4f55f5cb_ISDN_Cause_Codes__Cause_Usage
[Cause#] 1 [Fixit!] N/A [Cause Summary] Unallocated (unassigned number) [Cause Usage] 
Indicates that the destination requested by the calling user cannot be reached because, although the number is in a valid format, it is not currently assigned (allocated).
ISDN Cause Codes
Cause Usage