WO2016179963A1 - 无源光网络***的时钟同步方法、装置和存储介质 - Google Patents

无源光网络***的时钟同步方法、装置和存储介质 Download PDF

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WO2016179963A1
WO2016179963A1 PCT/CN2015/092280 CN2015092280W WO2016179963A1 WO 2016179963 A1 WO2016179963 A1 WO 2016179963A1 CN 2015092280 W CN2015092280 W CN 2015092280W WO 2016179963 A1 WO2016179963 A1 WO 2016179963A1
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onu
time
reference frame
time reference
olt
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PCT/CN2015/092280
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French (fr)
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王霞元
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深圳市中兴微电子技术有限公司
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter
    • H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
    • H04L7/033—Speed or phase control by the received code signals, the signals containing no special synchronisation information using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

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  • the present invention relates to a clock synchronization technology in the field of communications, and in particular, to a clock synchronization method, apparatus, and storage medium for a passive optical network (PON) system.
  • PON passive optical network
  • the PON system is composed of an optical line terminal (OLT) located at the core node or the aggregation node, and an optical network unit (ONU, Optical Network Unit) located at the customer premises.
  • OLT optical line terminal
  • ONU optical network unit
  • One central office OLT controls multiple ONUs, each of which The ONU provides a user-side interface to the access network.
  • IEEE Institute of Electrical and Electronics Engineers
  • the OLT can obtain accurate clock (ToD) through the IEEE 1588 protocol, but the buffer queue brings delay.
  • ToD Institute of Electrical and Electronics Engineers
  • the clock synchronization between the OLT and the ONU cannot use IEEE 1588, but must be implemented by the PON internal mechanism.
  • t2-t1 represents the transmission delay experienced by the round-trip on the optical fiber line, which is usually called Round-Trip Time (RTT).
  • RTT Round-Trip Time
  • t2-t1/2 is used as the time difference between the time when the OLT sends the message and the time when the ONU receives the same message, and the ONU receives the message sent by the OLT.
  • the system clock of the ONU is updated to the time +(t2-t1)/2 at which the OLT transmits the signal.
  • the existing scheme t2-t1 also includes the time for the ONU to identify the signal, etc., and the ONU is
  • the system will be ONU
  • the clock on the ONU is ahead of the clock on the OLT.
  • the clocks are not synchronized. Because the synchronization time between the ONU and the OLT is not accurate, the ONU is used as the controller to synchronize the user side. When the user equipment is used, the user equipment is also out of sync.
  • the embodiments of the present invention are directed to a clock synchronization method and apparatus for a PON system, which can more accurately synchronize the system clocks of the OLT and the ONU.
  • a first aspect of the embodiments of the present invention provides a clock synchronization method for a PON system, where the method includes:
  • the optical line terminal OLT Receiving, by the optical line terminal OLT, a time T sendN of the Nth time reference frame, a value of the N, and a round trip delay T RTT between the OLT and the optical network unit ONU; the N being an integer greater than or equal to 1;
  • updating the system clock of the ONU is a synchronization time
  • the synchronization time is the T receiveN plus a pre-stored update time
  • the ONU internal delay ⁇ ONU includes an equalization delay T EqD of the ONU and a response time T Rsp of the ONU.
  • the ONU is calculated to obtain the N-th received reference frames in time T receiveN comprising:
  • n is the wavelength of the downlink transmission time relative refractive index, the relative refractive index n of the wavelength uplink transmission time.
  • the time reference frame is identified by using a superframe counter, and then it is determined to be received.
  • the system clock of the ONU is updated to be a synchronization time, including:
  • the received data frame is a time reference frame and the super frame number is the N, it is determined that the received data frame is the Nth time reference frame.
  • a second aspect of the embodiments of the present invention provides a clock synchronization apparatus for a passive optical network PON system, where the apparatus includes:
  • the receiving module is configured to receive a time T sendN of the Nth time reference frame sent by the optical line terminal OLT, the N value, and a round trip delay T RTT between the OLT and the optical network unit ONU; the N is greater than or equal to An integer of 1;
  • the calculation module is configured to calculate, according to the T sendN and T RTT received by the receiving module, and the pre-stored ONU internal delay ⁇ ONU , the time T receiveN at which the ONU receives the Nth time reference frame;
  • the receiving module is further configured to receive a data frame
  • a determining module configured to determine whether the data frame received by the receiving module is an Nth time reference frame
  • an update module configured to: when the determining module determines that the received data frame is the Nth time reference frame, update the system clock of the ONU as a synchronization time, where the synchronization time is T receiveN calculated by the calculation module. Pre-stored updates take time.
  • the ONU internal delay ⁇ ONU includes an equalization delay T EqD of the ONU and a response time T Rsp of the ONU.
  • the calculating module is specifically configured to be used according to Calculating the T receiveN ;
  • n is the wavelength of the downlink transmission time relative refractive index, the relative refractive index n of the wavelength uplink transmission time.
  • the time reference frame is identified by using a superframe counter
  • the determining module is configured to determine that the received data frame is the Nth time reference frame when the data frame received by the receiving module is a time reference frame and the super frame number is the N.
  • a third aspect of the embodiments of the present invention further provides a computer storage medium having stored therein computer executable instructions for performing at least one of the foregoing methods of the claims.
  • the embodiment of the invention provides a clock synchronization method, device and storage medium for a PON system, according to the time T sendN of the Nth time reference frame, the round trip delay T RTT between the OLT and the ONU, and the pre-stored ONU according to the OLT.
  • the delay time ⁇ ONU is calculated to obtain the time T receiveN when the ONU receives the Nth time reference frame; and when the Nth time reference frame is received, the system clock of the ONU is updated to be the synchronization time, and the synchronization time is the T ReceiveN plus update takes time.
  • the embodiment of the present invention considers the ONU internal delay ⁇ ONU and the update time, so that the system clocks of the OLT and the ONU can be synchronized more accurately.
  • FIG. 1 is a structural block diagram of a PON clock synchronization system according to an embodiment of the present invention
  • FIG. 2 is a schematic flowchart of a clock synchronization method of a PON system according to Embodiment 1 of the present invention
  • FIG. 3 is a structural block diagram of a clock synchronization apparatus of a PON system according to Embodiment 1 of the present invention.
  • the PON clock synchronization system is mainly composed of OLT, ONU, and atomic clock.
  • the atomic clock is used to provide the OLT high-precision system clock (125M).
  • the OLT uses the clock as the system clock.
  • the ONU needs to send data from the OLT. Restore the clock as the system of the ONU Clock.
  • the method provided in this embodiment can accurately synchronize the system clock in the ONU with the system clock in the OLT.
  • the embodiment of the present invention provides a clock synchronization method for a PON system, which is applied to the ONU side.
  • the processing procedure of the method in this embodiment includes the following steps:
  • Step 201 Receive a time T sendN of the Nth time reference frame, a value of the N, and a round trip delay T RTT between the OLT and the ONU.
  • the OLT first selects a downlink data frame as a time reference frame, and the time reference frame is identified by a superframe counter, that is, several bits in the time reference frame are used to indicate the superframe number, the first time.
  • the superframe superframe number in the reference frame is 1, and the superframe superframe number in the Nth time reference frame is N; since the superframe counter takes about 37 hours (at 2.5 Gbit/s) in one cycle, the OLT can advance 37.
  • This time reference frame is selected in hours, and the time reference frame should be far enough to ensure that the ONU is ready for synchronization when it receives the Nth time reference frame.
  • the time reference frame selected by the OLT may be a GTC (GPON Transport Convergence Layer) frame. The OLT performs this process every 24 hours and when a new ONU is activated.
  • GTC GPON Transport Convergence Layer
  • the OLT After the OLT selects the time reference frame, the OLT knows the time T sendN at which it sends the Nth time reference frame. At this time, it is also necessary to calculate the round trip delay T RTT between the OLT and the ONU.
  • the calculation process of the T RTT is the same as that in the prior art. Specifically, the OLT records the system clock of the OLT, and the OLT records the time t1 when the OLT sends a data frame to the ONU, and the OLT receives the response of the ONU according to the feedback of the same data frame. time t2, can be obtained so that T RTT between the OLT and ONU is t2-t1; T RTT course, in order to ensure the accuracy of the measurement can be more time sets to calculate an average value obtained by calculation method T RTT.
  • the OLT After the OLT pre-calculates the T RTT , the OLT transmits the time T sendN of the Nth time reference frame, the value of the N, and the round trip delay T RTT between the OLT and the ONU to the ONU.
  • Step 202 Calculate , according to the T sendN , T RTT , and the pre-stored ONU internal delay, a time T receiveN at which the ONU receives the Nth time reference frame.
  • the farthest ONU is used as the reference to calculate the delay of the farthest ONU to the OLT and accurately calculate the difference between the two.
  • Distance add a delay to other ONUs that are closer to each other, so that the data sent to the OLT is the same as the farthest ONU. This delay is called equalization delay, and the OLT will configure an equalization delay for each ONU.
  • T EqD The time that the ONU recognizes and responds to the data frame after receiving the data frame is recorded as the response time of the ONU, and the response time T Rsp of the ONU is known to the ONU.
  • the time T receiveN at which the ONU receives the Nth time reference frame satisfies the following formula:
  • the round trip delay T RTT minus the internal delay of the ONU ⁇ ONU is calculated as the sum of the downlink transmission delay of the data frame on the optical fiber and the uplink transmission delay on the optical fiber; the relative refraction of the optical wavelength during the downlink transmission the ratio n, a relative refractive index of the uplink transmission on the wavelength of time n, the data frame transmission delay on a downlink optical fiber.
  • the time T sendN of the Nth time reference frame sent by the OLT plus the downlink transmission delay of the data frame The time T receiveN at which the ONU receives the Nth data frame at the time when the Nth data frame is transmitted to the ONU.
  • Step 203 When receiving the Nth time reference frame, update the system clock of the ONU to be a synchronization time, where the synchronization time is the T receiveN plus a pre-stored update time.
  • step 201 the time reference frame selected by the OLT should be far enough to ensure that the ONU has calculated, at step 202, the time T receiveN at which the Nth data frame is transmitted to the ONU when receiving the Nth time reference frame.
  • the ONU determines that the received data frame is the Nth time reference frame when the received data frame is a time reference frame and the super frame number is the N;
  • the system clock of the ONU is updated to be a synchronization time. This process of determining and updating takes a certain amount of time, so the synchronization time is time-consuming for the T receiveN plus the pre-stored update.
  • the ONU inputs the data frame from the PON interface of the ONU to the delay of starting the delimitation.
  • This time is the delay of the serdes recorded as T1; delimiting the input data frame.
  • the delay of the aligned output is recorded as T2; determining whether the received data frame is the Nth time reference frame and generating a pulse trigger to update the synchronization time delay when determining that the received data frame is the Nth time reference frame
  • the update time is T1+T2+T3.
  • T1, T2, and T3 are the time required for the internal modules of the ONU to process data. These times are known, and the update time can be calculated and stored in the ONU.
  • the ONU updates the system clock once using the above method for each time N sendN of the Nth time reference frame sent and the value of N.
  • the above method is implemented for any ONU under the control of the OLT.
  • the ONU includes three modules: a central processing unit (CPU), a GPON medium access control (MAC), and a task management (TM).
  • the OLT sends, to the ONU, the time T sendN at which the OLT transmits the Nth time reference frame, the value of the N, and the round trip delay T RTT between the OLT and the ONU, and the ONU receives the information and then passes through the optical network.
  • the Unit Management Control Interface (OMCI) channel extracts T sendN , N values, and T RTT to the CPU of the ONU.
  • OMCI Unit Management Control Interface
  • the CPU is based on the formula: Calculating the time T receiveN when the ONU receives the Nth time reference frame, and then the CPU reads the pre-stored update time from the register, adds the T receiveN to obtain the synchronization time, and writes the synchronization time.
  • the ToD counter in the TM is updated in the register gpn_updt_reg of the circuit.
  • the CPU of the ONU writes the N value into a register of the GMAC.
  • the GMAC determines whether the superframe number of the received time reference frame is N after each time a new time reference frame is received. If N, a pulse gpn_updt_ena is generated and sent to the ToD counter update circuit in the TM, informing the ToD counter update circuit to update the synchronization instant.
  • the ONU receives the Nth time reference frame.
  • time T receiveN when receiving the N-th time reference frame, the ONU updates the system clock synchronization time, the synchronization time consuming update of the T receiveN plus.
  • the embodiment of the present invention considers the ONU internal delay ⁇ ONU and the update time, so that the system clocks of the OLT and the ONU can be synchronized more accurately.
  • the embodiment of the present invention provides a clock synchronization device for a PON system, which may be disposed on an ONU.
  • the device includes: a receiving module 301, a computing module 302, a determining module 303, and an updating module 304. among them,
  • the receiving module 301 is configured to receive a time T sendN when the optical line terminal OLT sends the Nth time reference frame, the N value, and a round trip delay T RTT between the OLT and the optical network unit ONU; the N is greater than An integer equal to 1.
  • the time reference frame is identified by a superframe counter.
  • the calculating module 302 is configured to calculate, according to the T sendN and T RTT received by the receiving module 301 and the pre-stored ONU internal delay ⁇ ONU , the time T receiveN at which the ONU receives the Nth time reference frame; ONU internal delay ⁇ ONU includes the equalization delay T EqD of the ONU and the response time T Rsp of the ONU.
  • the calculating module 302 is configured to be configured according to Obtained by calculation of the T receiveN; where, n is the wavelength of the downlink transmission time relative refractive index, the relative refractive index for the wavelength of the uplink transmission time n.
  • the receiving module 301 is further configured to receive a data frame.
  • the determining module 303 is configured to determine whether the data frame received by the receiving module 301 is the Nth time reference frame.
  • the time reference frame is identified by a superframe counter; the determining module 303 is specifically configured to: when the data frame received by the receiving module 301 is a time reference frame and the super frame number is the N And determining that the received data frame is the Nth time reference frame.
  • the update module 304 is configured to update the system clock of the ONU as a synchronization time when the determining module 303 determines that the received data frame is the Nth time reference frame, where the synchronization time is the T calculated by the calculation module 302. ReceiveN plus update takes time.
  • the receiving module 301, the computing module 302, the determining module 303, and the updating module 304 may be configured by a central processing unit (CPU), a microprocessor (MPU), a digital signal processor (DSP), or Device implementation such as field programmable gate array (FPGA).
  • CPU central processing unit
  • MPU microprocessor
  • DSP digital signal processor
  • FPGA field programmable gate array
  • embodiments of the present invention can be provided as a method, system, or computer program product. Accordingly, the present invention can take the form of a hardware embodiment, a software embodiment, or a combination of software and hardware. Moreover, the invention can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) including computer usable program code.
  • These computer program instructions can also be stored in a bootable computer or other programmable data processing
  • the apparatus is readable in a computer readable memory in a particular manner such that instructions stored in the computer readable memory produce an article of manufacture comprising instruction means implemented in one or more flows and/or block diagrams of the flowchart The function specified in the box or in multiple boxes.
  • These computer program instructions can also be loaded onto a computer or other programmable data processing device such that a series of operational steps are performed on a computer or other programmable device to produce computer-implemented processing for execution on a computer or other programmable device.
  • the instructions provide steps for implementing the functions specified in one or more of the flow or in a block or blocks of a flow diagram.
  • the embodiment of the present invention further provides a computer storage medium, where the computer storage medium stores computer executable instructions, and the computer executable instructions are used to execute at least one of a clock synchronization method of the passive optical network PON system.
  • the computer storage medium may be a storage medium such as an optical disk, a hard disk, a USB flash drive or a flash disk, and may be a non-transitory storage medium.

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Abstract

本发明实施例公开了一种无源光网络(PON)***的时钟同步方法，所述方法包括：接收OLT发送第N个时间参考帧的时刻TsendN、所述N的值、OLT与ONU之间的往返时延TRTT；根据所述TsendN和TRTT，以及预存的ONU内部延时ΔONU计算获得所述ONU接收到第N个时间参考帧的时刻TreceiveN；在确定接收到的数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上预存的更新耗时。本发明实施例还公开了一种PON***的时钟同步装置及计算机存储介质。

Description

无源光网络***的时钟同步方法、装置和存储介质 技术领域
本发明涉及通信领域中的时钟同步技术，尤其涉及一种无源光网络(PON，Passive Optical Network)***的时钟同步方法、装置和存储介质。
背景技术
PON***由位于核心节点或汇聚节点的局端光线路终端(OLT，Optical Line Terminal)和位于用户驻地端的光网络单元(ONU，Optical Network Unit)共同组成，一个局端OLT控制多个ONU，各ONU为接入网提供用户侧的接口。目前，业界广泛采用电气与电子工程师协会(IEEE)1588传输协议实现基于以太网端口间的时钟同步，在PON中，OLT可通过IEEE 1588协议获得精确时钟(ToD)，但由于缓冲队列带来延时、光纤中上下行传输延时不对称等因素，OLT到ONU间的时钟同步不能使用IEEE 1588，而必须依靠PON内部机制实现。通常情况下，习惯以OLT的***时钟为标准时钟，同步ONU中的***时钟。
假设OLT t1时刻发送消息给ONU，并在t2时刻接收到ONU反馈的响应消息，则t2-t1表示光纤线路上往返一次经历的传输时延，通常叫做往返时延(RTT，Round-Trip Time)。在现有的同步方案中，假设上下行传输时延相等，将(t2-t1)/2作为OLT发送消息的时刻和ONU接收同一消息的时刻之间的时间差，ONU在接收到OLT发送的消息时，将ONU的***时钟更新为OLT发送该信号的时刻+(t2-t1)/2。
但是，由于ONU在接收到数据后需要对该消息进行识别，然后再向OLT发送相应的响应消息，故现有方案中t2-t1里还包含了ONU对信号进行识别等处理的时间，ONU在接收到OLT发送的消息时将ONU的***时 钟更新为了ONU处理完该消息的时刻，这就导致ONU上的时钟比OLT上的时钟超前，两者时钟不同步，由于ONU和OLT的同步时间不准，当ONU作为控制方同步用户侧的用户设备的时候，也会使用户设备不同步。
发明内容
有鉴于此，本发明实施例期望提供一种PON***的时钟同步方法及装置，可以更加精准地同步OLT和ONU的***时钟。
本发明实施例的技术方案是这样实现的：
本发明实施例第一方面提供一种PON***的时钟同步方法，所述方法包括：
接收光线路终端OLT发送第N个时间参考帧的时刻TsendN、所述N的值、所述OLT与光网络单元ONU之间的往返时延TRTT；所述N为大于等于1的整数；
根据所述TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得所述ONU接收到第N个时间参考帧的时刻TreceiveN；
在确定接收到的数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上预存的更新耗时。
上述方案中，所述ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp。
上述方案中，所述根据所述TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得所述ONU接收到第N个时间参考帧的时刻TreceiveN包括：
根据
Figure PCTCN2015092280-appb-000001
计算获得所述TreceiveN；
其中，n下为下行传输时光波长的相对折射率，n上为上行传输时光波长的相对折射率。
上述方案中，所述时间参考帧使用超帧计数器标识，则在确定接收到 的数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻，包括：
当接收到的所述数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧。
本发明实施例第二方面提供一种无源光网络PON***的时钟同步装置，所述装置包括：
接收模块，配置为接收光线路终端OLT发送第N个时间参考帧的时刻TsendN、所述N值、所述OLT与光网络单元ONU之间的往返时延TRTT；所述N为大于等于1的整数；
计算模块，配置为根据所述接收模块接收到的TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得ONU接收到第N个时间参考帧的时刻TreceiveN；
所述接收模块，还配置为接收数据帧；
确定模块，配置为确定所述接收模块接收到的数据帧是否为第N个时间参考帧；
更新模块，配置为在所述确定模块确定接收到的数据帧为第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述计算模块计算出的TreceiveN加上预存的更新耗时。
上述方案中，所述ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp。
上述方案中，所述计算模块，具体用于根据
Figure PCTCN2015092280-appb-000002
Figure PCTCN2015092280-appb-000003
计算获得所述TreceiveN；
其中，n下为下行传输时光波长的相对折射率，n上为上行传输时光波长的相对折射率。
上述方案中，所述时间参考帧使用超帧计数器标识；则
所述确定模块，配置为在所述接收模块接收的所述数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧。
本发明实施例第三方面还提供一种计算机存储介质，所述计算机存储介质中存储有计算机可执行指令，所述计算机可执行指令用于执行权利要求上述方法的至少其中之一。
本发明实施例提供了一种PON***的时钟同步方法、装置和存储介质，根据OLT发送第N个时间参考帧的时刻TsendN、OLT与ONU之间的往返时延TRTT以及预存的ONU内部延时△ONU，计算获得ONU接收到第N个时间参考帧的时刻TreceiveN；并在接收到第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上更新耗时。与现有技术相比，本发明实施例考虑到了ONU内部延时△ONU以及更新耗时，这样，可以更加精准地同步OLT和ONU的***时钟。
附图说明
图1为本发明实施例提供的一种PON时钟同步***的结构框图；
图2为本发明实施例1提供的一种PON***的时钟同步方法流程示意图；
图3为本发明实施例1提供的一种PON***的时钟同步装置结构框图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，应当理解，以下所说明的优选实施例仅用于说明和解释本发明，并不用于限定本发明。。
如图1所示，PON时钟同步***主要由OLT、ONU、原子钟3部分组成，其中原子钟用于提供OLT高精度***时钟(125M)，OLT使用该时钟作为***时钟，ONU需要从OLT发送的数据中恢复出时钟作为ONU的系 统时钟。本实施例提供的方法可以精确实现ONU中***时钟与OLT中***时钟的同步。
实施例1
本发明实施例提供了一种PON***的时钟同步方法，应用于ONU一侧，如图2所示，本实施例方法的处理流程包括以下步骤：
步骤201、接收OLT发送第N个时间参考帧的时刻TsendN、所述N的值、OLT与ONU之间的往返时延TRTT。
在实现本实施例方法时，OLT要首先选择一个下行数据帧作为时间参考帧，该时间参考帧用超帧计数器标识，即时间参考帧中有几位用来表示超帧号，第一个时间参考帧中的超帧超帧号为1，第N个时间参考帧中的超帧超帧号为N；由于超帧计数器一次循环需要大约37小时(在2.5Gbit/s)，OLT可以提前37小时选择这个时间参考帧，且该时间参考帧应该足够远，确保ONU在接收到第N个时间参考帧时，已准备好进行同步处理。示例的，OLT选择的时间参考帧可以是GTC(GPON传输汇聚层)帧。OLT执行这个过程可以每24小时一次，以及在有新的ONU被激活时执行。
OLT选定时间参考帧后OLT已知其发送第N个时间参考帧的时刻TsendN，此时还需要计算OLT与ONU之间的往返时延TRTT。TRTT的计算过程与现有技术中相同，具体可以是：以OLT的***时钟为准，OLT记录OLT发送一个数据帧到ONU的时刻t1，以及OLT接收到ONU根据同一数据帧反馈的响应的时刻t2，这样就可获得OLT与ONU之间的TRTT为t2-t1；当然为了保证TRTT的精确性，可以多测量几组时间，以计算平均值的方法计算获得TRTT。
OLT预先计算出TRTT后，就将该OLT发送第N个时间参考帧的时刻TsendN、所述N的值、OLT与ONU之间的往返时延TRTT发送给ONU。
步骤202、根据所述TsendN、TRTT、以及预存的ONU内部延时，计算获 得ONU接收到第N个时间参考帧的时刻TreceiveN。
在PON***中，为了保证不同ONU发送的数据可以同时到达OLT，不在分光器上产生冲突，需要以最远的ONU为基准计算最远的ONU到OLT的时延并精确计算两者之间的距离，对别的距离较近的ONU增加一个延时，使之发送的数据到达OLT的时间与最远的ONU一致，这个延时就叫做均衡延时，OLT会为各个ONU配置一个均衡延时TEqD。ONU接收到数据帧后对数据帧识别并响应的时间记为ONU的响应时间，ONU的响应时间TRsp为ONU已知的。
所述ONU会预先计算出ONU内部延时△ONU，ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp，即△ONU＝TEqD+TRsp。
ONU接收到第N个时间参考帧的时刻TreceiveN满足以下公式：
Figure PCTCN2015092280-appb-000004
其中，往返时延TRTT减去ONU的内部延时△ONU的计算结果为数据帧在光纤上的下行传输时延以及响应在光纤上的上行传输时延之和；下行传输时光波长的相对折射率为n下，上行传输时光波长的相对折射率为n上，则数据帧在光纤上的下行传输时延为
Figure PCTCN2015092280-appb-000005
OLT发送第N个时间参考帧的时刻TsendN加上数据帧的下行传输时延
Figure PCTCN2015092280-appb-000006
为第N个数据帧传输到ONU的时刻即ONU接收到第N个数据帧的时刻TreceiveN。
步骤203、在接收到第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上预存的更新耗时。
在步骤201中已经说明OLT选择的时间参考帧应该足够远，保证ONU在接收到第N个时间参考帧时，已经通过步骤202计算出第N个数据帧传输到ONU的时刻TreceiveN。这样ONU在接收到数据帧后，当接收到的所述 数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧；在确定接收到的所述数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻。这个确定并更新的过程需要耗费一定的时间，故所述同步时刻为所述TreceiveN加上预存的更新耗时。
示例的，ONU在接收到一个新的数据帧后，将该数据帧从ONU的pon接口输入到开始定界的延时，这个时间是serdes的延时记为T1；对输入数据帧进行定界对齐输出的延时记为T2；确定接收到的数据帧是否为第N个时间参考帧以及在确定接收到的数据帧是第N个时间参考帧时产生脉冲触发更新所述同步时刻的延时记为T3，则更新耗时为T1+T2+T3。T1、T2、T3都是ONU的内部模块处理数据所需的时间，这些时间都是已知的，可以将更新耗时计算好后预存在ONU中。
为了防止超帧计数器循环过，OLT每发送过来的一个第N个时间参考帧的时刻TsendN，以及所述N的值，ONU就使用一次上述方法更新一次***时钟。上述方法是针对所述OLT控制下的任意一个ONU来实施的。
将上述方法应用到ONU的具体实例中，举例如下：
所述ONU中包括中央处理器(CPU)、GPON媒体访问控制(MAC)和任务管理(TM)这3个模块。OLT向所述ONU发送OLT发送第N个时间参考帧的时刻TsendN、所述N的值、所述OLT与ONU之间的往返时延TRTT，所述ONU接收到这些信息后通过光网络单元管理控制接口(OMCI)通道将TsendN、N值以及TRTT提取给所述ONU的CPU。
所述CPU基于公式：
Figure PCTCN2015092280-appb-000007
计算出所述ONU接收到第N个时间参考帧的时刻TreceiveN，然后所述CPU从寄存器读取预存储的更新耗时，与TreceiveN相加后得出同步时刻，将所述同步时刻写入TM中的ToD计数器更新电路的寄存器gpn_updt_reg中。所述ONU的CPU将所述N值写入GMAC的寄存器。
这样所述GMAC在每次收到一个新的时间参考帧后确定接收到的时间参考帧的超帧号是否为N。如果为N，那么产生一个脉冲gpn_updt_ena送给TM中的ToD计数器更新电路，通知ToD计数器更新电路更新所述同步时刻。
本实施例方法，根据OLT发送第N个时间参考帧的时刻TsendN、OLT与ONU之间的往返时延TRTT以及预存的ONU内部延时△ONU计算获得ONU接收到第N个时间参考帧的时刻TreceiveN；并在接收到第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上更新耗时。与现有技术相比，本发明实施例考虑到了ONU内部延时△ONU以及更新耗时，这样可以更加精准地同步OLT和ONU的***时钟。
实施例2
本发明实施例提供了一种PON***的时钟同步装置，该装置可以设置在ONU上，如图3所示，所述装置包括：接收模块301、计算模块302、确定模块303、更新模块304，其中，
接收模块301，配置为接收光线路终端OLT发送第N个时间参考帧的时刻TsendN、所述N值、所述OLT与光网络单元ONU之间的往返时延TRTT；所述N为大于等于1的整数。所述时间参考帧用超帧计数器标识。
计算模块302，配置为根据所述接收模块301接收到的TsendN和TRTT，以及预存的ONU内部延时△ONU计算获得ONU接收到第N个时间参考帧的时刻TreceiveN；其中，所述ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp。
可选的，所述计算模块302，配置为根据
Figure PCTCN2015092280-appb-000008
Figure PCTCN2015092280-appb-000009
计算获得所述TreceiveN；其中，n下为下行传输时光波长的相对折射率，n上为上行传输时光波长的相对折射率。
所述接收模块301，还配置为接收数据帧。
确定模块303，配置为确定所述接收模块301接收到的数据帧是否为第N个时间参考帧。可选的，所述时间参考帧用超帧计数器标识；则所述确定模块303，具体用于在所述接收模块301接收的所述数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧。
更新模块304，配置为在所述确定模块303确定接收到的数据帧为第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述计算模块302计算出的TreceiveN加上更新耗时。
在实际应用中，所述接收模块301、计算模块302、确定模块303、更新模块304可以由位于ONU上的中央处理器(CPU)、微处理器(MPU)、数字信号处理器(DSP)或现场可编程门阵列(FPGA)等器件实现。
本领域内的技术人员应明白，本发明的实施例可提供为方法、***、或计算机程序产品。因此，本发明可采用硬件实施例、软件实施例、或结合软件和硬件方面的实施例的形式。而且，本发明可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器和光学存储器等)上实施的计算机程序产品的形式。
本发明是参照根据本发明实施例的方法、设备(***)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理 设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的步骤。
本发明实施例还提供一种计算机存储介质，所述计算机存储介质中存储有计算机可执行指令，所述计算机可执行指令用于执行上述无源光网络PON***的时钟同步方法的至少其中之一，例如图2所示的方法。所述计算机存储介质可为光盘、硬盘、U盘或闪盘等存储介质，可选为非瞬间存储介质。
以上所述，仅为本发明的较佳实施例而已，并非用于限定本发明的保护范围凡按照本发明原理所作的修改，都应当理解为落入本发明的保护范围。

Claims (9)

  1. 一种无源光网络PON***的时钟同步方法，所述方法包括：
    接收光线路终端OLT发送第N个时间参考帧的时刻TsendN、所述N的值、所述OLT与光网络单元ONU之间的往返时延TRTT；所述N为大于等于1的整数；
    根据所述TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得所述ONU接收到第N个时间参考帧的时刻TreceiveN；
    在确定接收到的数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻，所述同步时刻为所述TreceiveN加上预存的更新耗时。
  2. 根据权利要求1所述的方法，其中，所述ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp。
  3. 根据权利要求1所述的方法，其中，所述根据所述TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得所述ONU接收到第N个时间参考帧的时刻TreceiveN包括：
    根据
    Figure PCTCN2015092280-appb-100001
    计算获得所述TreceiveN；
    其中，n下为下行传输时光波长的相对折射率，n上为上行传输时光波长的相对折射率。
  4. 根据权利要求1所述的方法，其中，所述时间参考帧使用超帧计数器标识，则在确定接收到的数据帧为第N个时间参考帧时，更新所述ONU的***时钟为同步时刻，包括：
    当接收到的所述数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧。
  5. 一种无源光网络PON***的时钟同步装置，所述装置包括：
    接收模块，配置为接收光线路终端OLT发送第N个时间参考帧的时刻TsendN、所述N值、所述OLT与光网络单元ONU之间的往返时延TRTT；所述N为大于等于1的整数；
    计算模块，配置为根据所述接收模块接收到的TsendN、TRTT、以及预存的ONU内部延时△ONU，计算获得ONU接收到第N个时间参考帧的时刻TreceiveN；
    所述接收模块，还配置为于接收数据帧；
    确定模块，配置为确定所述接收模块接收到的数据帧是否为第N个时间参考帧；
    更新模块，配置为在所述确定模块确定接收到的数据帧为第N个时间参考帧时，更新ONU的***时钟为同步时刻，所述同步时刻为所述计算模块计算出的TreceiveN加上预存的更新耗时。
  6. 根据权利要求5所述的装置，其中，所述ONU内部延时△ONU包括ONU的均衡延时TEqD以及ONU的响应时间TRsp。
  7. 根据权利要求5所述的装置，其中，所述计算模块，配置为根据
    Figure PCTCN2015092280-appb-100002
    计算获得所述TreceiveN；
    其中，n下为下行传输时光波长的相对折射率，n上为上行传输时光波长的相对折射率。
  8. 根据权利要求5所述的装置，其中，所述时间参考帧使用超帧计数器标识；则
    所述确定模块，配置为在所述接收模块接收的所述数据帧为时间参考帧且超帧号为所述N时，确定接收到的数据帧为第N个时间参考帧。
  9. 一种计算机存储介质，所述计算机存储介质中存储有计算机可执行指令，所述计算机可执行指令用于执行权利要求1至4所述方法的至少其中之一。
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CN103905933A (zh) * 2014-04-25 2014-07-02 国家电网公司 以太网无源光网络时间同步方法、***及相关设备

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