I have found that it teturns 1 after removing the ethernet cable form my computer, and only returns 0 some time later, at which point the file gets closed due to lost connection anyway.
It appears that evaluating this fuction does not verify the connection by actually exchanging a message with FMS.
In IOS connections can break easily and I need to check whether the connection is good before doing sertain operations.
The only way I have found to accomplish this is to try wrting a byte or two to the host and checking for an error.
Also a get(cellularsignalstrength) function would be handy