The present invention concerns a process and a device for validating/invalidating a message sent over an information transmission network.
The present invention is more particularly concerned with a process and a device for validating a message sent over a network between at least two stations connected to the network by means of a response in a communication frame, the message including at least one header field sent by a first station and one data field sent by a second station.
In prior art transmission processes and devices of the above kind, also known as communication frame response processes and devices, at least one of the stations accesses the network in order to transmit the beginning of a message frame, also known as the header field, and in accordance with the message header field another station accesses the network to transmit the end of the message frame, containing event or data information from that station, the end of the frame being also generally known as the data field.
However, the above processes and devices give rise to a number of problems, in particular concerning updating and transmission of the data field. The time of transmission of the data is not under the control of the station producing the data, but rather that requiring the data.
If the station producing the data wishes to update it, there is a risk that the update will take place during the transmission of the data over the network, if the update is carried out in the meantime.
The risk is then that the corresponding station transmits internally inconsistent information, some of which has been updated and the remainder of which has not.
One prior art proposal for solving this problem is to add a validity marker to the data field, for example at the beginning of this field.
The marker is set to a particular value before any updating of the data and changed to a different value when the update has been done.
A station reading the data can then analyze the marker to determine if the data is being modified and updated or not and therefore if it should be regarded as valid or invalid.
However, this mechanism is inadequate as it does not solve the problem of transmitting an inconstant data field, in particular if the updates starts while the data is being transmitted.
The aim of the invention is therefore to solve these problems.