This attribute, if set to a value of allowed indicates that incoming
calls (from the network to the DTE) be made to this Dna. If set to a
value of disallowed, then incoming calls cannot be made to this
Dna - such calls will be cleared by the local DCE. This attribute
corresponds to the CCITT 'Incoming Calls Barred' feature for Dnas
in that incoming calls are barred if this attribute is set to a value of
disallowed.
Either outCalls, or incCalls (or both) be set to a value of allowed
for this Dna to be usable.