Realizing Content-Based Publish/Subscribe with P4

Publish/subscribe communication is used in distributed applications to loosely couple publishers and subscribers of notifications. Especially for content-based publish/subscribe, distributing notifications from publishers to subscribers with a matching subscription is a crucial and complex task, since a notification's set of receivers can potentially comprise any combination of subscribers. Various strategies are known for this task and each tackles the trade-off between efficiency and flexibility differently by applying unicast, network-assisted multi-cast, or application-layer multicast. However, with the advent of software-defined networking, new distribution strategies can now be realized combining the efficiency of network-assisted multicast with the flexibility of application-layer multicast.In this paper, we show that SDN and, in particular, the P4 programming language is well suited to implement notification distribution flexibly and efficiently. We present novel distribution strategies that place the information necessary for distributing a notification in the notification packet itself. We evaluate the strategies using an emulated network and compare them to OpenFlow multicast, application-layer multicast, unicast, and broadcast. The evaluation investigates packet size, consumed network bandwidth, table lookups, and notification delay. The results show that our strategies reach the intended goals.

I. Introduction

Publish/subscribe (pub/sub) is a messaging pattern for distributed systems that is used in many applications such as transport information monitoring, event-driven supply chain management, location-based services, ubiquitous computing, and the Internet of Things. Pub/sub encompasses two roles: publishers publish messages, called notifications, subscribers subscribe to those notifications they are interested in, and publishers optionally announce through advertisements that they will potentially publish certain notifications. Publishers and subscribers are not directly connected to each other, but are decoupled by an interposed notification service that ensures mediation of notifications, while publishers and subscribers do not need to know each other directly.