They propose a general purpose group communication, called Newtop, suited to large-scale systems. Newtop addresses membership changes within groups, process failures, process joins and new group formations. This protocol is efficient and simple. It can be used to solve problems as different as server migration or computer supported cooperative work. A server typically manages data.
Clients interact with servers either to read the data, or to update the data.
More elaborated operations can indeed be considered, which is typically the case in the object oriented programming model. This observation leads to replicate servers. The goal of replication is to guarantee liveness, assuming that the system satisfies some known properties. In a large scale system, the only reasonable assumption is to consider the system as being asynchronous. An asynchronous system is characterised by the absence of a global synchronised clock, and puts no bound on the transmission delay of messages.