Browse Prior Art Database

Switch-Based External Time Reference

IP.com Disclosure Number: IPCOM000037170D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Georgiou, CJ: AUTHOR [+2]

Abstract

Disclosed is a method of synchronizing the time-of-day (TOD) clocks in the individual processors of a multiprocessor complex with a switched- star topology. The method integrates a time reference within the switching system, which broadcasts the reference signal to the processors over dedicated fiber-optic links. This is an alternative to providing a separate time reference with its own network of fiber-optic links.

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Switch-Based External Time Reference

Disclosed is a method of synchronizing the time-of-day (TOD) clocks in the individual processors of a multiprocessor complex with a switched- star topology. The method integrates a time reference within the switching system, which broadcasts the reference signal to the processors over dedicated fiber-optic links. This is an alternative to providing a separate time reference with its own network of fiber-optic links.

The method is illustrated in the figure which shows a complex of processors interconnected through a central non-blocking switch and fiber-optic links. Each processor is connected to a switch-port through a pair of fiber-optic links which are used for data communication. The switch also has a number of ports meant for transmitting the time-reference signal to the processors that need synchronization. These ports are connected to the processors via simplex links. In the switch implementation, no distinction needs to be made between the ports used for sending the time information and those used for data communication. During system startup, the switch is configured so that all the ports used for transmitting the time information are statically connected by means of a broadcast connection to the clock signal generated by a TOD clock card within the switch. Since all the ports have the same capability, this affords flexibility in the way the system is set up.

The time reference information transmitted over the link is an encoded message containing the current TOD and calendar data. Such messages are transmitted continually with little or no intervals in between so as to use the full available link bandwidth. A processor receiving the me...