This attribute, if set to a value of allowed indicates that incoming
calls (from the network to the DTE) can be made using this
particular CUG. If set to a value of disallowed, then incoming calls
cannot be made using this CUG - such calls will be cleared by the
local DCE.
This attribute corresponds to the CCITT 'Incoming Calls Barred'
feature for CUGs in that incoming calls are barred if this attribute is
set to a value of disallowed.