## 3 Algorithm Design and Analysis
### TCP-SCTP Method
#### 3.3.3 Algorithm Design
In the case of different PERs, with the increase of data PERs, the probability of data packet loss in the three schemes increased. However, in each case of the same packet loss rate, the packet loss rate of TCP was higher than that of SCTP, and the loss rate curve of the TCP-SCTP switch process was in the middle. The packet loss rate of the TCP-SCTP switch process was small when the PER was small. The packet loss rate of the TCP-SCTP switch process was the lowest when the PER was less than 10%. With the continuous increase of the PER, the packet loss rate of the TCP-SCTP switch process increased faster and faster. With the increase of PER, the number of packets lost in the link increased, which easily triggered the condition of protocol switching between SCTP and TCP and also resulted in poor performance of the scheme. ### Implementation Analysis

This study simulated the MS-SCTP and the TCP-SCTP switch process proposed in this paper through network simulator version 2 (NS2). The TCP-SCTP method used packet loss rates to predict network conditions. In NS2, the packet loss rate was calculated by analyzing the trace file, which was used as a reference standard for packet retransmission analysis. In a practical application, when the transmission time out or packet loss, the sender retransmits the lost packet. In this paper, by calculating the proportion of retransmitted packets, the proportion of packets lost during data transmission was known. In this way, the TCP-SCTP method could do the statistics of retransmission packets more conveniently. The simulation took packet retransmission rate as a condition of protocol or path switching. From the analysis above, the MS-SCTP scheme had a significant effect on the throughput improvement under the same network conditions, regardless of the real-time throughput or the average throughput. At the same time, according to the throughput variance curve, although this scheme did not show satisfying stability when PER was relatively low, this scheme showed advantages in stability with higher packet loss rate. In terms of packet loss rate, it also optimized the SCTP protocol. The MS-SCTP scheme was the best of all three schemes. For the more conservative congestion control strategy of SCTP, the MS-SCTP improved the efficiency of congestion control to a certain extent, thus the multi-host feature of SCTP could play a better role. At the same time, the SCTP link redundancy features played a greater role. When SCTP was coupled, it was not necessary to wait for the primary path to fail completely before considering reselecting a primary path from the path. This not only increased the utilization of each path but also reduced the burden on each path. The TCP-SCTP method predicted the network status through packet loss rate. The current protocol was not ideal for congestion control, thus the TCP-SCTP switch process was carried out. However, the scheme did not directly change the status of the path itself or find a better path. Instead, it hoped to adjust the congestion of the current network by switching to another protocol so as to achieve more efficient data transmission. However, the scheme itself did not guarantee that network congestion could be dealt with by switching the protocol. Therefore, the optimal effect achieved by each switch of the protocol did not exceed the optimal effect achieved by the protocol alone for the adjustment of network conditions. From the analysis above, in the same network conditions, the switching scheme between SCTP and TCP could improve the throughput, either in real time or in average time. The TCP-SCTP switch process showed slightly better performance. At the same time, from the throughput variance curve, the TCP-SCTP switch process facilitated the transmission of data when the throughput performance was more stable. In terms of packet loss rate, it also performed better than TCP alone for data transmission. Therefore, we can consider using the TCP-SCTP switch process to improve system throughput.