This attribute defines the source of the transmit clock for the DS1 tributary. When the clocking source is selected from local, the crystal on the port generates the clocking for the DS1 tributary. When the clocking source is selected from line, the port synchronizes to the clock from the DS1 tributary. When the clocking source is selected from module, the ports clock synchronizes to the clock provided by the oscillator on the active CP. On a 1pDS3C card, if the NetworkSynchronization (NS) component is present the default value of this attribute will be module otherwise it will be line. On a 2pDS3cAal or 4pDS3ChAtm card, the only valid values are local and module. If the NS component is present the default value of this attribute will be module otherwise it will be local. On a 4pDS3ChAtm card the clocking source for all DS1 and all DS3 components on card must be the same, except when a DS1 is using line as a clocking source.