3.2.5.1.3 Processing a Server Close Request Message
The DeviceId and FileId fields of DR_DEVICE_IOREQUEST (as specified in [MS-RDPEFS] section 2.2.1.4) identify the previously-opened instance of the port to operate on.
After receiving the close request, the client MUST close the previously opened port instance. It MUST also cancel pending IO operations, if any, on the port. The client MUST respond with close response message (section 3.2.5.1.8).