A synchronization transport network (100) for distributing a time reference between external clocks (103, 203, 104), comprises a first input node (110) connected to a first external master clock (103), a second input node (210) connected to a second external master clock (203), and an output node (120) connected to an external slave clock (104). The first and second input nodes (110, 210) record a time-of-arrival of a primary timestamp and forward the primary timestamp (141, 241) and the corresponding time-of-arrival to the output node (120). The first and second input nodes forward a clock status report (150, 250) to the output node. The output node processes the clock status reports from the first and second external master clocks so as to select one of external master clocks (103, 203) as a reference clock and generates a secondary timestamp (142) as a function of the primary timestamp received from the selected reference clock.