On a point to point circuit with a fully initialized
adjacency to a peer IS, the value of this object is
the circuit ID negotiated during adjacency initialization.
On a point to point circuit without such an adjacency,
the value is the concatenation of the local system ID
and the one byte ciiCircLevelIDOctet for this circuit
i.e. the value that would be proposed for the circuit ID.
On other circuit types, the value returned is the zero
length OCTET STRING.