Current Clock Holdover State. As a last resort, in the absence of higher quality timing: - a SONET/SDH object can enter 'holdover' state, until higher quality external timing becomes available again. In this state (value=yes) the SONET/SDH object uses its own timing circuits for clock of the SONET/SDH signal. - for other objects, the 'holdover'=yes state means that the object uses last available clock (stored by the object) for a pre-defined time, until another clock source is used.