On-Demand Multicasting in Ad-Hoc Networks: Comparing AODV and ODMRP

Multicasting is the transmission of datagrams to a group of hosts identified by a single destination address. Multicasting is intended for group-oriented computing sSuch as applications characterized by the close collaboration of teams (e.g. rescue patrol, battalion, scientists, etc) with requirements for audio and video conferencing and sharing of text and images. The use of multicasting within a network has many benefits. Multicasting reduces the communication costs for applications that send the same data to multiple recipients. Instead of sending via multiple unicasts, multicasting minimizes the link bandwidth consumption, sender and router processing, and delivery delay [1]. Maintaining group membership information and efficiently delivering the multicast packets to all members is challenging even in wired networks. However, nodes are increasingly mobile. One particularly challenging environment for multicast is a mobile ad-hoc network (MANET). A MANET consists of a dynamic collection of nodes with sometimes rapidly changing multi-hop topologies that are composed of relatively lowbandwidth wireless links. Since each node has a limited transmission range, a source-to-destination path could pass through several intermediate nodes. Unlike typical wireline routing protocols, ad-hoc routing protocols must address a diverse range of issues [2]. The network topology can change randomly and rapidly, at unpredictable times. Since wireless links generally have lower capacity, congestion is typically the norm rather than the exception. The majority of nodes will rely on batteries, thus routing protocols must limit the amount of control information that is passed between nodes. The majority of applications for the MANET technology are in areas where rapid deployment and dynamic reconfiguration are necessary and the wireline network is not available. These include military battlefields, emergency search and rescue sites, classrooms, and conventions where participants share information dynamically using their mobile devices. These applications lend themselves well to multicast operation. In addition, within a wireless medium, it is even more crucial to reduce the transmission overhead and power consumption. Multicasting can improve the efficiency of the wireless link when sending multiple copies of messages by exploiting the inherent broadcast property of wireless transmission. This paper summarizes our results when comparing two multicast protocols developed for MANETs: AODV and ODMRP.