# US 10,320,508 B2 · Time synchronization system

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- Number: US 10,320,508 B2
- Document ID: US10320508B2
- Status: Granted
- Kind: B2
- Application number: 15/680,762
- Filed: 2017-08-18
- Published: 2018-03-01
- Granted: 2019-06-11
- Earliest claimed: 2016-08-31
- Assignees: Media Links Co., Ltd.
- Applicants: Media Links Co., Ltd.
- Inventors: Takeshi Shimizu; Kazuki Narita
- Web page: https://patentgrep.com/patent/US10320508B2

## CPC

- H04J 3/0667: {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)}
- H04J 3/0641: {Change of the master or reference, e.g. take-over or failure of the master}
- H04J 3/0644: {External master-clock}
- H04J 3/0676: {Mutual}
- H04N 21/242: Synchronisation processes, e.g. processing of PCR [Programme Clock References] {(arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18)}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A time synchronization system includes master nodes and slave nodes configured to correct a local slave clock by synchronizing time with time in a local master clock. A first master node corrects a first local master clock at predetermined periodic intervals by synchronizing with a timing synchronization signal from a source clock node having a source clock. If a second local master clock has a greater error from the source clock than the error in the first local master clock, the second master node performs first correction by synchronizing time with time in the first local master clock and performs second correction by synchronizing with the timing synchronization signal from the source clock node on condition that an error in the second local master clock is within a predetermined range after the first correction has been performed.

## Claims

### Claim 1

A time synchronization system comprising:
a plurality of master nodes including a first master node and a second master node; and
a slave node configured to correct a local slave clock of the slave node by synchronizing with a local master clock of one of the plurality of master nodes,
wherein:
the first master node is configured to correct a first local master clock of the first master node at predetermined periodic intervals by synchronizing with a timing synchronization signal transmitted from a source clock node having a source clock specified in a clock domain,
if a second local master clock of the second master node has a greater error from the source clock than an error of the first local master clock from the source clock, the second master node is configured to:
perform a first correction on the second local master clock by synchronizing with the first local master clock; and
perform a second correction on the second local master clock by synchronizing with the timing synchronization signal from the source clock node when there is an error in the second local master clock from the first local master clock that occurs after the first correction, the error being within a preset threshold, and
the slave node is further configured to determine whether to synchronize the local slave clock with the first local master clock, or synchronize the local slave clock with the second local master clock when there is an error in the second local master clock from the first local master clock that occurs after the second correction, the error being within the preset threshold.

### Claim 2 (depends on 1)

The time synchronization system according to claim 1, wherein the second master node is further configured to perform a third correction on the second local master clock at predetermined periodic intervals by synchronizing with the timing synchronization signal from the source clock node when there is an error in the second local master clock from the first local master clock that occurs after the second correction, the error being within the preset threshold.

### Claim 3 (depends on 1)

The time synchronization system according to claim 1, wherein the second master node is further configured to perform a fourth correction on the second local master clock by synchronizing with clock information from a node outside the clock domain before performing the first correction.

### Claim 4 (depends on 1)

The time synchronization system according to claim 1, wherein the second master node is further configured to:
check presence of the first master node by exchanging messages with the first master node before performing the first correction; and
perform the first correction if the second master node confirms the presence of the first master node.

### Claim 5 (depends on 1)

The time synchronization system according to claim 1, wherein the second master node is further configured to:
check presence of the first master node by exchanging messages with the first master node before performing the first correction; and
perform a fifth correction on the second local master clock by synchronizing with the timing synchronization signal from the source clock node if the second master node fails to confirm the presence of the first master node.

### Claim 6 (depends on 1)

The time synchronization system according to claim 1, wherein the second master node is further configured to:
check presence of the first master node by exchanging messages with the first master node before performing the first correction; and
send an abnormality notification if the second master node fails to confirm the presence of the first master node.