Evaluation and analysis of realizing broker-based content routing protocols in SDN

Abstract

Publish/subscribe provides a valuable communication model to the future Internet due to the decoupling of end-users from each other. One of the stubborn challenges that face recent content-based publish/subscribe systems is the trade-off between the usage of the network bandwidth and the end-to-end delay of published events. This trade-off is imposed by the fact that most implementations depend on software brokers to filter incoming messages towards received requests from subscribers. Although this approach for filtering may present the most bandwidth efficient solutions, the use of brokers adds to the network end-to-end delay. The installed brokers are implemented at the application layer and hence the original path between publishers and subscribers is extended which adds to the delay in which messages are forwarded from publishers to subscribers. Along with the delay imposed by the extended path, another processing delay is added to the system based on the time needed for filtering incoming messages at the brokers. As the time factor is crucial to the real-world applications that depend on the content-based publish/subscribe paradigm, recent implementations try to tackle this problem by exploiting the deployed hardware in the underlying infrastructure for filtering operations. In-network filtering is enabled with the help of Software Defined Networking (SDN) technology as it allows the installment of content filters directly to the network switches/routers. Even though this approach significantly reduces the end-to-end delay, it suffers when the bandwidth efficiency is evaluated. Caused by the inherited hardware limitations, installing content filters on hardware network elements limits their expressiveness. This increases the number of published messages from publishers to subscribers on different network links which requires more bandwidth. As an intermediate solution between the two filtering approaches, the work of this thesis is the realization of a hybrid content-based publish/subscribe middleware that allows filtering operations in both network and application layers.