# A Single-Rate Multicast Congestion Control (SRMCC) Mechanism in Information-Centric Networking
## 4 Rate Adaptation
### Rate Selection Strategy
On the other hand, in Figure 9a, the bandwidth utilization of TFMCC is 19.7%, 3.8%, and 7.8% higher than that of SRMCC in scenarios 1, 2 and 3, respectively, However, the total bandwidth utilization of the two is almost the same, and the difference is less than 1%. This is because when TFMCC and TCP coexist, TFMCC greatly squeezes out TCP traffic, which also verifies the conclusion of the last section that TFMCC is extremely unfriendly to TCP. However, the situation with PerfwithECN is the opposite of TFMCC. Although the total bandwidth utilization of PerfwithECN and SRMCC is similar, the former is mainly contributed by TCP, and the bandwidth utilization of multicast streams under PerfwithECN is extremely low. Therefore, the multicast under PerfwithECN cannot coexist with TCP fairly. Moreover, taking into account the conclusions of the last section, we can conclude that SRMCC achieves almost the same total bandwidth utilization as TFMCC and PerfwithECN under the same link conditions, while maintaining better TCP friendliness than ASMP. In addition, it can be seen from Figure 8 that the increase in total bandwidth utilization of SRMCC is contributed to by both SRMCC and TCP. #### 5.3.3 Packet Loss Rate

We compared the packet loss rate for the mechanisms under the four scenarios. As shown in Figure 10, the packet loss rates of SRMCC and PerfwithECN are almost 0 in all experiment scenarios. However, the packet loss rates of TFMCC and ASMP are higher. In particular, except for in scenario 1, the packet loss rate of ASMP is about 2%. It can be seen that the proposed SRMCC mechanism can significantly reduce the packet loss rate, and this is because it adjusts the rate based on the congestion state indicated by the queue occupancy ratio, while also controlling the queue occupancy ratio by introducing a rate selection factor. Keeping in mind the conclusions of Section 5.3.1, it can be verified that by reasonably setting the value of the rate selection factor, a balance between packet loss rate and throughput can be achieved. Figure 9: The variation in bandwidth utilization under different scenarios. (**a**) The bandwidth utilization of multicast traffic under different scenarios; (**b**) The total bandwidth utilization of all traffic under different scenarios. #### 5.3.4. Overhead Analysis

In order to perform multicast congestion control, various mechanisms bring additional overhead. Due to the fact that these mechanisms adjust the sending rate based on the feedback information, we analyzed overhead with this aspect in mind. Figure 11 shows the number of feedback packets received by the multicast source of each multicast mechanism under different scenarios. It can be seen that SRMCC achieves the smallest number of feedback packets in all scenarios, while PerfwithECN achieves the largest number of feedback packets, followed by TFMCC. This is because there is an MCC table in each MTN to perform feedback aggregation to ensure that only one feedback packet is sent upstream. However, in TFMCC, in addition to the current limiting receiver (CLR) sending continuous instant feedback to the source, any receiver whose expected throughput is lower than the current rate of the source also sends feedback packets. For PerfwithECN, once the outgoing interface queue of the router detects that the congestion condition is met, the router immediately sends the suggested rate to the corresponding source node. Furthermore, seeing as there is no feedback aggregation mechanism, it is conceivable that with the expansion of the scale of the network, the overhead of PerfwithECN would be greater. Moreover, the number of feedback packets of SRMCC decreases by an average of 82.4%, 50.8%, and 94.1% compared with TFMCC, ASMP, and PerfwithECN, respectively. It can be proved that the proposed MCC message aggregation mechanism is effective. Figure 11: The variation in the number of feedback packets under different scenarios. Figure 10: The variation in packet loss rate under different scenarios.