  Cyclic or general overlays may provide multiple paths between publishers and
subscribers. However, an advertisement tree and a matching subscription
activates only one path for notifications routing in publish/subscribe systems.
This poses serious challenges in handling network conditions like congestion,
and link or broker failures. Further, content-based dynamic routing of
notifications requires instantaneous updates in routing paths, which is not a
scalable option. This paper introduces a clustering approach with a bit-vector
technique for inter-cluster dynamic routing of notifications in a structured
cyclic topology that provides multiple paths between publishers and interested
subscribers. The advertisement forwarding process exploits the structured
nature of the overlay topology to generate advertisement trees of length 1
without generating duplicate messages in the advertisement forwarding process.
Issued subscriptions are divided into multiple disjoint subgropus, where each
subscription is broadcast to a cluster, which is a limited part of the
structured cyclic overlay network. We implemented novel static and
intra-cluster dynamic routing algorithms in the proposed overlay topology for
our advertisement-based publish/subscribe system, called OctopiA. We also
performed a pragmatic comparison of our two algorithms with the
state-of-the-art. Experiments on a cluster testbed show that our approach
generates fewer inter-broker messages, and is scalable.
