by Dr. Rajive Joshi, Ph.D.
Co-Chair, Connectivity Task Group, Industrial Internet Consortium (IIC)
Principal Solution Architect, Real-Time Innovations Inc (RTI)
Three of the main goals of the Industrial Internet of Things (IIoT)community are (1) clarify the rich but often confusing landscape of IIoT connectivity, (2) set a stable long-term foundation for IIoT interoperability and architecture strategy, (3) provide practical, useful and tangible guidance for IIoT connectivity requirements assessment, technology evaluation and selection. The ‘Industrial Internet Connectivity Framework’ (IICF), published by the Industrial Internet Consortium (IIC) in February 2017, accomplishes these goals.
The IICF, the latest in a series of technical publications laying the groundwork for the IIoT, is a collaboration from members of the IIC and reflects thousands of hours of knowledge and experiences from connectivity experts, collected, researched and evaluated for the benefit of all IIoT system deployments.
The IICF introduces a new ‘IIoT Connectivity Stack Model’ that is an evolution of the 4-Layer Internet stack model (circa 1989) and the 7-Layer OSI stack model (circa 1994) with IIoT considerations added in.
The new IIoT Connectivity Stack model, shown below, is notable for clarifying the layers above the networking layer: it introduces a new Framework layer and clarifies the Transport layer. The IICF deliberately chose to focus on the connectivity stack above the network layer since those layers have evolved rapidly in the last decade and are not as widely recognized or understood in the context of IIoT. In particular, the newly introduced connectivity framework layer, while critical for building IIoT systems, is the least understood. The IICF specifically elaborates on the core functions and the key considerations of the framework and transport layers from an IIoT perspective.
Most profoundly, the IICF defines the minimum expectation: an IIoT connectivity stack provides syntactic interoperability between IIoT components and subsystems. Syntactic interoperability is the unambiguous exchange of structured data between participants. The IICF clarifies that syntactic interoperability is the essential building block for interoperable systems and thus critical for unleashing the potential of IIoT.
So, what does syntactic interoperability really mean in practice? Consider a scenario where a participant wants to share a datatype containing a string and two numbers. The other participants may be on different platforms and may be built at different times by different people in different places using different programming languages. Syntactic interoperability ensures that the datatype is interpreted unambiguously by all the parties. That requires the connectivity infrastructure to maintain sufficient context, including for example, the string representation (e.g. ASCII or Unicode), the number representation (e.g. integer or floating point), the field sizes and names. It also requires that the connectivity infrastructure encode the data on the wire in an unambiguous manner such that it is decoded correctly by the connectivity infrastructure independently of the implementation, computing platform, or the programming language.
The framework layer in the IIoT connectivity stack is responsible for providing syntactic interoperability. Thus, the minimum expectation of an IIoT connectivity stack is that the connectivity infrastructure is able to handle sharing of structured data types between participants, regardless of the computing platform or the programming language used by applications.
In the syntactic interoperability example above, the connectivity framework ensures that the datatype containing a string and two numbers is shared unambiguously. However, the connectivity infrastructure is not required to provide any additional context on how those members are to be interpreted. For example, does the string represent a room in a building and the numbers represent the temperature and pressure? Or, does the string represent the address of a parking lot and the numbers represent the location of a car in that parking lot? What are the units and ranges of the fields? Semantic interoperability infrastructure provides that additional context beyond syntax so that structured data can be meaningfully interpreted. The IICF suggests the ‘Distributed Data Interoperability and Management’ layer as the place in the reference architecture for providing the support needed for semantic interoperability. Higher layers of interoperability (e.g., semantic interoperability) increase integration automation; they continue to be an active area of research, and beyond the scope of the connectivity framework.
So, how does the new IIoT connectivity stack model juxtapose with current IIoT connectivity standards? A connectivity standard may span multiple layers of the IIoT connectivity stack, it may (or may not) provide all the functions of a layer, it may place different priorities on the typical considerations for each layer, it may place different weight on various system architectural qualities. In order to develop an objective evaluation of any connectivity technology, the IICF provides a detailed 4-page assessment template worksheet that can be used to place a technology correctly on the IIoT connectivity stack. The worksheet can also be used to determine an IIoT system’s connectivity requirements, select the right connectivity standard for that system, and identify any gaps.
As one would expect, filling out the worksheet for a connectivity technology is a laborious process requiring deep technical expertise in the technology and its usage. The IICF offers a starter set of completed assessment template worksheets for relevant IIoT connectivity frameworks (DDS, oneM2M, OPC-UA) and transports (CoAP, MQTT, HTTP) standards. The rollup of the assessment templates is shown in the diagram below, highlighting the placement of the relevant IIoT connectivity standards on the IIoT connectivity stack.
The IICF is the first extensive work by a major consortium that provides useful, tangible, and practical guidance for those looking to build IIoT solutions today. The IICF explains how connectivity fits within the business of industrial operations and its foundational role in providing system and component interoperability when building IIoT systems. It establishes a starting point for IIoT architects and system designers looking to make sense of the connectivity options available today for IIoT projects. It takes designers from the highest-level architectural considerations all the way down to very specific implementation choices.
You can learn more by joining the April 5th webinar on IIoT Connectivity. You can use the assessment template worksheet for your IIoT project. You can use the starter catalog of assessments to get a jump start on your IIoT project. And you can participate in the evolution of IIoT connectivity by joining the IIC.