A Practical Approach to Reliable Flooding in Mobile Ad hoc Networks

Flooding in Mobile Ad hoc Networks (MANET) is an important communication primitive. It serves as a building block for higher layer protocols like content distribution, route discovery in routing protocols as well as used by services like Address Resolution Protocol (ARP) and Dynamic Host Configuration Protocol (DHCP). The nodes in real MANETs are not uniformly distributed. There are always dense and sparse parts in the network. For the dense parts of the network the redundancy provided by naive flooding is to high leading the packet loss due to collisions, wasting radio resources and thus need to be reduced. On the other hand, even in stationary networks without node mobility wireless links are lossy due to external and internal interference, fading or weak signal. Thus the transmission of a packet can fail. Both characteristics need to be considered when designing a flooding protocol. The proposed flooding scheme operates using purely local information about the network topology and is therefore in contrast to methods which rely on an overlay routing structures suitable for MANETs. It achieves a very high reliability while still being efficient as follows. First, we repeat the transmission of the flooding message at the network layer as long as we find strongly connected neighboring nodes which so far have not successfully received the flooding message. In each iteration the most promising neighboring node is selected according to a novel metric. Second, to achieve a high reliability we use unicasting at the link-layer for the transmission of flooding messages to the selected peer node. This allows us to compensate for dropped flooding messages due to lossy links or MAC collisions and allows us to adapt the level of redundancy in order to improve reachability while keeping the message overhead low. As long as the selected peer does not successfully acknowledge the packet reception or a passive acknowledgment was overheard the MAC transmission is repeated. Third, to achieve an efficient solution we piggyback flooding messages with the address of nodes we expect that they will receive the flooding message which is feasible due to the used link-layer unicasting. The proposed peer selection metric is of low complexity and thus can be computed on a per packet basis. The proposed flooding scheme can be implemented on top of existing IEEE 802.11 or 802.15.4 PHY/MAC stacks without any modifications. Results from extensive network simulation show that the proposed scheme is able to achieve a reachability of close to one even in very challenging networks where all other known methods fail. Moreover, our proposed scheme is able to achieve a high reachability in a very efficient way with low delay, e.g. in challenging networks the best known solutions requires up to four times more MAC transmissions to achieve the same level of reachability.