Synchronization of time-of-day clocks in a distributed processing network system

DETAILED DESCRIPTION It is an object of the present invention to provide improved means for synchronizing station time-of-day clocks in a distributed processing system.
It is another object of the invention to achieve this primary object with minimum specialized hardware.
It is an additional object of the invention to achieve the previous objects utilizing each station's operating system time-of-day clock, and to do so even when the operating system time-of-day clock does not have the resolution demanded by the network system.
It is also an object of the invention to provide such an improved means for synchronizing station time-of-day clocks which accommodates for network delays and for dynamic changes in the network delays, such as would accompany changes in network topography.
These and other objects are realized by the invention which is directed to a distributed processing system with means for synchronization of station time-of-day clocks which includes in each station a free-running counter in the network interface which maintains a count of time intervals.
It further includes means within a designated timekeeper station periodically generating a timing signal which is transmitted over the data communications network to all of the stations including the timekeeper station.
Means in each network interface latches the count in the free-running counter upon receipt of the timing signal.
The timekeeper station further includes means transmitting to all the stations the timekeeper time-of-day signal representing the time of day that the time the timekeeper station received the timing signal.
Each of the other stations include means determining a station reference time of day from the latched count, and the count in the free-running counter, and from the time of day in the operating system time-of-day clock at the time of receipt of the timekeeper time-of-day signal.
Each station further includes means determining the difference between the station reference time of day and the received timekeeper time of day and adjusting the time of day clock in the operating system based on this difference