A list of circuits. Each new circuit will create a conceptual row
in the table.
When the circuit disconnects, the row will be deleted from the table.
End station 1 (S1) and End station 2 (S2) are used to
represent the two end stations of the circuit.
S1 is always an end station which is locally attached.
S2 may be locally attached or remote.
This table augments the dlswCircuitTable.