On efficient replication-based routing in vehicular networks

Abstract

Efficient routing in vehicular networks is one of the most challenging problems because of frequent network disruption and fast topological change. Some replication-based routing protocols such as epidemic routing have been proposed. However, these existing replicationbased routing protocols cannot achieve high delivery ratio, low end-to-end delay and low delivery cost. In this paper, we design an efficient replication-based routing protocol called ERR for efficient routing in vehicular networks. ERR is a fully distributed protocol, and it has the following three desirable design objectives: first, ERR delivers the majority of the messages generated in time-to-live; second, ERR achieves low end-to-end delay; third, ERR introduces as little delivery cost as possible. To achieve these design objectives, ERR adopts an adaptive strategy for the number of copies of a message in a distributed fashion. In addition, we propose two forwarding rules for a message carrier with some copies to decide whether it should forward the message when it meets a vehicle. Based on real traces of vehicles, we have conducted real trace-driven simulations. Performance results demonstrate that ERR can increase delivery ratio, decrease end-to-end delay, and decrease delivery cost, when compared with four other alternative protocols.A number of protocols have been proposed for routing in Delay Tolerant Networks (DTNs), which can also be used in vehicular networks. The majority of these routing protocols are replication-based, such as epidemic routing [17], direct transmission [15] and spray-and-wait routing [16]. Replication-based routing protocols spread some duplicate copies of a message to a subset of nodes in the network, and the message is successfully delivered if one of these nodes encounters the destination. In epidemic routing, every message carrier forwards the message to any node it meets, until the message times out. Epidemic routing can achieve the maximum delivery ratio and minimum end-to-end delay. However, it also introduces unacceptable communication overhead, so that it is inappropriate for resource-constrained networks. In direct transmission, the source carries the message all the way unless it meets the destination. Direct transmission performs extremely low delivery ratio and high end-to-end delay, although it introduces little communication overhead. Spray-and-wait routing is a multiple-copy routing protocol, and it divides routing into two phases: spraying phase and waiting phase. In spraying phase, the source of a message generates a certain number of copies for the message, then spreads the message copies to some distinct relays. In waiting phase, each relay transmits the message only when it meets the message destination. Spray-andwait routing can be viewed as a tradeoff between delivery ratio and communication overhead. However, there are still two weaknesses in spray-and-wait routing: (1) once the number of copies of a message is determined, it is not changed during routing process, and (2) it is difficult to set...