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