retrieve the net name connected to pcell symbol

Hi 

I have pcell symbol. I would like to invoke callback "update_net_prop" when a CDF parameter of this pcell instance is updated. The callback would change the property of the net connected  to the terminal of this pcell instance. How do I retrieve the net name connected to the terminal of this pcell instance ?

cdfCreateParam( cdfId
?name "padNum"
?prompt "Number of ports"
?defValue 1
?type "int"
?display "artParameterInToolDisplay('padNum)"
 ?callback "update_net_prop()"
)

Thanks,

ManChak