## 2 Related Work  
In this section, the existing VANET routing protocols based on multicast routing are reviewed along with those developed for military purposes. The multicast protocols and their advantages and disadvantages are also analyzed in a [PERSON] et al. review article [16]. In this survey, the taxonomy of multicast routing protocols is also developed. In addition to this, the reviewed protocols are also classified into multicast routing methods and types. The clustering for open inter-vehicle communication network (COIN) protocol [31] and cluster-based directional routing protocol (CBDRP) [32] are based on multicast routing protocols developed for urban traffic, but these protocols are unsuitable for real-time applications where the topology changes dynamically and unpredictably. Therefore, these protocols cannot work efficiently for MDM dissemination where the scenarios change rapidly. Additionally, the CBDRP depends upon the geographical position information for disseminating messages, which may be inaccessible at the required time and cause a delay in message transmission [16]. Alternatively, the proposed protocol has been designed to adapt to the vehicle movements in real time to meet the requirements of VANET and to fulfill the safety standards for saving human lives. The inter-vehicle geocast (IVG) [33] protocol experiences high delay and overhead in remote and hilly areas because of its dependence upon the position information for routing messages. The cached geocast [34,35] protocol causes high network overhead that is due to the maintenance of cache records within the dynamic vehicular mobility. The message transmission scheme of the abiding geocast protocol [34] is based upon the short message duration, which results in low throughput within dense traffic. GVGrid [36] faces a high delay in message transmission because of the formation of complex routes within the congested traffic, creating unstable IVC links. The mobile just-in-time multicasting protocol (Mobicast) is a spatiotemporary multicast protocol along with the feature of geography in which the messages are transmitted at a specified geographical area and at a given time 't' only. The specified area is called a zone of reference (ZOR). The packet delivery ratio of the protocol is high, but the connection suddenly fails in the case of a change of ZOR. Hence, the protocol is unsuitable for MDM dissemination where the scenario is unpredictable [37]. Dynamic time-stable geocast routing (DTSG) is a geographical and time-stable protocol that keeps messages saved within the desired area for a specified period. The protocol is useful for disseminating short-term information within a specified area. Hence, the protocol's performance remains unaffected by the density of the vehicles using the store-and-carry scheme. On the other hand, the protocol experiences network overhead in managing message saving for delivery in the specified area and in handling the sudden switching between the stability modes [38]. The constrained geocast protocol has been developed for cooperative adaptive cruise control (CACC) for automatic traffic control systems where the future positions of vehicles are estimated for routing decisions. The protocol's performance increases in dense traffic because the future positions can be better estimated. At the same time, the performance decreases in the case of high mobility, where the density decreases [39]. The geocache protocol has been developed to control the density of the vehicles by distributing the load on all possible routes. The incoming vehicles are informed ahead of time by disseminating messages about the density of the vehicles on approaching routes. The performance of the protocol increases by using the cache mechanism for storing the information and sharing it during road congestion, whereas the response time increases in dense traffic [40]. In this paper [41], the communication between military vehicles has been established by proposing the dynamic routing algorithm.