[asterisk-users] monitoring - hangup channel

[Joseph]

How can I monitor channel that "hangup"?
I'm using asterisk 1.8.15.1 and there are many times that nobody is using the line but when I run:
asterisk -rx "core show channels" it show:

Channel              Location             State   Application(Data)             
SIP/pstn-4444-000000 (None)               Up      AppDial((Outgoing Line))      
SIP/pstn-9998-000000 7807586576 at internal: Up      Dial(SIP/97807807586576 at pstn-4
2 active channels
1 active call

How can I prevent it or monitor it? 
At this point I have to hang it up manually or I will not be able to restart the asterisk.

-- 
Joseph