Question: Etherenet Link Detection

[Robert Cantu]

Is there a method of detecting the link status of an ethernet NIC? If not,
is it feasible? And if it is, then would it be something in each driver,  
or on a level above the driver, thereby available to all drivers? I figure
the list is the best place to ask this, although it might be a moot point.
                                                                
Example: Have a cable modem hooked into a computer's NIC. Cable service   
goes out, link light on back of NIC goes out. A hypothetical program says 
that the link is gone via some hook in /proc somewhere.

Is this a worthwhile endeavor, if possible?

Thanks in advance,
Robert