Synchronization of real-time clocks in a packet switching system
AssigneeAT&T Bell Laboratories
InventorGary B. Crockett
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AssigneeAT&T Bell Laboratories
InventorGary B. Crockett
Estimating the term…
A packet switching system in which a remote real-time clock is accurately synchronized to a standard real-time clock via X.25 (CCITT) controlled high-speed transmission links. Synchronization is achieved by the transmission of an interrupt packet and a data packet between a remote processor controlling the remote real-time clock and an administrative processor controlling the standard real-time clock. Synchronization involves the following steps: (1) assembling an interrupt packet comprising the least significant bits of the remote real-time clock for transmission to the administrative processor by the remote processor, (2) calculating bits representing the difference between the transmitted least significant bits of the remote real-time clock and the least significant bits of the standard real-time clock by the administrative processor, (3) assembling a data packet comprising bits representing the state of the standard real-time clock and the difference bits for transmission to the remote processor by the administrative processor, (4) adding the difference bits to the bits representing the state of the remote real-time clock by the remote processor, and (5) adding a predefined value to the most significant bits of the remote real-time clock by the remote processor if the transmitted least significant bits of the standard real-time clock are numerically greater than the least significant bits of the remote real-time clock.
contents. 15. The arrangement of claim 14 wherein said remote processor means further responsive to a second set of program instructions for replacing another group of bit signals of said contents of said one of said real-time clocks with a corresponding group of said other one of said real-time clock means' transmitted bit signals to synchronize said other group of bit signals of said contents with the corresponding group of bit signals of said other one of said real-time clock means;