Transmission device, time transmission system, and delay compensation method

Patent metadata

Field	Value
Publication number	US-11855760-B2
Application number	US-202017428240-A
Country	US
Kind code	B2
Filing date	Feb 6, 2020
Priority date	Feb 14, 2019
Publication date	Dec 26, 2023
Grant date	Dec 26, 2023

Abstract

The accuracy of an offset value is improved by correcting an error in time synchronization caused by link asymmetry. PTP packets are exchanged between a master node 3 and a slave node 4 vis a first transmission device 1 connected to the master node 3 and a second transmission device 2 corresponding to the first transmission device 1 and connected to the slave node 4 . The second transmission device 2 includes: a transmission section 16 configured to transmit PTP packets for a plurality of wavelengths to the corresponding transmission device simultaneously; and a reception section 17 configured to calculate a propagation delay Dms on a path from the corresponding transmission device to the second transmission device 2 based on a difference between the arrival times of the PTP packets for the plurality of wavelengths received from the corresponding transmission device, and provide the propagation delay Dms to the slave node 4 as a correction parameter used in a process of synchronizing the time of the slave node 4.

First claim

The invention claimed is:

1. A transmission device for use in a time transmission system, the time transmission system synchronizing time of a second time synchronization device based on time information of transmission and reception of packets for time synchronization between a first time synchronization device and the second time synchronization device via a first transmission device connected to the first time synchronization device and a second transmission device corresponding to the first transmission device and connected to the second time synchronization device, the transmission device being operable as the first transmission device or the second transmission device, comprising one or more processors configured to:
transmit packets for time synchronization for a plurality of wavelengths to the other transmission device simultaneously, wherein the first transmission device is paired with the first time synchronization device, and the second transmission device is paired with the second time synchronization device,
wherein an uplink wiring length and a downlink wiring length between the first time synchronization device and the first transmission device are the same, and an uplink wiring length and a downlink wiring length between the second transmission device and the second time synchronization device are the same;

receive the packets for time synchronization for the plurality of wavelengths from the other transmission device, measure a propagation delay on a path from the other transmission device to the transmission device based on a difference between arrival times of the received packets for time synchronization for the plurality of wavelengths, wherein measuring the propagation delay comprises:
determining, using the difference between arrival times of the received packets, a length of a downlink transmission line and a length of an uplink transmission line between the first and second transmission devices, and
determining the propagation delay for each of the downlink transmission line and the uplink transmission line using the corresponding length, a temperature correction, and a predetermined delay for each length unit due to temperature change; and

provide the propagation delay to the second time synchronization device as a correction parameter used in a process of synchronizing time of the second time synchronization device.

2. A time transmission system comprising a transmission device, a first time synchronization device and a second time synchronization device, the time transmission system synchronizing time of the second time synchronization device based on time information of transmission and reception of packets for time synchronization between the first time synchronization device and the second time synchronization device via a first transmission device connected to the first time synchronization device and a second transmission device corresponding to the first transmission device and connected to the second time synchronization device, wherein the transmission device being operable as the first transmission device or the second transmission device, comprising one or more processors configured to:
transmit packets for time synchronization for a plurality of wavelengths to the other transmission device simultaneously, wherein the first transmission device is paired with the first time synchronization device, and the second transmission device is paired with the second time synchronization device,
wherein an uplink wiring length and a downlink wiring length between the first time synchronization device and the first transmission device are the same, and an uplink wiring length and a downlink wiring length between the second transmission device and the second time synchronization device are the same; and

receive the packets for time synchronization for the plurality of wavelengths from the other transmission device, measure a propagation delay on a path from the other transmission device to the transmission device based on a difference between arrival times of the received packets for time synchronization for the plurality of wavelengths, and provide the propagation delay to the second time synchronization device as a correction parameter used in a process of synchronizing time of the second time synchronization device, wherein measuring the propagation delay comprises:
determining, using the difference between arrival times of the received packets, a length of a downlink transmission line and a length of an uplink transmission line between the first and second transmission devices, and
determining the propagation delay for each of the downlink transmission line and the uplink transmission line using the corresponding length, a temperature correction, and a predetermined delay for each length unit due to temperature change; and

the second time synchronization device is configured to calculate an offset value that is a difference between a clock of the first time synchronization device and a clock of the second time synchronization device by using transmit times and receive times of the packets for time synchronization at the first and second time synchronization devices and correction parameters provided by the first transmission device and the second transmission device.

3. A delay correction method implemented by a time transmission system, the time transmission system synchronizing time of a second time synchronization device based on time information of transmission and reception of packets for time synchronization between a first time synchronization device and the second time synchronization device via a first transmission device connected to the first time synchronization device and a second transmission device corresponding to the first transmission device and connected to the second time synchronization device,
each of the first transmission device and the second transmission device comprising one or more processors configured to:
transmit packets for time synchronization for a plurality of wavelengths to the other transmission device simultaneously, wherein the first transmission device is paired with the first time synchronization device, and the second transmission device is paired with the second time synchronization device,
wherein an uplink wiring length and a downlink wiring length between the first time synchronization device and the first transmission device are the same, and an uplink wiring length and a downlink wiring length between the second transmission device and the second time synchronization device are the same; and

receive the packets for time synchronization for the plurality of wavelengths from the other transmission device, measure a propagation delay on a path from the other transmission device to the transmission device based on a difference between arrival times of the received packets for time synchronization for the plurality of wavelengths, and provide the propagation delay to the second time synchronization device as a correction parameter used in a process of synchronizing time of the second time synchronization device, wherein measuring the propagation delay comprises:
determining, using the difference between arrival times of the received packets, a length of a downlink transmission line and a length of an uplink transmission line between the first and second transmission devices, and
determining the propagation delay for each of the downlink transmission line and the uplink transmission line using the corresponding length, a temperature correction, and a predetermined delay for each length unit due to temperature change.

Assignees

• Nippon Telegraph & Telephone

Inventors

• Nakagawa Masahiro
• Arai Kaoru
• Sakuma Hiroki
• Tsuboi Shunichi

Classifications

• H04J3/0667 Primary

  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

• H04J3/0682

  by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging · CPC title

• H04L7/0033

  Correction by delay · CPC title

• G04G5/00

  Setting, i.e. correcting or changing, the time-indication (radio-controlled time-pieces G04R) · CPC title

• H04J3/14

  Monitoring arrangements {(for SDH/SONET rings H04J3/085)} · CPC title