The Clientcloses the connection by sending a CloseSecureChannelrequest and closing the socket gracefully. When the Serverreceives this Message,it shall release all resources allocated for the channel. The body of the CloseSecureChannelrequest is empty. The Serverdoes not send a CloseSecureChannel response.

If security verification fails for the CloseSecureChannel Message,then the Servershall report the error and close the socket.

The sequence of Messageswhen closing an OPC UA Connection Protocol connection is shown in Figure 18.


Figure 18– Closing a OPC UA Connection Protocol connection

The Serverapplication does not do any processing when the SecureChannelis closed; however, the Stackshall provide notifications to the Serverapplication whenever a CloseSecureChannelrequest is received or when the Stackcleans up an abandoned SecureChannel.