Causal Deliveries in Unreliable Networks With Real-Time Delivery Constraints
Abstract
Causal order states that for any process the order in which it is delivered messages cannot violate the \em happened-before relation of the corresponding sendings. The aim of this communication abstraction is to cope with the asynchrony of communication channels in distributed systems. This abstraction has been defined for distributed systems without real-time delivery constraints. In this paper we extend this abstraction to cope with unreliable communication networks with real-time delivery constraints: messages have a lifetime, $\Dter which their contentsaiai can no longer be used, moreover some of them can be lost. This new abstraction, called $\Dal order, requires to delivers s as much messages as possible within their lifetime in such a way that these deliveries respect causal order. A simple efficient implementation is proposed. Examples of distributed multimedia real-time applications, in which scheduling messages deliveries respecting $\Dal order is a crucial point for the quality ofarar the service, are given.