Overview
ISO 9506-2:2003 - part of the Manufacturing Message Specification (MMS) family - is the protocol specification that defines how MMS messages are encoded and exchanged at the Application Layer (OSI model). Working together with ISO 9506‑1 (abstract models and services), Part 2 specifies the concrete PDUs, ASN.1 encodings and procedural rules a client (MMS-user) and server (MMS-user/MMPM) must follow to realize the abstract MMS services. The standard is designed for use over any full‑duplex, reliable network (for example Ethernet/Internet) and follows a client–server interaction model to support communications between automated equipment and supervisory/control systems.
Key topics and requirements
- Protocol structure and PDUs: Defines Confirmed-RequestPDU, Confirmed-ResponsePDU, Confirmed-ErrorPDU and Unconfirmed-PDU formats and their use.
- Message encoding: Includes ASN.1 definitions and presentation conventions to ensure consistent message serialization and parsing.
- Service procedures and protocols: Detailed protocol procedures for core MMS domains such as:
- Environment & general management (initiate, conclude, abort, cancel)
- VMD (Virtual Manufacturing Device) support: status, identify, capability lists
- Domain management (download/upload, load/store domains)
- Program invocation and unit control
- Variable access (read, write, named variables/types, alternate access)
- Data exchange, semaphore management, operator communication
- Event management, event conditions/actions/enrollment, journals
- Error handling & conformance: Rules for handling errors, rejects, negative confirmations and determining protocol subsets and conformance.
- Mapping to underlying services: Guidance for mapping MMS PDUs to lower-layer transport/association services and flow control.
- Configuration & initialization: Statements and procedures for initializing the VMD and system configuration.
Applications and who uses it
ISO 9506-2 (MMS protocol) is used where standardized, interoperable messaging is required between control devices and supervisory systems:
- Industrial control system integrators implementing cross-vendor communications
- PLC / RTU / DCS vendors adding standardized application-layer protocols
- SCADA and MES developers for reliable data exchange, alarms/events, and program control
- Automation architects and system engineers designing multi-vendor networks
- Test labs and compliance teams validating conformance to MMS protocol behaviors
Benefits include improved interoperability, clear message semantics, and a vendor-neutral approach to variable access, event management, and program control over reliable networks.
Related standards
- ISO 9506‑1 - MMS: abstract information models and services (complements Part 2)
- OSI model references (Application Layer guidance for mappings)
Keywords: ISO 9506-2, Manufacturing Message Specification, MMS protocol, industrial automation, application layer, variable access, event management, ASN.1, VMD, domain management.