4452d530_able___FreeSWITCH___Confluence__Description
[ITU-T Q.850 Code] 34 [SIP Equiv.] 503 [Enumeration] NORMAL_CIRCUIT_CONGESTION [Cause] no circuit/channel available [Q.850] [Description] 
This cause indicates that there is no appropriate circuit/channel presently available to handle the call.
Hangup Cause Code Table - FreeSWITCH - Confluence
Description