RESTful Industrial Communication With OPC UA

Representational state transfer (REST) is a wide-spread architecture style for decentralized applications. REST proposes the use of a fixed set of service interfaces to transfer heterogeneous resource representations instead of defining custom interfaces for individual applications. This paper explores the advantages of RESTful architectures, i.e., service-oriented software architectures comprised RESTful services, in industrial settings. These include communication advantages such as reduced communication overhead and the possibility to introduce caching layers, and system design advantages including stable service interfaces across applications and the use of resource-oriented information models in cyber-physical systems. Additionally, a RESTful extension to the open platform communications (OPC) unified architecture (OPC UA) binary protocol is proposed in order to leverage these advantages. It requires only minimal modifications to the existing OPC UA stacks and is fully backward compatible with the standard protocol. Performance benchmarks on industrial hardware show a throughput increase up to a factor of eight for short-lived interactions. This reduction of overhead is especially relevant for the use of OPC UA in the emerging Industrial Internet of Things.