WO2012038644A1 - Procede de correction d'une asymetrie de delai - Google Patents
Procede de correction d'une asymetrie de delai Download PDFInfo
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- WO2012038644A1 WO2012038644A1 PCT/FR2011/052126 FR2011052126W WO2012038644A1 WO 2012038644 A1 WO2012038644 A1 WO 2012038644A1 FR 2011052126 W FR2011052126 W FR 2011052126W WO 2012038644 A1 WO2012038644 A1 WO 2012038644A1
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- Prior art keywords
- node
- link
- delay asymmetry
- signals
- optical fiber
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Classifications
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- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
-
- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0226—Fixed carrier allocation, e.g. according to service
-
- 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
- H04J3/0673—Clock or time synchronisation among packet nodes 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L43/00—Arrangements for monitoring or testing data switching networks
- H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
- H04L43/0852—Delays
Definitions
- the embodiments of the present invention relate to the field of packet-switched communication networks and more particularly to the distribution of a time reference in these networks.
- time synchronization in English
- time synchronization in English
- delay asymmetry in English
- slave master-clock and a packet (of the same sequence number) transmitted in the opposite direction corresponds to a difference in the transmission time between a packet transmitted in the clockwise direction.
- slave master-clock and a packet (of the same sequence number) transmitted in the opposite direction corresponds to a difference in the transmission time between a packet transmitted in the clockwise direction.
- a solution of the state of the art corresponds to the compensation of the time difference between the two directions.
- a co-located external time reference generally a Global Positioning System (GPS).
- GPS Global Positioning System
- Embodiments of the present invention focus on compensating for propagation delay asymmetry inherent in links. It should be noted that Embodiments described apply not only to networks using optical fibers but also in a manner similar to other transport mediums such as air with radio frequency transmissions. Therefore, the invention is not limited to optical fibers.
- the embodiments of the present invention relate to a method of correcting a delay asymmetry of the synchronization messages transmitted in a packet-switched network between a master clock and a slave clock in which the delay asymmetry of the path connecting the master clock to the slave clock is determined and corrected locally at least one link of said path by means of measuring and correction of a time offset located at the nodes of the course, said means of measurement being means for measuring the signal transmission times in said at least one link.
- the time synchronization of the nodes of the packet-switched network is provided by an IEEE 1588V2 type protocol.
- the measurement means allowing the local determination of the delay asymmetry comprise transparent peer-to-peer ("peer”) transparent clocks.
- the measuring means for the local determination of the delay asymmetry comprise end-to-end transparent clocks ("end-to-end transparent clock” in English). According to another embodiment, the measuring means for the local determination of the delay asymmetry comprise boundary clocks ("boundary clock" in English).
- the measuring means for local determination of the delay asymmetry comprise at least two transmitters (or possibly only one wavelength tunable optical transmitter), located in a first node of the link, configured to transmit (simultaneously or with a time offset determined in advance by configuration) two signals at two distinct wavelengths on the same optical fiber and in the same direction and at least one receiver, located in a second node of the link, configured to receive and detect said two signals at two distinct wavelengths and to determine the time delay (delay) of arrival between the two signals.
- transmitters or possibly only one wavelength tunable optical transmitter
- the measuring means for local determination of the delay asymmetry comprise at least two transmitters (or possibly only one wavelength tunable optical transmitter), located in a first node of the link, configured to transmit (simultaneously or with a time offset determined in advance by configuration) two signals at two distinct wavelengths on the same optical fiber and in the same direction and at least one receiver, located in a second node of the link, configured to receive and detect said two signals at two distinct wavelength
- the measurement means for the local determination of the delay asymmetry comprise at least two transmitters, located in a first node of the link, configured to transmit two signals at two distinct wavelengths on two fibers. separate optics and in the same direction and at least one receiver, located in a second node of the link, configured to receive and detect said two signals at two distinct wavelengths and to determine the arrival time offset between the two signals .
- the transmission and detection are at the level of the physical layer. According to a further embodiment, the transmission and detection are at the level of the packet layer.
- the measurement means for the local determination of the delay asymmetry comprise at least a first transceiver, located in a first node of the link, configured to transmit a signal at a first wavelength. on a first optical fiber and for receiving and detecting a signal at a second wavelength on the first or second optical fiber and at least a second transceiver located in a second node of the link configured to receive and detect the signal transmitted at the first wavelength on the first optical fiber and for looping back to said first node at the second wavelength on the first or second optical fiber, said first transceiver comprising means for determining the round trip time of the signal and means for calculating the delay asymmetry from said round trip time, optical indices associated with the signal wavelengths, respective lengths of the fibers and environmental parameters (eg temperature).
- first transceiver comprising means for determining the round trip time of the signal and means for calculating the delay asymmetry from said round trip time, optical indices associated with the signal wavelengths, respective lengths of the fibers and environmental parameters (eg
- the measuring means for the local determination of the delay asymmetry comprise at least one transceiver, located in a first node of the link, configured to transmit a first signal on a first wavelength. on a first optical fiber and for receiving and detecting two signals on a second and a third wavelength on a second optical fiber and a module comprising an optical circulator and a wavelength converter located in a second node of the link configured to retransmit the first received signal on the first wavelength on the first optical fiber to said first node on the second and third wavelengths on the second optical fiber, said transceiver comprising means for determining round trip time of the signals and means for calculating the delay asymmetry from said travel times , optical indices associated with signal wavelengths, respective fiber lengths and environmental parameters.
- the measuring means for the local determination of the delay asymmetry comprise at least a first transceiver, located in a first node of the link, configured to transmit a first signal to a first length of time. wave on a first optical fiber, said first signal being looped back to the first node at a second node of the link by a first optical circulator on said first optical fiber and at least a second transceiver located in a second node of the link, configured to transmit a second signal at a second wavelength on a second optical fiber, said second signal being looped back to the second node at the first node of the link by a second optical circulator on said second optical fiber, said first and second nodes of the link also comprising means for determining travel times return of the first and second signals respectively and means for calculating the delay asymmetry from said round trip times.
- the measurement means for the local determination of the delay asymmetry comprise at least two transmitters (TX), situated in a first node of the link, configured to transmit two distinct electromagnetic signals on the same medium of transport and in the same direction and at least one receiver (RX), located in a second node of the link, configured to receive and detect said two separate electromagnetic signals and to determine the arrival time offset between the two signals.
- TX transmitters
- RX receiver
- the measuring means for the local determination of the delay asymmetry comprise at least two transmitters (TX) located in a first node of the link, configured to transmit two distinct electromagnetic signals over two transport mediums. separate and in the same direction and at least one receiver (RX), located in a second node of the link, configured to receive and detect said two separate electromagnetic signals and to determine the arrival time offset between the two signals.
- TX transmitters
- RX receiver
- the embodiments of the present invention also relate to a node of a packet-switched network comprising transmission means (simultaneous or with a predetermined time-shift by configuration) of at least two signals over at least two wavelengths on at least one optical fiber and means for receiving and detecting at least two signals with at least two wavelengths on at least one optical fiber, said node comprising means for determining an offset arrival time between two received and detected signals and means for calculating delay asymmetry of an adjacent link as a function of said time offset.
- Embodiments of the present invention also relate to a node of a packet-switched network comprising means for transmitting at least one signal over at least one wavelength on at least one optical fiber and receiving means. and detecting at least one signal with at least one wavelength on at least one optical fiber, said node comprising means for determining a round trip time of the at least one received and detected signal and means for calculating a delay asymmetry of an adjacent link as a function of said at least one travel time - back.
- FIG. 1 represents a portion of the synchronization network, comprising a slave clock-master clock pair, in a diagram in which the synchronization on-path support equipments are fully deployed ( "Fully deployed" in English);
- FIG. 2 represents a graph showing the influence of the temperature on the propagation index of the optical fibers
- FIG. 3 represents a diagram of the correction of link-by-link delay asymmetry, according to the embodiments of the present invention.
- FIG. 4 represents an operational mode diagram of the synchronization network where the signals are transmitted in one direction on a first fiber at a first wavelength and in the other direction on a second fiber at a second wavelength. ;
- FIG. 5 represents an example of determining the delay asymmetry of a link according to a first embodiment
- FIG. 6 represents an operational mode diagram of a link transmitting messages of the protocol of the IEEE Std 1588 TM -2008 standard (hereinafter referred to as 1588V2) of the Sync type in one direction and of the Delay Req type in the other. meaning;
- FIG. 7 represents an example of determining the delay asymmetry of a link according to a second embodiment using the messages of the 1588V2 protocol
- FIG. 8 represents an example of determining the delay asymmetry of a link according to a third embodiment based on the determination of the transmission time of a signal on the return trip of the link
- FIG. 9 represents an example of determining the delay asymmetry of a link according to a fourth embodiment based on the determination of the transmission time of two signals on the return trip of the link;
- FIG. 10 represents an example of determining the delay asymmetry of a link according to a fifth embodiment based on the determination of the transmission time of two signals transmitted on two distinct wavelengths on the return trip. the link;
- NTP Network Time Protocol
- the term "environmental parameter" corresponds to an influence parameter of the transport of optical signals depending on the environment such as temperature or humidity, for example;
- end-to-end transparent clock (“end-to-end transparent clock” in English) corresponds to a clock comprising means for determining the transit delay of a packet at a network element;
- peer-to-peer transparent clock corresponds to a clock comprising means for determining the transit delay of a packet at a network element level and the delay of a link adjacent to the node in which the clock is located;
- boundary clock corresponds to a clock for segmenting the synchronization network in small areas.
- the boundary clocks include means for determining the delay of a link adjacent to the node in the network. which is the clock;
- advanced clock is used to define a transparent, peer-to-peer, transparent or boundary end-to-end clock
- link also called “segment” defines the portion of network located between two nodes and allowing the transmission of optical signals, a link generally comprising at least one optical fiber;
- IEEE1588V2 corresponds to the acronym “Institute of Electrical and Electronics Engineers 1588 Version 2";
- CAPEX is the abbreviation of “Capital Expenditure” and refers to investment in equipment
- OPEX is the abbreviation of "Operational Expenditure” and corresponds to the operating costs
- Embodiments of the present invention relate to determining and correcting delay asymmetry of synchronization messages in a scheme where synchronization support equipment is fully deployed, i.e. network comprises a peer-to-peer or end-to-end or border type transparent clock, said clocks being managed by a single operator.
- FIG. 1 Such a network diagram is shown in FIG. 1.
- a master clock 1 distributes a time reference via synchronization signals 3 through the network elements, corresponding to nodes of the network, to a slave clock. 5, each intermediate node comprising an evolved clock 7.
- the synchronization signals are transmitted through optical fibers including silica.
- the characteristics of the silica vary according to environmental conditions (here temperature). Curves c1, c2 and c3 representing the group indices and the curves c4, c5 and c6 representing the refractive indices for respective temperatures of 0, 100 and 200 ° C.
- the delay asymmetry is determined and corrected at each link during the distribution of a frequency reference between the master clock and the slave clock as shown in FIG.
- the time differences ⁇ , ⁇ 2, ⁇ 3, ⁇ 4 and ⁇ 5 respectively corresponding to the delay asymmetry of the links L1, L2, L3, L4 and L5 are determined and taken into account locally at the nodes N2, N3, N4, N5 and N6, these measurements (of time differences) being carried out periodically in order to take into account the variation of the environmental parameters and thus to increase the precision of the distribution of a reference of time.
- the network elements performing the time difference measurements transmit the values of these deviations to the elements of the IEEE1588V2 plane, that is to say the evolved clocks 7 of the nodes to enable them to perform a node-to-node correction of the asymmetry delay generated at each link.
- FIG. 4 represents a diagram of a link between a node N2 and a node N3 (for example the nodes N2 and N3 of FIG. 3).
- the node N2 receives a synchronization message 9 from the master clock, this message is then sent by a TX transmitter to the receiver RX of the node N3 through a first optical fiber at a wavelength ⁇ .
- the node N3 receives a synchronization message from the slave clock, this message is then sent by a TX transmitter to the receiver RX node N2 through the first optical fiber or through a second optical fiber at a wavelength ⁇ .
- the difference between the wavelengths induces a delay asymmetry of the link, that is to say that the transmission times of the signals in one direction and in the other are different.
- the signals can be, for example, signal signals (ie pulses) easily detectable at the level of the rising edge and making it possible to precisely determine the instant of reception.
- the offset of time (or delay) At makes it possible to obtain a good estimate of the delay asymmetry of the synchronization link between the nodes N2 and N3.
- the signals are therefore detected directly at the level of the physical layer.
- the messages exchanged between the nodes comprise PTPV2 type packets.
- These packets are messages of Sync type 13 in the Master-Slave direction and of Delay_Req type in the Slave-Master direction as shown in FIG. 6, because of differences in optical indices due to the difference in wavelengths. (between ⁇ and ⁇ ), a delay asymmetry is introduced.
- two signals of Sync type 13 are transmitted simultaneously from node N2 to node N3 at wavelengths ⁇ '' and ⁇ '' close to wavelength ⁇ and ⁇ Sync and Delay Req messages for which we want to estimate the delay asymmetry.
- the delay offset At 'between the two messages transmitted at the wavelengths ⁇ ' and ⁇ ' is measured.
- the shift of time ⁇ between the messages transmitted at the wavelengths ⁇ and ⁇ is then deduced from ⁇ '.
- the following demonstration is given as an indication. The latter applies in the case of one and the same optical fiber or two optical fibers of identical lengths 1. More generally, this embodiment applies to two fibers of different lengths, this embodiment making it possible to also achieve the delay asymmetry inherent in the length difference of the optical fibers.
- the average delay d on a wavelength ⁇ can be defined by
- ⁇ can be deduced from ⁇ 'and different optical propagation indices.
- the wavelengths ⁇ 'and ⁇ ' can be reserved or dedicated to the determination of the delay asymmetry or the control wavelengths.
- measurements can be made in the opposite direction if the latter is less in demand in terms of bandwidth.
- the clocks must be able to generate event messages such as Sync type messages.
- This function can be performed by generating Sync messages in advance and manually, which are then saved in a specific location in the clock memory. This avoids the complex implementation of the protocol stack 1588V2 (also called PTPV2). In this In the second case, signal transmission and detection occur at the packet layer.
- a delay measurement is performed on a signal performing a round trip between two nodes, the forward path being made at a first wavelength ⁇ corresponding to a first optical index. ni and the return being at a second wavelength 12 corresponding to a second optical index n2.
- this embodiment therefore applies essentially in the case where the courses go and return are on the same optical fiber. It is also necessary to know precisely the optical indices ni and n2 since the accuracy of the determination of the delay asymmetry depends on these indices.
- time of the outward journey can be defined by:
- the second node (N3) can not loop back the instantaneously received signal, a transit / transit delay correction mechanism of the node, as present in the transparent clocks (peer-to-peer or end-to-end). end) must be applied to compensate for the delay introduced by this loopback. In addition, this second node (N3) must be able to perform a wavelength conversion ( ⁇ to 12).
- FIG. 9 A signal at a first wavelength ⁇ is transmitted by the node. N2 on a first optical fiber to the node N3.
- the signal is looped back to node N2 at a second and a third wavelength on a second optical fiber (in this case the first and second wavelengths are identical and denoted ⁇ , the third wavelength being denoted ⁇ 2).
- the loopback of the signals is done at a module M comprising an optical circulator and a wavelength converter, the module M being located at a close distance or known Rx receivers and transmitters Tx node N3.
- the RTT1 and RTT2 round trip times, corresponding to the two signals received by the node N2 can be described by the following equations:
- RTTl n 'J + ⁇ RTT2 - n ⁇ ⁇ + n 2: ⁇
- the two optical fibers are considered to have identical physical characteristics (or very close), that is to say that at a given wavelength, they have the same optical index (or a very close optical index).
- a first signal is transmitted by a first node N2 at a first wavelength ⁇ on a first optical fiber to a second node N3 and then looped back to the first node N2 at the same first wavelength and on the same first optical fiber; and secondly, a second signal is transmitted by the second node N3 at a second wavelength ⁇ 2 on a second optical fiber to the first node N2 and then looped back to the second node N3 at the same second wavelength and on the same second optical fiber.
- the delay asymmetry d (between a message of Sync type 13 transmitted at a wavelength ⁇ and a Delay message Req 15 transmitted at a wavelength ⁇ 2) can then be calculated:
- RTT1 and RTT2 must be available. at the node ensuring the calculation of d. Therefore, one or other of the RTT1 or RTT2 values must be transmitted to the adjacent node, preferably by a method called "packets".
- the embodiments of the present invention describe a determination of the delay asymmetry, locally at the links of the path, by the difference of measurement of instants representative of signals exchanged between the two nodes of the link, these signals being able to be transmitted at the physical layer or the packet layer.
- these measurements correspond to the measurement of a time difference by a single clock located in one of the two nodes of the link. Indeed, this applies
- the knowledge of the correction of the determined link delay asymmetry is carried only by the signals of the SYNC type, that is to say signals transmitted from the master clock to the slave clock, so that the messages Delay req transmitted from the slave clock to the master clock do not undergo modifications, which simplifies the implementation of a correction delay asymmetry according to the embodiments of the present invention in the case of a network comprising a multicast capability.
- the mechanisms of the embodiments described above are manageable at the level of the network elements and can be controlled automatically and remotely by a network management entity.
- these mechanisms can also be managed at the level of the control plan through the use of specific exchange messages between different network elements to plan, trigger, and control delay metric measurements at the link level.
- This management can be supported by the synchronization plan by the exchange of messages of the IEEE 1588 V2 type comprising an additional extension of type Type Length Value (TLV) dedicated.
- TLV Type Length Value
- the embodiments of the present invention make it possible, by determining the delay asymmetry at each link of the path between the master clock and the slave clock and correcting this delay asymmetry at each node of the route. , to improve the quality (ie the accuracy) of the time distribution in a network in order to strive to respect the constraints imposed by operators without requiring major investments or operating costs (CAPEX and OPEX).
- the implementation of the various embodiments presented is easy to implement and control because automatically manageable at the network level and allows for regular measurements to take into account the variations in environmental parameters.
- the embodiments are applicable to radio frequency transmissions with some nuances of language and complexity. Indeed for such a case the transport medium is in first approximation the same in both directions of propagation of the signals and is then similar to the embodiments considering a single optical fiber (a single medium of transport). Moreover, for such a medium (air) the electromagnetic signals are preferably described in terms of frequency rather than in terms of wavelength.
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Abstract
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Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
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US13/819,363 US20130209096A1 (en) | 2010-09-20 | 2011-09-15 | Method for correcting a delay asymmetry |
CN2011800451068A CN103119872A (zh) | 2010-09-20 | 2011-09-15 | 用于修正延迟不对称的方法 |
KR1020137010084A KR101479483B1 (ko) | 2010-09-20 | 2011-09-15 | 지연의 비대칭을 보정하는 방법 |
EP11773098.6A EP2619936A1 (fr) | 2010-09-20 | 2011-09-15 | Procede de correction d'une asymetrie de delai |
JP2013528748A JP5671619B2 (ja) | 2010-09-20 | 2011-09-15 | 遅延非対称を補正するための方法 |
Applications Claiming Priority (2)
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FR1003727A FR2965131B1 (fr) | 2010-09-20 | 2010-09-20 | Procede de correction d'une asymetrie de delai. |
FR1003727 | 2010-09-20 |
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WO2012038644A1 true WO2012038644A1 (fr) | 2012-03-29 |
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PCT/FR2011/052126 WO2012038644A1 (fr) | 2010-09-20 | 2011-09-15 | Procede de correction d'une asymetrie de delai |
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US (1) | US20130209096A1 (fr) |
EP (1) | EP2619936A1 (fr) |
JP (1) | JP5671619B2 (fr) |
KR (1) | KR101479483B1 (fr) |
CN (1) | CN103119872A (fr) |
FR (1) | FR2965131B1 (fr) |
WO (1) | WO2012038644A1 (fr) |
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- 2011-09-15 US US13/819,363 patent/US20130209096A1/en not_active Abandoned
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
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CN103840877A (zh) * | 2012-11-23 | 2014-06-04 | 中兴通讯股份有限公司 | 自动检测光纤非对称性的时间同步装置及方法 |
JP2016502649A (ja) * | 2012-11-23 | 2016-01-28 | 中興通訊股▲分▼有限公司 | 光ファイバの非対称性を自動的に検出する時間同期装置及び方法 |
US9762318B2 (en) | 2012-11-23 | 2017-09-12 | Zte Corporation | Time synchronization apparatus and method for automatically detecting the asymmetry of an optical fiber |
CN103840877B (zh) * | 2012-11-23 | 2017-11-24 | 中兴通讯股份有限公司 | 自动检测光纤非对称性的时间同步装置及方法 |
JP2016508337A (ja) * | 2013-01-07 | 2016-03-17 | マイクロセミ フリクエンシー アンド タイム コーポレーション | パケットタイミングプロトコルのための一般的な非対称修正 |
WO2014187207A1 (fr) * | 2013-05-20 | 2014-11-27 | 中兴通讯股份有限公司 | Procede et appareil de correction de temps pour un dispositif d'horloge esclave |
US9813174B2 (en) | 2013-05-20 | 2017-11-07 | Xi'an Zhongxing New Software Co., Ltd | Time correction method and apparatus for slave clock device |
US11206095B1 (en) | 2019-03-22 | 2021-12-21 | Equinix, Inc. | Timing synchronization for clock systems with asymmetric path delay |
Also Published As
Publication number | Publication date |
---|---|
JP2013538022A (ja) | 2013-10-07 |
EP2619936A1 (fr) | 2013-07-31 |
KR20130064808A (ko) | 2013-06-18 |
CN103119872A (zh) | 2013-05-22 |
JP5671619B2 (ja) | 2015-02-18 |
FR2965131B1 (fr) | 2012-09-28 |
KR101479483B1 (ko) | 2015-01-06 |
US20130209096A1 (en) | 2013-08-15 |
FR2965131A1 (fr) | 2012-03-23 |
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