Causal multicast in unreliable networks for multimedia applications

Multicast communications are of primary importance for multimedia real-time applications where participants are required to exchange real-time audio and video information over a communication network. This flow of information must preserve the causal dependency even though part of the information can be lost or discarded if it violates the timing constraints imposed by a real-time interaction. As it is, a causal order communication mode concerns distributed systems without real-time delivery constraints and assumes unpredictable but finite messages transmission delays and, hence, protocols implementing this communication mode do not cope with real-time issues. We first propose a communication abstraction to cope with unreliable communication networks with real-time delivery constraints: messages have a lifetime, Δ, after which their contents can no longer be used, moreover some of them can be lost. Secondly, we propose a protocol imposing Δ-causal order in the case of one-to-one and one-to-many (multicast) communications