Hi,

Is this a “just a question” or did you observe something that doesn’t seem correct?

The server by the specification (and our implementation) retry infinite times. See https://reference.opcfoundation.org/Core/Part4/v104/docs/6.7 near the end:
“
OPC 10000-6defines a reverse connect mechanism where the Serverinitiates the logical connection. All subsequent steps like creating a SecureChannelare initiated by the Client. In this scenario the Clientis only able to initiate a reconnect if the Serverinitiates a new logical connection after a connection interruption. The Clientside reconnect handling described in Figure 36applies also to the reverse connect case. A Serveris not able to actively check the connection status; therefore the Servershall initiate a new connection in a configurable interval, even if a connection to the Clientis established. This ensures that an initiated connection is available for the reconnect handling in addition to other scenarios where the Clientneeds more than one connection.
“
Though, It has been a while since I last looked this, but our implementation is not 1:1 on that yet: the interval cannot be configured and it is more like retrying when opening the connection failed (or a successful opened connection is closed) instead of a real interval. We will probably improve this at some point.

When using https://www.prosysopc.com/products/opc-ua-browser/ + https://www.prosysopc.com/products/opc-ua-simulation-server/, you can make the Browser listen to reverse connections by typing “inv:60000” (i.e. inv:port, 60000 here is just an example), it will then transform the uri to “inv+opc.tcp://YOUR_HOSTNAME_HERE:60000” (you can also type this directly), copy this on Simulation Server (use Options menu to switch to Expert Mode first) Endpoints tab in the Reverse Connections, press apply and restart the SimulationServer. You might need to press connect on Browser again (it will timeout after a while if no connections was opened) you should see the connection being formed after Simulation Server starts. If you then disconnect and connect Browser again, it should be re-formed (and this should work infinite times). Note that Browser accepts the first reverse connection made to this inv+opc.tcp address (i.e. it doesn’t open multiple tabs, we might some day do that as well).

In the SDK, you can add the reverse connections via UaServer.addReverseConnection(…) (read the javadocs, it is important to get the ‘endpointUrlForClientConnection’ parameter right as basically the reverse connection “jump starts” the real connection, this parameter is what the client will give in the Hello message and it must match one it would have given in a non-reverse connection; and note that this is separate from the first ‘clientServerEndpointUrl’ parameter, which is the “inv+opc.tcp://YOUR_HOSTNAME_HERE:60000” using the previous example ).

Let us know if this helped (and if you use this if improvements would be needed and when).

P.S.
In case you wonder why it is infinite, I assume it was specified so because normally servers are not observed actively (no one to press a “reverse connect button” actively) and it cannot be known when the client starts to listen for the connections (because if you need reverse connection there most likely is not a way to connect directly to the server), thus it basically has to be infnite.