The Cached-Loading option provides a model where the transfer of the Software Package and its installation are separate steps. To support the Cached-Loading model the Server has to provide the Current Version and the Pending Version. Optionally the Fallback Version can be supported.
With the Current Version the Client can decice if an update is required and which version to transfer. With the Pending Version the Client can ensure to install the desired version. With the Fallback Version the Client can install an alternative version.
Software Packages are transferred using the TemporaryFileTransferType (OPC 10000-5). The new software may be transferred in the background without stopping the device. The actual installation of the software can be done later using the installation option.