Multicast Routing Protocols in Mobile Ad Hoc Networks: A Comparative Survey and Taxonomy <s> Fireworks: An Adaptive Multicast/Broadcast Protocol <s> An ad hoc network is a dynamically reconfigurable wireless network with no fixed infrastructure or central administration. Each host is mobile and must act as a router. Routing and multicasting protocols in ad hoc networks are faced with the challenge of delivering data to destinations through multihop routes in the presence of node movements and topology changes. This paper presents the On-Demand Multicast Routing Protocol (ODMRP) for wireless mobile and hoc networks. ODMRP is a mesh-based, rather than a conventional tree-based, multicast scheme and uses a forwarding group concept; only a subset of nodes forwards the multicast packets via scoped flooding. It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRP performance with other multicast protocols proposed for ad hoc networks via extensive and detailed simulation. <s> BIB001 </s> Multicast Routing Protocols in Mobile Ad Hoc Networks: A Comparative Survey and Taxonomy <s> Fireworks: An Adaptive Multicast/Broadcast Protocol <s> In group communications, we find that current multicast protocols are far from ''one size fits all'': they are typically geared towards and optimized for particular scenarios. As a result, when deployed in different scenarios, their performance and overhead often degrades significantly. A common problem is that most of these protocols incur high overheads with a high density of group members and in high mobility. Our objective is to design a protocol that adapts in response to the dynamics of the network. In particular, our objective is to provide efficient and lightweight multicast data dissemination irrespective of the density of group members and node density. Our work is motivated by two observations. First, broadcasting in some cases is more efficient than multicasting. Second, member and node layout distributions are not necessarily homogeneous. For example, many MANET applications result in a topological clustering of group members that move together. Thus, we develop Fireworks, an adaptive approach for group communications in mobile ad hoc networks. Fireworks is a hybrid 2-tier multicast/broadcast protocol that adapts to maintain performance given the dynamics of the network topology and group density. In a nutshell, our protocol creates pockets of broadcast distribution in areas with many members, while it develops a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads. <s> BIB002
Protocol Description. Fireworks BIB002 is a hybrid 2-tier multicast/broadcast protocol that adapts to maintain performance, given the dynamics of the network topology and group density. It creates a cohort of broadcast (lower tier) distribution in areas with many members, while it develops a multicast backbone (upper tier) to interconnect these dense pockets (see Figure 27 ). The multicast tree is constructed as follows. When a node wishes to join a multicast group, it broadcasts an ADVERTISE message to its 2-hop neighborhood. Upon reception of a unique ADVERTISE message, nodes update their joining group table, as per the message contents. Following this (discovery) phase, each joining node would have obtained the 2-hop local topology information. This information may be used during the decision phase, in which, if the joining node receives multiple LEADER messages, it will pick the cohort leader with the shortest distance and highest cohesiveness (a state variable that maintains the affinity of group members within a node's 2-hop neighborhood). It then joins the cohort leader by unicasting a CHILD message containing its address, mcastaddress, and hop-count to the selected cohort leader. If there are two or more cohort leaders with the same distance and cohesiveness, the joining node will select the cohort leader with the highest nodeID. If the joining node does not receive any LEADER message, then it elects itself as a cohort leader and serves a cohort. After that, it broadcasts a LEADER message to its 2-hop neighborhood so as to notify them of the presence of a new cohort leader. At the end of these phases, the lower tier is created. To enable the creation of the upper tier, the multicast source periodically broadcasts a SOURCE-QUERY message to the network. Intermediate nodes forward unique SOURCE-QUERY messages further. When a cohort leader receives the SOURCE-QUERY message, it unicasts a SOURCE-REPLY message back to the source via the reverse path. The nodes along the unicast path toward the source become the forwarding nodes for the multicast group. A cohort member could leave a multicast group anytime by stopping unicasting of the CHILD message to its cohort leader. If a cohort leader decides to leave the multicast group, it stops transmitting the LEADER message. Cohort members, upon discovering the absence of a leader, will perform the joining and discovery phases as described before. Discussion. Fireworks significantly reduces the protocol overhead by exploiting the broadcast nature of the mobile ad hoc network in the area with many group members (cohort). Moreover, since Fireworks employs broadcasting within a cohort, the inherent redundancy provides reliability and packet delivery performance that is comparable with that of ODMRP BIB001 . Fireworks develops a multicast backbone (Tree-based) to interconnect the dense pocket, which means that a link failure could affect multiple paths and, therefore, reduce the packet delivery ratio and introduce more overhead as well, especially in a highly dynamic environment. Another disadvantage is that Fireworks depends on the 2-hop local topology information during the decision phase, therefore, in the case of packet loss, a reduction in the accuracy of the topology information could affect the performance of Fireworks.