This attribute indicates the source of the clock when working in dce or ext-dce clock mode. notApplicable(1) - is applied for dte(3) and lbt(5) clock modes. When clock mode is dte, the clock source is always external, therefore this object's value is notApplicable. local(2) and nodalTiming(3) - are valid in dce(1), extDce(2) or int(4) clock modes. The recommended clock source is local(2).