4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 79 [SIP Equiv.] 501 [Enumeration] SERVICE_NOT_IMPLEMENTED [Cause] service or option not implemented, unspecified [Q.850] [Description] 
This cause is used to report a service or option not implemented event only when no other cause in the service or option not implemented class applies.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description