This paper presents a new algorithm to implement causal ordering. Causal ordering
was first proposed in the ISIS system developed at Cornell University. The interest
of causal ordering in a distributed system is that it is cheaper to realize than total
ordering. The implementation of causal ordering proposed in this paper uses logical
clocks of Mattern-Fidge (which define a partial order between events in a distributed
system) and presents two advantages over the implementation in ISIS: (1) the information
added to messages to ensure causal ordering is bounded by the number of sites in the
system, and (2) no special protocol is needed to dispose of this added information when
it has become useless. The implementation of ISIS presents however advantages in the case
of site failures.