A coordination-level middleware for supporting flexible consistency in CSCW

Highly interactive collaborative applications need to offer each user a consistent view of the interactions represented by the streams exchanged between dispersed groups of users. At the coordination level, strong ordering protocols for capturing and delivering streams´ interactions (e.g. CAUSAL, TOTAL order) may be too expensive due to the variability of the network conditions. This paper builds upon previous work on expressing streams causality and proposes a flexible coordination middleware in order to integrate different delivery modes (e.g. FIFO, CAUSAL, TOTAL) into a single channel (with respect to each of these protocols). Moreover, the proposed abstract channel can handle the mix of any partial or total order protocols. We present a cooperative streaming scenario and an experimental platform for measuring the cost of combining several protocols on various network conditions and show how our coordination service can adjust the degree of synchronization according to network variations.