Dynamic Probabilistic Retransmission in Ad Hoc Networks

Ad Hoc networks are self-organizing wireless networks, absent any fixed infrastructure. Nodes in such networks communicate through radio transmissions of limited range, sometimes requiring the use of intermediate nodes to reach a destination. Nodes in ad hoc networks are also limited in their power supply and wireless bandwidth. Node mobility further complicates the environment. A communication protocol must take into account not only the restrictions on resources imposed by the nodes in ad hoc networks, but must also be robust enough to deal with the dynamic network topology. One well-known solution to routing in ad hoc networks is flooding [1]. The flooding protocol works as follows: upon receiving the message for the first time, each node retransmits the message to all neighbors. Although a very simplistic protocol, flooding has the virtue of being reliable, while requiring minimal state retention. Unfortunately, flooding often results in redundant messages, consuming valuable bandwidth and power as well as causing contention, collision, and packet loss. Probabilistic flooding [2, 3, 4. ] was introduced to address these problems, but has many problems of its own. In this paper, we discuss approaches to address problems of broadcast storms in dense networks and message delivery in sparse networks of ad hoc organization. We begin by reviewing probabilistic rebroadcast, or gossip. In the next section, we address density and distribution as they relate to broadcast storms. We follow with a theoretical discussion of optimal retransmission and introduce dynamic, probabilistic rebroadcast in Sections 3 and 4. We summarize and conclude the paper in the final section. While flooding is a reliable transmission protocol, it is prone to the broadcast storm problem in dense networks [5, 6]. A simple solution to the broadcast storm problem is to send fewer redundant messages. This is the approach taken in probabilistic retransmission protocols, also referred to as gossip protocols. The difficulty in gossip is to know which messages are necessary and which are redundant. In the absence of better information, gossip assumes that all messages are equally important. The most straightforward version of gossip behaves in much the same way as flooding, beginning with the source node broadcasting the message. Since the source node always sends out this message, we say that the source transmits this Abstract Ad hoc networks are becoming more common. In order for these networks to be effective, they need a proper routing protocol. Although many probabilistic protocols have been …