SOLA: A Decentralized Communication Middleware Developed with ns-3

The transformation from static production facilities into a flexible and decentralized cyber-physical production system (CPPS) is part of the current ongoing Industry 4.0. A CPPS will enable and support communication between people, machines and virtual objects, e.g., as material flow or products, alike. However, communication in CPPS relies often on centralized approaches using a message broker or is not considered at all. We present in this paper the decentralized communication middleware called SOLA with an emphasis on, but not limited to, CPPS. SOLA uses the inherent given capability to communicate of participating nodes and eliminates the need for a central instance. A structured overlay network is created and managed, which appears to its users as a single coherent system. The main building blocks of SOLA are the management overlay and the event dissemination. Within this building blocks, no single peer has a global view and all operations are based on each peer's local view. The local view represents some selected links to a subset of all peers in the network. In addition to this, we also present how SOLA was developed with the help of the discrete-event simulator ns-3. Finally, we also show how we have used ns-3 to simulate a self-organizing material flow where participants use SOLA to communicate.