Implementing Content-based Publish/Subscribe on the Network Layer with P4

In content-based publish/subscribe systems, publishers produce notifications and subscribers register subscriptions to receive certain notifications based on their content. It is the task of the middleware to deliver the published notifications to subscribers having a matching subscription. Content-based publish/subscribe is challenging to implement efficiently, because the resulting delivery tree can be different for each notification, set of active subscriptions, and location of the subscribers. Therefore, content-based routing of notification has often been implemented in the application layer resulting in high notification delays and a waste of network bandwidth. In this work, we report on the research and actual development of a novel middleware, which uses the P4 SDN programming language to perform the content-based forwarding of notifications solely in the network layer. We present a hybrid approach that combines (i) encoding of routing information into the notification to be distributed and (ii) installing forwarding rules into the switches. In particular, we combine different types of routing information that either represent individual network links or virtual links referencing pre-installed distribution trees. We derive the latter from topological information about the network and from publish/subscribe relationships as well as forwarding statistics.