A network device includes a master physical layer and a slave physical layer device configured to communicate with a plurality of network devices. The master physical layer device includes a signal generator module configured to generate a first clock that is syntonized to a grandmaster clock having a fixed frequency; and a frequency adjusting module configured to, at a predetermined time interval, adjust a frequency of the first clock to the fixed frequency of the grandmaster clock. The slave physical layer device includes a time of day calculating module configured to calculate a first time of day of the slave physical layer device based on a second clock that is asynchronous to the first clock, and a period adjusting module configured to synchronize the first time of day to a second time of day of the master physical layer device based on the predetermined time interval.