Type Specific Routing for Reliability in Event Based Middleware

Guaranteeing Quality of Service (QoS) for event delivery has been recognized as a important but challenging issue in Event Based Middleware (EBMs). Amongst the numerous QoS parameters, in this effort, we focus on reliability as a service guarantee to subscribers in an EBM. While there exist some work in this area, our focus is primarily on providing subscribers with an additional level of granularity in terms of subscription filters. Subscribers can now specify individual reliability requirements on a per event type basis. The broker network will establish reliable routes that guarantee the subscriber requested reliability requirement for each event type. This is achieved by maintaining eventtype specific path-quality information at every broker node occurring in the route to the destination. Each broker node is modeled to measure the drop probability of a particular event type. We theoretically prove that the drop probabilities experienced by individual event types are proportional to the ratio of their inter-arrival times at the broker. Based on this model of the broker node, we present the TSAR (Type Specific Adaptive Reliability) algorithm. In TSAR, the route establishment is done in an adaptive fashion using persistent type-specific path quality information stored as a matrix of reliability estimates. Our results show that TSAR (1) reduces the overall message complexity as compared to existing efforts in this area by updating information at a broker only on the occurrence of a trigger (2) provides subscribers with a higher level of granularity when subscribing to events (3) adapts to the dynamics of the broker network with varying reliabilities of broker nodes (4) and is highly scalable in terms of the number of subscriptions in the network, the size of the broker network and the connectivity of the overlay.