Supporting Mobility in Content-Based Publish/Subscribe Middleware

Abstract

Abstract. Publish/subscribe (pub/sub) is considered a valuable middleware architecture that proliferates loose coupling and leverages reconfigurability and evolution. Up to now, existing pub/sub middleware was optimized for static systems where users as well as the underlying system structure were rather fixed. We study the question whether existing pub/sub middleware can be extended to support mobile and location-dependent applications. We first analyze the requirements of such applications and distinguish two orthogonal forms of mobility: the system-centric physical mobility and an application-centric logical mobility (where users are aware that they are changing location). We introduce location-dependent subscriptions as a suitable means to exploit the power of the event-based paradigm in mobile applications. Briefly spoken, location-dependency refines a subscription to accept only events related to a mobile user's current location. Implementations for both forms of mobility are presented within the content-based pub/sub middleware Rebeca, drawing from its refined routing capabilities (namely, covering and merging).

Supporting mobility with persistent notifications in publish/subscribe systems

“…The existing solutions for client mobility in distributed pub/sub systems use the queuing approach (Q-app) for storing notifications in special queues during subscriber disconnections [1,5]. We propose an approach based on persistent notifications (PN-app) that requires the delivery of valid notifications after the activation of a new subscription in the system.…”

“…The existing solutions extent the established pub/sub systems that are optimized for stationary environments by adding special proxy subscribers taking the subscriber's role for disconnected subscribers [1,5].…”

“…The solution presented in this paper is compliant with the algorithm for physical mobility developed within the project REBECA [5,12] that uses the Q-app where the last serving broker takes the role of a proxy subscriber. When a subscriber connects to a new broker, it re-issues its subscriptions, and the broker network finds the old broker by locating a broker at the junction of delivery paths to the new and the old broker.…”

“…However, the subscriber will not receive notifications that are published during the time of disconnection. The queuing approach is commonly applied to solve the problem of lost notifications [1,5,10]. A system broker, or a special proxy acts as a proxy subscriber during subscriber disconnections.…”

Engineering mobile wireless publish/subscribe systems for high performance

“…Although their work addresses the issues in the deployment of these systems over wireless networks, they have not given any concrete results on the behavior of these systems in such environments. Concurrent with our research, there have been researches to support mobility with SIENA [2] and REBECA [10] [15]. However, unlike other works, our research is more focused on the performance of publish/ subscribe extensions to mobile domain.…”