RMAC: A New MAC Protocol with Reliable Multicast Support for Wireless Ad-Hoc Networks

In most of the MAC protocols for wireless ad hoc networks today, no reliable multicast service is provided. For example, IEEE 802.11[5], the most widely used MAC protocol at present, only supports reliable unicast with the RTS/CTS/DATA/ACK scheme; while for broadcast or multicast frames1, it simply performs one transmission of them without any reliability guarantee. In this report, we propose a new MAC protocol called RMAC which provides reliable multicast service to the upper layer. Our propose of this new protocol with reliable multicast support is mainly based on the following observations. First, we notice that multihop multicast communication in wireless ad hoc networks needs reliable multicast service from the MAC layer. Recently, many network layer multicast protocols have been proposed. They can be largely classified into two categories— tree-based multicast protocols([4, 9, 14, 1]) and meshbased multicast protocols([7, 3]). However, people find out both of the two kinds of approaches have serious problems if high reliability is needed by the multicast communication. In tree-based multicast protocols, no matter how the tree is built in different protocols, they all eventually use a tree to do multicast. And it is shown by some research works[3, 8] that multicasting with a tree in wireless networks suffers from severe packet loss due to the unreliable wireless channel and the lean connectivity of the tree. An illustration of this problem is given in Figure 1, which shows that if one node in the multicast tree, say node B, does not receive the packet, then all its children can not receive the packet, thus resulting in significant packet loss.