# A Reverse Shortest Path Tree-Based Multicast Joining Node Selection Method
## 2 Related Work  
In this chapter, we focus on traditional IP multicast and existing ICN multicast. In traditional TCP/IP multicast, WAVE [13] is an important MJN selection method that influences many multicast mechanisms [14; 15; 16; 17]. This method requires the DR to first send a request to the root of the multicast tree. When the multicast tree root receives the request, it will forward the request along the multicast tree. Each multicast tree node that receives the request will reply to the DR with a probe message, that will collect the load status information along the way. Upon receiving the probe messages, the DR can understand the load status of the downlink multicast paths, and then select the path with the lowest load to join the multicast tree. This method is essentially a greedy method that selects the path with the lowest load to join the multicast tree each time. It can effectively deal with situations where the routing is asymmetric. However, because it requires probing all of the nodes on the multicast tree, this method can lead to long multicast service delays, heavy network loads, and difficulty in deploying in engineering environments. In order to meet the deployment requirements in engineering environments, many mature TCP/IP multicast techniques directly select the root node of the multicast tree as the MJN. Among them, some multicast technologies construct source trees, in which the root node of the multicast tree is located at the data source. Therefore, the MJNs of these multicast technologies are data sources, such as PIM-SSM [18], PIM-DM [19], MOSPF [20], etc. There are also some multicast technologies that construct shared trees, in which the root node of the multicast tree is located at the core or Rendezvous Point(RP). Therefore, the MJNs of these multicast technologies are all cores or RPs. These MJN selection methods cannot consider the network load status, which may easily lead to network load congestion and limit the scalability of multicast. In ICN, routing is based on the content name rather than the IP address. This name-based routing allows receivers to request data from any position on the multicast tree, which is beneficial for optimizing the path of multicast data transmission [21; 22; 23; 24]. The following is an introduction to some of the MJN selection methods used in ICN multicast technologies. ILDM [25] is a multicast technology based on ICN. This technology proposes a path-state-aware MJN selection method. The method requires the control plane to calculate the path from MJN to DR and to detect various load statuses. Upon obtaining the load status of the downlink multicast path, the control plane returns the MJN with the lowest path load to DR. The MJN selection method of ILDM is essentially the same as WAVE, both of which adopt a greedy strategy to select the path with the lowest load to join the multicast tree. The difference is that the path detection of WAVE is distributed, while ILDM utilizes the control plane. ILDM can effectively deal with asymmetric routing issues. However, ILDM is a centralized MJN selection mechanism, that requires the control plane to perform a large amount of calculation, resulting in long multicast service delays and high pressure on the central node. Classic ICN solutions, such as DONA [26], CCN [27], and NDN [28; 29] inherently support multicast. The multicast mechanism of these solutions aggregates identical data \begin{table}
\begin{tabular}{c c} \hline \hline
**Notation** & **Definition** \\ \hline MJN & Multicast Joining Node \\ RP & Rendezvous Point \\ SST & Source Based Tree \\ ST & Shared Tree \\ MFT & Multicast Forwarding Table \\ DR & Designated Router \\ NRS & Name Resolution System \\ NA & Network Address \\ MID & Multicast Group ID \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Notations and definitions. requests by preserving existing data forwarding paths, thus supporting multicast services. When selecting MJN in these multicast solutions, they essentially choose the node closest to the receiver.