Efficient causally ordered communications for multimedia real-time applications

Multimedia real-time collaborative applications or groupware real-time applications require participants 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 can be discarded if it violates the tinting constraints imposed by a real-time interaction. In this paper we 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. This new abstraction, called Δ-causal order, requires to deliver as much messages as possible within their lifetime in such a way that these deliveries respect causal order. An efficient protocol is proposed in the case of one-to-one communications. A variation of this protocol weld suited to broadcast communications is also shown