Reflects the source of Transmit Clock. 'loopTiming' indicates that the recovered receive clock is used as the transmit clock. Only set if this DS1 has zhoneClockSourceEligibility equal to 'eligible' and the state of that ds1 is 'up' and the ds1 resource provider decided this DS1 is to provide the transmit clock for all the DS1s. Only one DS1 will have this set per platform. 'localTiming' indicates that a local clock source is used or when an external clock is attached to the box containing the interface. 'throughTiming' indicates that recovered receive clock from another interface is used as the transmit clock. Example: If a DS1 other than this one reflects 'loopTiming', this DS1 will use that DS1 as its transmit clock. Therefore this DS1 reflects 'throughTiming'. 'sonetThroughTiming' indecates that recovered receive clock from the far-side sonet node is used as the transmit clock.