Subject How to trigger "Connection shutdown" error.

My application is handling different kinds of connection errors:

335544721 network_error Unable to complete network request to host "@1".
335544722 net_connect_err Failed to establish a connection.
335544726 net_read_err Error reading data from the connection.
335544727 net_write_err Error writing data to the connection.

Today I've found another error:

335544856 att_shutdown Connection shutdown

In order to handle it properly I need to know how to cause it so I could test behaviour of my application.
Could you tell me what this error means exactly, and how to cause it?
My test environment is Windows 7 with Firebird 2.5.2 and my client application is on the same machine.

Thank you.