ISA-95 is an international standard series, also published as IEC 62264, for integrating enterprise business systems with manufacturing control systems. It defines levels, activities, terms and data models for exchanging information between them.
ISA-95 is best known for its functional hierarchy. Level 0 is the physical process. Level 1 is sensing and actuation. Level 2 is monitoring and control: PLCs, DCS, SCADA. Level 3 is manufacturing operations management: MES functions such as scheduling, dispatch, quality and maintenance execution, measured in shifts and hours. Level 4 is business planning and logistics, the ERP world, measured in days and weeks.
The standard does more than draw levels. Its parts define object models for personnel, equipment, material and process segments, an activity model for production, quality, maintenance and inventory operations, and the transactions exchanged between Level 3 and Level 4. B2MML, an XML implementation, is a common way to apply it. The approach is technology-neutral: it describes activities, not products.
Two common misreadings. First, the levels describe functions, not boxes or network zones; one software product can span several levels. Second, ISA-95 is not the same as the Purdue model used in network security, although the two share a similar layered view. Many unified namespace designs borrow the ISA-95 equipment hierarchy for their topic names.
ISA-95 vs the Purdue model vs a unified namespace
| ISA-95 | Purdue model | Unified namespace | |
|---|---|---|---|
| Purpose | Integrate business systems with manufacturing control systems | Separate control system networks from enterprise networks and the internet | Replace point-to-point connections with one shared place to publish and read plant data |
| Origin | ISA standard series, established in the mid-1990s; also published as IEC 62264 | Purdue Enterprise Reference Architecture, first developed at Purdue University in 1990 | A design approach; the term was coined around 2015 by Walker Reynolds |
| What it describes | Functions and activities, and the information exchanged between Level 3 and Level 4 | Levels of systems and networks, usually with a DMZ (Level 3.5) between plant and enterprise | A data architecture: one hierarchy of topics on a broker, usually MQTT |
| Typical use | Scoping an MES project or an ERP-to-plant interface | Planning how the plant network is segmented | Connecting many machines and applications without custom interfaces |
Questions about ISA-95
What are the ISA-95 levels?
ISA describes five. Level 0 is the physical production process. Level 1 is sensing and manipulating that process: sensors, smart devices, valves. Level 2 is monitoring and supervising control: PLCs, DCSs and other control devices. Level 3 is manufacturing operations management, where MES sits. Level 4 is business planning and logistics, which includes ERP.
Is ISA-95 the same as the Purdue model?
No. ISA says the ISA-95 framework is based on the Purdue Reference Model, so the levels look alike. But ISA-95 defines functions and the information exchanged between them, while the Purdue model is used mostly to segment networks. NIST SP 800-82 lists the Purdue model and the ISA-95 levels as separate models an organization can use to organize its OT network.
What is ISA-95 Level 3?
Level 3 is manufacturing operations management: the systems, such as MES, that manage production between the control layer and the business layer. ISA says the standard deals mainly with the interface between Level 3 and Level 4. Sources place SCADA differently: ISA's own summary lists it with Level 3 systems, while many network diagrams put SCADA and HMIs at Level 2.
Is ISA-95 the same as IEC 62264?
Yes, in content. ISA says ISA-95 is also known as ANSI/ISA-95 or IEC 62264. The IEC publishes the parts as IEC 62264; its current Part 1 is the 2013 edition. ISA lists its own Part 1 as ANSI/ISA-95.00.01-2025 (IEC 62264-1 Modified).
How does ISA-95 relate to a unified namespace?
A unified namespace needs a naming scheme, and the ISA-95 equipment hierarchy is the usual choice: enterprise, site, area, production line, work cell. The standard supplies the structure and the vocabulary. The unified namespace is the place where the data is published.
Related terms
MES (manufacturing execution system)
An MES (manufacturing execution system) is software that manages and records production on the shop floor.
Purdue model
The Purdue model is a reference model that arranges industrial control systems in levels, from the physical process up to enterprise IT.
Unified namespace (UNS)
A unified namespace (UNS) is an architecture pattern in which plant and business systems publish their current data to one shared, hierarchically organized hub, usually an MQTT broker, instead of exchanging it through point-to-point integrations.
Sparkplug B
Sparkplug B is the current payload definition of Eclipse Sparkplug, an open specification that tells MQTT clients in industrial systems which topic names to use, how to encode data, and how to report whether a device is online.
IT/OT convergence
IT/OT convergence is the integration of information technology, the systems that handle business data, with operational technology, the systems that monitor and control physical equipment, so data and practices flow between them.
SCADA
SCADA (supervisory control and data acquisition) is a computerized system that gathers data from remote or distributed equipment and lets operators monitor and control it.
Sources
- ISA: ISA-95 Standard, Enterprise-Control System Integration
- IEC: IEC 62264-1:2013, Enterprise-control system integration, Part 1: Models and terminology
- NIST: SP 800-82 Rev. 3, Guide to Operational Technology (OT) Security (September 2023)
- National Petroleum Council (hosted by the US Department of Energy): Topic Paper 4-14, Purdue Model Framework for Industrial Control Systems and Cybersecurity Segmentation (2019)
- Sirris: Unified Namespace, a next step in Industry 4.0 standardisation