4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 31 [SIP Equiv.] 480 [Enumeration] NORMAL_UNSPECIFIED [Cause] normal, unspecified [Q.850] [Description] 
This cause is used to report a normal event only when no other cause in the normal class applies.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description