Reliable causal delivery with probabilistic design

Ensuring reliable and ordered communication between computers usually requires acknowledgment messages. In systems with a high rate of broadcast communication, the cost of such acknowledgment messages can be large. We propose to use the causal ordering information required by some applications to detect and request missing messages. To circumscribe the number of unnecessary requests we combine local awareness and probabilistic methods. Our model allow to obtain reliable communication within a latency equivalent to unordered communication and lower network usage than acknowledgment systems.Assurer une communication ordonnée et fiable entre ordinateurs requière usuellement l'utilisation de messages d'accusé de réception. Dans les systèmes ayant un rythme élevé de communication d'ensemble, la charge de ces accusés de réception sur le réseau peut-être importante. Nous proposons d'utiliser les méta-données permettant l'ordonnancement causal pour détecter et récupérer les messages perdus. Afin de limiter le nombre de récupération inutiles nous combinons une connaissance locale du comportement du système ainsi que des méthodes probabilistes. Notre modèle nous permet d'obtenir une communication fiable avec des latences équivalente à une communication non-ordonnée et une charge réseau plus faible que les systèmes classique d'accusé de réception

An efficient and reliable multi-hop geographical broadcast protocol in vehicular ad-hoc networks

In Intelligent Transportation Systems (ITS), disseminating warning messages in a timely and efficient way through wireless short-range communications can save many lives and reduce traffic congestion. A geographical broadcast protocol provides data delivery to specified geographical areas, using multi-hop communications if needed. Among the main challenges for such protocols are forwarder selection and the reduction of the number of hops required to reach and cover the destination area. In this paper we propose an efficient geographical broadcast protocol called Preferred and Contention Based Forwarding (PCBF) and evaluate it through simulations. PCBF uses a combination of contention-based forwarding and selecting preferred forwarders also found in other protocols like Emergency Message Dissemination for Vehicular Environments (EMDV). Since the preferred forwarder is allowed to immediately forward the packet (evading contention among other potential forwarders), this approach reduces end-to-end delays. Notable extensions of PCBF compared to EMDV are the use of direct negative acknowledgements in case of unnecessary rebroadcasts and the use of forwarders outside the target region. Our simulation results show that the PCBF protocol outperforms selected other protocols in terms of end-to-end delay, re-broadcast overhead and reliability in both sparse and dense networks. © 2013 IEEE