## 3 Algorithm Design and Analysis
### TCP-SCTP Method
#### 3.3.3 Algorithm Design
This shows that the TCP-SCTP played a certain role in the process of predicting the merits and the demerits of the network, and that the prediction of the scheme had certain accuracy and improved the reliability of data transmission. For the MS-SCTP scheme, it was inevitable that the increase of PER would cause more packets to be lost in the link. With the increase of PER, the MS-SCTP did not have the sharp increase of packet loss rate as the SCTP and the TCP protocols did, but the change was gentler. This also shows that it could better avoid congestion in the link by predicting the network status. ### Simulation Results of TCP-SCTP Switch Process

In simulations, the same simulation scenario was used as 3.1, and the PERs were 0%, 10%, 20%, 30%, 40%, and 50%. The metrics throughput and packet loss rates of the TCP, the SCTP, and the TCP-SCTP switch process were used in the simulations to analyze the advantages of the TCP-SCTP switch process. Figure 9 shows the real-time throughput of the three schemes when the PER changed from 0% to 50%. As shown in the figures, the throughputs of the three schemes were occasionally similar (as in Figure 9a), while the throughput was different most of the time. From Figure 9a, when the data PER was zero, the TCP-SCTP switch process was used for data transmission, and its real-time throughput curve basically coincided with the real-time throughput curve when SCTP was used alone for data transmission. The real-time throughput could be assumed to be the same, except for a few time points where there was a large difference in real-time throughput. This was related to the scheme initialization settings using the SCTP protocol for data transfer. In Figure 9b, when the PER was more than 10%, the TCP-SCTP switch process had certain advantages in throughput compared to using SCTP and TCP alone. The throughput of the TCP-SCTP switch process reached 60 KBps; the throughput of SCTP was 50 KBps. From Figure 9c, where the PER was greater than 20%, the TCP-SCTP switch process was not obvious in terms of performance improvement. All three curves went up and down around 10 KBps. From Figure 9d, when the PER reached 30%, the throughputs of TCP and SCTP and the TCP-SCTP switch process were under 10 KBps. When the data PER reached 40% in Figure 9e, the real-time throughput of the scheme was also close to zero. Figure 10 shows the comparisons of other metrics among the three schemes. Figure 9: Real-time throughput compare when the error rate was 0–50%. (**a**) PER: 0%; (**b**) PER: 10%; (**c**) PER: 20%; (**d**) PER: 30%; (**e**) PER: 40%; (**f**) PER: 50%. Figure 10: Comparison of three schemes performance. (**a**) Average throughput; (**b**) throughput variance; (**c**) packet loss rate. Figure 9(a) shows the comparison results of the average throughput of the three schemes under different data PERs. When the data PERs increased, the average throughput rapidly decreased, either using the TCP-SCTP switch process or using them alone for data transmission. The average throughput of the TCP-SCTP switch process was always higher than that of TCP and SCTP alone for data transmission. When the data PER was more than 30%, the average throughput of all three schemes dropped below 10 KBps. When the data PER reached 40%, the data transmission performance was very poor. Figure 9(b) shows the comparison of throughput variance under different PERs. The throughput variance for data transfer using the TCP-SCTP switch process was larger than TCP but smaller than SCTP. The throughput fluctuation of the TCP-SCTP switch process was between the curves of transmission using SCTP and TCP. When the PER was at 30%, the variance of the throughput of the scheme was slightly less than that of TCP. All three curves had similar trends. Before the PER reached 10%, the throughput variances of all three were on the rise. The data PER was between 10% and 50%, and the throughput variance curves of all three were in the decline stage. Figure 9(c) shows the packet loss rate of three schemes under different PERs.