Supporting Mobility in Content-Based Publish/Subscribe Middleware

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 was 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). For logical-mobility we introduce location-dependent subscriptions as a suitable means to exploit the power of the event-based paradigm in mobile applications. Briefly spoken, a location-dependent subscription offers to express interest in all events which are related to a user's current location. We present efficient implementations for both forms of mobility within the content-based pub/sub middleware Rebeca. Our solutions draw much of their efficiency from the refined routing capabilities (namely, covering and merging) of the Rebeca system.