Executive Summary (Introduction to MMS Nr.1)
The Manufacturing Message Specifcation (MMS) is an international standard that addresses the integration of shopfloor devices such as intelligent electronic devices (IED), personal computers, numerically controlled (NC) machine tools, robots, programmable logic controllers (PLCS) and the computer systems that control them. MMS defines a structure for the messages required to control and monitor these devices; it is not concerned with the way the messages are transferred between devices over a network.
Its development stems from manufacturing companies who were facing the real problems of making their various manufacturing systems operate effectively with one another. MMS is the result of a major international development initiative, involving most industrialised countries, which has taken more than 5 years to complete. Recently the MMS standard has been published by the International Standards Organisation (ISO) in its second version (1999).
As it is an international standard, MMS is not owned or controlled by any single commercial organisation and is therefore widely available for exploitation by both system vendors and users. Its adoption will lead to lower costs in systems integration and support, and will enable users to select products using "fit for purpose" criteria.
MMS is considered to be one of the most important standards to emerge from the international Programme of work in computer integrated manufacturing. However products incorporating MMS are available from a number of systems vendors and are being successfully used in automation projects worldwide.
MMS will play an increasingly important role in the development of computer integrated manufacturing, and should feature in the planning of systems to meet your future automation strategy.
Because MMS is an internationally agreed standard, it is widely available and not controlled by any single commercial organisation. It can be used by product developers, system integrators and users to develop computer integrated nianufacturing systems. By the Adoption and implementation of MMS across manufacturing industry both technical and commercial benefits can be realised. These are summarised as follows:
Increased Choice and Flexibility
Selection of devices supporting MMS allows purchases to be made using "fit for purpose" criteria and reduces the risk of becoming locked into a single vendor. MMS provides independence from the type of network used. This leads to increased competition on price and quality for both the initial implementation and future extensions.
Reduced Litetime Costs
Adopting MMS allows reductions in total costs and in the resources required throughout the life of an integrated manufacturing system. The savings occur because each device conforms to a single communications protocol and therefore the time taken to specify, design and commission the implementation is reduced. Similarly, computer program development and maintenance costs are reduced because the systems integrators and service engineers only need to understand a single protocol.
Although all devices supporting MMS will be functionally similar from the communications point of view, NMS does not restrict vendors from "adding value" to their products. Competitive advantage can be maintained through innovatiors performance, quality and cost. The design and commercial constraints are limited to the additional resident communications software required to implement that part of the MMS protocol relevant to that type of device.
Concepts within MMS
MMS specifies a way to emulate, or model, the capabilities and functionality of a programmable device, and the means to manipulate this model. The emulation and the protocol facilitate the transfer of control information and data between computers, application programs and programmable devices on a network. The following sections explain in more detail the important concepts within the MMS standard.
The Messaging Service
The MMS standard defines a range of services each having a unique function. The services are used to transfer data within messages across the network.
The exchange of messages over the network first requires a logical connection or association to be established. This is analogous to placing a Telephone call in that both the caller's and the receiver's telephones are connected to the network, but until the caller correctly dials the receiver's number there is no connection. When the receiver answers the call the association is made and the exchange of Information can begin.
The Telephone analogy can be extended to the international service. lf a caller wishes to communicate with a number of overseas contacts, the desired international codes are dialled and the network makes the connections. However for the caller to be able to communicate with each receiver a common language must be adopted, otherwise information cannot be exchanged. One solution is for the receivers to adopt the language of the caller through a local translator. Here MMS is equivalent to the language of the caller, and the VMD is equivalent to the translator ensuring the correct understanding of the messages at each of the receivers.
As in any language, the semantic is defined in common or specialized dictionaries. With regard to MMS the semantic "communicated" by MMS is outside the scope of ISO 9506 (MMS). MMS just provides syntax rules, objects and services applicable for accessing and exchanging information. The Utility Communications
Architecture (UCATM) provides a wide selection of terms and definitions that define common semantic and utility specific semantic.
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