How to check which com ports are being used by what application?

[ashjas]

Hi,

I have a modem installed..which some times work correctly but some
times it continuposly shows an error when dialing up,which says that
the com port is being used by some other application,try closing it..

but i just cant figure out what application is using the com port..

Is there any way within windows by which i can check what application
is using the com ports?or is there any software that can help me in
doing so??

Thanks.