# US 10,873,442 B2 · Measure and improve clock synchronization using combination of transparent and boundary clocks

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- Number: US 10,873,442 B2
- Document ID: US10873442B2
- Status: Granted
- Kind: B2
- Application number: 16/590,757
- Filed: 2019-10-02
- Published: 2020-01-30
- Granted: 2020-12-22
- Earliest claimed: 2017-10-13
- Assignees: Cisco Technology, Inc.
- Applicants: Cisco Technology, Inc.
- Inventors: Anshul Tanwar; Vineet Kumar Garg; N V Hari Krishna N
- Web page: https://patentgrep.com/patent/US10873442B2

## CPC

- H04L 7/0033: {Correction by delay}
- 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 3/0673: {using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet}
- H04J 3/0641: {Change of the master or reference, e.g. take-over or failure of the master}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- 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)

## Abstract

The present technology improves synchronization of a slave node with a master node in a network using PTP packets in which the slave node is coupled to the working master node through at least one boundary node. The technology establishes a synchronization communication session between the boundary node and the slave node in which the synchronization communication session is configured to measure a first timing delay from the boundary node to the slave node, and establishes a transparent communication session between the master node and the slave node through the boundary timing node in which the transparent communication session configured to measure a second timing delay from the master node to the slave node. Using the sessions, the technology adjusts a timing delay correction factor according to the first timing delay and the second timing delay, and synchronizes the slave node with the master node according to the correction factor.

## Claims

### Claim 1

A method for a plurality of slave nodes to select a primary master node from a plurality of master nodes, the method comprising:
determining an overall offset between each of the slave nodes and each of the master nodes, the determining comprising for each of the slave nodes:
measuring a first timing delay from the slave node to an adjacent boundary node over a synchronization communication session;
measuring a second timing delay from the slave node to each of the master nodes over a transparent communication session;
determining the overall offset as the difference between the first and second timing delays; and
selecting, by the slave nodes and based on results of the measuring, the primary master node from the plurality of master nodes.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
establishing, for each of the slave nodes, the synchronization communication session between the each of the slave nodes and the adjacent boundary node.

### Claim 3 (depends on 1)

The method of claim 1, further comprising, for each of the slave nodes, the transparent communication session between the each slave node to each of the plurality of master nodes.

### Claim 4 (depends on 1)

The method of claim 1, wherein the selecting the primary master node comprises the slave nodes conducting an arbitration to select an available master node to be the primary master node.

### Claim 5 (depends on 4)

The method of claim 4, wherein the arbitration is conducted using a telemetry message conveyed among the slave nodes.

### Claim 6 (depends on 1)

The method of claim 1, wherein the synchronization and transparent communication sessions conform to an IEEE 1588 protocol.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
deleting, in response to the selecting, the transparent communication session from each of the plurality of master nodes that were not selected as the primary master node.

### Claim 8

A non-transitory computer readable media storing instruction which when executed cause a plurality of slave nodes to perform operations to select a primary master node from a plurality of master nodes, the operations comprising:
determining an overall offset between each of the slave nodes and each of the master nodes, the determining comprising for each of the slave nodes:
measuring a first timing delay from the slave node to an adjacent boundary node over a synchronization communication session;
measuring a second timing delay from the slave node to each of the master nodes over a transparent communication session;
determining the overall offset as the difference between the first and second timing delays; and
selecting, by the slave nodes and based on results of the measuring, the primary master node from the plurality of master nodes.

### Claim 9 (depends on 8)

The non-transitory computer readable media of claim 8, the operations further comprising:
establishing, for each of the slave nodes, the synchronization communication session between the each of the slave nodes and the adjacent boundary node.

### Claim 10 (depends on 8)

The non-transitory computer readable media of claim 8, the operations further comprising, for each of the slave nodes, the transparent communication session between the each slave node to each of the plurality of master nodes.

### Claim 11 (depends on 8)

The non-transitory computer readable media of claim 8, wherein the selecting the primary master node comprises the slave nodes conducting an arbitration to select an available master node to be the primary master node.

### Claim 12 (depends on 11)

The non-transitory computer readable media of claim 11, wherein the arbitration is conducted using a telemetry message conveyed among the slave nodes.

### Claim 13 (depends on 8)

The non-transitory computer readable media of claim 8, wherein the synchronization and transparent communication sessions conform to an IEEE 1588 protocol.

### Claim 14 (depends on 8)

The non-transitory computer readable media of claim 8, the operations further comprising:
deleting, in response to the selecting, the transparent communication session from each of the plurality of master nodes that were not selected as the primary master node.

### Claim 15

A system for a plurality of slave nodes to select a primary master node from a plurality of master nodes, the system comprising:
a non-transitory computer readable memory storing instructions;
a processor programmed to cooperate with the instruction in the memory to perform operations comprising:
determining an overall offset between each of the slave nodes and each of the master nodes, the determining comprising for each of the slave nodes:
measuring a first timing delay from the slave node to an adjacent boundary node over a synchronization communication session;
measuring a second timing delay from the slave node to each of the master nodes over a transparent communication session;
determining the overall offset as the difference between the first and second timing delays; and
selecting, by the slave nodes and based on results of the measuring, the primary master node from the plurality of master nodes.

### Claim 16 (depends on 15)

The system of claim 15, the operations further comprising:
establishing, for each of the slave nodes, the synchronization communication session between the each of the slave nodes and the adjacent boundary node.

### Claim 17 (depends on 15)

The system of claim 15, the operations further comprising, for each of the slave nodes, the transparent communication session between the each slave node to each of the plurality of master nodes.

### Claim 18 (depends on 15)

The system of claim 15, wherein the selecting the primary master node comprises the slave nodes conducting an arbitration to select an available master node to be the primary master node.

### Claim 19 (depends on 18)

The system of claim 18, wherein the arbitration is conducted using a telemetry message conveyed among the slave nodes.

### Claim 20 (depends on 15)

The system of claim 15, the operations further comprising:
deleting, in response to the selecting, the transparent communication session from each of the plurality of master nodes that were not selected as the primary master node.