(Note: The original of this document can be found here. -thb)

Frequently Asked Questions on MMS

P. Pleinevaux
Swiss Federal Institute of Technology, Lausanne
Computer Engineering Dept.
EPFL- DI- LIT
Version 2

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Questions

What is MMS ?
How is MMS specified ?
What is MMSI ?
What is a companion standard ?
Examples of applicatins using MMS
Who is using MMS ?
Why use MMS ?
Limitations of MMS ?
Which communication architectures offer MMS services ?
Where can I find more information on MMS ?
What products are available on the marketplace ?
Is there a public domain implementation of MMS ?

1. What is MMS ?

MMS (Manufacturing Message Specification) is an OSI application layer protocol designed for the remote control and monitoring of industrial devices such as PLCs, NCs or RCs. It is a set of services allowing the remote manipulation of variables, programs, semaphores, events, journals, terminals, etc.

As can be seen from the description below, MMS offers a wide range of services satisfying both simple and complex applications.

MMS variables can be simple (booleans, integers, strings...) or structured (arrays or records). MMS variables can be read or written individually, in lists (predefined or explicitly defined). Partial access to fields of records or particular elements of arrays is possible when using the alternate access parameter.

MMS programs can be remotely started, stopped, resumed, killed.

MMS allows for the download or upload of areas called domains which can contain code, data or both.

MMS defines two classes of semaphores which can be used to ensure mutual exclusion or synchronisation of processes.

MMS offers a large number of services for the definition or modification of events. A user can attach an action to an event and can enroll himself or another process to receive the corresponding event notifications.

The majority of MMS confirmed services can be modified, i.e. their execution can be conditioned on the occurrence of an event or the release of a semaphore. MMS modifiers thus allow a wide variety of synchronizations.

2. How is MMS specified ?

MMS is specified in two documents:

ISO/IEC 9506-1 describes the services that are provided to remotely manipulate the MMS objects. For each service, a description is given of the parameters carried by the service primitives. The services are described in an abstract way which does not imply any particular implementation. In other words, the standard does not specify application programming interfaces.
ISO/IEC 9506-2 specifies the MMS protocol in terms of PDUs (the OSI term for message) and automata. The PDUs are described with a notation called ASN.1 which gives the syntax of the PDUs. There exist tools called ASN.1 compilers to translate these definitions into C code for example. The main part of ISO/IEC 9506-2 is devoted to these PDUs. The automata indicate how MMS reacts to certain events, such as reception of a request PDU or response PDU. The automata are a very small part of the MMS protocol.

3. What is MMSI ?

MMSI (MMS Interface) is a de facto standard interface to MMS adopted by manufacturers such as Bull, HP, IBM in their products. MMSI was defined in MAP 3.0 by General Motors to ensure that applications developed on one machine are portable on another machine.

4. What is a companion standard ?

A companion standard is a document which explains how MMS can be used for a class of applications such as Numerical Control of machine tools, Robot control, Programmable Controllers or Process Control.

A companion standard models an application area in terms of objects which are then mapped onto MMS objects. To manipulate the application objects you actually manipulate the corresponding MMS objects with the appropriate services.

5. Examples of applications using MMS

Manufacturing cell or shop control
Assembly cell control
Process control
Building automation
Remote control of energy distribution network
Configuration of field bus nodes (FIP network)
Inter-control Center Communications

6. Who is using MMS ?

Car manufacturers:

Isuzu (UK)
GM (UK, Germany)
Mercedes Benz (Germany)
Opel (Germany)
Renault (France)
Volvo (Sweden)
Volkswagen (Germany)

Aircraft manufacturers:

Aerospatiale
Boeing

Electric Utilities:

Ohio Edison (US, pilot)
Houston Lighting & Power Company (US, pilot)
Western Power Administration - Loveland Area Office (US, pilot)

Others:

Copenhagen Airport (Denmark)
EDF (France)
NASA
Magneti Marelli (Italy)
EFACEC (Portugal)
Tuborg (Denmark)

7. Why use MMS ?

MMS is a standard protocol, widely implemented by industrial device manufacturers, relieving you of the problems of heterogeneity so often found in industrial applications. MMS is the lingua franca of industrial devices.

MMS is very powerful and can solve a large number of industrial problems

MMS products, even if apparently expensive, are cheaper than many developments that you or your company could do. MMS provides much more than TCP/IP which essentially offers a mechanism to transfer streams of bytes. MMS transfers commands with parameters between machines. To build a protocol on top of TCP, UDP or even Ethernet that offers the minimum that MMS offers, you will spend tens of man-months.

In summary, MMS allows a user to concentrate on his applications and not on communication problems, which are complex and the matter of specialists.

8. Limitations of MMS ?

The size of a full MMS provider, implementing all MMS services, is approximately 300 koctets for both client and server role.

The size of a full MMS server, implementing all MMS services, is more than 1 Mbyte of object code on a RISC machine.

9. Which communication architectures offer MMS services ?

The Manufacturing Automation Protocol (MAP) 3.0 architecture defined by general motors offers MMS on a connection-oriented communication profile.
The CNMA (Communications Network for Manufacturing Applications) architecture defined by the ESPRIT CNMA and CCE-CNMA projects offers MMS on a connection-oriented communication profile. CNMA is a superset of MAP 3.0 and is compatible with the latter.
Mini-MAP -- a three layer architecture defined in MAP 3.0 for real time applications -- offers MMS on a connectionless profile: the LLC type 3 protocol offering reliable transfer of limited size PDUs.
The FIP (Factory Instrumentation Protocol) field bus offers MMS on a connectionless profile.
The ICCP (Inter Control Center communications Profile) specifies the use of MMS over X.25 for communication between electric utilities companies and plants.

10. Where can I find more information on MMS ?

A bibliography on MMS articles or books is available in:

Server: litsun.epfl.ch (128.178.151.50)
Directory: /pub/MMS
File: MMS.bib
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