Phone keeps ringing after hanging up..

I have noticed that with VoIP the phone will keep ringing even after the
other person has hung up.. So if I ring from my mobile to my VoIP line,
let it ring a couple of times, then hang up the mobile, the VoIP will
keep ringing for another 3-4-5 rings before it will stop. I have noticed
this with a number of providers, so Im not sure where the problem is.
Can anything be done for the ATA to register the fact that the caller
has hung up?

I am using a PAP2.