When updating several connected devices in a machine or plant the devices might first need to be set into a special “state” where they wait for the start of the update and don’t start operating again. After that the updates can be installed in an order defined by the Client (e.g., sensors first, switches last). Finding the best sequence is task of the client implementation or the operator and not in scope of this specification.
The “state” is defined depending on the type of machine / plant. For factory automation this normally means that production and the software on the devices is stopped. For a sensor in process automation this could mean that a replacement value is configured in the controller for the value measuered in the device. If a controller needs to be updated in process automation it often needs to be the passive part of a redundant set of controllers.
A Client also needs to consider the proper sequence when updating the devices. For example, if parts of the network become unreachable due to the update of an infrastructure device.
A server can support the prepare for update option (184.108.40.206) to enable this use case.