WO2012048643A1 - 一种实现无源光网络拉远的方法和系统及中继装置 - Google Patents

一种实现无源光网络拉远的方法和系统及中继装置 Download PDF

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Publication number
WO2012048643A1
WO2012048643A1 PCT/CN2011/080700 CN2011080700W WO2012048643A1 WO 2012048643 A1 WO2012048643 A1 WO 2012048643A1 CN 2011080700 W CN2011080700 W CN 2011080700W WO 2012048643 A1 WO2012048643 A1 WO 2012048643A1
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WIPO (PCT)
Prior art keywords
olt
onu
data stream
overhead
bandwidth
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PCT/CN2011/080700
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English (en)
French (fr)
Inventor
胡幸
蒋红丽
陈娟
马腾
李汉国
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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Priority to EP11832040.7A priority Critical patent/EP2618508B1/en
Publication of WO2012048643A1 publication Critical patent/WO2012048643A1/zh
Anticipated expiration legal-status Critical
Priority to US13/862,853 priority patent/US9154221B2/en
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • 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
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
    • H04J3/1605—Fixed allocated frame structures
    • H04J3/1652—Optical Transport Network [OTN]
    • 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
    • H04Q2011/009—Topology aspects

Definitions

  • the present invention relates to the field of network transmission, and in particular, to a method and system for implementing remote access to a passive optical network and a relay device.
  • PON Passive Optical Network
  • FTTH Fiber To The Home
  • BPON Broadband Passive Optical Network
  • GPON Gigabit-Capable Passive Optical Network
  • EPON Ethernet Passive Optical Network
  • FIG. 1 a network architecture diagram for access using a conventional PON system.
  • the PON is used to connect the user terminal to the transport network, and then to the core network through the transport network, namely, a digital video (Video) network, an Internet (Internet), and a Public Switched Telephone Network (PSTN).
  • a digital video (Video) network namely, an Internet (Internet), and a Public Switched Telephone Network (PSTN).
  • PSTN Public Switched Telephone Network
  • the most basic components of a PON system include: an Optical Line Terminal (OLT), an Optical Network Unit (ONU), and an Optical Distribution Network (ODN).
  • OLT and the passive optical splitter are connected by a trunk optical fiber, and the optical splitter realizes optical power distribution of one point to multiple points, and is connected to multiple ONUs through multiple branch fibers.
  • the backbone fiber, passive optical splitter, and branch fiber between the OLT and the ONU are collectively referred to as ODN.
  • the direction from the OLT to the ONU is called the downlink direction
  • the direction from the ONU to the OLT is called the uplink direction.
  • the Time Division Multiple Address (TDMA) multiplexing mode is adopted, and each ONU transmits the uplink data stream only in the time slot designated by the OLT.
  • the downlink direction uses a Time Division Multiplexing (TDM) broadcast mode.
  • the OLT sends a downlink data stream to each ONU, and uses a specific identifier to indicate which ONU each time slot belongs to, and carries the light of the downlink data stream of all ONUs.
  • the signal is divided into several parts at the optical splitter of the ODN, and each branch fiber reaches each ONU, and each ONU collects its own data according to the corresponding identifier, and discards the data of other time slots.
  • the OLT covers the ONU within a range of no more than 20km, through the optical splitter pair.
  • the number of connected ONUs is small, resulting in a large number of OLTs in the traditional PON network architecture, remote and scattered location areas, inconvenient management and maintenance, and high equipment investment and maintenance costs.
  • an OTN device is added between the optical splitter of the OLT and the ODN, and data is implemented by using Wavelength Division Multiplexing (WDM) technology.
  • WDM Wavelength Division Multiplexing
  • the OTN device transparently maps (bit maps) the uplink and downlink data frames of the GPON to the OTU ⁇ k frame, and transmits the data to the peer device through the OTN network, and then demaps the original GPON uplink and downlink data frames to implement the GPON system. Pulling away.
  • the maximum value of the waiting time T that the OLT can tolerate is converted into the number of kilometers of the fiber, which is the protocol definition.
  • the maximum logical distance of the OLT for example, the maximum logical distance of the OLT defined by the current GPON standard is 60 km. In the existing PON remote solution, the distance is limited by the maximum logical distance of the OLT defined by the protocol. If the PON system is extended beyond the maximum logical distance specified by the protocol, the OLT will not receive the specified time T.
  • the upstream data stream sent by the ONU causes the OLT to fail to receive the upstream data stream. Summary of the invention
  • Embodiments of the present invention provide a method and system for implementing P0N remote and a relay device, so that long distance extension of P0N can be realized without changing any existing P0N protocol and 0LT device.
  • a method for implementing remote access of a passive optical network includes: extracting an overhead in an upstream data stream sent by the ONU to the 0LT, demaping the payload in the upstream data stream, and storing the payload in the buffer; extracting 0LT and transmitting to 0 The bandwidth authorization information in the downlink data stream; and the payload stored in the downlink according to the bandwidth authorization information, inserting a corresponding overhead, and generating a new uplink data stream to send to the OLT.
  • a system for implementing remote optical network extension includes an OLT, a relay, and at least one ONU.
  • a downlink data stream containing bandwidth grant information is transmitted to the ONU via the relay device.
  • the ONU obtains the bandwidth authorization information from the downlink data flow, and sends an uplink data flow according to the bandwidth authorization information.
  • the relay device extracts the overhead in the uplink data stream sent by the ONU to the OLT, demaps the payload in the uplink data stream, and stores the payload; and extracts the bandwidth grant information in the downlink data stream sent by the OLT to the ONU;
  • the bandwidth authorization information reassembles the stored payload, inserts a corresponding overhead, and generates a new uplink data stream to send to the OLT.
  • a relay device for implementing remote optical network remotely includes: a processing module, an overhead extraction module, a decapsulation module, a buffer, a data stream regeneration module, a sending module, a receiving module, and a bandwidth map extraction module.
  • the receiving module receives the downstream data stream sent by 0LT to 0.
  • the bandwidth map extraction module extracts bandwidth authorization information from the downlink data stream.
  • the overhead extraction module extracts the overhead from the upstream data stream sent by the 0NU to the 0LT, and sends it to the processing module for storage in the buffer.
  • the decapsulation module demaps the payload from the upstream data stream from which the overhead is extracted, and sends it to the processing module for storage in the buffer.
  • the data stream regeneration module generates a new uplink data stream by inserting a corresponding overhead according to the payload stored in the bandwidth authorization information reassembly buffer, and sends the new uplink data stream to the 0LT through the sending module.
  • the uplink data stream sent by the relay device to the Q and transmitted to the 0LT is relayed in the existing P0N remote system, and the maximum logical distance limit of the 0LT defined by the P0N protocol is exceeded, without changing any existing P0N.
  • P0Ns that achieve longer distances are farther away.
  • Figure 1 is a schematic diagram of a network architecture using a conventional PON system access.
  • Figure 2 is a schematic diagram of the architecture of an existing OTN-based GPON remote system.
  • FIG. 3 is a schematic structural diagram of a PON remote system according to an embodiment of the present invention, and a relay device is added between the OLT and the ODN.
  • Figure 4 is a functional block diagram of the relay device of Figure 3.
  • FIG. 5 is a flow chart showing the operation of the relay device in FIG. 3 during the ONU activation process.
  • FIG. 6 is a flow chart of data transmission and reception by the OLT and the ONU in FIG. detailed description
  • FIG. 3 it is a schematic diagram of the architecture of the PON remote system 300 in the embodiment of the present invention.
  • the PON remote system 300 includes an optical line termination (OLT) 30, a relay device 32, an OTN device 34, an optical distribution network (ODN) 36, and a plurality of optical network units (ONUs) 38.
  • the trunk fiber, optical splitter 362, and branch fiber between the OLT 30 and the plurality of ONUs 38 constitute an ODN 36.
  • the OTN device 34 includes optical fibers and routers that make up the optical transport network.
  • the relay device 32 is located between the OLT 30 and the optical splitter 362 of the ODN 36, and processes the data stream transmitted between the OLT 30 and the ONU 38, so that the PON remote system 300 does not change the existing PON protocol and the OLT device. Under the long-distance remote function that realizes the maximum logical distance beyond the PON protocol.
  • the OTN device 34 uses the WDM technology to transmit the data stream transmitted and received between the OLT 30 and the plurality of ONUs 38, and uses the electrical relay mode of photoelectric optical conversion to realize the long distance extension of the PON.
  • the relay device 32 cooperates with the OLT 30 to activate the ONU 38, and specifically includes: completing registration of one of the ONUs 38; forwarding a ranging request sent by the OLT 30 to the ONU 38; receiving a ranging response message returned by the ONU 38 in response to the ranging request, and receiving The time delay of the ranging response message is transmitted in the OTN device 34, and a new ranging response is sent to the OLT 30; the ONU 38 forwards the OLT 30 according to the ranging response message.
  • the equalization delay value Td calculated by the arrival time of the arrival time, and the response message (Ploam ACK) returned by the ONU 38 to the OLT 30 after receiving the equalization delay value Td, indicating that the equilibrium delay value Td has been received. Thereby the ONU 38 is activated.
  • an upstream data stream in which the idle frame is inserted in the payload area is generated, and is transmitted to the OLT 30 when the data transmission time specified by the OLT 30 arrives.
  • the delay of the ranging response message transmitted in the OTN device 34 can be tested after the OTN device 34 is constructed.
  • the value is mainly determined by the length and characteristics of the fiber in the OTN device 34.
  • the step of completing the registration of any ONU 38 is specifically as follows: extracting the bandwidth authorization information in the downlink data stream sent by the OLT to the ONU; forwarding the sequence number (SN) request sent by the OLT 30 to each ONU 38 periodically; buffering one of the ONUs 38 in response to the Serial number request returned to OLT30 a serial number, and when receiving the serial number request sent by the OLT 30 again, transmitting the serial number to the OLT 30 according to the bandwidth authorization information; and forwarding an identifier assigned by the OLT 30 to the ONU 38, thereby completing registration of the ONU.
  • SN sequence number
  • the relay device 32 forwards the downlink data stream sent by the OLT 30 to the ONU 38, and extracts and buffers the uplink bandwidth grant information (also referred to as a bandwidth map) sent by the OLT 30.
  • the uplink bandwidth grant information is used to indicate the start and end times of the uplink data streams sent by the multiple ONUs 38 or the start time and duration of the uplink data streams sent by the multiple ONUs 38, and the time slots of the multiple ONUs 38 for transmitting the uplink data are not overlapped. That is, a plurality of ONUs 38 are caused to share the same transmission channel by time division multiplexing.
  • the relay device 32 also extracts the overhead from the upstream data stream transmitted by each ONU 38, demaps each ONU payload from the upstream data stream from which the overhead is extracted, and performs buffering separately.
  • the relay device 32 also reassembles each ONU payload according to the latest bandwidth grant information sent by the OLT 30, inserts a corresponding overhead to generate a new uplink data stream, and transmits it to the OLT 30 when the data transmission time specified by the OLT 30 arrives.
  • the technical solution of the present invention can be applied to a PON system under the protocols of GPON, EPON, BPON, etc.
  • the data stream can be a data format such as a frame or a packet in different PON protocols, and the data stream includes voice in any format. Video, multimedia content and other data.
  • the technical solution of the present invention adds a relay device 32 in the existing PON remote system 300, and breaks through the limitation of the maximum logical distance of the OLT 30 defined by the PON protocol, and realizes without changing any existing PON protocol and OLT device.
  • the long distance PON is far away.
  • the relay device 32 includes a processing module 322, an overhead extraction module 324, a decapsulation module 325, a buffer 326, a data stream regeneration module 328, a sending module 330, a receiving module 332, and a bandwidth map extraction module 334.
  • the bandwidth map extraction module 334 extracts the bandwidth authorization information in the downlink data stream sent by the OLT 30 to the ONU 38, and sends it to the processing module 322 for storage in the buffer 326.
  • the processing module 322 stores the sequence number returned by one of the ONUs 38 in response to the serial number request sent by the OLT 30 to the OLT 30 to the buffer 326, and when the serial number request sent by the OLT 30 is received again, the sequence is determined according to the bandwidth grant information. The number is sent to the OLT30.
  • the processing module 322 also receives the ranging response message returned by the ONU 38 in response to the ranging request, and connects Receiving the ranging response message minus the delay of the ranging response message transmitted in the OTN device, generating a new ranging response message, and when receiving the ranging request sent by the OLT again, The new ranging response is sent to the OLT.
  • the extraction module 324 extracts the overhead from the upstream data stream sent by each ONU, and sends it to the processing module 322 for storage in the buffer 326.
  • the overhead includes a minimum physical layer overhead (PLOu), an uplink physical layer OAM (PLOAMu), a power levelling sequence upstream (PLSu), and an uplink dynamic bandwidth request ( One or more types of overhead information in Dynamic Bandwidth Report upstream, DBRu ).
  • the decapsulation module 325 demaps the payload from the upstream data stream from which the overhead is extracted, and sends it to the processing module 322 for storage in the buffer 326.
  • the data stream regeneration module 328 reassembles the payload stored in the buffer 326 according to the latest bandwidth grant information sent by the OLT 30, inserts a corresponding overhead to generate a new uplink data stream, and sends it through the sending module 330 when the data transmission time specified by the OLT 30 arrives.
  • the data stream regeneration module 328 When any ONU payload stored in the buffer 326 is empty, the data stream regeneration module 328 generates an upstream data stream in which the idle frame is inserted in the payload area, and transmits it to the OLT 30 when the data transmission time specified by the OLT 30 arrives.
  • the buffer 326 is configured to store the bandwidth authorization information sent by the OLT 30 and the overhead and payload sent by each ONU, and report the status of each stored ONU payload to the processing module 322.
  • the state of each ONU payload includes the number of bytes of the ONU payload.
  • the receiving module 332 receives the downlink data stream sent by the OLT 30, and sends the downlink data stream to the bandwidth map extraction module 334.
  • the bandwidth map extraction module 334 extracts the bandwidth authorization information sent by the OLT 30 from the downlink data stream, and sends the bandwidth authorization information to the processing module 322 for storage in the buffer 326.
  • the relay device 32 of the embodiment of the present invention reorganizes the uplink data stream sent by the ONU 38 to the OLT 30, so as to break the limitation of the maximum logical distance of the OLT 30 defined by the PON protocol without changing any existing PON protocol and OLT device. , to achieve longer distance PON pull far.
  • FIG. 5 is an operation flowchart of the relay device 32 in the activation process of the ONU in FIG. 3, the following describes the operation flow by taking the ONU activation process in the GPON protocol as an example.
  • the bandwidth authorization information in the downlink data stream sent by the OLT 30 to the ONU 38 is extracted and stored.
  • Forwarding overhead (upstream-overhead) and sequence number request sent by the OLT 30 to each ONU 38 periodically, the uplink overhead specifies configuration parameters such as the transmitted optical power, the number of preamble bytes, and the pre-allocated equalization delay value Td of each ONU 38. .
  • the ONU 38 After receiving the uplink overhead and sequence number request, the ONU 38 sends the sequence number of the ONU 38 to the OLT 30 according to the configuration parameter in the uplink.
  • the ONU 38 can be an ONU newly added to the GPON system or an ONU that is rebooted.
  • the ONU 38 transmits its sequence number through the PLO AM field in the uplink data frame, and uses P10AMu_SN to indicate the sequence number transmitted in the PLOAM field.
  • the response time period T1 of the OLT 30 receiving the serial number of the ONU 38 is designed according to the maximum logical distance between the OLT 30 and the ONU 38 defined by the PON protocol (for example, 60 km in the GPON protocol), when the OLT 30 and the ONU 38 are When the actual distance between (eg, 100 KM) exceeds the maximum logical distance, the OLT 30 will not receive the sequence number returned by the ONU 38 within the response time period T1. Column number, and store it.
  • the relay device 32 When the relay device 32 receives the serial number request sent by the OLT 30 again, the stored serial number of the ONU 38 is inserted into the PLOAM field of the uplink data frame, and the uplink data frame inserted with the serial number is sent according to the stored bandwidth authorization information. OLT30.
  • the OLT 30 When the OLT 30 receives a new serial number, it determines the serial number. If the serial number is valid, it confirms that a new ONU 38 request is activated, and the OLT 30 assigns an identifier ( Assign_ONUID) to the ONU 38, and the The overhead field of the identifier insertion downlink data frame is sent to the relay device 32, and the relay device 32 forwards the downlink data frame containing the identifier to the corresponding ONU 38.
  • Assign_ONUID an identifier
  • the OLT 30 starts to measure the ONU 38 within a preset time period T2 after the identifier is assigned to the ONU 38.
  • the preset time period T2 is at least 750us, because the data transmission and reception of the ONU 38 in the running period needs to be interrupted during the ranging.
  • the ONU 38 needs to buffer the received data during this period. To avoid overflow of data received by the ONU 38, the ONU 38 can transmit part of the data to the OLT 30 within a preset time period T2.
  • the OLT 30 forwards a ranging request to the ONU 38 via the relay device 32. After receiving the ranging request, the ONU 38 returns a ranging response message to the OLT 30. Since the ranging window T3 of the OLT 30 (ie, a preset time period ⁇ 3) is designed according to the maximum logical distance (ie, 60 km) between the OLT 30 and the ONU 38 defined by the GPON protocol, when the actual distance between the OLT 30 and the ONU 38 exceeds At 60 km, the OLT 30 will not receive the ranging response message within the ranging window T3.
  • the OLT 30 When the OLT 30 does not receive the ranging response message in a ranging window T3, it considers that the ranging fails, and waits for at least one of the preset time periods T2, and then sends a ranging request to the ONU 38, if If the ranging response message returned by the ONU 38 is still not received in the ranging window T3, the ONU 38 is considered to be invalid, and the identifier of the ONU is deleted.
  • the relay device 32 extracts the ranging response message in the uplink data frame sent by the ONU 38, and subtracts the time delay of the uplink data frame from being transmitted in the OTN device 34 by receiving the uplink data frame.
  • a new ranging response message is generated, and when the relay device 32 extracts the ranging request from the downlink data frame transmitted by the OLT 30 again, the new ranging response message is sent to the OLT 30.
  • the OLT 30 calculates the loop delay time of the ONU 38 (referred to as the equalization loop delay value Teqd) according to the arrival time of the ranging response message, and calculates the equalization delay value of the ONU 38 according to the loop delay time Teqd.
  • Td the loop delay time Teqd of all ONUs 38 after inserting their respective equalization delay values Td are equal.
  • the loop delay time Teqd is the time required for the signal to be sent back from the OLT 30 to the ONU 38 and then returned to the OLT 30. It also includes the processing time of the ONU 38 for the signal.
  • the relay device 32 forwards the equalization delay value Td to the ONU 38.
  • the ONU 38 After receiving the equalization delay value Td, the ONU 38 returns a response message (Ploam_ACK) to the OLT 32 to indicate that the equalization delay has been received.
  • the value Td is a response message (Ploam_ACK) to the OLT 32 to indicate that the equalization delay has been received.
  • the OLT 30 After the OLT 30 extracts the response message returned by the ONU 38 from the uplink data frame forwarded by the relay device 32, the ranging is completed and the ONU 38 is activated. When the ONU 38 is activated, the OLT 30 performs normal data transmission and reception with the ONU 38 via the relay device 32.
  • FIG. 6 a flow chart of data transmission and reception between the OLT 30 and the ONU 38 in FIG. 3 is shown.
  • the ONU 38 when the OLT 30 sends a new bandwidth map to the ONU 38, the ONU 38 must send an uplink data frame to the OLT 30 according to the new bandwidth map when the data transmission time period T4 specified by the protocol ends.
  • the data transmission time period T4 is 125us.
  • the data transmission time period T4 is designed according to the maximum logical distance between the OLT 30 and the ONU 38 defined by the GPON protocol (ie, 60 km), when the actual distance between the OLT 30 and the ONU 38 exceeds 60 km, the OLT 30 is at the data transmission time.
  • the ONU38 will not be received in the segment T4 according to the new The upstream data frame sent by the bandwidth map, at this time, the OLT 30 will consider that the ONU 38 is dropped, thereby interrupting data transmission and reception with the ONU 38.
  • the relay device 32 when forwarding the downlink data frame transmitted by the OLT 30, the relay device 32 extracts a bandwidth map from the downlink data frame and stores it.
  • the OLT 30 can allocate one or more transmission containers (Transmission Containers) for each ONU 38.
  • T-CONT is used to send and receive data frames and is identified by Alloc-ID.
  • Relay device 32 also from each
  • the overhead is extracted from the uplink data frame of the T-CONT, and the payload is demapped from the uplink data frame from which the overhead is extracted, and stored separately.
  • the overhead includes overhead information for one or more types of PLOu, PLOAMu, PLSu, and DBRu.
  • the relay device 32 When the data transmission time period T4 specified by the protocol arrives, the relay device 32 reassembles each T-CONT payload of the cache according to the latest bandwidth map sent by the OLT 30, inserts a corresponding overhead to generate a new uplink data frame, and transmits the new uplink data frame to the OLT 30.
  • the relay device 32 calculates a new bandwidth requirement according to the current bandwidth of each T-CONT buffer and the bandwidth requirement in the DBRu before the end of the data transmission time period T4 specified by the GPON protocol, and the new bandwidth requirement is Updated to DBRu.
  • the new bandwidth requirement is calculated because the bandwidth requirements of each T-CONT received by the relay device 32 do not reflect the size of each T-CONT buffer in the current relay device 32.
  • the maximum size of the -CONT buffer and the bandwidth requirement in DBRu is used as the new bandwidth requirement.
  • the OLT 30 generates bandwidth authorization information according to the new bandwidth requirement.

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

本发明实施例公开了一种实现PON拉远的方法和系统及实现该方法的中继装置。所述方法包括：提取ONU发送给OLT的上行数据流中的开销，解映射出该上行数据流中的净荷，并存储到缓存器；提取OLT发送给ONU的下行数据流中的带宽授权信息；及根据所述带宽授权信息重组存储的净荷，插入对应的开销生成新的上行数据流发送给OLT。本发明实施例的中继装置对ONU传送给OLT的上行数据流进行中继，突破PON协议定义的OLT的最大逻辑距离的限制，在不更改任何现有PON协议和OLT设备的情况下，实现更长距离的PON拉远。

Description

一种实现无源光网络拉远的方法和系统及中继装置 本申请要求于 2010年 10月 14日提交中国专利局、 申请号为 201010507110.9、 名称为 "一种实现无源光网络拉远的方法和系统及中继装置"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
本发明涉及网络传输领域，尤其涉及一种实现无源光网络拉远的方法和系 统及中继装置。
背景技术
无源光网络 ( Passive Optical Network, PON )技术是目前应用最广泛的光 纤到户 （ Fiber To The Home, FTTH )技术之一。 现有的 PON包括宽带无源光网 絡 （ Broadband Passive Optical Network, BPON ) 、 吉比特无源光网絡 ( Gigabit-capable Passive Optical Network, GPON )和以太无源光网络（ Ethernet Passive Optical Network, EPON ) 。
如图 1所示， 为使用传统的 PON系统接入的网络架构图。 PON用于将用户 终端接入到传送网， 再通过传送网接入到核心网， 即数字视频 （Video ) 网、 因特网 （Internet ) 和公共交换电话网 （Public Switched Telephone Network, PSTN ) 。
PON系统最基本的组成包括： 光线路终端（ Optical Line Terminal, OLT )、 光网洛单元 （Optical Network Unit, ONU ) 和光分配网 （Optical Distribution Network, ODN )等部分。 OLT和无源光分路器之间由主干光纤连接， 光分路器 实现一点对多点的光功率分配， 通过多个分支光纤连接到多个 ONU。 OLT和 ONU之间的主干光纤、 无源光分路器和分支光纤统称为 ODN。 其中， 从 OLT 到 ONU的方向称为下行方向， 从 ONU到 OLT的方向称为上行方向。
上行方向釆用时分多址 （ Time Division Multiple Address, TDMA ) 复用方 式， 各 ONU只在 OLT指定的时隙发送上行数据流。 下行方向采用时分复用 ( Time Division Multiplexing, TDM )广播方式， OLT向各 ONU发送下行数据流， 并用特定的标识来指示各时隙是属于哪个 ONU的， 载有所有 ONU的下行数据 流的光信号在 ODN的光分路器处被分成若干份， 经各分支光纤到达各 ONU, 各 ONU根据相应的标识收取属于自己的数据， 并丢弃其他时隙的数据。
传统的 PON系统中， OLT覆盖 ONU的范围不超过 20km, 通过光分路器对 接的 ONU数量较少，导致传统的 PON网络架构中 OLT数量较多，位置区域偏远 且分散， 很不方便管理和维护， 设备投资和维护成本较高。
随着下一代光接入网络的兴起， 运营商要求扩大 PON的覆盖范围， 为此， 提出了长距离 PON ( long reach PON, LR-PON )拉远技术。 其中， 基于光传送 网 （ Optical Transport Network, OTN ) 和波分复用 （Wavelength Division Multiplexing, WDM )技术对 PON系统进行拉远的方案具有节省光纤、 易于维 护管理、 可靠性高等优点， 因此受到业界的广泛关注和推动。 尤其是， 基于 OTN的 GPON系统的拉远方案（ GPON over OTN ) 已经成功纳入标准并被多家 运营商采纳。
如图 2所示， 为基于 OTN的 GPON拉远系统的架构示意图， 在 OLT与 ODN 的光分路器之间增加 OTN设备， 并使用波分复用 （ Wavelength Division Multiplexing, WDM )技术实现数据的双向传输。 该 OTN设备将 GPON的上行和 下行数据帧透明地映射 （bit映射） 到 OTU^k帧， 并通过 OTN网络传输到对端 设备，然后解映射出原始的 GPON上行和下行数据帧，实现 GPON系统的拉远。
假设 OLT从发送下行数据流开始到接收到 ONU发送的上行数据流时所等 待的时间为 T, 那么将 OLT所能容忍的等待时间 T的最大值， 换算成光纤的公 里数， 即为协议定义的 OLT的最大逻辑距离， 例如目前 GPON标准定义的 OLT 的最大逻辑距离为 60km。 现有 PON拉远方案， 拉远距离都受限于协议定义的 OLT的最大逻辑距离， 如果将 PON系统拉远到超过协议规定的最大逻辑距离， OLT在上述规定的时间 T内将接收不到 ONU发送的上行数据流， 导致 OLT无法 正常接收上行数据流。 发明内容
本发明实施例提供了一种实现 P0N拉远的方法和系统及中继装置， 使得在 不更改任何现有 P0N协议和 0LT设备的情况下实现 P0N的长距离拉远。
一种实现无源光网络拉远的方法包括：提取 0NU发送给 0LT的上行数据流中 的开销， 解映射出该上行数据流中的净荷， 并存储到緩存器； 提取 0LT发送给 0而的下行数据流中的带宽授权信息； 及根据所述带宽授权信息重组存储的净 荷， 插入对应的开销生成新的上行数据流发送给 0LT。
一种实现无源光网络拉远的系统包括 0LT、 中继装置和至少一个 0NU。 0LT 经由中继装置向 ONU发送含有带宽授权信息的下行数据流。所述 0NU从所述下行 数据流中获取所述带宽授权信息，根据所述带宽授权信息发送上行数据流。 中 继装置提取 0NU发送给 0LT的上行数据流中的开销，解映射出该上行数据流中的 净荷， 并进行存储； 提取 0LT发送给 0NU的下行数据流中的带宽授权信息； 根据 存储的所述带宽授权信息重组存储的净荷，插入对应的开销生成新的上行数据 流发送给 0LT。
一种实现无源光网络拉远的中继装置包括： 处理模块、 开销提取模块、 解 封装模块、 緩存器、 数据流再生模块、 发送模块、 接收模块和带宽地图提取模 块。接收模块接收 0LT发送给 0皿的下行数据流。 带宽地图提取模块从所述下行 数据流中提取出带宽授权信息。开销提取模块从 0NU发送给 0LT的上行数据流中 提取出开销， 并送给处理模块存储到緩存器中。解封装模块从提取出开销的上 行数据流中解映射出净荷， 并送给处理模块存储到緩存器。数据流再生模块根 据所述带宽授权信息重组緩存器中存储的净荷，插入对应的开销生成新的上行 数据流， 并通过发送模块发送给 0LT。
本发明实施例在现有 P0N拉远系统中增加中继装置对 Q而发送给 0LT的上行 数据流进行中继， 突破 P0N协议定义的 0LT的最大逻辑距离的限制 , 在不更改任 何现有 P0N协议和 0LT设备的情况下 , 实现更长距离的 P0N拉远。 附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施 例或现有技术描述中所需要使用的附图作简单地介绍， 显而易见地， 下面描述 中的附图仅仅是本发明的一些实施例， 对于本领域普通技术人员来讲， 在不付 出创造性劳动的前提下， 还可以根据这些附图获得其他的附图。
图 1为使用传统的 PON系统接入的网絡架构示意图。
图 2为现有基于 OTN的 GPON拉远系统的架构示意图。
图 3为本发明实施例中 PON拉远系统的架构示意图， 在 OLT和 ODN之间增 加中继装置。
图 4为图 3中的中继装置的功能框图。
图 5为图 3中的中继装置在 ONU激活过程中的操作流程图。
图 6为图 3中的 OLT与 ONU进行数据收发的流程图。 具体实施方式
为了便于本领域一般技术人员理解和实现本发明，现结合附图描绘本发明 的实施例。 在此， 本发明的示意性实施例及其说明用于解释本发明， 但并不作 为对本发明的限定。
下面结合附图和实施例， 对本发明的技术方案进行描述。 如图 3所示， 为 本发明实施例中 PON拉远系统 300的架构示意图。所述 PON拉远系统 300包括光 线路终端 （OLT ) 30、 中继装置 32、 OTN设备 34、 光分配网 （ ODN ) 36和多 个光网络单元 （ONU ) 38。 OLT30和多个 ONU38之间的主干光纤、 光分路器 362和分支光纤构成 ODN36。 OTN设备 34包括组成光传送网的光纤以及路由器。
中继装置 32位于 OLT30与 ODN36的光分路器 362之间， 对 OLT30与 ONU38 之间传输的数据流进行处理， 使得所述 PON拉远系统 300在不改变现有 PON协 议和 OLT设备的情况下，实现超出 PON协议定义的最大逻辑距离的长距离拉远 功能。
OTN设备 34采用 WDM技术传送 OLT30与多个 ONU38之间收发的数据流， 并采用光电光转换的电中继方式实现 PON的长距离拉远。
中继装置 32与 OLT30配合激活 ONU38 , 具体包括： 完成其中一 ONU38的 注册； 转发 OLT30发送给该 ONU38的测距请求； 接收所述 ONU38响应所述测 距请求返回的测距响应消息，将接收到所述测距响应消息的时间减去所述测距 响应消息在 OTN设备 34中传输的时延， 生成新的测距响应消发送给 OLT30; 向 ONU38转发， OLT30根据所述测距响应消息的到达时间计算出的均衡时延值 Td; 转发， 该 ONU38接收到所述均衡时延值 Td后向 OLT30返回的应答消息 ( Ploam ACK ) ， 表明自己已收到所述均衡时延值 Td， 从而激活该 ONU38。
当中继装置 32中存储的某一 ONU净荷为空时， 生成一个在净荷区插入空 闲帧的上行数据流， 并在 OLT30规定的数据发送时间到达时发送给 OLT30。
所述测距响应消息在 OTN设备 34中传输的时延可以在构建好 OTN设备 34 后测试得到， 其数值主要由 OTN设备 34中光纤的长度和特性决定。
完成任一 ONU38的注册步骤具体为： 提取 OLT发送给 ONU的下行数据流 中的带宽授权信息； 转发 OLT30定期发送给各 ONU38的序列号 （ Sequence Number, SN )请求； 緩存其中一 ONU38响应所述序列号请求返回给 OLT30的 序列号， 并当再次接收到 OLT30发送的序列号请求时， 根据所述带宽授权信息 发送所述序列号给 OLT30; 及转发 OLT30为该 ONU38分配的标识符，从而完成 该 ONU的注册。
所述 ONU38被激活后， 中继装置 32转发 OLT30发送的下行数据流到所述 ONU38, 提取并緩存 OLT30发送的上行带宽授权信息（也称为带宽地图）。 所 述上行带宽授权信息用于指示多个 ONU38发送上行数据流的开始和结束时间 或者指示多个 ONU38发送上行数据流的开始时间和时长， 保证多个 ONU38发 送上行数据流的时隙互不重叠， 也就是， 使得多个 ONU38通过时分复用共享 同一传输信道。
中继装置 32还从每一 ONU38传送的上行数据流中提取出开销， 从提取出 开销的所述上行数据流中解映射出每一 ONU净荷， 并分别进行緩存。
中继装置 32还根据 OLT30发送的最新的带宽授权信息重组每一 ONU净荷， 插入对应的开销生成新的上行数据流，并在 OLT30规定的数据发送时间到达时 发送给 OLT30。
本发明的技术方案可以应用在 GPON、 EPON、 BPON等协议下的 PON系统 中， 所述数据流在不同的 PON协议中可以为帧、 包等数据格式， 所述数据流包 括任何格式的语音、 视频、 多媒体内容等数据。
本发明的技术方案在现有 PON拉远系统 300中增加中继装置 32， 突破 PON 协议定义的 OLT30的最大逻辑距离的限制，在不更改任何现有 PON协议和 OLT 设备的情况下， 实现更长距离的 PON拉远。
如图 4所示， 为图 3中的中继装置 32的功能框图。 所述中继装置 32包括处理 模块 322、开销提取模块 324、解封装模块 325、緩存器 326、数据流再生模块 328、 发送模块 330、 接收模块 332和带宽地图提取模块 334。
在激活 ONU的过程中：
带宽地图提取模块 334提取 OLT30发送给 ONU38的下行数据流中的带宽授 权信息， 并发送给处理模块 322存储到緩存器 326中。
处理模块 322将其中一 ONU38响应 OLT30发送的序列号请求返回给 OLT30 的序列号存储到緩存器 326中， 并当再次接收到 OLT30发送的序列号请求时， 根据所述带宽授权信息将所述序列号发送给 OLT30。
处理模块 322还接收所述 ONU38响应测距请求返回的测距响应消息， 将接 收到所述测距响应消息的时间减去所述测距响应消息在 OTN设备中传输的时 延， 生成新的测距响应消息， 并当再次接收到 OLT发送的测距请求时， 将所述 新的测距响应消发送给 OLT。
在上行数据传输方向 （即数据从 ONU38传输到 OLT30 ) ：
提取模块 324从每一 ONU发送的上行数据流中提取出开销， 并送给处理模 块 322存储到緩存器 326中。 所述开销包括最小的物理层开销 （Phisical Layer Overload upstream, PLOu ) 、 上行物理层 OAM ( Phisical Layer OAM upstream, PLOAMu ) 、 上行功率电平序列 ( Power Levelling Sequence upstream, PLSu ) 和上行动态带宽请求 ( Dynamic Bandwidth Report upstream, DBRu ) 中的一个 或多个类型的开销信息。
解封装模块 325从提取出开销的上行数据流中解映射出净荷， 并送给处理 模块 322存储到緩存器 326中。
数据流再生模块 328根据 OLT30发送的最新的带宽授权信息重组緩存器 326中存储的净荷， 插入对应的开销生成新的上行数据流， 并在 OLT30规定的 数据发送时间到达时通过发送模块 330发送给 OLT30。 当緩存器 326中存储的任 一 ONU净荷为空时 , 数据流再生模块 328生成一个在净荷区插入空闲帧的上行 数据流， 并在 OLT30规定的数据发送时间到达时发送给 OLT30。
緩存器 326用于存储 OLT30发送的带宽授权信息以及每一 ONU发送的开销 和净荷，并将存储的每一 ONU净荷的状态上报给处理模块 322。其中，每一 ONU 净荷的状态包括该 ONU净荷的字节数。
在下行数据传输方向 （即数据从 OLT30传输到各 ONU38 ) ：
接收模块 332接收 OLT30发送的下行数据流， 并将所述下行数据流发送给 带宽地图提取模块 334。
带宽地图提取模块 334从所述下行数据流中提取出 OLT30发送的带宽授权 信息， 并发送给处理模块 322存储到緩存器 326中。
本发明实施例的中继装置 32,对 ONU38发送给 OLT30的上行数据流进行重 组， 使得突破 PON协议定义的 OLT30的最大逻辑距离的限制， 在不更改任何现 有 PON协议和 OLT设备的情况下， 实现更长距离的 PON拉远。
如图 5所示， 为图 3中的中继装置 32在 ONU激活过程中的操作流程图， 下 面以 GPON协议中 ONU激活过程为例说明所述操作流程。 提取 OLT30发送给 ONU38的下行数据流中的带宽授权信息， 并进行存储。 转发 OLT30定期发送给各 ONU38的上行开销（ upstream— overhead )和序列 号请求， 所述上行开销规定了各 ONU38的发射光功率、 前导码字节数、 预先 分配的均衡时延值 Td等配置参数。
当其中一 ONU38接收到所述上行开销和序列号请求后， 根据所述上行开 销中的配置参数， 向 OLT30发送该 ONU38的序列号。 该 ONU38可以是新加入 GPON系统的 ONU或者是重新开机的 ONU。 在 GPON系统中， ONU38通过上行 数据帧中的 PLO AM字段传输其序列号， 用 P10AMu_SN表示 PLOAM字段中传 输的序列号。
由于 OLT30接收所述 ONU38的序列号的响应时间段 T1是依据 PON协议定 义的 OLT30与所述 ONU38之间的最大逻辑距离（例如 GPON协议中为 60km )设 计的， 因此， 当 OLT30与所述 ONU38之间的实际距离 （例如 100KM ) 超过所 述最大逻辑距离时， OLT30在所述响应时间段 T1内将接收不到所述 ONU38返 回的序列号。 列号， 并进行存储。
当中继装置 32再次收到 OLT30发送的序列号请求时， 将存储的该 ONU38 的序列号插入上行数据帧的 PLOAM字段中， 根据存储的带宽授权信息将插入 所述序列号的上行数据帧发送给 OLT30。
当 OLT30收到一个新的序列号时， 对该序列号进行判断， 如果该序列号合 法， 则确认一个新的 ONU38请求被激活， OLT30则为该 ONU38分配标识符 ( Assign_ONUID ) , 并将所述标识符插入下行数据帧的开销字段发送给中继 装置 32， 中继装置 32将包含所述标识符的下行数据帧转发给对应的 ONU38。
OLT30为该 ONU38分配标识符后的一个预设时间段 T2内， 开始对该 ONU38进行测距。 GPON系统中， 预设时间段 T2至少为 750us， 原因是测距期 间需要中断运行中的 ONU38的数据收发。 ONU38在此期间需要緩存接收的数 据， 为了避免 ONU38接收的数据溢出， ONU38可以在预设时间段 T2内将部分 数据发送给 OLT30。
OLT30通过中继装置 32转发一个测距请求给该 ONU38， 该 ONU38接收到 所述测距请求后， 向 OLT30返回一个测距响应消息。 由于 OLT30的测距窗口 T3 (即一个预设时间段 Τ3 )是依据 GPON协议定义 的 OLT30与 ONU38之间的最大逻辑距离 （即 60km )设计的， 因此， 当 OLT30 与 ONU38之间的实际距离超过 60km时， OLT30在所述测距窗口 T3内将接收不 到所述测距响应消息。
当 OLT30在一个测距窗口 T3内未收到所述测距响应消息时，即认为测距失 败， 并至少等待一个所述预设时间段 T2后再向该 ONU38发送一次测距请求， 如果在所述测距窗口 T3内仍然收不到该 ONU38返回的测距响应消息， 则认为 该 ONU38失效， 并删除该 ONU的标识符。
为此， 中继装置 32提取出该 ONU38发送的上行数据帧中的测距响应消息， 将接收到所述上行数据帧的时间减去所述上行数据帧在 OTN设备 34中传输的 时延， 生成新的测距响应消息， 并当中继装置 32再次从 OLT30发送的下行数据 帧中提取到测距请求时， 将所述新的测距响应消息发送给 OLT30。
OLT30根据所述测距响应消息的到达时间，计算出该 ONU38的环路延迟时 间（称为均衡环路延时值 Teqd )， 并根据该环路延迟时间 Teqd计算出该 ONU38 的均衡时延值 Td, 使所有 ONU38在插入各自的均衡时延值 Td后的环路延迟时 间 Teqd都相等。 该环路延迟时间 Teqd是指信号从 OLT30发送到 ONU38后再返 回到 OLT30所需的时间， 也包含 ONU38对信号的处理时间。
中继装置 32转发所述均衡时延值 Td给该 ONU38， 该 ONU38接收到所述均 衡时延值 Td后， 向 OLT32返回一个应答消息 （ Ploam— ACK )表明自己已收到 所述均衡时延值 Td。
OLT30从中继装置 32转发的上行数据帧中提取到所述 ONU38返回的应答 消息后， 测距完成且所述 ONU38被激活。 当所述 ONU38被激活后， OLT30通 过中继装置 32与该 ONU38进行正常的数据收发。
如图 6所示， 为图 3中的 OLT30与 ONU38进行数据收发的流程图。 按照 GPON协议的规定， 当 OLT30发送一幅新的带宽地图给 ONU38时， ONU38必须 在协议规定的数据发送时间段 T4结束时，按照新的带宽地图发送上行数据帧给 OLT30。 GPON协议中， 数据发送时间段 T4为 125us。
由于所述数据发送时间段 T4是依据 GPON协议定义的 OLT30与 ONU38之 间的最大逻辑距离 （即 60km )设计的， 因此， 当 OLT30与 ONU38的实际距离 超过 60km时， OLT30在所述数据发送时间段 T4内将接收不到该 ONU38按照新 的带宽地图发送的上行数据帧，此时 OLT30会认为该 ONU38掉线，从而中断与 该 ONU38的数据收发。
为此， 中继装置 32在转发 OLT30发送的下行数据帧时， 从所述下行数据帧 中提取出带宽地图， 并进行存储。
OLT30可为每个 ONU38分配一个或多个传输容器（ Transmission Container,
T-CONT ) , 用于收发数据帧， 并用 Alloc— ID来标识。 中继装置 32还从每一
T-CONT的上行数据帧中提取出开销， 并从提取出开销的上行数据帧中解映射 出净荷， 并分别进行存储。 所述开销包括 PLOu、 PLOAMu、 PLSu和 DBRu中 的一个或多个类型的开销信息。
当协议规定的数据发送时间段 T4到达时，中继装置 32根据 OLT30发送的最 新带宽地图重组緩存的每一 T-CONT净荷， 插入对应的开销生成新的上行数据 帧， 并发送给 OLT30。
当中继装置 32中存储的任一 T-CONT净荷为空时， 生成一个在净荷区插入 空闲帧的上行数据流， 并在 OLT30规定的数据发送时间段 T4结束时发送给 OLT30。
中继装置 32在 GPON协议规定的数据发送时间段 T4结束前，还根据当前每 一 T-CONT緩冲区的大小与 DBRu中的带宽需求计算新的带宽需求， 并将所述 新的带宽需求更新到 DBRu中。 计算所述新的带宽需求是因为中继装置 32接收 到的各 T-CONT的带宽需求， 不能反映当前中继装置 32中各 T-CONT緩冲区的 大小。 为了避免中继装置 32中任一 T-CONT緩冲区溢出， 需要依据中继装置 32 中各 T-CONT緩冲区的大小重新计算 DBRu中的带宽需求， 例如取中继装置 32 中该 T-CONT緩沖区的大小与 DBRu中的带宽需求中的最大值作为所述新的带 宽需求。 OLT30根据所述新的带宽需求生成带宽授权信息。
以上所述， 仅为本发明较佳的具体实施方式，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、 一种实现无源光网络拉远的方法， 其特征在于， 所述方法包括： 提取 ONU发送给 OLT 的上行数据流中的开销， 解映射出该上行数据流中 的净荷， 并存储到緩存器； 及
提取 OLT发送给 ONU的下行数据流中的带宽授权信息；
根据所述带宽授权信息重组存储的净荷，插入对应的开销生成新的上行数 据流发送给 OLT。
2、 如权利要求 1所述的方法， 其特征在于， 提取 ONU发送给 OLT的上行数 据流中的开销之前还包括：
提取 OLT发送给 ONU的下行数据流中的带宽授权信息；
转发 OLT定期发送给 ONU的序列号请求；
緩存 ONU响应所述序列号请求返回的序列号，并当再次接收到 OLT发送的 序列号请求时， 根据所述带宽授权信息发送所述序列号给 OLT ； 及
转发 OLT为 ONU分配的标识符。
3、 如权利要求 2所述的方法， 其特征在于， 转发 OLT为 ONU分配的标识符 之后还包括：
转发 OLT发送给 ONU的测距请求；
接收 ONU响应所述测距请求返回的测距响应消息；
将接收到所述测距响应消息的时间减去所述测距响应消息在 OTN设备中 传输的时延 ， 生成新的测距响应消息发送给 OLT;
向 ONU转发， OLT根据所述测距响应消息的到达时间计算出的均衡时延值； 及
转发， ONU接收到所述均衡时延值后向 OLT返回的应答消息， 从而激活 ONU 。
4、 如权利要求 1所述的方法， 其特征在于， 还包括： 在所述緩存器中为所 述 ONU的每一 T-CONT分配 T-CONT緩冲区， 根据 T-CONT緩冲区的大小和所 述开销中的带宽需求计算新的带宽需求，并将所述新的带宽需求插入所述开销 中 。
5、 如权利要求 4所述的方法， 其特征在于， 计算所述新的带宽需求为， 取 T-CONT緩冲区的大小与所述开销中的带宽需求中的最大值作为所述新的带 宽需求。
6、 一种实现无源光网络拉远的系统， 其特征在于， 所述系统包括 OLT、 中继装置和至少一个 ONU;
OLT经由中继装置向 ONU发送含有带宽授权信息的下行数据流；
所述 ONU从所述下行数据流中获取所述带宽授权信息， 根据所述带宽授 权信息发送上行数据流；
中继装置提取 ONU发送给 OLT的上行数据流中的开销，解映射出该上行数 据流中的净荷， 并进行存储； 提取 OLT发送给 ONU的下行数据流中的带宽授权 信息； 根据所述带宽授权信息重组存储的净荷， 插入对应的开销生成新的上行 数据流发送给 OLT。
7、 如权利要求 6所述的系统， 其特征在于， 中继装置提取 ONU发送给 OLT 的上行数据流中的开销之前还执行下列步骤：
提取 OLT发送给 ONU的下行数据流中的带宽授权信息；
转发 OLT定期发送给 ONU的序列号请求；
缓存 ONU响应所述序列号请求返回的序列号，并当再次接收到 OLT发送的 序列号请求时， 根据所述带宽授权信息发送所述序列号给 OLT; 及
转发 OLT为 ONU分配的标识符。
8、 如权利要求 7所述的系统， 其特征在于， 中继装置转发 OLT为 ONU分配 的标识符之后还执行下列步骤：
转发 OLT发送给 ONU的测距请求；
接收 ONU响应所述测距请求返回的测距响应消息；
将接收到所述测距响应消息的时间减去所述测距响应消息在 OTN设备中 传输的时延， 生成新的测距响应消息发送给 OLT；
向 ONU转发， OLT根据所述测距响应消息的到达时间计算出的均衡时延值； 及
转发， ONU接收到所述均衡时延值后向 OLT返回的应答消息， 从而激活
9、 如权利要求 6所述的系统， 其特征在于， 中继装置还为所述 ONU的每 一 T-CONT分配 T-CONT緩冲区，根据 T-CONT緩冲区的大小和所述开销中的带 宽需求计算新的带宽需求， 并将所述新的带宽需求插入所述开销中。
10、 如权利要求 9所述的系统， 其特征在于， 中继装置计算所述新的带宽 需求为， 取 T-CONT緩冲区的大小与所述开销中的带宽需求中的最大值作为所 述新的带宽需求。
11、 一种实现无源光网络拉远的中继装置， 其特征在于， 所述中继装置包 括： 处理模块、 开销提取模块、 解封装模块、 緩存器、 数据流再生模块、 发送 模块、 接收模块和带宽地图提取模块；
接收模块接收 OLT发送给 ONU的下行数据流；
带宽地图提取模块从所述下行数据流中提取出带宽授权信息；
开销提取模块从 ONU发送给 OLT的上行数据流中提取出开销，并送给处理 模块存储到緩存器中；
解封装模块从提取出开销的上行数据流中解映射出净荷，并送给处理模块 存储到緩存器；
数据流再生模块根据所述带宽授权信息重组緩存器中存储的净荷，插入对 应的开销生成新的上行数据流， 并通过发送模块发送给 OLT。
12、 如权利要求 11所述的中继装置， 其特征在于， 处理模块还执行下列步 骤：
提取 OLT发送给 ONU的下行数据流中的带宽授权信息；
转发 OLT定期发送给 ONU的序列号请求；
緩存 ONU响应所述序列号请求返回的序列号，并当再次接收到 OLT发送的 序列号请求时， 根据所述带宽授权信息发送所述序列号给 OLT; 及
转发 OLT为 ONU分配的标识符。
13、 如权利要求 12所述的中继装置， 其特征在于， 处理模块还执行下列步 骤：
转发 OLT发送给 ONU的测距请求；
接收 ONU响应所述测距请求返回的测距响应消息；
将接收到所述测距响应消息的时间减去所述测距响应消息在 OTN设备中 传输的时延， 生成新的测距响应消息发送给 OLT；
向 ONU转发， OLT根据所述测距响应消息的到达时间计算出的均衡时延值； 及
转发， ONU接收到所述均衡时延值后向 OLT返回的应答消息， 从而激活
14、 如权利要求 11所述的系统， 其特征在于， 处理模块还在还存器中为所 述 ONU的每一 T-CONT分配 T-CONT緩冲区， 根据 T-CONT緩冲区的大小和所 述开销中的带宽需求计算新的带宽需求，并将所述新的带宽需求插入所述开销 中。
15、 如权利要求 14所述的系统， 其特征在于， 处理模块计算所述新的带宽 需求为， 取 T-CONT緩冲区的大小与所述开销中的带宽需求中的最大值作为所 述新的带宽需求。
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