Monitor Server state|OPC UA Standard|Forum|OPC Foundation

Test case Description:
The client monitors the ServerState either by polling or subscribing to data changes.
1.
2. Server changes the ServerState to Shutdown

Expected Result:
1. All calls during normal operation are successful.
2. Client notices the change of the ServerState and disconnects from the server.

The above test case suggests that the client should monitor the server state. We are checking the server state periodically so that the session will not get timed out.
Is it expected that we monitor the server state continuously or is it fine to just check it periodically?