With the vision of Internet of Things gaining popularity at a global level, efficient publish/subscribe middleware for communication within and across datacenters is extremely desirable. In this respect, the very popular Software-defined Networking (SDN), which enables publish/subscribe middleware to perform line-rate filtering of events directly on hardware, can prove to be very useful. While deploying content filters directly on switches of a software-defined network allows optimized paths, high throughput rates, and low end-to-end latency, it suffers from certain inherent limitations w.r.t. no. of bits available on hardware switches to represent these filters. Such a limitation affects expressiveness of filters, resulting in unnecessary traffic in the network.

In this paper, we explore various techniques to represent content filters expressively while being limited by hardware. We implement and evaluate techniques that i) use workload, in terms of events and subscriptions, to represent content, and ii) efficiently select attributes to reduce redundancy in content. Moreover, these techniques complement each other and can be combined together to further enhance performance. Our detailed performance evaluations show the potential of these techniques in reducing unnecessary traffic when subjected to different workloads.