Synchronizing Device Discovery on Loss of Update Messages in the Pervasive Middleware Palcom

PalCom is a pervasive middleware that enables users to combine the services on devices into useful configurations. Interconnected PalCom devices can discover, and keep track of, the existence of each other by exchanging periodic heartbeats within local networks, and once-sent device appearance/disappearance notifications across interconnected networks. This approach has the advantage of eliminating the need to forward periodic heartbeats beyond the boundaries of the local networks of their originator devices. However, when a device appearance/disappearance notification is sent only once over an unreliable channel, there is a possibility of losing that notification. As a result, the device discovery information on PalCom devices will be out-of-sync. In this paper, we present the design, model-based evaluation, and the implementation status of a solution to this synchronization problem.