This read-write enumerated value indicates whether Don't Use for Synchronization (DUS) is forced on the transmit side of this interface: if enabled, the switch generates a DUS message on transmit regardless of actual clock quality; if disabled, it transmits the appropriate SSM per protocol. Admins enable this to explicitly signal downstream equipment not to use this interface's clock, for example on a link known to have an unreliable timing source. For example, an admin sets this to enabled(1) on an interface with a suspect clock source so downstream switches won't select it for synchronization.