This attribute defines the type of clocking source used for synchronizing the DS3 transmit clock: local means direct use of the local clock oscillator at its centre frequency; line means use of a signal phase-locked to the incoming DS3 line rate; module means the use of a signal phase-locked to the CP reference clock. Note that the multiport cell-based cards have one common clock source for all ports. For this reason, the following rules apply for the value of clockingSource across the board's three ports: All three clockingSource values must be 'local' OR All three clockingSource values must be 'module' OR One clockingSource value must be 'line' and the other two must be 'otherPort'. If there is no NS component provisioned, the default value for this attribute will be local. If the NS component has been provisioned, the default value is module, except for the 1pDS3C cards. For the 1pDS3C cards, the default and only valid value for this attribute is local. The clockingSource of the DS1 sub-component becomes the effective clocking source for this attribute. All the DS1 sub-components have the same clocking source.