Fault tolerant clock network

Patent metadata

Field	Value
Publication number	US-9973601-B2
Application number	US-201414198351-A
Country	US
Kind code	B2
Filing date	Mar 5, 2014
Priority date	Mar 15, 2013
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

Fault tolerant and redundant grand master clock scheme may reduce or eliminate precision time transition caused by a network link or device failure. A primary synchronization message may be sent by a primary grandmaster clock and one or more backup synchronization message may be sent by respective backup grandmaster clocks. The primary and backup grandmaster clocks may be concurrently operated. The primary and backup synchronization messages may be sent to an end station over a network. The end station may derive a local clock based on one, some, or all of the received messages. The end station may or may not distinguish between the messages based on the clock source. The end station may validate messages received from a particular clock source.

First claim

What is claimed is:

1. A device, comprising:
a clock operable as a backup grandmaster clock due to the device being selected from a list of grandmaster clock devices throughout a network, the list of grandmaster clock devices being organized in order of priority based on at least clock traceability and device location within the network;
an interface configured to communicate on the network, and receive a primary synchronization message, the primary synchronization message received continuously over the network from another device selected from the list of grandmaster clock devices to be a primary grandmaster clock device and identified to the device and the other devices throughout the network as the primary grandmaster clock device, and the primary synchronization message comprising a clock signal of the primary grandmaster clock device;
a processor configured to maintain the backup grandmaster clock substantially synchronous with the clock signal received in the primary synchronization message; and
the processor further configured, while receiving a primary synchronization message, to generate a backup synchronization message based on the backup grandmaster clock, as a redundant message to the primary synchronization message presently being received, the backup synchronization message comprising a clock signal of the backup grandmaster clock, and the interface further configured to transmit the generated backup synchronization message over the network for receipt by all other devices as a duplicative clock signal, wherein the backup synchronization message is received substantially simultaneously with the primary synchronization message or within a predetermined time interval of the primary synchronization message.

2. The device of claim 1 , wherein the interface configured to redundantly transmit the generated backup synchronization message over the network in an active mode, and in a passive mode, the interface configured to transmit the backup synchronization message to a temporary buffer in response to receipt of the primary synchronization message.

3. The device of claim 2 , wherein, in the passive mode, the processor is configured to:
detect an absence of receipt of the primary synchronization message from the primary grandmaster clock device for a predetermined holdover time; and, in response,
trigger retrieval of the backup synchronization message and transmission of the backup synchronization message for receipt by the other network devices throughout the network.

4. The device of claim 3 , wherein the predetermined holdover time after which transmission of the backup synchronization message to the other network devices throughout the network is triggered is shorter than a predetermined holdover time of the other network devices throughout the network.

5. The device of claim 3 , wherein, the processor is configured to detect receipt of the primary synchronization message from the primary grandmaster clock device after the predetermined holdover time, and, in response, discontinue the transmission of the backup synchronization message for receipt by the other network devices throughout the network.

6. The device of claim 3 , wherein, in response to the absence of receipt of the primary synchronization message from the primary grandmaster clock device, the processor is configured to initiate the backup grandmaster clock device as a new primary grandmaster clock device of the network and the primary grandmaster clock device as a new backup grandmaster clock device of the network.

7. The device of claim 1 , wherein the backup synchronization message is transmitted for receipt by the other network devices throughout the network regardless of the receipt of the primary synchronization message.

8. The device of claim 1 , wherein the processor is further configured to:
extract a global identifier from the received primary synchronization message; and
include the global identifier in the generated backup synchronization message prior to transmission of the backup synchronization message.

9. The device of claim 8 , wherein the processor is further configured to include an identifier representative of the primary grandmaster clock device in the generated backup synchronization message prior to transmission of the backup synchronization message.

10. A device comprising:
a clock;
an interface configured to continuously receive a first clock signal over a network from a first device selected from a list of grandmaster clock devices as a first grandmaster clock device and identified to the device as the first grandmaster clock device, the first grandmaster clock device operable as a primary source of time for all devices in the network;
the interface further configured to consecutively receive a second clock signal, as a duplicative clock signal, substantially simultaneously with receipt of the first clock signal or within a predetermined time interval of receipt of the first clock signal, the second clock signal received over the network from a second device selected from the list of grandmaster clock devices, the second grandmaster clock device being a redundant grandmaster clock device to the first grandmaster clock device and redundantly operable as another primary source of time for all the devices in the network, the list of grandmaster clock devices being organized in order of priority based on at least clock traceability and device location within the network; and
a processor configured to operate the device as an end station device, the processor further configured to adjust the clock based on the received first clock signal and the received second clock signal.

11. The device of claim 10 , wherein the processor is configured to adjust the clock at the first frequency, wherein the first frequency being a rate at which the first clock signal and the second clock signal are received.

12. The device of claim 11 , wherein the processor is configured to adjust the clock at a second frequency, wherein the second frequency is a rate at which the second clock signal is received.

13. The device of claim 10 , wherein the interface is configured to receive a third clock signal from a third device identified to the device as a third grandmaster clock device redundantly operable as another primary source of time for all the devices in the network, and wherein the processor is configured to adjust the clock based on the first, second and third received clock signals irrespective of a source of the received clock signals.

14. The device of claim 10 , wherein,
the processor is configured to identify a source of a received clock signal based on an identifier, representative of an identity of the source, in the clock signal, and
the processor is further configured to validate the clock signal from the source based on a time-value difference between successive messages of the clock signal from the source.

15. The device of claim 14 , wherein,
the processor is configured to indicate, via a message transmitted over the network to a network manager, the source as an unreliable source of the clock signal based on the time-value difference being outside a predetermined range.

16. A method, comprising:
receiving continuously at a time interval, at a network device, from over a network, a primary synchronization message, the primary synchronization message received from a first device selected from a list of grandmaster clock devices as a primary grandmaster clock device and identified to the network device as the primary grandmaster clock device, the first device being operable as a primary source of time for

Assignees

• Avago Technologies General Ip

Inventors

• Spada Eric John
• Kim Yongbum

Classifications

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title

• H04J3/0641

  Change of the master or reference, e.g. take-over or failure of the master · CPC title

• H04L69/28 Primary

  Timers or timing mechanisms used in protocols · CPC title