On some occasions a call will come in to our office and our phones will ring. I believe that if the caller hangs up before it is picked up then one of the phones in the dial plan - probably the last one to get the call, will continue to ring for about 2 minutes.
I suspect it is because the callers phone system is not sending us a notification that Asterisk can understand.
Is this the correct assumption or is something else going on. What can one do to fix this.
If your are using analog phone line without disconnect supervision yes it’s normal.
Take a look at hanguponpolarityinversal in zapata.conf
Thanks -definately looks like the culprit. What is strange is how the phones work correctly 99% of the time.
My apologies. I couldnt locate this hanguponpolarityinversal in the zapata.conf or in Google. Is this the correct spelling?
“hanguponpolarityreversal”
it’s actually “hanguponpolarityswitch=”, the “reversal” is a UK’ism 
The phones will start ringing in our office according to the dialplan. We have it setup to ring a couple of phones first and them a few more a few seconds later and so on.
On some occassions one of the phones will continue to ring even though someone has picked up the call. As if the phone hasnt got the message that the call has already been pciked up.