## 2 Related Work  
In the field of reliable multicast, the design of many router cache management strategies is limited by the network environment with a single multicast group. In a network environment where router cache resources are shared by multiple multicast groups, using such a strategy cannot improve the overall loss recovery performance. Therefore, some related literatures have studied some cache allocation mechanisms in reliable multicast, and the representative works are as follows:  
Reference [23] proposed a cache management method called adaptive cache pool (ACP). In ACP, the router calculates the ratio of the number of NACKs received for a multicast group to the total number of NACKs received, and allocates cache space for each multicast group accordingly. It also proposes a \"borrow\" and \"return\" policy to allow a multicast group to \"borrow\" unused cache space in ACP when it runs out of allocated space. When all cache space in active router is used up, ACP will activate the \"return\"policy. Additionally, it prioritizes the group with the smallest number of NACKs to execute the \"return\" policy first. However, burst traffic often occurs on the Internet. When the number of multicast groups or group members change, the ACP allocation method has disadvantages such as slow convergence speed and unstable allocation results. Reference [18] proposed an adaptive and active reliable multicast (AARM) protocol suitable for large-scale multicast networks, in which the cache allocation algorithm is divided into two steps. Step 1 is to estimate the average packet loss rate of the multicast group according to the exponentially weighted moving average of NACK, and pre-allocate cache space according to the ratio of the number of NACK of the multicast group to the total number of NACK. In order to avoid the unfair phenomenon caused by the group with high packet loss rate occupying too much cache space, step 2 performs secondary correction on the group whose cache quota does not meet the retransmission requirement. Although AARM improves bandwidth consumption and network throughput, and decreases recovery delay compared with ACP, AARM does not consider the influence of the relative position of routers on the multicast tree. In [19], for the cache management problem of reliable multicast, the authors have studied three cache strategies based on timer, simple FIFO (S-FIFO) and probabilistic FIFO (P-FIFO), and three cache allocation mechanisms--namely equal sharing, least requirement first (LRF), and proportional allocation. Then, the authors compared the performance of various combinations of cache strategies and cache allocation mechanisms. In most cases, the combination of proportional allocation and P-FIFO performs the best. The router cache resource configuration has a great impact on network performance, therefore it has always been a research direction of attention. Different cache allocation mechanisms can be obtained based on different network environments. Under the current complex time-varying network characteristics, the router cache allocation mechanisms need to consider different factors, and dynamically adjust the cache configuration according to network state changes [24]. The following cache allocation mechanisms are considered from different aspects, reflecting some factors that affect the cache demand. In CCN, a dynamic cache size transfer scheme (DCSTS) [25] based on replacement rate has been proposed. In view of the differences in the usage of cache space, DCSTS allows dynamic loaning of cache resources between nodes. Nodes with large cache demand can use relatively idle resources of other nodes, so the cache performance of overloaded nodes can be improved. However, it also introduces additional overhead. Additional buffer block allocation (ABBA) on demand is a dynamic allocation mechanism for the buffer space of packet switches or routers.