CCA Is LIA  
Figure 4 shows the total received data for the considered MPTCP schedulers while the CCA is LIA. As we can observe, BLEST performs the best among the tested MPTCP schedulers. Redundant scheduler performs the second best. SRTT, Round-robin, and ECF perform almost similarly. As we know, Redundant scheduler sends the same data through all the available paths. This helps reduce the out-of-order delivery of packets at the receiver and, ultimately, helps to eliminate HoL blocking. That is the key reason behind the better performance of the Redundant scheduler than SRTT, Round-robin, and ECF. Biest scheduler also implements the subflow blocking mechanism targetting the elimination of HoL blocking at the receiver. This mechanism proves to be more efficient even than the Redundant one. In Biest, when it estimates that the possibility of HoL blocking at the receiver is low, it sends packets through all the available paths. In contrary, when it estimates that there is a high possibility of HoL blocking at the receiver if packets are sent through a specific SF, it temporarily stops sending via that SF. In this way, it ensures sending more data packets on the one hand and significantly reduces the HoL blocking on the other hand. In support of this hypothesis, we can observe that BLEST could best utilize the 5G network by receiving the highest amount of data via it. This implies that when a stable 5G network is available, BLEST could take the best performance out of it. Combinedly with the 4G network, BLEST could successfully attain the highest amount of received data. Now, to further investigate how the schedulers are operating in real-time, we plot the throughput and \(\Delta\)_PDUI_ observed at the UE in Figure 5. Note that, aiming at the proper comparison of the results, we present the results of the experiments where the received SINR was the same as in Figure 3. Here, by having a close observation, we can find a direct relationship between the throughput, \(\Delta\)_PDUI_, and SINR (Figure 3). For example, let us closely observe the spike on the \(\Delta\)_PDUI_ at the 8-second time for SRTT, Round-robin, and ECF schedulers. As already mentioned, such a negative spike indicates significant packet losses. We can observe that, right before the 8-second time, the 5G signal's SINR (Figure 3) improves. At the same time, throughput also increases. This indicates that when the 5G SINR grows, the UE receives the ACKs for the previously sent packets through the 5G SF, resulting in better throughput. By receiving the ACKs, the CCA, which is the LIA in this experiment, increases the CWND of that SF. As the CWND is available and 5G offers the lowest RTT, SRTT, Round-robin, and ECF schedulers send data through this SF. However,  
Figure 4: Performance of the tested MPTCP schedulers in terms of total received data for LIA as a CCA. the SINR drops at that time, resulting in a loss of packets, which is indicated by the sharp negative spike. Ultimately, this causes a significant HoL blocking at the receiver and a substantial reduction in throughput. As the Redundant scheduler sends the same data through both the SFs, it could avoid such drastic packet losses and reduction in throughput. Due to the intelligent HoL estimation and SF blocking mechanism, BLEST could also avoid such a situation and obtain a considerably better throughput. Figure 5: Real-time performance of the tested MPTCP schedulers for LIA as a CCA in terms of throughput and \(\Delta\)_PDUI_ for: (**a,b**) SKTT, (**c,d**) Round-robin, (**e,f**) Redundant, (**g,h**) ECF, and (**i,j**) BLEST, respectively. Finally, Table 2 summarizes the observed FCT for the tested MPTCP schedulers. Similar to the observed throughput, the FCT of BLEST and Redundant schedulers are significantly lower than that of the SRTT, Round-robin, and ECF. BLEST could complete the flows in the shortest possible time with an average of 7.219 ms. ECF takes the highest time with an average of 11.655 ms.