This read-write enumerated value sets the interface's clock signal direction: input(1), output(2), both(3), or none(4), with none meaning the interface is disabled; only Ethernet and VLAN interfaces can be set to 'both.' Admins set this to configure whether a given timing interface receives a reference clock, distributes one, or both. For example, an admin sets this to output(2) on a T1 interface that should distribute the device's synchronized clock to downstream equipment, or to both(3) on an Ethernet interface used for PTP that both sends and receives timing.