A GDS in push-mode initiates the certification deployment for a CertificateGroup on a OPC UA server, which is used as a gateway, for underling devices.

The first problem now, can be that on the TrustList.CloseAndUpdate, different scenarios can occur when the calls are transferred from the gateway to the corresponding devices:

1. The device can be reached and gives it’s answer in an appropriate time. (good case)
2. The device needs longer for the answer then the timeout is configured.
3. The device is not reachable at the moment.
4. The device will not be able to be reached future.
5. The device was changed.

For the scenarios 2-5 there are also no suitable return-values in the specification at the moment.

The above-mentioned sequences can be mapped to “CreateSigingRequest”, “UpdateCertificate”, “CreateKeyPair” and even furth thought on other functionality’s like aggregating another server.

Besides the return values, a corresponding behavior how the counter part reacts to these return values is needed to be specified.
For CloseAndUpdate, there is already the ApplyChanges defined, but is hard to understand and not perfectly suitable.
For the sequences of “CreateSigingRequest”, “UpdateCertificate” and “CreateKeyPair” there does not exist any behavior if we run in one of the scenarios.
There should be an async solution for synchronizing such calls in one general matter.