WO2005002100A1 - Synchronisation de haute precision du signal d'horloge dans un reseau - Google Patents

Synchronisation de haute precision du signal d'horloge dans un reseau Download PDF

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Publication number
WO2005002100A1
WO2005002100A1 PCT/IB2004/051057 IB2004051057W WO2005002100A1 WO 2005002100 A1 WO2005002100 A1 WO 2005002100A1 IB 2004051057 W IB2004051057 W IB 2004051057W WO 2005002100 A1 WO2005002100 A1 WO 2005002100A1
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WO
WIPO (PCT)
Prior art keywords
clock
node
offset
skew
network
Prior art date
Application number
PCT/IB2004/051057
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English (en)
Inventor
Laurent P. F. Bousis
Original Assignee
Koninklijke Philips Electronics N.V.
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Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2005002100A1 publication Critical patent/WO2005002100A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0658—Clock or time synchronisation among packet nodes
    • H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
    • H04J3/0667—Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays

Definitions

  • This invention relates to methods and apparatus for estimating clock offset and clock skew, and for synchronizing clocks in remote devices, for application to internet coupled devices and to synchronization of time sensitive streams of data such as digital bit streams especially video or audio streams.
  • Clock synchronization between different devices on networks such as Personal Area Networks (PAN), Controller Area Networks (CAN), Local Area Networks (LAN), Wide Area Networks (WAN), Metropolitan Area Networks (MAN), wireless or satellite networks or the internet for example is becoming more important.
  • Applications include providing time information or time interval information, or determining an order of events at distributed locations. This can be useful for a wide variety of advanced applications on distributed hosts or distributed clients.
  • clocks of internet hosts and clients can be synchronized using the Network Time Protocol NTP, (RFC-1305), to within a few milliseconds. This involves exchanging timestamps, computing delays and offsets and selecting and filtering the values from different sources. Higher accuracy synchronization can be achieved in more strictly controlled environments such as telephone networks or the Global Positioning System GPS.
  • NTP Network Time Protocol
  • a network may be provided with a reference clock.
  • One way of implementing a reference clock is to provide a master device and the time reported by a clock of the master device is considered to be the reference clock for that network. This often makes sense since the content streamed by the master device will most likely contain timestamps issued by that clock.
  • the present invention is not limited to this definition of how a reference clock is provided.
  • the offset of the clock of a client device is defined as the difference at a particular moment in time between the time reported by that clock and the time reported by the reference clock.
  • the skew of the clock of a client device is defined as the difference at a particular moment in time between the frequency of that clock and a frequency of the reference clock.
  • the skew of the clock of a client device is in fact the first derivative of its offset with respect to the time of the reference clock.
  • "Estimation of clock offset from one-way delay measurement on asymmetric paths" by Masato Tsuru, Tetsuya Takine and Yuji Oie (Saint 2002 Workshop, Feb 1 2002, Nara) acknowledges that it was known to estimate the clock offset, clock skew and bandwidth separately.
  • the clock skew could be estimated from one-way delay measurements with fixed size packets in one direction.
  • the clock offset could be estimated from one-way delay measurements with fixed size packets in both directions (like NTP) when delay is symmetric.
  • Prograrnrning It involves finding a minimum of a function Qi ( ⁇ , ⁇ , ⁇ ) where 1/ ⁇ is the skew, ⁇ is a function of transmission delays, and ⁇ is a function of propagation delays, over many timestamped messages. It is known from International patent publication WO 00/16509 to estimate relative skew between clocks in packet networks from timestamps in received packets and the local time of receipt. The delay in receipt is calculated, then compared to a previous delay to determine jitter. Average jitter is then used to determine skew. It is known from "Improved Algorithms for synchronizing computer network clocks" Mills, JJEEE/ACM transactions on networking Vol.
  • the invention provides apparatus for estimating skew and offset of a first clock at a first node of a network relative to a second clock at a second node of the network, the apparatus having means for: - . recording times of transmission and receipt of a series of messages exchanged between the nodes, dete ⁇ nining a series of instantaneous offsets at a series of time instants, from the recorded times of transmission and receipt, and determining an estimated offset, and an estimated skew from the series using a statistical method.
  • statistical method is meant a method used to find relationships between the measurements in order to predict future values.
  • a suitable statistical method is regression analysis, especially linear regression.
  • the combination of the series of instantaneous offsets and applying a statistical method to the series to estimate the skew and offset can produce more accurate results than other methods such as the Network Time Protocol [NTP] using other variables as set out above. Accuracy still depends on the skew being fairly constant, the measurements being accurate and well defined, an appropriate number of measurements, and the delays in each direction tending to be symmetric on average, and other practical factors.
  • NTP Network Time Protocol
  • the statistical method is regression, especially linear regression. This is one suitable way of fitting a line to the points in the series.
  • the linear regression is determined using a least squares algorithm. This is one suitable and efficient way of fitting a line to the series.
  • the steps are repeated to update the set and determine an updated estimated offset and an updated estimated skew. This enables the estimates to be continuously updated to maintain accuracy and adapt to changing conditions.
  • the instantaneous offset is determined from the relation
  • the apparatus is located at the first node.
  • the network is an IP network.
  • the messages comprise ICMP (Internet Control Message Protocol) timestamp request and reply messages.
  • the apparatus further comprises means for correcting the first clock to match the second clock.
  • the apparatus is arranged to carry out the recording of times of transmission and receipt during transmission of user data between the nodes.
  • the apparatus is arranged to delay user data passing through the first node on the basis of the estimated offset and skew. This is another way of reducing errors or distortion caused by the offset and skew.
  • the user data is video or audio or multimedia data for presentation to a user from a number of network nodes synchronously, or for recording from a number of network nodes synchronously.
  • Another aspect of the invention provides consumer equipment having an interface for coupling to a network, a first clock, and means for estimating skew and offset of the first clock relative to a second clock at a second node of the network by determining a series of instantaneous offsets at a series of time instants, from the recorded times of transmission and receipt, and determining an estimated offset, and an estimated skew from the series using a statistical method.
  • Other aspects of the invention include methods of estimating the skew and offset, methods of using the skew and offset estimated by this method, methods of synchronizing consumer equipment using the estimated skew and offset, and signals synchronized using the estimated skew and offset. How the present invention may be put into effect will now be described with reference to the appended schematic drawings. Obviously, numerous variations and modifications can be made without departing from the scope of the claims of the present invention. Therefore, it should be clearly understood that the form of the present invention is illustrative only and is not intended to limit the scope of the claims.
  • Fig. 1 shows an example of an ICMP timestamp request/reply
  • Fig. 2 shows an example of the time flow of an exchange of messages between a client-master pair of nodes
  • Fig. 3 shows a graph of a normal distribution of values of the difference of delay between the two directions of transmission
  • Fig. 4 shows a graph of a series of offsets for a series of messages at different times
  • Fig. 5 shows a flow chart of estimating skew and offset according to an embodiment of the invention
  • Fig. 6 shows an application of the estimated skew and offset, for synchronization, according to another embodiment.
  • any such terms as top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
  • Embodiments of this invention are preferred that concern clock synchronization of devices in an IP based network where the difference between the network reception delay and the network transmission delay is non-negligible but the present invention is not limited thereto. Rather, the present invention can have advantage use in a wide variety of networks comprising nodes linked by communications paths.
  • Fig. 1 shows the format of an ICMP Timestamp Request/Reply as specified in RFC792.
  • the time is recorded as a 32bit value with the higher order bit set to one to "indicate this non-standard value"
  • Fig. 2 illustrates the time flow for the exchange of these messages between the client-master pair.
  • a subscript of C on time values indicates the time has been reported by the clock of the client device; a subscript of M on time values indicates the time has been reported by the clock of the master device.
  • OT c is the time of the client sending the first message
  • RT M is the time of receipt of the first message at the master
  • TT M is the time of transmission of the second message from the master.
  • the completion timestamp CT is defined as the time the sender of the ICMP Timestamp request first touched the ICMP Timestamp reply on receipt and the offset O is defined as the offset between the clock of the client device and the clock of the master device.
  • TD is the transmission delay of the first message
  • RD is the transmission delay in the other direction of the second message
  • PD is the processing delay at the master between the first and second messages.
  • the network reception delay RD can be approximated by the network transmission delay TD, where e is the difference between the delays:
  • the instantaneous offset O can thus be found by the following equation: 2 -, ⁇ -c e 2 TTM +RTM 2 ⁇ 0TC ⁇ CTC
  • the skew was zero or negligible, it would have been sufficient to make a large number of measurements to find the average value of O' and use that value as the estimated offset O between the client device and the master device. However, since the skew is non-negligible compared to the desired accuracy, the estimate based on the average value of O' will no longer be representative of the offset O between the client device and the master device. Indeed, the effect of the skew will start to show during the measurements and if it is assumed the drift is negligible (meaning the skew will be constant) the measurements will trend towards a non-horizontal (non-horizontal if the skew is non-zero) straight line over time. Fig.
  • the line can be derived by various statistical methods, one preferred method involves applying linear regression to the set of samples (0 OTa). A filter could optionally be applied on the values O'i of the collected samples in order to reduce or eliminate noise in the samples.
  • n the number of measurements
  • n the number of measurements
  • the client at the first node sends the first message with a timestamp request to the second node.
  • the client receives the reply, the second message, records the time of receipt, and extracts from it a time of receipt of the first message and a time of transmission of the second message.
  • step 115 uses these measurements at step 115 to calculate the instantaneous offset O'j. These measurements are repeated by sending more messages, to build up a list at step 120 of instantaneous values.
  • step 130 the linear regression is carried out as discussed above, to derive the estimated values of skew and offset.
  • step 140 more measurements are taken and the estimated values are updated using the more recent measurements. There are a number of different uses for the estimated values. Once the value of the offset O and the skew S have been estimated, the client has enough information (in combination with the originate timestamp OTco of the first measurement) to know with high accuracy how its clock T c relates to the clock of the master T M at every moment in time i:
  • Fig. 6 shows an embodiment in which a first node (the client) is household consumer equipment such as an audio speaker 200. It is connected to receive an audio signal in the form of packets over a household LAN 210 from a second node (the master) which is a Personal Computer PC 220.
  • the LAN can use the household power supply wiring or be a wireless LAN, to overcome the inconvenience of conventional speaker cables.
  • the speaker is accurately synchronized to the PC to avoid the problems described above.
  • the speaker includes a network interface card or chip 230, a packet processing part 240 for recording time of receipt and transmission, and for extracting information from received measurement packets.
  • An estimation part 250 uses the measured times to create the set of offsets and derive the estimated skew and offset, using a statistical method. This can be implemented as discussed above, or in other ways.
  • An audio generator part 260 recreates the audio signal from the received streamed packets, with a clock variation according to the estimated skew and offset.
  • the clock to be synchronized is the first clock 280 used by the audio generator part 260 to produce sound. This will for example typically be 44100 Hz for CD quality sound.
  • This clock is adapted to speed up or slow down the clock time based on the estimated skew and offset of that clock with regards to the master clock.
  • the speeding up or slowing down is a typically small change.
  • the link between the first clock 280 and the audio generator part 260 is provided through estimation part 250.
  • These parts can be implemented in various conventional types of hardware and software depending on the application, following established principles.
  • a single general purpose microprocessor or Application Specific Integrated Circuit can be used to implement the NIC, the packet processing part and the estimation part for example. In order to produce better estimations of the offset O and skew S with fewer measurements, the measurements can be carried out on an idle network right before the content is being streamed.
  • the measurements could be done continuously during the streaming thereby producing updated values of the offset O and skew S at fixed time intervals.
  • the present invention provides several advantages. Being able to accurately synchronize the clocks of devices inside home or other networks is of importance if content is to be streamed in separate channels to separate devices. Not only synchronization between audio channels, but also synchronization between audio and video channels has to be achieved with accuracies that are orders of magnitude higher than that achieved by traditional network synchronization protocols used in the PC environment.
  • the embodiments of the invention described here are able to achieve better accuracies and could therefore be implemented in any consumer electronic devices (and PCs) that stream and receive content inside home networks for example.
  • Network clock synchronization can be implemented with an accuracy that is orders of magnitudes better than traditional network synchronization protocols like NTP by applying a well-defined statistical analysis to a well-defined series of measurements to precisely estimate the skew and offset of the clock of the client.
  • skew and offset of a clock at a first node of a network relative to a second clock at a second node is estimated by recording times of transmission and receipt of a series of messages exchanged between the nodes, determining a series of instantaneous offsets at a series of time instants, from the recorded times and deriving offset and skew from the series using a statistical method such as regression, especially linear regression.
  • Accuracy still depends on the skew being fairly constant, the measurements being accurate and well defined, an appropriate number of measurements, and the delays in each direction tending to be symmetric on average.
  • the measurements can be repeated periodically to update the estimates. Apphcations include audio or visual packet data streamed to multiple nodes to enable them to be synchronized so that a user does not perceive distortion from relative delays or delay variation.
  • Other variations can be envisaged by those skilled in the art and are intended to be encompassed by the claims.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

Pour estimer l'asymétrie et le décalage d'un premier signal d'horloge (280) au niveau d'un premier noeud (200) d'un réseau par rapport à un deuxième signal d'horloge (270) au niveau d'un deuxième noeud (220), on enregistre les moments d'émission et de réception d'une série de messages échangés (100, 110) entre les noeuds, on détermine (115) à partir desdits moments enregistrés une série de décalages instantanés à une série d'instants temporels et on dérive à partir de ladite série le décalage et l'asymétrie au moyen d'une régression linéaire (130). La précision dépend néanmoins de la quasi-constance de l'asymétrie, de l'exactitude et de la définition précise des mesures effectuées, de leur nombre approprié, et de la tendance des retards dans chaque direction à être en moyenne symétriques. Les mesures peuvent être répétées périodiquement (120) pour actualiser les estimations. Parmi les applications de l'invention, on peut citer l'émission en continu de paquets de données audio ou vidéo à destination de multiples noeuds en vue de permettre leur synchronisation de sorte qu'un utilisateur ne perçoive pas la distorsion résultant des retards relatifs ou des variations des retards.
PCT/IB2004/051057 2003-06-30 2004-06-30 Synchronisation de haute precision du signal d'horloge dans un reseau WO2005002100A1 (fr)

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Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007055627A1 (fr) * 2005-11-14 2007-05-18 Telefonaktiebolaget L M Ericsson (Publ) Generation de signal d'horloge de flux de paquets reçu
GB2443868A (en) * 2006-03-21 2008-05-21 Zarlink Semiconductor Ltd Synchronising slave clocks in non-symmetric packet networks
US8139489B2 (en) 2008-08-06 2012-03-20 International Business Machines Corporation Robust jitter-free remote clock offset measuring method
EP2523372A1 (fr) 2011-05-09 2012-11-14 British Telecommunications Public Limited Company Système de livraison de contenu
US8533355B2 (en) 2009-11-02 2013-09-10 International Business Machines Corporation Techniques for improved clock offset measuring
WO2013144760A1 (fr) * 2012-03-29 2013-10-03 Ramot At Tel-Aviv University Ltd Localisation, synchronisation et navigation au moyen de réseaux de capteurs passifs
ITTO20120740A1 (it) * 2012-08-22 2014-02-23 Selex Elsag Spa Metodo per sincronizzare i nodi di una rete a pacchetto, nodo di rete e rete a pacchetto
CN105406932A (zh) * 2009-04-29 2016-03-16 瞻博网络公司 通过处理分组延迟值补偿时钟频率和相位变化的装置和方法
WO2017212205A1 (fr) * 2016-06-10 2017-12-14 Khalifa University Of Science, Technology And Research Procédés et systèmes destinés à une estimation d'obliquité
AT518674A1 (de) * 2016-06-06 2017-12-15 Sprecher Automation Gmbh Verfahren zur synchronisierten Erfassung von zur Steuerung von Differentialschutzeinrichtungen elektrischer Energieleitungen benötigten Messdaten
US10142088B2 (en) 2014-01-31 2018-11-27 University Of North Dakota Network clock skew estimation and calibration
EP3598247A4 (fr) * 2017-03-17 2020-03-04 Hangzhou Hikvision Digital Technology Co., Ltd. Procédé et dispositif de synchronisation de réseau
WO2020081564A1 (fr) * 2018-10-15 2020-04-23 Bose Corporation Synchronisation sans fil d'un contenu audio
WO2021018407A1 (fr) * 2019-07-31 2021-02-04 Telefonaktiebolaget Lm Ericsson (Publ) Synchronisation d'horloge dans des réseaux de communication par paquets
CN112684992A (zh) * 2020-12-18 2021-04-20 深圳乐播科技有限公司 一种投屏播放同步的实现方法、装置及计算机主设备
CN116471211A (zh) * 2023-06-19 2023-07-21 威胜信息技术股份有限公司 一种电力物联网精准对时方法
EP3231111B1 (fr) * 2014-12-11 2024-07-24 Khalifa University of Science and Technology Procédé et dispositifs pour une synchronisation d'horloge sur des liaisons comportant des débits de transmission asymétriques

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0697774A1 (fr) * 1994-08-15 1996-02-21 Hewlett-Packard Company Estimation de décalage d'une horloge
US5802082A (en) * 1995-07-25 1998-09-01 Deutsche Telekom Ag Method and device for measuring cell propagation time in ATM networks
US20020136335A1 (en) * 2000-12-19 2002-09-26 Shih-Ping Liou System and method for clock-synchronization in distributed systems

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0697774A1 (fr) * 1994-08-15 1996-02-21 Hewlett-Packard Company Estimation de décalage d'une horloge
US5802082A (en) * 1995-07-25 1998-09-01 Deutsche Telekom Ag Method and device for measuring cell propagation time in ATM networks
US20020136335A1 (en) * 2000-12-19 2002-09-26 Shih-Ping Liou System and method for clock-synchronization in distributed systems

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
LEI GUO ET AL: "Performance analysis of general tracking algorithms", DECISION AND CONTROL, 1994., PROCEEDINGS OF THE 33RD IEEE CONFERENCE ON LAKE BUENA VISTA, FL, USA 14-16 DEC. 1994, NEW YORK, NY, USA,IEEE, US, 14 December 1994 (1994-12-14), pages 2851 - 2855, XP010144672, ISBN: 0-7803-1968-0 *
MILLS D L: "IMPROVED ALGORITHMS FOR SYNCHRONIZING COMPUTER NETWORK CLOCKS", IEEE / ACM TRANSACTIONS ON NETWORKING, IEEE INC. NEW YORK, US, vol. 3, no. 3, 1 June 1995 (1995-06-01), pages 245 - 254, XP000510988, ISSN: 1063-6692 *
TSURU M ET AL: "Estimation of clock offset from one-way delay measurement on asymmetric paths", APPLICATIONS AND THE INTERNET (SAINT) WORKSHOPS, 2002. PROCEEDINGS. 2002 SYMPOSIUM ON NARA, JAPAN 28 JAN.-1 FEB. 2002, LOS ALAMITOS, CA, USA,IEEE COMPUT. SOC, US, 28 January 2002 (2002-01-28), pages 126 - 133, XP010587872, ISBN: 0-7695-1450-2 *

Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007055627A1 (fr) * 2005-11-14 2007-05-18 Telefonaktiebolaget L M Ericsson (Publ) Generation de signal d'horloge de flux de paquets reçu
CN101310462B (zh) * 2005-11-14 2013-01-02 艾利森电话股份有限公司 根据接收到的分组流产生时钟信号的装置和方法
GB2443868A (en) * 2006-03-21 2008-05-21 Zarlink Semiconductor Ltd Synchronising slave clocks in non-symmetric packet networks
US8139489B2 (en) 2008-08-06 2012-03-20 International Business Machines Corporation Robust jitter-free remote clock offset measuring method
CN105406932A (zh) * 2009-04-29 2016-03-16 瞻博网络公司 通过处理分组延迟值补偿时钟频率和相位变化的装置和方法
CN105406932B (zh) * 2009-04-29 2018-09-18 瞻博网络公司 用于计算机网络的装置
US8788689B2 (en) 2009-11-02 2014-07-22 International Business Machines Corporation Techniques for improved clock offset measuring
US8533355B2 (en) 2009-11-02 2013-09-10 International Business Machines Corporation Techniques for improved clock offset measuring
WO2012153081A1 (fr) 2011-05-09 2012-11-15 British Telecommunications Plc Système de diffusion de contenu
EP2523372A1 (fr) 2011-05-09 2012-11-14 British Telecommunications Public Limited Company Système de livraison de contenu
WO2013144760A1 (fr) * 2012-03-29 2013-10-03 Ramot At Tel-Aviv University Ltd Localisation, synchronisation et navigation au moyen de réseaux de capteurs passifs
US11140645B2 (en) 2012-03-29 2021-10-05 Sulu Networks Ltd. Localization, synchronization and navigation using passive sensor networks
ITTO20120740A1 (it) * 2012-08-22 2014-02-23 Selex Elsag Spa Metodo per sincronizzare i nodi di una rete a pacchetto, nodo di rete e rete a pacchetto
US10142088B2 (en) 2014-01-31 2018-11-27 University Of North Dakota Network clock skew estimation and calibration
EP3231111B1 (fr) * 2014-12-11 2024-07-24 Khalifa University of Science and Technology Procédé et dispositifs pour une synchronisation d'horloge sur des liaisons comportant des débits de transmission asymétriques
AT518674A1 (de) * 2016-06-06 2017-12-15 Sprecher Automation Gmbh Verfahren zur synchronisierten Erfassung von zur Steuerung von Differentialschutzeinrichtungen elektrischer Energieleitungen benötigten Messdaten
AT518674B1 (de) * 2016-06-06 2018-02-15 Sprecher Automation Gmbh Verfahren zur synchronisierten Erfassung von zur Steuerung von Differentialschutzeinrichtungen elektrischer Energieleitungen benötigten Messdaten
EP3255820B1 (fr) * 2016-06-06 2024-01-24 Sprecher Automation GmbH Procédé d'enregistrement synchronisé de données de mesure nécessaires à la commande de dispositif de protection différentielle de lignes électriques
WO2017212205A1 (fr) * 2016-06-10 2017-12-14 Khalifa University Of Science, Technology And Research Procédés et systèmes destinés à une estimation d'obliquité
EP3598247A4 (fr) * 2017-03-17 2020-03-04 Hangzhou Hikvision Digital Technology Co., Ltd. Procédé et dispositif de synchronisation de réseau
US10708033B2 (en) 2017-03-17 2020-07-07 Hangzhou Hikvision Digital Technology Co., Ltd. Network time correction method and apparatus
WO2020081564A1 (fr) * 2018-10-15 2020-04-23 Bose Corporation Synchronisation sans fil d'un contenu audio
US10805664B2 (en) 2018-10-15 2020-10-13 Bose Corporation Wireless audio synchronization
WO2021018407A1 (fr) * 2019-07-31 2021-02-04 Telefonaktiebolaget Lm Ericsson (Publ) Synchronisation d'horloge dans des réseaux de communication par paquets
CN112684992A (zh) * 2020-12-18 2021-04-20 深圳乐播科技有限公司 一种投屏播放同步的实现方法、装置及计算机主设备
CN116471211A (zh) * 2023-06-19 2023-07-21 威胜信息技术股份有限公司 一种电力物联网精准对时方法
CN116471211B (zh) * 2023-06-19 2023-10-13 威胜信息技术股份有限公司 一种电力物联网精准对时方法

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