4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 16 [Enumeration] NORMAL_CLEARING [Cause] normal call clearing [Q.850] [Description] 
This cause indicates that the call is being cleared because one of the users involved in the call has requested that the call be cleared. Under normal situations, the source of this cause is not the network.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description