Manufacturing Message Specification
Manufacturing Message Specification is an international standard dealing with messaging systems for transferring real time process data and supervisory control information between networked devices or computer applications. The standard is developed and maintained by the ISO Technical Committee 184. MMS defines the following
- A set of standard objects which must exist in every device, on which operations like read, write, event signaling etc. can be executed. Virtual manufacturing device is the main object and all other objects like variables, domains, journals, files etc. comes under VMD.
- A set of standard messages exchanged between a client and a server stations for the purpose of monitoring or controlling these objects.
- A set of encoding rules for mapping these messages to bits and bytes when transmitted.
MMS original communication stack
- ISO/IEC 9506-1 : Industrial Automation systems - Manufacturing Message Specification - Part 1: Service Definition
- ISO/IEC 9506-2 : Industrial Automation systems - Manufacturing Message Specification - Part 2: Protocol Specification
| Application | Application Common Service Element - ISO 8649/8650 |
| Presentation | Connection Oriented Presentation - ISO 8822/8823 Abstract Syntax Notation - ISO 8824/8825 |
| Session | Connection Oriented Session - ISO 8326/8327 |
| Transport | Connection Oriented Transport - ISO 8072/8073 |
| Network | Connectionless network - ISO 8348 |
| Link | MAC - ISO 8802-3 MAC - ISO 8802-4 |
| Physical | Ethernet Token Ring |
MMS stack over TCP/IP
Because the Open Systems Interconnection protocols are challenging to implement, the original MMS stack never became popular. In 1999, Boeing created a new version of MMS using Internet protocols instead of the bottom four layers of the original stack plus RFC 1006 in the transport layer. The top three layers use the same OSI protocols as before.In terms of the seven-layer OSI model, the new MMS stack looks like this:
| Application | Application Common Service Element - ISO 8649/8650 |
| Presentation | Connection Oriented Presentation - ISO 8822/8823 Abstract Syntax Notation - ISO 8824/8825 |
| Session | Connection Oriented Session - ISO 8326/8327 |
| Transport | ISO transport over TCP - RFC 1006 Transmission Control Protocol - RFC 793 |
| Network | Internet Control Message Protocol - RFC 792 Internet Protocol - RFC 791 Address Resolution Protocol - RFC 826 |
| Link | IP datagrams over Ethernet - RFC 894 MAC - ISO 8802-3 |
| Physical | Ethernet |
With the new stack, MMS has become a globally accepted standard.