The subscription state machine in https://reference.opcfoundation.org/Core/Part4/v104/docs/5.13.1 has the following “condition” defined:

SubscriptionAssignedToClient A boolean value that is set to TRUE only when the Subscription requested to be deleted is assigned to the Client that issued the request. A Subscription is assigned to the Client that created it. That assignment can only be changed through successful completion of the TransferSubscriptions Service.

This condition is only validated in the DeleteSubscription event.

Which led us to believe that it is possible to modify a subscription e.g., using ModifySubscription or CreateMonitoredItems with an identifier of a subscription not created and part of the client session used to make the call. Except for the DeleteSubscription call which requires “ownership”. We could not find anywhere in the specifications anything contrary or explict.

After discussing with Randy he suggested to open this Mantis issue as it is not intended to access subscriptions in other sessions. I assume the following would need to be changed:

• Remove the SubscriptionAssignedToClient Condition from the state machine description
• as well as the transition 0000026 related to it (then it should not reset the lifetime counter of a session that is not owned by the client, or?)
• Clarify in the subscription section that it is invalid to access a subscription from a session that does not own it. Specify the error code to return if a subscription id is provided that is owned by another session (Bad_SubscriptionIdInvalid is assumed).

Unless it is found that accessing a subscription by id that is assigned to a different session is desired.