Mechanisms to ensure ordered execution in MMS

MMS (Manufacturing Message Specification) applications are composed of clients and servers that interact through MMS to perform a given task. A client is for example a cell control application running on a minicomputer while servers generally are industrial devices such as programmable logic controllers or numerical controllers of machine tools. In the case of the Manufacturing Automation Protocol (MAP), clients and servers are linked by so-called associations, that are application level connections. On a given association, requests sent by a client are delivered to the server in the order they were sent. Indeed, the association implements a FIFO (First In First Out) policy. The MMS standard does not impose however that requests received on an association are executed in the order they were sent. The problem addressed in this paper is the following: how can one ensure that MMS service requests are executed by a server in a given order