This Service is used to transfer a Subscription and its MonitoredItems from one Session to another. For example, a Client may need to reopen a Session and then transfer its Subscriptions to that Session. It may also be used by one Client to take over a Subscription from another Client by transferring the Subscription to its Session.
The authenticationToken contained in the request header identifies the Session to which the Subscription and MonitoredItems shall be transferred. The Server shall validate that the Client of that Session is operating on behalf of the same user and that the potentially new Client supports the Profiles that are necessary for the Subscription. If the Client uses an ANONYMOUS user token, the Server shall validate if the ApplicationUri is the same for the old and the new Session and the MessageSecurityMode is SIGN or SIGNANDENCRYPT. If the Server transfers the Subscription, it returns the sequence numbers of the NotificationMessages that are available for retransmission. The Client should acknowledge all Messages in this list for which it will not request retransmission.
If the Server transfers the Subscription to the new Session, the Server shall issue a StatusChangeNotification notificationMessage with the status code Good_SubscriptionTransferred to the old Session. The StatusChangeNotification notificationMessage type is defined in 7.25.4.