WO2008064546A1 - Procédé, système et unité de réseau optique pour une télémétrie dans un réseau optique passif - Google Patents

Procédé, système et unité de réseau optique pour une télémétrie dans un réseau optique passif Download PDF

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Publication number
WO2008064546A1
WO2008064546A1 PCT/CN2007/001657 CN2007001657W WO2008064546A1 WO 2008064546 A1 WO2008064546 A1 WO 2008064546A1 CN 2007001657 W CN2007001657 W CN 2007001657W WO 2008064546 A1 WO2008064546 A1 WO 2008064546A1
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WIPO (PCT)
Prior art keywords
signal
ranging
loopback
ranging signal
optical
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PCT/CN2007/001657
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English (en)
French (fr)
Inventor
Xiaogeng Xu
Chang Zhao
Original Assignee
Huawei Technologies Co., Ltd.
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Publication date
Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to CN2007800001708A priority Critical patent/CN101310463B/zh
Publication of WO2008064546A1 publication Critical patent/WO2008064546A1/zh

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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
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q2011/0079—Operation or maintenance aspects

Definitions

  • the present invention relates to the field of communication transmission, and more particularly to a method and system for ranging of a passive optical network and an optical network unit.
  • PON Passive Optical Access Network
  • ODN Optical Distribution Network
  • FIG. 1 A schematic diagram of a topology of a PON system in the prior art is shown in FIG. 1.
  • the PON is installed by an optical line terminal (OLT) 110, an optical distribution network (ODDN) installed in a central control station, and
  • the optical network unit 130 (ONU1, ONU2, ... ONU N ) of the user site is composed of three parts.
  • the above optical distribution network may include the optical splitting device 120 of FIG. 1, and may further include an optical fiber.
  • the PON downlink is transmitted in the broadcast mode.
  • the downlink information sent from the OLT is received by all the ONUs.
  • Each ONU Optical Network Unit
  • the uplink uses time division multiplexing technology, and multiple ONUs share uplink bandwidth.
  • each ONU must be ranging to ensure that the logical time of each ONU arriving at the OLT does not conflict.
  • a ranging time must be reserved for the ONUs of the measured distance.
  • other ONUs do not send uplink services to avoid collisions. This period of time is called the ranging window.
  • the length of this time is called the windowing window.
  • the OLT periodically issues an authorization signal for the ranging, and the authorization signal carries local time information. When receiving an authorization signal, each ONU temporarily does not send an uplink service.
  • the existing ranging method uses ONU1 as the distance measurement. The steps are as follows:
  • the ONU1 After the ONU1 receives the authorization signal sent by the OLT, the ONU1 reads the time information in the authorization signal and writes it to the local clock.
  • ONU 1 sends a response frame carrying local time information.
  • the OLT After receiving the response frame carrying the local time information sent by the ONU1, the OLT compares the carried time information t2 with the local time of the local clock to obtain a round trip time RTT (Round Trip Time), and further according to the round trip time RTT Realize ranging.
  • RTT Round Trip Time
  • the window of the window When measuring the ONU, the window of the window must cover the entire system, and the window of the window must contain the transmission time corresponding to the distance from the beam splitter to the OLT.
  • the ONU must configure a large data store in order not to lose traffic.
  • the distance between the ranging is too large, and the ranging time is too long, so that the ONU is configured with a large data memory.
  • other ONUs must stop their respective services, wait for the ONUs that need to be ranging to complete the ranging, and occupy a large amount of bandwidth; when performing ranging, it must undergo two photoelectric conversions, which takes up a lot of time; and the ranging time uses the standard maximum round trip. Time, therefore, introduces a large delay.
  • Embodiments of the present invention provide a method and system for ranging of a passive optical network and an optical network unit to avoid disadvantages such as excessive time required for ranging.
  • a method for ranging of a passive optical network includes the following steps:
  • Receiving a loopback ranging signal from the optical split loopback device determining whether the loopback ranging signal is a loopback signal of the initial ranging signal; if yes, recording current receiving time information as second time information;
  • the first time information and the second time information are subtracted to obtain ranging information, and ranging is implemented according to the ranging information.
  • a system of passive optical networks comprising:
  • a split-loopback device configured to receive an initial ranging signal, loop-loop the initial ranging signal into a loopback ranging signal, and send the loopback ranging signal;
  • the optical network unit ONU is configured to send the initial ranging signal to the optical split loopback device, and record current transmit time information as first time information; and receive the loopback ranging sent by the optical split loopback device a signal, after determining that the loopback ranging signal is a loopback signal of the initial ranging signal, recording current receiving time information as second time information; and subtracting the first time information from the second time information
  • the ranging information is obtained, and the ranging is implemented according to the ranging information.
  • An optical network unit comprising:
  • a clock module configured to record first time information and second time information when transmitting the initial ranging signal and receiving the loopback ranging signal
  • control module configured to send the initial ranging signal, receive a loopback ranging signal, and determine, after the loopback ranging signal is a loopback signal of the initial ranging signal, record the clock module
  • the first time information and the second time information are subtracted to obtain ranging information, and ranging is implemented according to the ranging information.
  • the optical signal is not processed by the OLT by using the ranging method of the optical split loop device, thereby reducing the distance measurement. Therefore, it is not necessary to configure a large data buffer, which greatly improves the performance of the system.
  • the re-ranging is not required; when the optical splitting device fails to the ONU, the switching time can be greatly reduced, thereby improving the robustness of the system. .
  • the system of the embodiment of the invention has good upgradeability. When the distance of the PON system is extended and the rate is increased, there is no need to change the system setting and ranging method.
  • FIG. 1 is a schematic diagram of a topology structure of a PON system in the prior art
  • FIG. 2 is a schematic diagram of a topology structure of a PON system according to an embodiment of the present invention
  • FIG. 3 is a schematic diagram of a split loopback module of a split-loop loopback device according to an embodiment of the present invention.
  • FIG. 2 A schematic diagram of the topology of the PON system according to the embodiment of the present invention is shown in FIG. 2.
  • the distance L between the optical line terminal OLT 210 and the optical split loopback device 220 is the distance that each optical network unit ONU 230 must travel during the ranging process, and has no effect on the ranging time of the ONU. Therefore, it is not necessary to measure the distance of L during the ranging. In actual situations, it is generally preferred to place the optical ringback device 220 closer to the final access user, so that the optical ringback device 220 between the optical line terminal OLT 210 and the optical network unit ONU 230 is closer to the ONU than the ONU.
  • the fiber distance L is larger than the fiber distance Li (Ll, L2, L3) of the access portion.
  • the loopback loopback device 220 is used to form a loopback, and the loopback is performed by loopback, so that the logical time of each ONU is the same to ensure no conflict.
  • the first embodiment of the present invention is: ⁇ a method of adding a low-frequency low-amplitude signal to mark an initial ranging signal of an ONU for performing ranging, and the specific steps are as follows:
  • the initial ranging signal to which the low-frequency low-amplitude signal is added is transmitted to the optical split-loop back device, and the time information of the optical network unit ONU stored at this time is recorded as the first time information, which is recorded as Tl.
  • the initial ranging signal includes ID information of the ONU, and is marked for whether it is the first ranging or the re-ranging.
  • the ONU receives the ranging authorization signal sent by the optical line terminal OLT via the optical ringback device, and determines that the initial ranging signal is sent after being authorized.
  • the ranging grant signal may include issuing a ranging grant to all ONUs or issuing a ranging grant to an ONU. 2)
  • the optical ringback device receives and loops back the initial ranging signal of the low frequency low amplitude signal, and then sends the obtained loopback ranging signal to the optical network unit ONU.
  • the ONU After receiving the loopback ranging signal, the ONU determines whether the ranging is successful.
  • the frequency information of the low frequency low amplitude signal carried by the initial ranging signal is the same as the frequency information of the low frequency low amplitude signal carried by the loopback ranging signal, it indicates that the loopback ranging signal is a loopback signal of the initial ranging signal, That is to say, if the ranging can be successful, the time information of the optical network unit ONU stored at this time is recorded as the second time information, which is recorded as t2.
  • the signal is a loopback signal of the initial ranging signal, such as determining whether the initial ranging signal and the cell of the loopback ranging signal are the same, or determining whether the power of the initial ranging signal is the power of the loopback ranging signal and The sum of the power losses, etc., to determine whether the loopback ranging signal is a loopback signal of the initial ranging signal, and thereby determining whether the ranging can be successful.
  • the process of determining whether the loopback ranging signal is a loopback signal of the initial ranging signal may be: determining the location carried by the initial ranging signal Whether the frequency information is the same as the frequency information of the loopback ranging signal, and if so, determining that the loopback ranging signal is a loopback signal of the initial ranging signal.
  • the above frequency information is loaded on the optical signal or added to the optical signal by changing the drive current of the laser.
  • Step 1) that is, resending the new initial ranging signal to the optical split loopback device. If the distance measurement is unsuccessful, or if the ranging is unsuccessful within a set time value T, the network management or fault indication manager is reported. That is, if the ranging is unsuccessful within the preset number of times, or if the ranging is unsuccessful within a set time value T, the optical network unit ONU reports the fault information to the network management or the fault indication manager.
  • tl and t2 are subtracted to obtain the round-trip time of the ONU of the optical network unit, thereby calculating the delay adjustment time, that is, the ranging information, and then performing ranging according to the ranging information.
  • a second embodiment of the present invention is: a ranging system for a passive optical network, including an optical line terminal OLT, a split optical loopback device, and one or more optical network units ONU,
  • the optical line terminal OLT is configured to send a ranging authorization signal to the optical split loopback device.
  • Light The line terminal OLT sends downlink signal from the upper layer network, such as telephone, video, data and other service source signals, to the optical split loopback device, and then transmits it to the final user.
  • the OLT is also used to generate a ranging authorization signal and send it to the optical split loop device through the transmitting module to complete related control processing, registration, management and other functions.
  • the optical ringback device is configured to split the ranging authorization signal and transmit it to one or more optical network units ONU, and to loopback the signal from the optical network unit ONU into a loopback ranging signal.
  • the downlink signal from the OLT is split and transmitted to each ONU in the downlink direction, and the optical signal of the ONU is transmitted to the OLT in the uplink direction.
  • the optical network unit ONU receives the downlink signals sent by the OLT, such as telephone, video, data and other service source signals, and then forwards them to the final client (such as telephone, computer, TV, etc.).
  • the customer signal received from the client's end customer is sent to the OLT.
  • the optical network unit ONU performs ranging, it sends an initial ranging signal to the optical split loop back to the device.
  • the optical network unit ONU specifically includes a control module and a clock module.
  • the clock module is used to record the time information tl when the ONU sends the initial ranging signal.
  • the initial ranging signal reaches the split loopback device, the initial ranging signal is looped back to the loopback ranging signal. After the loopback ranging signal is transmitted through the optical fiber, it will reach the ONU.
  • the control module After receiving the loopback ranging signal, the control module parses the received loopback ranging signal to determine whether the loopback ranging signal is a loopback signal of the initial ranging signal, and if so, the clock module The clock information t2 at this time is read. After the clock module processes the clock information tl and t2, the ranging information is obtained, and the ranging information is notified to the control module to implement ranging.
  • an optical network unit (not shown) provided by the embodiment of the present invention includes: a clock module, configured to record first time information and a second time when transmitting an initial ranging signal and receiving a loopback ranging signal a control module, configured to send the initial ranging signal, receive a loopback ranging signal, and determine that the loopback ranging signal is a loopback signal of the initial ranging signal, and record the clock module
  • the first time information and the second time information are subtracted to obtain ranging information, and the ranging is implemented according to the ranging information.
  • the optical network unit further includes an authorization determining module, configured to receive the ranging authorization signal and perform parsing, and after determining that the authorization is authorized, notify the control module to send the initial ranging signal to the optical split loopback device.
  • an authorization determining module configured to receive the ranging authorization signal and perform parsing, and after determining that the authorization is authorized, notify the control module to send the initial ranging signal to the optical split loopback device.
  • the optical network unit may further include an adjustment module, where the control module determines the loopback After the ranging signal is not the loopback signal of the initial ranging signal, the adjusting module is notified; the adjusting module is configured to perform random delay adjustment on the initial ranging signal according to the received notification. Or power adjustment, and then notify the control module to resend the new initial ranging signal.
  • a split optical loopback module diagram of the optical split loopback device provided by the embodiment of the present invention is shown in FIG. 3.
  • the function of the splitting loopback is to complete the splitting and loopback function of the signal.
  • the optical split loopr distributes the downlink signal sent from the OLT to each branch to the ONU, and the ONU receives the downlink signal.
  • the optical loopback In the uplink direction, when the initial ranging signal is transmitted, the optical loopback loopbacks the ranging signal, and the ONU completes the function of ranging.
  • the ONU sends an uplink service, the ONU does not receive the loopback optical signal, but only receives the downlink signal.
  • the frequency information of the loopback ranging signal and the initial ranging signal are the same, so that the ONU can easily distinguish whether the received signal is looped back to the ranging signal or
  • the downlink service signal can avoid the influence of the loopback light on the downlink signal.
  • the dotted line in Figure 3 is for the purpose of indicating that the loopback function can be achieved by the split loopback.
  • This loopback part can be looped back through the same path or looped through a different path.
  • the spectroscopic loopback device in the embodiment of the present invention can implement splitting loopback of the signal by using a combination device or a separate device.
  • the optical ringback device in the embodiment of the present invention may specifically be: a ⁇ coupler, a beam splitter and a fiber grating combination device, a 2-turn coupler and a reflection film combination device, a 2-turn coupler and a fiber grating combination device.
  • the specific options are as follows:
  • Option 1 ( ⁇ +1) ⁇ ( ⁇ +1) coupler scheme. This scheme is accomplished using the characteristics of the ( ⁇ +1) ⁇ ( ⁇ +1) coupler.
  • the beam emitted by the OLT is divided into N+1 beams, and a beam of light is terminated, thereby completing the function of splitting.
  • the ONU can perform a loopback, so that the loopback mechanism can be used to measure the ONU.
  • splitting device and fiber grating combined device solution In the downstream direction, a beam of a certain wavelength is divided into bundles and received by each ONU. In the upstream direction, when a certain wavelength of light reaches the spectroscopic reflector, this wavelength is reflected back to each ONU, which forms a loopback mechanism.
  • the coupler is not necessarily limited to the 2 ⁇ form.
  • the optical signal emitted by the OLT is split into beams by the optical splitting device and received by each ONU.
  • the upstream direction when an optical signal from an ONU reaches the coupler, a part Between the points passes through the coupler, and a portion is reflected back at one end of the coupler to reach each ONU. Thereby completing the loopback of the ONU.
  • the optical splitting device in the PON in the prior art adopts the optical split loop device by using the ranging method of the optical split loop device. Instead, a loopback mechanism is formed between the splitter and each ONU.
  • the split-loop loopback device has both a splitting function and a loopback function.
  • the optical signal is not processed by the OLT, thus reducing the ranging time, thereby eliminating the need to configure a large data buffer and greatly improving the performance of the system.
  • the embodiment of the present invention when the OLT and the optical splitting device fail to perform the switching protection during the ranging, the re-ranging is not required; when the optical splitting device fails to the ONU, the switching time can be greatly reduced. Thereby improving the robustness of the system.
  • the system of the embodiment of the invention has good upgradeability. When the distance of the PON system is extended and the rate is increased, there is no need to change the system setting and ranging method.

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Description

一种无源光网络的测距方法与系统及光网络单元
本申请要求于 2006 年 11 月 27 日提交中国专利局、 申请号为 200610157093.4、 发明名称为"一种无源光网络的测距方法与系统 "的中国专利 申请的优先权， 其全部内容通过引用结合在本申请中。
技术领域
本发明涉及通信传输领域， 尤指一种无源光网络的测距方法与系统及 光网络单元。
背景技术
随着光器件及相关技术的发展， 主干网的单信道速率已经有了很大的 提高。 光放大器、 色散补偿技术和光纤技术的发展， 使得密集波分复用 ( DWDM, Dense Wavelength Division Multiplexing )的复用波长数目更多。 这两方面的技术发展使主干网的容量有了长足的进步。 在客户一侧， 人们 对信息的需求更加迫切。 网络游戏、 网上电影、 网络下载以及将来开通的 数字电视（IPTV ) 等， 用户对带宽的要求会越来越高， 于是就产生了接入 瓶颈限制的问题。 为了解决这个问题， 人们提出了很多的解决方案： 非对 称数字用户线（ ADSL), 甚高速数字用户线 (VDSL),光接入网（ OAN, Optical Access Network )。 在光接入网中， 根据是否采用有源器件分为有源光接入 网和无源光接入网 （PON, Passive Optical Network ) 。
在现有的接入方案中， 无源光接入网 （PON )技术是最吸引人、 应用 最广的解决方案。 它具有独特的优点： 1) ΡΟΝ在光配线网 （ODN, Optical Distribution Network )中全部采用无源器件， 可以减少站点。 2) PON维护简 单， 且具有可升级性。 3) 接入采用光传输， 具有高带宽， 可以满足现有及 将来的带宽需求。
现有技术中的 PON 统拓朴结构示意图如图 1所示， PON由安装于中心 控制站的光线路终端（ OLT, Optical Line Terminals ) 110、光分配网（ ODN, Optical Distribution Network )和安装于用户场所的光网络单元 130(ONU1、 ONU2、 ...ONUN)三部分组成。上述光分配网可以包括图 1中的分光器件 120， 还可以包括光纤。 PON下行链路采用广播方式发送， 从 OLT发出的下行信 息被所有 ONU接收到，各个 ONU(Optical Network Unit)遵循一定的机制只提 取属于自己的下行信息。 上行链路采用时分复用技术， 多个 ONU共享上行 带宽。
由于 ONU所处的物理位置不一样， 所以各自所发数据帧到达 OLT的时 间会不一样， 就有可能产生发送碰撞冲突。 为了解决这个问题， 必须对各 个 ONU进行测距，从而保证各个 ONU到达 OLT的逻辑时间上不会发生冲突。 在测距的时候， 必须对所测距的 ONU保留一段测距时间， 在此测距时间内 其它 ONU不发送上行业务以避免发生沖突。 此段时间被称为测距开窗时间 ( ranging window ) ， 此时间的长短被称为开窗窗口。 OLT周期性的发出测 距的授权信号， 授权信号携带本地的时间信息。 各 ONU在接收到授权信号 时， 暂时不发送上行的业务。 现有的测距方法以 ONU1进行测距为例， 步骤 为：
1) ONU1收到 OLT发送的授权信号后， ONU1读取授权信号中的时间信 息 tl写入本地时钟。
2) ONU 1发送携带有本地时间信息的响应帧。
3) OLT收到 ONU1发送的携带有本地时间信息的响应帧后，将所携带时 间信息 t2与本地时钟的本地时间作差， 从而得到往返时间 RTT ( Round Trip Time ) , 进而根据该往返时间 RTT实现测距。
发明人在发明过程中发现如下问题：
在对 ONU进行测距的时候， 开窗的窗口必须覆盖整个系统， 且开窗窗 口必须包含分光器到 OLT端这段距离所对应传输时间。 ONU为了不丟失业 务， 必须配置大的数据存储器。 测距的距离过大， 测距时间过长， 从而使 ONU配置大的数据存储器。 另外， 其它的 ONU必须停止各自的业务， 等待 需要测距的 ONU完成测距， 占用大量带宽； 测距时必须经过两次的光电转 换， 占用大量时间； 并且测距时间釆用标准的最大往返时间， 因此会引入 较大的延时。
当系统的速率升高时， 需要重新定义 ONU的处理时间。 测距方法不具 备鲁棒性。 当系统的距离超过标准规定的最大距离时， 需要重新对平衡时 间进行定义。 在测距时， 在 ONU端存在着读出 OLT时钟标签和写入 ONU时 间标签的处理， 引入了延时并增加了系统的复杂度。 发明内容
本发明实施例提供了一种无源光网络的测距方法与系统及光网络单 元， 以避免测距时所需时间过大等缺点。
本发明实施例提供的一种无源光网络的测距方法， 包括：
一种无源光网络的测距方法， 包括以下步驟：
向分光环回器件发送初始测距信号， 记录当前发送时间信息为第一时 间信息；
接收来自所述分光环回器件 的环回测距信号， 判断所述环回测距信 号是否为所述初始测距信号的环回信号； 若是， 则记录当前接收时间信息 为第二时间信息；
将所述第一时间信息和所述第二时间信息相减得到测距信息， 并根据 该测距信息实现测距。
一种无源光网络的系统， 包括：
分光环回器件， 用于接收初始测距信号， 对所述初始测距信号环回处 理为环回测距信号， 并发送所述环回测距信号；
所述光网络单元 ONU, 用于向所述分光环回器件发送所述初始测距信 号， 记录当前发送时间信息为第一时间信息； 接收所述分光环回器件发送 的所述环回测距信号， 确定所述环回测距信号为所述初始测距信号的环回 信号后， 记录当前接收时间信息为第二时间信息； 将所述第一时间信息和 所述第二时间信息相减得到测距信息， 并根据所述测距信息实现测距。
一种光网络单元， 包括：
时钟模块， 用于记录发送初始测距信号和接收环回测距信号时的第一 时间信息和第二时间 信息；
控制模块， 用于发送所述初始测距信号， 接收环回测距信号， 确定所 述环回测距信号是所述初始测距信号的环回信号后， 将所述时钟模块记录 的所述第一时间信息和所述第二时间信息相减得到测距信息， 并根据所述 测距信息实现测距。
由上述本发明实施例提供的技术方案可见， 本发明实施例通过釆用分 光环回器件的测距方法， 光信号没有经过 OLT的处理， 因此减少了测距时 间， 从而可以不必配置大的数据緩冲器， 大大提高了系统的性能。 本发明 实施例在测距时， 当 OLT和分光器件发生故障， 进行倒换保护时， 不需要 进行重新测距； 当分光器件到 ONU发生故障时， 可大大降低倒换时间， 从 而提高系统的健壮性。 同时， 本发明实施例的系统升级性好， 当 PON系统 距离延长和速率提高时， 并不需要改变系统设置及测距方法。
附图说明
图 1为现有技术中的 PON 统拓朴结构示意图；
图 2为本发明实施例的 PON系统拓朴结构示意图；
图 3为本发明实施例提供的分光环回器件的分光环回模块图。
具体实施方式
本发明实施例的 PON系统拓朴结构示意图如图 2所示。 光线路终端 OLT 210到分光环回器件 220的这段距离 L，是每个光网络单元 ONU 230在测距过 程中都必须经过的距离， 对 ONU的测距时间并没有影响。 因此在测距的时 候， 没有必要对 L这段距离进行测距。 在实际情况下， 一般是把分光环回器 件 220放在越靠近最终的接入用户越好， 因此位于光线路终端 OLT 210与光 网络单元 ONU 230之间的分光环回器件 220， 距离 ONU较近， 从而光纤距离 L大于接入部分的光纤距离 Li ( Ll、 L2、 L3 ) 。 利用分光环回器件 220形成 一种环回， 通过环回进行测距， 目的是为了使各个 ONU的逻辑时间相同保 证不沖突。
下面结合两个具体实施例来说明本发明的技术方案。
本发明的第一个具体实施例为： 釆用加入低频低幅信号来标志 ONU的 初始测距信号进行测距的方法， 具体步骤如下：
1)光网络单元 ONU进行测距时， 向分光环回器件发送加入了低频低幅 信号的初始测距信号， 并记录存储此时的光网络单元 ONU的时间信息为第 一时间信息， 记为 tl。
初始测距信号包括 ONU的 ID信息， 并且针对是首次测距还是再次测距 进行标记。 通常， ONU是接收到了光线路终端 OLT经由分光环回器件发送 的测距授权信号， 确定被授权之后才发送初始测距信号的。 此测距授权信 号可包括是对所有的 ONU发出测距授权或是对某一个 ONU发出测距授权。 2 )分光环回器件接收并环回处理加入了低频低幅信号的初始测距信号 后，将得到的环回测距信号发送给光网络单元 ONU。
3)光网络单元 ONU接收到环回测距信号后， 判断测距是否成功。
若初始测距信号携带的低频低幅信号的频率信息与环回测距信号携带 的低频低幅信号的频率信息相同， 则表示环回测距信号是所述初始测距信 号的环回信号，也即表示可以测距成功，则记录存储此时的光网络单元 ONU 的时间信息为第二时间信息， 记为 t2。 信号是否为所述初始测距信号的环回信号， 如判断初始测距信号与环回测 距信号的信元是否相同， 或判断初始测距信号的功率是否为环回测距信号 的功率与损耗功率之和等， 来确定所述环回测距信号是否为所述初始测距 信号的环回信号， 并以此来判断测距是否可以成功。
如果初始测距信号为携带频率信息的光信号； 则判断所述环回测距信 号是否为所述初始测距信号的环回信号的过程还可以是： 判断所述初始测 距信号携带的所述频率信息与所述环回测距信号的频率信息是否相同， 若 是则确定所述环回测距信号是所述初始测距信号的环回信号。 上述频率信 息加载在光信号上或者是通过改变激光器的驱动电流加入到光信号上。
若所述环回测距信号不是所述初始测距信号的环回信号， 则表示测距 不成功， 则光网络单元 ONU对初始测距信号进行随机延时调整和 /或功率调 整，返回执行步骤 1 )， 即向所述分光环回器件重新发送新的初始测距信号。 如果多次测距不成功， 或者在设定一个时间值 T内测距不成功， 则上报网管 或故障指示管理者。 也就是说， 如果预设次数内测距不成功， 或者在设定 一个时间值 T内测距不成功， 则所述的光网络单元 ONU向网管或故障指示 管理者上报故障信息。
4) tl和 t2相减得到光网络单元 ONU的往返时间， 从而计算出延时调整 时间即测距信息， 进而根据该测距信息实现测距。
本发明的第二个具体实施例为： 一种无源光网络的测距系统， 包括光 线路终端 OLT、 分光环回器件和一个或多个光网络单元 ONU，
光线路终端 OLT, 用于发送测距授权信号给所述的分光环回器件。 光 线路终端 OLT将来自上层网络的下行信号， 如电话、 视频、 数据等业务源 信号， 发送给分光环回器件， 然后传送到最终的用户。 同时 OLT还用于产 生测距授权信号经过发射模块发送到分光环回器件， 完成相关的控制处理 以及注册、 管理等功能。
分光环回器件， 用于将测距授权信号分光后传送给一个或多个光网络 单元 ONU， 及用于将来自光网络单元 ONU的信号环回处理为环回测距信 号。 在下行方向上对来自 OLT的下行信号进行分光传输到每个 ONU, 上行 方向上传输 ONU的光信号到 OLT。
光网路单元 ONU接收到 OLT发送的下行信号， 如电话、 视频、 数据等 业务源信号， 再转发给最终的客户端 （如电话、 电脑、 电视等） 。 并把从 客户端的最终客户接收的客户信号发送给 OLT。 光网络单元 ONU进行测距 时， 向分光环回器件发送初始测距信号。 光网络单元 ONU具体包括控制模 块和时钟模块。 时钟模块用于记录存储 ONU发送初始测距信号时的时间信 息 tl。 当初始测距信号到达分光环回器件时， 初始测距信号会被环回为环 回测距信号。 该环回测距信号经过光纤的传输后， 会到达 ONU。
ONU接收到环回测距信号后， 控制模块将接收到的环回测距信号进行 解析， 判断所述环回测距信号是否为所述初始测距信号的环回信号， 如果 是， 时钟模块会读取此时时钟信息 t2。 时钟模块对时钟信息 tl和 t2进行处理 后， 即可得到测距信息， 并把测距信息告知控制模块， 以实现测距。
可以理解， 本发明实施例提供的一种光网络单元 （图未示） ， 包括： 时钟模块， 用于记录发送初始测距信号和接收环回测距信号时的第一 时间信息和第二时间信息； 控制模块， 用于发送所述初始测距信号， 接收 环回测距信号，确定所述环回测距信号是所述初始测距信号的环回信号后， 将所述时钟模块记录的所述第一时间信息和所述第二时间信息相减得到测 距信息， 并根据所述测距信息实现测距。
所述光网络单元还包括授权判定模块， 用于接收测距授权信号并进行 解析， 确定被授权之后， 再通知所述控制模块向所述分光环回器件发送所 述初始测距信号。
所述光网络单元还可以包括调整模块， 在所述控制模块确定所述环回 测距信号不是所述初始测距信号的环回信号后， 通知所述调整模块； 所述 调整模块， 用于根据接收到的所述通知对所述初始测距信号进行随机延时 调整和 /或功率调整， 之后再通知所述控制模块重新发送新的初始测距信 号。
本发明实施例提供的分光环回器件的分光环回模块图如图 3所示。分光 环回器的作用是完成对信号的分光及环回功能。 下行方向上， 分光环回器 把从 OLT发送的下行信号分配到每个支路上到达 ONU，ONU接收下行信号。 在上行方向上， 当发送初始测距信号时分光环回器对测距信号进行环回， ONU完成测距的功能。 ONU在发送上行业务的时候， ONU不接收环回的光 信号， 而仅仅接收下行的信号。 根据前面的第一个具体实施例可以理解， 环回的测距信号和初始测距信号的频率信息是相同的， 因而 ONU可以很容 易地分辨出接收到的信号是环回到测距信号还是下行业务信号， 从而可避 免环回光对下行信号的影响。
图 3中的虚线部分是为了表明， 可以通过分光环回器达到环回的功能。 此环回部分可以通过同一路径环回也可通过不同的路径环回。 本发明实施 例中的分光环回器件可以用组合器件也可以用单独器件来实现信号的分光 环回。 本发明实施例中的分光环回器件可以具体为： ΝχΝ耦合器、 分光器 件和光纤光栅组合器件、 2χΝ耦合器和反射膜组合器件、 2χΝ耦合器和光纤 光栅组合器件。 具体方案分述如下：
方案 1 : (Ν+1)χ(Ν+1)的耦合器方案。 此种方案是利用（Ν+1)χ(Ν+1)耦合 器的特性来完成的。 在下行方向上， OLT发出的光束被分成了 N+1束光， 并 且一束光被终结， 从而完成分光的功能。 在上行方向， ONU可以完成一种 环回， 从而利用这种环回机制可以对 ONU进行测距。
方案 2， 分光器件和光纤光栅组合器件方案。 下行方向上， 某一波长的 光束被分成 Ν束被各个 ONU接收。 上行方向上， 某一波长的光到达分光反 射器件时， 此波长被反射回各个 ONU, 则形成了一种环回机制。
方案 3， 2χΝ 合器和反射膜组合器件方案 （其中的耦合器并不一定限 于 2χΝ形式） 。 下行方向上， OLT发出的光信号被分光器件分成 Ν束， 被各 个 ONU接收。 上行方向上， 当某一 ONU发出的光信号到达耦合器后， 一部 分之间通过耦合器， 一部分在耦合器的一端反射回来， 到达每个 ONU。 从 而完成了 ONU的环回。
方案 4, 2χΝ耦合器和光纤光栅组合器件方案 （其中的耦合器并不一定 限于 2χΝ形式） 。 下行方向上， OLT发出的光信号被分光器件分成 N束， 被 各个 ONU接收。 上行方向上， 某一波长的光信号在分光器件输出被光栅所 反射， 从而形成环回。
从以上描述可以看出， 由上述本发明实施例提供的技术方案可见， 本 发明实施例通过采用分光环回器件的测距方法， 把现有技术中的 PON中的 分光器件采用分光环回器件替代， 从而在分光器和各 ONU之间形成一种环 回机制。 分光环回器件既具备分光功能， 又具备环回功能。 光信号没有经 过 OLT的处理， 因此减少了测距时间， 从而可以不必配置大的数据緩冲器， 大大提高了系统的性能。 与现有技术相比，本发明实施例在测距时， 当 OLT 和分光器件发生故障进行倒换保护时， 不需要进行重新测距； 当分光器件 到 ONU发生故障时， 可大大降低倒换时间， 从而提高系统的健壮性。 同时， 本发明实施例的系统升级性好， 当 PON系统距离延长和速率提高时， 并不 需要改变系统设置及测距方法。
以上所述， 仅为本发明具体实施方式， 但本发明的保护范围并不局限 于此， 任何熟悉本技术领域的技术人员在本发明揭露的技术范围内， 可轻 易想到的变化或替换， 都应涵盖在本发明的保护范围之内。 因此， 本发明 的保护范围应该以权利要求书的保护范围为准。

Claims

权 利 要 求
1、 一种无源光网络的测距方法， 其特征在于， 包括以下步骤： 向分光环回器件发送初始测距信号， 记录当前发送时间信息为第一时 间信息；
接收来自所述分光环回器件的环回测距信号， 判断所述环回测距信号 是否为所述初始测距信号的环回信号； 若是， 则记录当前接收时间信息为 第二时间信息；
将所述第一时间信息和所述第二时间信息相减得到测距信息， 并根据 该测距信息实现测距。
2、 如权利要求 1所述的方法， 其特征在于， 判断所述环回测距信号是 否为所述初始测距信号的环回信号的方法包括： 判断所述初始测距信号与 所述环回测距信号的信元是否相同， 若相同则确定所述环回测距信号是所 述初始测距信号的环回信号。
3、 如权利要求 1所述的方法， 其特征在于， 判断所述环回测距信号是 否为所述初始测距信号的环回信号的方法包括： 判断所述初始测距信号的 功率是否为所述环回测距信号的功率与损耗功率之和， 若是则确定所述环 回测距信号是所述初始测距信号的环回信号。
4、 如权利要求 1所述的方法， 其特征在于，
所述初始测距信号为采用加入低频低幅信号作标志的信号；
判断所述环回测距信号是否为所述初始测距信号的环回信号的方法包 括： 判断所述环回测距信号是否为加入所述低频低幅信号标志的信号， 若 是则确定所述环回测距信号是所述初始测距信号的环回信号。
5、 如权利要求 1所述的方法， 其特征在于，
所述初始测距信号为携带频率信息的光信号；
判断所述环回测距信号是否为所述初始测距信号的环回信号的方法包 括： 判断所述初始测距信号携带的所述频率信息与所述环回测距信号的频 率信息是否相同， 若是则确定所述环回测距信号是所述初始测距信号的环 回信号。
6、 如权利要求 5所述的方法， 其特征在于， 所述频率信息加载在光信 号上或者是通过改变激光器的驱动电流加入到光信号上。
7、 如权利要求 1至 5所述的任一项方法， 其特征在于， 进一步包括， 若 所述环回测距信号不是所述初始测距信号的环回信号， 则对所述初始测距 信号进行随机延时调整和 /或功率调整， 之后， 重新向所述分光环回器件发 送新的初始测距信号。
8、 如权利要求 7所述的方法， 其特征在于， 进一步包括， 若预设次数 内测距不成功， 或者在设定一个时间值 T内测距不成功， 则上报故障信息。
9、 如权利要求 1所述的方法， 其特征在于， 进一步包括， 接收来自光 线路终端 OLT的测距授权信号并进行解析， 确定被授权之后， 再向所述分 光环回器件发送所述初始测距信号。
10、 一种无源光网络的测距系统， 其特征在于， 包括：
分光环回器件， 用于接收初始测距信号， 对所述初始测距信号环回处 理为环回测距信号， 并发送所述环回测距信号；
所述光网络单元 ONU， 用于向所述分光环回器件发送所述初始测距信 号， 记录当前发送时间信息为第一时间信息； 接收所述分光环回器件发送 的所述环回测距信号， 确定所述环回测距信号为所述初始测距信号的环回 信号后， 记录当前接收时间信息为第二时间信息； 将所述第一时间信息和 所述第二时间信息相减得到测距信息， 并根据所述测距信息实现测距。
11、 如权利要求 10所述的测距系统， 其特征在于， 所述系统进一步包 括： 光线路终端 OLT, 用于发送测距授权信号给所述分光环回器件；
所述的分光环回器件进一步用于将所述测距授权信号分光后传送给所 述光网络单元 ONU;
所述光网络单元 ONU进一步用于将接收到的所述分光后的测距授权信 号进行解析， 确定被授权之后， 再向所述分光环回器件发送所述初始测距 信号。
12、 如权利要求 9所述的测距系统， 其特征在于， 所述分光环回器件具 体为： NxN耦合器、 分光器件和光纤光栅组合器件， 或 2χΝ耦合器和光纤 光栅组合器件， 或 2χΝ輛合器和反射膜组合器件。
13、 一种光网络单元， 其特征在于， 包括： 时钟模块，用于记录发送初始测距信号和接收环回测距信号时的第一时间 信息和第二时间信息；
控制模块， 用于发送所述初始测距信号， 接收环回测距信号， 确定所述环 回测距信号是所述初始测距信号的环回信号后，将所述时钟模块记录的所述第 一时间信息和所述第二时间信息相减得到测距信息，并 居所述测距信息实现 测距。
14、 根据权利要求 13所述的光网络单元， 其特征在于， 所述光网络单元 还包括授权判定模块， 用于接收测距授权信号并进行解析， 确定被授权之后， 再通知所述控制模块向所述分光环回器件发送所述初始测距信号。
15、根据权利要求 13或 14所述的光网络单元， 其特征在于， 所述光网络 单元还包括调整模块，
在所述控制模块确定所述环回测距信号不是所述初始测距信号的环回信 号后， 通知所述调整模块；
所述调整模块， 用于根据接收到的所述通知对所述初始测距信号进行随 机延时调整和 /或功率调整， 再通知所述控制模块重新发送新的初始测距信号。
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