An Efficient Causal Ordering Algorithm for Mobile Computing Environments

Causal message ordering is required for several distributed applications. In order to preserve causal ordering, only direct dependency information between messages, with respect to the destination process(es), should be sent with each message. By eliminating other kinds of control information from the messages, the communication overheads can be signiicantly reduced. In this paper we present an algorithm that uses this knowledge to eeciently enforce causal ordering of messages. The proposed algorithm does not require any prior knowledge of the network or communication topology. As computation proceeds, it acquires knowledge of the logical communication topology and is capable of handling dynamically changing multicast communication groups. With regard to communication overheads, the algorithm is optimal for the broadcast communication case. Its energy eeciency and low bandwidth requirement make it suitable for mobile computing systems. We present a strategy that employs the algorithm for causally ordered multicasting of messages in mobile computing environments. Un protocole d'ordonnancement causal pour les syst emes a agents mobiles R esum e : L'ordonnancement causal a pour but de r eduire l'asynchronisme des ex ecutions r eparties en r epercutant sur les livraisons de messages l'ordre de causalit e qui pr eside a leurs emissions. Cet article examine un protocole qui assure un tel ordonnancement causal. Ce protocole, fond e sur la seule utilisation de la d ependance directe entre emissions de messages, est particuli erement eecace. Motiv e par les applications compos ees d'agents mobiles, il est peu couteux en information de contr^ ole.