XNet: a reliable content based publish subscribe system

Content-based publish/subscribe systems are usually implemented as a network of brokers that collaboratively route messages from information providers to consumers. A major challenge of such middleware infrastructures is their reliability and their ability to cope with failures in the system. In this paper, we present the architecture of the XNET XML content network and we detail the mechanisms that we implemented to gracefully handle failures and maintain the system state consistent with the consumer population at all times. In particular, we propose several approaches to fault tolerance so that our system can recover from various types of router and link failures. We analyze the efficiency of our techniques in a large scale experimental deployment on the PlanetLab testbed. We show that XNET does not only offer good performance and scalability with large consumer populations under normal operation, but can also quickly recover from system failures.