Abstract
A publish/subscribe communication system (PSS) realizes a many-to-many anonymous interaction among its participants. Producers of information (publishers) issue notifications to the PSS. These are delivered by the PSS to all subscribers that declared interest in it. However, this decoupled form of interaction introduces delays between i) the production of a notification and its delivery to subscribers (diffusion delay) and ii) the declaration of interest by a subscriber and its registration in the PSS (subscription/unsubscription delay). Such delays could lead to notification loss scenarios where an event is not delivered to an intended subscriber even though it was issued when the subscription was active. This paper studies this notification loss phenomenon by presenting a simulation study of a PSS and an analytical model. The latter measures the percentage of notifications guaranteed by a PSS implementation to a subscriber. To our knowledge this is the first paper that addresses such a QoS issue. The model is based on a formal framework of a distributed computation. The framework abstracts the PSS through the two delays, de.ning safety and liveness properties that precisely characterize the semantics of the PSS.