WO2021008224A1 - 一种降低无源光网络上行时延的方法及相关设备 - Google Patents

一种降低无源光网络上行时延的方法及相关设备 Download PDF

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Publication number
WO2021008224A1
WO2021008224A1 PCT/CN2020/090935 CN2020090935W WO2021008224A1 WO 2021008224 A1 WO2021008224 A1 WO 2021008224A1 CN 2020090935 W CN2020090935 W CN 2020090935W WO 2021008224 A1 WO2021008224 A1 WO 2021008224A1
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channel
onu
wavelength channel
extended
basic
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PCT/CN2020/090935
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English (en)
French (fr)
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马焕南
卢金树
张伟良
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中兴通讯股份有限公司
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Priority to US17/627,621 priority Critical patent/US20220264203A1/en
Priority to JP2022501000A priority patent/JP2022540600A/ja
Priority to EP20839819.8A priority patent/EP3985893A4/en
Publication of WO2021008224A1 publication Critical patent/WO2021008224A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0254—Optical medium access
    • H04J14/0256—Optical medium access at the optical channel layer
    • 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
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0282—WDM tree architectures
    • 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
    • H04Q11/0005—Switch and router aspects
    • 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
    • H04Q2011/0064—Arbitration, scheduling or medium access control aspects
    • 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
    • H04Q2011/0086—Network resource allocation, dimensioning or optimisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2213/00—Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/1301—Optical transmission, optical switches

Definitions

  • the embodiments of the present application relate to but are not limited to passive optical network (PON, Passive Optical Network) technology, and more specifically relate to a method and related equipment for reducing the uplink delay of a passive optical network.
  • PON passive optical network
  • Passive Optical Network Passive Optical Network
  • FIG. 1 The traditional network architecture of passive optical network is shown in Figure 1. There is only one wavelength channel for the uplink and downlink between OLT (Optical Line Terminal) and ONU (Optical Network Unit, optical network unit).
  • OLT Optical Line Terminal
  • ONU Optical Network Unit, optical network unit
  • Passive optical networks are currently widely used in FTTH (Fibre To The Home). With the development of mobile networks, there is a need for passive optical networks for mobile fronthaul, mobile backhaul, sensor networks, and V2X (Vehicle to Everything) bearer technology. It is too expensive to establish an independent ODN (Optical Distribution Network) for the mobile bearer alone, and it is necessary to consider implementing support for the mobile bearer on the basis of inheriting and compatible with the existing FTTH passive optical network.
  • ODN Optical Distribution Network
  • the transmission delay requirements of mobile networks are very strict. For example, the transmission delay carried by 5G (Fifth Generation Mobile Communication Network) is 100us. If the passive optical network is used as a mobile bearer technology, the transmission delay needs to be improved. problem.
  • the traditional base station is divided into a remote unit (RU) and a central unit (CU).
  • PON can be used as a good system and technology for connecting RU and CU. Because PON can reduce fiber deployment.
  • the total delay (T1) between CU and UE (user equipment) is required to be less than 10ms, where Including the propagation delay (T2) between the CU and the RU, and the processing delay of each device, the transmission delay between the CU and the RU is less than 250 us.
  • the overall delay requirement is less than 4ms.
  • the transmission delay between CU and RU should be less than 100us.
  • the optical distribution network and registration mechanism of the passive optical network that meets the low-latency requirements is quite different from the traditional FTTH passive optical network. It is necessary to carry both low-latency services and traditional FTTH in the same passive optical network. Business needs to resolve the contradiction between the two.
  • an embodiment of the present application provides an optical line terminal OLT, including: a basic wavelength channel unit and a corresponding extended wavelength channel unit; the basic wavelength channel unit is used to support the basic wavelength channel, and the The optical network unit ONU discovery and ranging is realized on the channel; it is also used to establish the first ONU management and control channel OMCC channel with the ONU on the basic wavelength channel.
  • the ONU When the ONU supports extended wavelength channels and is configured as low In the delay mode, the ONU is notified through the first OMCC channel to switch from the basic wavelength channel to the extended wavelength channel; the extended wavelength channel unit is used to support one or more extended wavelength channels, A second OMCC channel is established with the ONU to perform low-latency service transmission; the ONU supports switching between the basic wavelength channel and the extended wavelength channel.
  • An embodiment of the application also provides an ONU of an optical network unit, including: a media access control MAC module and a corresponding optical module; the optical module includes two or more sub-optical modules, and the sub-optical modules correspond to different Wavelength; the MAC module is connected to the first sub-optical module to support a basic wavelength channel, and the MAC module is connected to other sub-optical modules to support one or more extended wavelength channels; or, the optical module is a wavelength tunable optical module, The wavelength tunable optical module corresponds to different wavelengths; the MAC module is connected to the optical module to support switching between a basic wavelength channel and an extended wavelength channel.
  • An embodiment of the present application also provides a passive optical network PON system, including: an optical line terminal OLT, an optical distribution network ODN, and an optical network unit ONU; the OLT supports a basic wavelength channel and one or more corresponding extended wavelength channels; The ONU supports switching between a basic wavelength channel and an extended wavelength channel; the OLT is connected to the ONU through the ODN, and the ODN supports carrying basic wavelength channel signals and extended wavelength channel signals; The wavelength channel realizes the discovery and ranging of the optical network unit ONU; it is also used to establish the first ONU management and control channel OMCC channel with the ONU on the basic wavelength channel, when the ONU supports extended wavelength channels and is configured as In low-latency mode, notify the ONU to switch from the basic wavelength channel to the extended wavelength channel through the first OMCC channel; establish a second OMCC channel with the ONU on the extended wavelength channel to transmit low-latency services .
  • a passive optical network PON system including: an optical line terminal OLT, an optical distribution network ODN, and an optical network unit
  • the embodiment of the present application also provides a method for reducing the upstream delay of a passive optical network, which includes: an optical line terminal OLT realizes the discovery and ranging of an ONU of an optical network unit on a basic wavelength channel;
  • the ONU establishes the first ONU management and control channel OMCC channel, and when the ONU supports extended wavelength channels and is configured in low latency mode, the ONU is notified through the first OMCC channel to switch from the basic wavelength channel to Extended wavelength channel; establishing a second OMCC channel on the extended wavelength channel with the ONU for low-latency service transmission;
  • the OLT supports a basic wavelength channel and one or more extended wavelength channels, and the ONU supports a basic wavelength Switch between channels and extended wavelength channels.
  • the embodiment of the present application also provides a method for reducing the uplink delay of a passive optical network, which includes: an optical network unit ONU registers with an optical line terminal OLT on a basic wavelength channel; and establishes a second OLT with the OLT on the basic wavelength channel.
  • An OMCC channel receiving the notification of the OLT through the first OMCC channel, switching from the basic wavelength channel to an extended wavelength channel; establishing a second OMCC channel with the OLT on the extended wavelength channel for low latency Transmission of business.
  • Figure 1 is a schematic diagram of the traditional network architecture of a passive optical network
  • Figure 2 is a schematic diagram of an existing PON system supporting mobile fronthaul application scenarios
  • FIG. 3 is a schematic structural diagram of an optical line terminal OLT according to an embodiment of the application.
  • FIG. 4 is a schematic structural diagram of an ONU of an optical network unit provided by an embodiment of this application.
  • FIG. 5 is a schematic structural diagram of an ONU of an optical network unit provided by an embodiment of the application.
  • FIG. 6 is a schematic structural diagram of a passive optical network PON system provided by an embodiment of the application.
  • FIG. 7 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of this application.
  • FIG. 8 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of this application.
  • FIG. 9 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of this application.
  • FIG. 10 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of this application.
  • FIG. 11 is a schematic flowchart of a method for reducing uplink delay of a passive optical network according to an embodiment of the application
  • FIG. 12 is a schematic flowchart of a method for reducing the uplink delay of a passive optical network according to another embodiment of the application.
  • Transmission delays in passive optical networks include: optical transmission delays, bandwidth allocation delays, and delays caused by the discovery of ONU opening quiet windows.
  • the optical transmission delay is related to the fiber distance and wavelength, and the transmission delay of the specific fiber distance and wavelength is fixed.
  • the transmission time of 1310nm wavelength signal in 20KM fiber is about 100us, which can reduce the optical transmission by shortening the fiber distance Time, such as limiting 20KM to 10KM (too short fiber distance will limit the range of users that a single OLT can access).
  • the bandwidth allocation delay is related to the allocation algorithm and the allocation cycle. If a fixed bandwidth allocation algorithm is used, the response delay of the allocation algorithm can be eliminated, but the bandwidth cannot be effectively statistically multiplexed. Using a smaller allocation cycle can reduce the time slice interval and shorten the time slice scheduling delay. However, because the burst overhead of each time slice is fixed, it is necessary to ensure reasonable bandwidth utilization. To reduce the bandwidth allocation cycle, the number of ONUs under the OLT needs to be constructed. For example, the DBA (Dynamic Bandwidth Assignment, dynamic bandwidth allocation) allocation cycle is changed to 125us. 1/4 of the number of ONUs can be controlled within 8.
  • DBA Dynamic Bandwidth Assignment
  • the open quiet window is used for the OLT to discover and range the ONU, which is an overhead caused by the initialization of the channel connection between the OLT and the ONU.
  • a quiet window of 200 microseconds must be opened. During this period, the ONU that works normally cannot communicate with the OLT.
  • the OLT needs to periodically open a quiet window to discover ONUs.
  • this quiet window is used for ONUs to be registered and activated to send upstream signals, and other normally working ONUs that have completed registration and activation cannot send upstream signals in the quiet window, then if the normally working ONU happens to have upstream data at the beginning of the quiet window To send, you must wait for the end of the quiet window to have a chance to send uplink data. In this case, the uplink data sent by a normally working ONU may cause a maximum delay of 200 microseconds. If the ONU information and fiber distance are known in advance, the discovery and testing process can be removed to eliminate the delay caused by the window.
  • passive optical networks can meet the requirements of low latency for mobile bearers.
  • the traditional FTTH service hopes to have a large splitting ratio, a large access range, high bandwidth statistical multiplexing efficiency, and convenient opening.
  • the optical distribution network and registration mechanism of the passive optical network that meets the low-latency requirements is quite different from the traditional FTTH passive optical network. It is necessary to carry both low-latency services and traditional FTTH services in the same passive optical network. , The contradiction between the two needs to be resolved.
  • FIG. 3 is a schematic structural diagram of an optical line terminal OLT according to an embodiment of the application. As shown in Figure 3, the OLT includes:
  • the basic wavelength channel unit is used to support a basic wavelength channel, and realize the discovery and ranging of an optical network unit ONU on the basic wavelength channel; and is also used to establish a first ONU with the ONU on the basic wavelength channel
  • the management and control channel OMCC channel when the ONU supports extended wavelength channels and is configured in a low-latency mode, notify the ONU to switch from the basic wavelength channel to the corresponding extended wavelength channel through the first OMCC channel;
  • the extended wavelength channel unit is configured to support one or more extended wavelength channels, and establish a second OMCC channel with the ONU on the extended wavelength channel to perform low-latency service transmission;
  • the ONU supports switching between the basic wavelength channel and the extended wavelength channel.
  • the OLT further includes: a demultiplexer
  • the basic wavelength channel unit includes: a basic channel media access control MAC module and a corresponding basic channel optical module;
  • the extended wavelength channel unit includes: one or more extended channel MAC modules and corresponding one or more extended channel optical modules, one extended channel MAC module corresponds to one extended channel optical module;
  • the basic channel optical module is connected to the demultiplexer to support the basic wavelength channel; one or more extended channel optical modules are connected to the demultiplexer to support one or more Expand the wavelength channel.
  • a fixed bandwidth or a small bandwidth allocation period is used on the extended wavelength channel.
  • the extended wavelength channel unit is further configured to calculate the round-trip time of the corresponding extended wavelength channel on the extended wavelength channel according to the ranging result of the basic wavelength channel and the wavelength characteristics of the two channels, and adjust the ONU's Equalization delay value EqD.
  • FIG. 4 is a schematic structural diagram of an ONU of an optical network unit provided by an embodiment of the application. As shown in Figure 4, the ONU includes:
  • the optical module includes two or more sub-optical modules, and the sub-optical modules respectively correspond to different wavelengths; the MAC module is connected to the first sub-optical module to support basic wavelength channels, and the MAC module is connected to other sub-optical modules.
  • the connection supports one or more extended wavelength channels.
  • FIG. 5 is a schematic structural diagram of an ONU of an optical network unit provided by an embodiment of the application. As shown in Figure 5, the ONU includes:
  • the optical module is a wavelength tunable optical module, and the wavelength tunable optical module corresponds to different wavelengths; the MAC module is connected to the optical module to support switching between a basic wavelength channel and an extended wavelength channel.
  • FIG. 6 is a schematic structural diagram of a passive optical network PON system provided by an embodiment of the application. As shown in Figure 6, the PON system includes:
  • the OLT supports a basic wavelength channel and one or more extended wavelength channels; the ONU supports switching between a basic wavelength channel and an extended wavelength channel;
  • the OLT is connected to the ONU through the ODN, and the ODN supports carrying basic wavelength channel signals and extended wavelength channel signals;
  • the OLT is used to realize the discovery and ranging of the optical network unit ONU on the basic wavelength channel; it is also used to establish the first ONU management and control channel OMCC channel with the ONU on the basic wavelength channel.
  • the ONU supports extended wavelength channels and is configured in the low-latency mode, inform the ONU to switch from the basic wavelength channel to the extended wavelength channel through the first OMCC channel; establish a second wavelength channel with the ONU on the extended wavelength channel
  • the OMCC channel performs low-latency service transmission.
  • the OLT is also used to calculate the round trip time of the corresponding extended wavelength channel on the extended wavelength channel according to the ranging result of the basic wavelength channel and the wavelength characteristics of the two channels, and adjust the equalization delay value of the ONU EqD.
  • FIG. 7 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of the application. As shown in Figure 7, the PON system includes:
  • Optical line terminal OLT optical distribution network ODN and optical network unit ONU.
  • the OLT supports basic wavelength channels and extended wavelength channels. All ONU discovery and ranging and service transmission of ordinary ONUs are completed on the basic wavelength channel, and low-latency ONU services are transmitted on the extended wavelength channel.
  • the upstream and downstream of the OLT respectively support multiple channels of different wavelengths, one of which is the basic wavelength channel and one or more extended wavelength channels.
  • the grouping relationship between the basic wavelength channel and the extended wavelength channel is controlled through software configuration, that is, the basic wavelength channel Correspondence with extended wavelength channel.
  • ONUs are divided into ordinary ONUs and low-latency ONUs, and ordinary ONUs use basic wavelength channels to carry ordinary services.
  • the low-latency ONU supports switching between the basic wavelength channel and the extended wavelength channel, ONU discovery and ranging on the basic wavelength channel, and low-latency services on the extended wavelength channel.
  • the OLT supports a basic wavelength channel and a corresponding extended wavelength channel in the upstream and downstream respectively as an example; wherein the ONUs are all low-latency ONUs.
  • the low-latency ONU supports optical module receiving and sending wavelength switching or tuning, and the ONU can choose to work on the basic wavelength channel or the extended wavelength channel at different times.
  • ODN adopts power splitter to realize point-to-multipoint topological connection.
  • the basic wavelength channel independently completes the discovery and ranging of ordinary ONUs and service transmission, and the basic wavelength channel and the extended wavelength channel cooperate to realize the discovery and ranging of low-latency ONUs and low-latency service transmission.
  • ONU discovery and ranging are performed on the basic wavelength channel, the ranging result on the basic wavelength channel is synchronized to the extended wavelength channel, and the extended wavelength channel is calculated based on the basic wavelength channel ranging result and the wavelength characteristics of the two channels to calculate the corresponding extended wavelength
  • the round-trip time of the channel thus obtains the ranging of the ONU, and the extended wavelength channel does not perform the ONU discovery and ranging process to eliminate the time delay caused by the window.
  • a fixed bandwidth and a smaller bandwidth allocation period can be used on the extended wavelength channel to further reduce the delay.
  • the use of a fixed bandwidth and a smaller bandwidth allocation period on the extended wavelength channel will not affect the bandwidth of the ONU on the basic PON channel.
  • the basic wavelength channel can be compatible with common ONU access and common service bearer, and the number of ONUs on the basic wavelength channel will not affect the delay of ONUs on the extended wavelength channel.
  • the technical solution provided in the embodiments of the present application adopts a PON system that combines a basic wavelength channel and an extended wavelength channel to implement expansion and support for low-latency services on the basis of an ordinary PON network.
  • FIG. 8 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of this application.
  • the PON system includes: an optical line terminal OLT, an optical distribution network ODN, and an optical network unit ONU.
  • the upstream and downstream of the OLT respectively support two or more channels of different wavelengths.
  • Figure 8 shows that it supports two channels, that is, a common wavelength channel and a corresponding extended wavelength channel. This is only an example and not It constitutes a limitation to the embodiments of the present application. For example, it can also support more than two channels, such as one common wavelength channel and one or more corresponding extended wavelength channels.
  • ONU supports optical module receiving and transmitting wavelength switching or tuning.
  • ordinary ONUs and low-latency ONUs can be connected, and both ordinary ONUs and low-latency ONUs have only one MAC.
  • the low-latency ONU adopts wavelength switchable or wavelength tunable optical modules, or multiple independent optical modules corresponding to multiple extended wavelength channels,
  • an ONU can only select one wavelength channel to work at the same time.
  • the optical module supports multiple wavelengths, it only supports one wavelength at a time.
  • the optical module is controlled to work at a specific wavelength through a wavelength switch or a wavelength tuning mechanism.
  • the optical modules corresponding to the specified wavelength are in working state at the same time by controlling the switch of the optical module.
  • ODN can use a splitter to achieve point-to-multipoint topological connection.
  • one or more extended wavelength channels are added on the basis of the original PON architecture.
  • multiple channels correspond to multiple MAC (Media Access Control) modules.
  • One MAC module corresponds to the basic PON channel, and the other one or more MAC modules correspond to one or more extended wavelength channels.
  • the OLT can use multiple optical modules to cooperate with an external partial multiplexer to multiplex multiple channel signals into the same ODN, or multiple wavelength channels within the optical module.
  • the OLT includes: PON OLT basic channel MAC module 111, PON OLT extended channel MAC module 112, PON OLT basic channel optical module 121, PON OLT extended channel optical module 122; low latency ONU-1 includes : PON ONU MAC module and PON ONU wavelength tunable optical module.
  • Other ONUs can also be set as ordinary ONUs or low-latency ONUs.
  • 122 can have multiple corresponding to different wavelengths, and the three parts 121, 122, and splitter 13 can be integrated into one optical module entity (built-in splitter, supporting multiple wavelength channels). When there are multiple corresponding 122, the PON ONU wavelength tunable optical module also needs to support multiple wavelengths.
  • the low-latency ONU uses different wavelengths in the registration phase and the working phase, corresponding to the basic wavelength channel and the extended wavelength channel respectively.
  • the low-latency ONU works on the basic wavelength channel in the offline state and during the registration process.
  • the OLT determines whether to switch the ONU to the extended wavelength channel according to the ONU capabilities and OLT configuration. The discovery process is no longer carried out in the extended wavelength channel, but the work is performed according to the ONU identification information and the ranging result obtained in the basic wavelength channel.
  • the ranging result on the basic wavelength channel is synchronized to the extended wavelength channel, and the extended wavelength channel calculates the round trip time of the corresponding extended wavelength channel based on the basic wavelength channel ranging result and the wavelength characteristics of the two channels to obtain the ONU ranging on the extended channel. Since the discovery and ranging process is not performed on the extended wavelength channel, the delay introduced by the discovery and ranging window can be avoided.
  • ordinary ONU registration and ranging and ordinary service transmission can be performed in the basic wavelength channel; the low-latency ONU can also be compatible with ordinary ONUs for ordinary service transmission.
  • PON Gigabit-Capable PON, Gigabit Passive Optical Network
  • XGPON enhanced passive optical network
  • XGSPON enhanced next-generation passive optical network
  • EPON Error Network Passive Optical Network
  • the GPON standard is used as an example to illustrate that the basic wavelength channel and the extended wavelength channel cooperate to realize the specific registration and service transmission process of the low-latency ONU, including:
  • the OLT periodically opens a quiet window on the basic wavelength channel and sends SN (Serial Number) requests;
  • the ONU waits for the quiet window opened by the OLT in the basic wavelength channel and captures the SN request, and then competes to send SN in the quiet window;
  • the OLT obtains the SN of the new ONU on the basic wavelength channel
  • the OLT allocates an ONU-ID identifier to the ONU on the basic wavelength channel, continues to open the ranging window, and sends a ranging request to the ONU;
  • ONU sends a ranging response on the basic wavelength channel
  • the OLT obtains the ranging response, calculates the ranging result of the basic wavelength channel and sends it to the ONU;
  • OMCC channel is established between OLT and ONU;
  • OLT obtains the ability of ONU to support extended wavelength channels
  • the OLT decides whether to switch the ONU to the extended wavelength channel according to the ONU's ability to support the extended wavelength channel and the configuration of the ONU on the OLT. If switching is not required, it will work as a normal ONU on the basic wavelength channel. To switch to the extended wavelength channel, continue the following steps:
  • the OLT may send a message to the ONU to obtain whether to support the extended wavelength channel, and determine whether to support the extended wavelength channel according to the response message of the ONU.
  • the ONU can be configured to carry common services or low-latency services on the OLT.
  • the message for the OLT to query the ONU whether to support the extended wavelength channel can be a PLOAM ((Physical Layer Operation Administration and Maintenance, physical layer operation and maintenance management) message or an OMCI (Optical Network Unit Management Control Interface, ONU Management and Control Interface) message.
  • PLOAM Physical Layer Operation Administration and Maintenance, physical layer operation and maintenance management
  • OMCI Optical Network Unit Management Control Interface, ONU Management and Control Interface
  • the OLT synchronizes the ONU identification and ranging information from the basic wavelength channel to the corresponding extended wavelength channel;
  • the OLT notifies the ONU to switch the wavelength channel on the basic PON channel. After the ONU receives the switching command, it adjusts the receiving and sending wavelength of the optical module to the wavelength corresponding to the specified extended wavelength channel;
  • the OLT notifies the ONU to switch wavelengths, either by using OMCI (ONU Management and Control Interface) messages, or PLOAM (Physical Layer Operations, Administration and Maintenance) messages.
  • OMCI ONU Management and Control Interface
  • PLOAM Physical Layer Operations, Administration and Maintenance
  • the OLT performs EqD adjustment on the ONU switched to the extended wavelength channel on the extended wavelength channel;
  • the EqD (Equalization Delay) calculated by the basic wavelength channel is used as the initial value of the EqD of the extended channel, and then the extended wavelength channel is used later. Adjust according to the alignment of the ONU upstream information received by the OLT.
  • the OLT and ONU perform bandwidth allocation and service transmission after completing the OMCC chain establishment of the extended wavelength channel.
  • a fixed bandwidth and a smaller bandwidth allocation period can be used on the extended wavelength channel to further reduce the delay.
  • the use of a fixed bandwidth and a smaller bandwidth allocation period on the extended wavelength channel will not affect the bandwidth of the ONU on the basic PON channel.
  • the registration process of other PON technology standards is similar to the above-mentioned GPON process, except that there are differences in specific exchange messages.
  • PLOAM messages and OMCI messages are used for registration process interaction and control.
  • MPCP (Multi-Point Control Protocol) messages and OAM messages are used for registration interaction and control.
  • FIG. 9 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of the application.
  • the PON system includes: an optical line terminal OLT, an optical splitter splitter, and optical network units ONU-1, ONU-2, and ONU-3.
  • ONU-1 and ONU-2 correspond to ordinary FTTH services
  • ONU-3 corresponds to low-latency services
  • OLT PON MAC-1 corresponds to the basic wavelength channel
  • OLT PON MAC-2 corresponds to the extended wavelength channel. That is, ONU-1 and ONU-2 are ordinary ONUs, and ONU-3 is a low-latency ONU.
  • the OLT includes PON MAC-1 and MAC-2 and optical modules connected to PON MAC-1 and MAC-2 respectively.
  • the optical module has a built-in splitter and supports basic wavelength channels and extended wavelength channels.
  • MAC-2 does not enable the periodic windowing mechanism.
  • ONU-1 and ONU-2 register and perform service transmission according to the standard XGSPON standard process.
  • ONU-3 first discovers and registers on OLTPON MAC-1 and then switches to OLTPON MAC-1. 2 for business transfer.
  • the process from ONU-3 registration to the start of service delivery includes:
  • ONU-3 performs ONU discovery and registration on OLT PON MAC-1, including:
  • OLT regularly opens quiet windows on PON MAC-1 and sends SN requests;
  • ONU-3 waits for the SN request message sent by OLT PON MAC-1 in the basic wavelength channel using the downstream 1577nm/upstream 1270nm wavelength, and then competes to send the SN message in the quiet window;
  • the OLT obtains the SN of ONU-3 on PON MAC-1;
  • the OLT allocates ONU-ID to ONU-3 on PON MAC-1, continues to open the ranging window and sends a ranging request to the ONU;
  • ONU-3 sends a ranging response message on the basic wavelength channel
  • OLT PON MAC-1 obtains the ranging response message, calculates the ranging result of the basic PON channel and sends it to ONU-3;
  • OLT obtains ONU-3's ability to support extended wavelength channels
  • the OLT decides whether to switch the ONU to the extended wavelength channel according to the ONU-3 to support the extended wavelength channel and configure the ONU with a low-latency mode at the same time.
  • the OLT synchronizes the identification and ranging information of the ONU-3 from PON MAC-1 to PON MAC-2;
  • the OLT sends a message to ONU-3 on PON MAC-1 to notify the ONU to switch from the basic wavelength channel using the downstream 1577nm/upstream 1270nm to the extended wavelength channel using the downstream 1490nm/upstream 1310nm, and ONU-3 receives the switching command Then adjust the receiving and sending wavelength of the optical module to the downstream 1490nm/ upstream 1310nm wavelength;
  • the OLT performs EqD (Equalization Delay) adjustment on ONU-3 on PON MAC-2;
  • the ONU-3 upstream signal arrival time is monitored on the PON MAC-2, and if the deviation exceeds a certain threshold, the EqD is adjusted.
  • OLT PON MAC-2 and ONU-3 perform bandwidth allocation and service transmission after the extended wavelength channel completes the OMCC chain establishment.
  • a fixed bandwidth and a smaller bandwidth allocation period can be used on the extended wavelength channel to further reduce the delay.
  • the use of a fixed bandwidth and a smaller bandwidth allocation period on the extended channel will not affect the bandwidth of the ONU on the basic PON channel.
  • Fig. 10 is a schematic structural diagram of a passive optical network PON system provided by another embodiment of the application.
  • the PON system includes: an optical line terminal OLT, an optical splitter splitter, and optical network units ONU-1, ONU-2, and ONU-3.
  • the OLT includes MAC-1 and MAC-2, optical module-1 and optical module-2 connected to MAC-1 and MAC-2 respectively, and WM (wavelength module) connected to optical module-1 and optical module-2 respectively. division multiplexer, wavelength division multiplexer).
  • an optical module is connected to a MAC interface, and the MAC module works in XGSPON mode.
  • the optical module can have optical modules of different wavelengths, one of which uses a wavelength of 1577nm downstream and 1270nm upstream (corresponding to the standard XGSPON wavelength) for the basic wavelength channel , Others use TWDM-PON (Time and Wavelength Division Multiplexed Optical Network, Time Division Multiplexed Passive Optical Network) wavelength to extend the wavelength channel.
  • TWDM-PON Time and Wavelength Division Multiplexed Optical Network, Time Division Multiplexed Passive Optical Network
  • the PON port needs to support low-latency services, add a splitter multiplexer on the OLT side of the ODN network, and connect two or more OLT optical modules of different wavelengths to the same ODN through the splitter multiplexer. ), the common ONU and the low-latency ONU are connected to the splitter at the same time, and the low-latency ONU is opened for the low-latency service.
  • the number of ODN branches is sufficient but the bandwidth does not meet the requirements of new ONUs or bandwidth expansion, newly added OLT PON ports of different wavelengths are linked to the same ODN for capacity expansion.
  • ONU-1 and ONU-2 correspond to ordinary FTTH services
  • ONU-3 corresponds to low-latency services. That is, ONU-1 and ONU-2 are ordinary ONUs, and ONU-3 is a low-latency ONU.
  • OLT MAC-1 and optical module-1 correspond to the basic wavelength channel
  • OLT MAC-2 and optical module-2 correspond to the extended wavelength channel.
  • the working wavelength of optical module-1 is 1577nm downstream and 1270nm upstream
  • the working wavelength of optical module-2 is downstream 1596nm/upstream 1528nm.
  • MAC-2 does not enable the periodic windowing mechanism.
  • ONU-1 and ONU-2 register and perform service transmission according to the standard XGSPON standard process.
  • ONU-3 first discovers and registers on OLTPON MAC-1 and then switches to OLTPON MAC-1. 2 for business transfer.
  • the process from ONU-3 registration to the start of service delivery includes:
  • ONU-3 performs ONU discovery and registration on OLT PON MAC-1, including:
  • OLT regularly opens quiet windows on PON MAC-1 and sends SN requests;
  • ONU-3 waits for the SN request message sent by OLT PON MAC-1 in the basic wavelength channel using the downstream 1577nm/upstream 1270nm wavelength, and then competes to send the SN message in the quiet window;
  • the OLT obtains the SN of ONU-3 on PON MAC-1;
  • the OLT allocates ONU-ID to ONU-3 on PON MAC-1, continues to open the ranging window and sends a ranging request to the ONU;
  • ONU-3 sends a ranging response message on the basic wavelength channel
  • OLT PON MAC-1 obtains the ranging response message, calculates the ranging result of the basic wavelength channel and sends it to ONU-3;
  • OLT obtains ONU-3's ability to support extended wavelength channels
  • the OLT decides whether to switch the ONU to the extended wavelength channel according to the ONU-3 to support the extended wavelength channel and at the same time configures the ONU with a low delay mode in the OLT, and then continues the following steps:
  • the OLT synchronizes the identification and ranging information of the ONU-3 from PON MAC-1 to PON MAC-2;
  • the OLT sends a message to ONU-3 on PON MAC-1 to notify the ONU to switch from the basic wavelength channel using the downstream 1577nm/uplink 1270nm to the extended wavelength channel using the downstream 1596nm/uplink 1528nm, and ONU-3 receives the switching command Then adjust the receiving and sending wavelength of the optical module to the downstream 1596nm/upstream 1528nm;
  • OLT performs EqD adjustment on ONU-3 on PON MAC-2;
  • the ONU-3 upstream signal arrival time is monitored on the PON MAC-2, and if the deviation exceeds a certain threshold, the EqD is adjusted.
  • OLT PON MAC-2 and ONU-3 perform bandwidth allocation and service transmission after the extended wavelength channel completes the OMCC chain establishment.
  • a fixed bandwidth and a smaller bandwidth allocation period can be used on the extended wavelength channel to further reduce the delay.
  • the use of a fixed bandwidth and a smaller bandwidth allocation period on the extended channel will not affect the bandwidth of the ONU on the basic PON channel.
  • FIG. 11 is a schematic flowchart of a method for reducing the uplink delay of a passive optical network according to an embodiment of the application. As shown in Figure 11, the method includes:
  • Step 1101 the optical line terminal OLT realizes the discovery and ranging of the optical network unit ONU on the basic wavelength channel;
  • Step 1102 Establish a first ONU management and control channel OMCC channel with the ONU on the basic wavelength channel, and when the ONU supports extended wavelength channels and is configured in a low latency mode, notify via the first OMCC channel Switching the ONU from the basic wavelength channel to an extended wavelength channel;
  • Step 1103 Establish a second OMCC channel with the ONU on the extended wavelength channel to perform low-latency service transmission;
  • the OLT supports a basic wavelength channel and one or more extended wavelength channels
  • the ONU supports switching between a basic wavelength channel and an extended wavelength channel.
  • a fixed bandwidth or a small bandwidth allocation period is used on the extended wavelength channel.
  • the method also includes:
  • the OLT calculates the round trip time of the corresponding extended wavelength channel on the extended wavelength channel according to the ranging result of the basic wavelength channel and the wavelength characteristics of the two channels, and adjusts the equalization delay value EqD of the ONU.
  • FIG. 12 is a schematic flowchart of a method for reducing the uplink delay of a passive optical network according to another embodiment of the application. As shown in Figure 12, the method includes:
  • Step 1201 The ONU of the optical network unit registers with the optical line terminal OLT on the basic wavelength channel;
  • Step 1202 Establish a first OMCC channel with the OLT on the basic wavelength channel, receive a notification from the OLT through the first OMCC channel, and switch from the basic wavelength channel to an extended wavelength channel;
  • Step 1203 Establish a second OMCC channel with the OLT on the extended wavelength channel for low-latency service transmission.
  • Performance improvement Cancel the discovery and ranging window in the extended PON channel, and transmit low-latency services through the extended channel, which greatly reduces the delay;
  • Such software may be distributed on a computer-readable medium
  • the computer-readable medium may include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium).
  • the term computer storage medium includes volatile and non-volatile memory implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data).
  • Computer storage media include but are not limited to RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disk (DVD) or other optical disk storage, magnetic cassette, tape, magnetic disk storage or other magnetic storage device, or Any other medium used to store desired information and that can be accessed by a computer.
  • communication media usually contain computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as carrier waves or other transmission mechanisms, and may include any information delivery media .

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Abstract

本申请实施例公开了一种降低无源光网络上行时延的方法及相关设备，其中光线路终端OLT，包括：基础波长通道单元和对应的扩展波长通道单元；所述基础波长通道单元，用于支持基础波长通道，在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；所述扩展波长通道单元，用于支持一个或多个扩展波长通道，在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输。

Description

一种降低无源光网络上行时延的方法及相关设备
相关申请的交叉引用
本申请基于申请号为201910637087.6、申请日为2019年07月15日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此以引入方式并入本申请。
技术领域
本申请实施例涉及但不限于无源光网络(PON，Passive Optical Network)技术，更具体地涉及一种降低无源光网络上行时延的方法及相关设备。
背景技术
无源光网络传统网络架构如图1所示。OLT(Optical Line Terminal，光线路终端)和ONU(Optical Network Unit，光网络单元)之间的上下行分别只有一个波长通道。
无源光网络目前大量用于FTTH(光纤到户，Fibre To The Home)。随着移动网络的发展，存在无源光网络用于移动前传、移动回传、传感网络、V2X(Vehicle to Everything，车到一切)的承载技术的需求。单独为移动承载建立独立的ODN(Optical Distribution Network，光分配网络)代价太高，需要考虑在继承和兼容现有的FTTH的无源光网络的基础上实现对移动承载的支持。
移动网络的传输时延要求很严格，例如5G(第五代移动通信网络，Fifth Generation Mobile Communication Network)承载的传输时延为100us，无源光网络要作为移动承载技术，需改进传输时延相关问题。以移动前传应用场景为例，基于功能分离考虑，传统的基站分成一个远端设备remote unit(RU)和一个中心设备central unit(CU)，PON可以作为连接RU和CU很好的系统和技术，因为PON可以减少光纤部署。如图2所示，在LTE(Long Term Evolution，长期演进)及其演进系统中，要求CU和UE(用户设备，user equipment)之 间的总体时延(Total delay(T1))小于10ms，其中包括CU和RU之间的传输时延(Propagation delay(T2))，以及各设备的处理时延，CU和RU之间的传输时延低于250us。另一方面，在5G移动系统中，总体时延要求小于4ms，对eMBB(Enhanced Mobile Broadband，增强移动宽带)业务，CU和RU之间的传输时延要小于100us。
但是满足低时延要求的无源光网络的光分配网与注册机制和传统的FTTH无源光网络有较大差别，要在同一个无源光网络中同时承载低时延业务和传统的FTTH业务，需要解决两者之间的矛盾。
发明内容
有鉴于此，本申请实施例提供了一种光线路终端OLT，包括：基础波长通道单元和对应的扩展波长通道单元；所述基础波长通道单元，用于支持基础波长通道，在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；所述扩展波长通道单元，用于支持一个或多个扩展波长通道，在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；所述ONU支持基础波长通道和扩展波长通道的切换。
本申请实施例还提供了一种光网络单元ONU，包括：媒体访问控制MAC模块和对应的光模块；所述光模块包括两个或两个以上的子光模块，子光模块分别对应不同的波长；所述MAC模块与第一子光模块连接支持基础波长通道，所述MAC模块与其他子光模块连接支持一个或多个扩展波长通道；或者，所述光模块为波长可调光模块，所述波长可调光模块对应不同的波长；所述MAC模块与所述光模块连接支持基础波长通道和扩展波长通道的切换。
本申请实施例还提供了一种无源光网络PON系统，包括：光线路终端OLT、光分配网络ODN和光网络单元ONU；所述OLT支持基础波长通道和对应的一个或多个扩展波长通道；所述ONU支持基础波长通道和扩展波长通道的切换；所述OLT通过所述ODN连接所述ONU，所述ODN支持承载基础波长通道信号和扩展波长通道信号；所述OLT用于在所述基础波长通道上 实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输。
本申请实施例还提供了一种降低无源光网络上行时延的方法，包括：光线路终端OLT在基础波长通道上实现光网络单元ONU的发现和测距；在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；在所述扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；所述OLT支持基础波长通道和一个或多个扩展波长通道，所述ONU支持基础波长通道和扩展波长通道的切换。
本申请实施例还提供了一种降低无源光网络上行时延的方法，包括：光网络单元ONU在基础波长通道上向光线路终端OLT进行注册；在基础波长通道上与所述OLT建立第一OMCC通道，通过所述第一OMCC通道接收所述OLT的通知，从所述基础波长通道切换为扩展波长通道；在所述扩展波长通道上与所述OLT建立第二OMCC通道进行低时延业务的传输。
本发明的其它特征和优点将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点可通过在说明书、权利要求书以及附图中所特别指出的结构来实现和获得。
附图说明
附图用来提供对本发明技术方案的进一步理解，并且构成说明书的一部分，与本申请的实施例一起用于解释本发明的技术方案，并不构成对本发明技术方案的限制。
图1为无源光网络传统网络架构示意图；
图2为现有PON系统支持移动前传应用场景的示意图；
图3为本申请一实施例提供的一种光线路终端OLT的结构示意图；
图4为本申请一实施例提供的一种光网络单元ONU的结构示意图；
图5为本申请一实施例提供的一种光网络单元ONU的结构示意图；
图6为本申请一实施例提供的一种无源光网络PON系统的结构示意图；
图7为本申请另一实施例提供的一种无源光网络PON系统的结构示意图；
图8为本申请另一实施例提供的一种无源光网络PON系统的结构示意图；
图9为本申请另一实施例提供的一种无源光网络PON系统的结构示意图；
图10为本申请另一实施例提供的一种无源光网络PON系统的结构示意图；
图11为本申请一实施例提供的一种降低无源光网络上行时延的方法的流程示意图；
图12为本申请另一实施例提供的一种降低无源光网络上行时延的方法的流程示意图。
具体实施方式
为使本发明的目的、技术方案和优点更加清楚明白，下文中将结合附图对本发明的实施例进行详细说明。需要说明的是，在不冲突的情况下，本申请中的实施例及实施例中的特征可以相互任意组合。
在附图的流程图示出的步骤可以在诸如一组计算机可执行指令的计算机系统中执行。并且，虽然在流程图中示出了逻辑顺序，但是在某些情况下，可以以不同于此处的顺序执行所示出或描述的步骤。
无源光网络中的传输时延包括：光传输时延，带宽分配时延，发现ONU开放安静窗口造成的时延等。
其中，光传输时延与光纤距离及波长相关，对特定的光纤距离和波长传输延时是固定的，如1310nm波长信号在20KM光纤中的传输时间约100us，可以通过缩短光纤距离来减少光传输时间，比如将20KM限制在10KM(光纤距离过短会限制单个OLT可以接入的用户范围)。
其中，带宽分配延时和分配算法以及分配周期相关。如果采用固定带宽分配算法可以消除分配算法响应时延，但是会造成带宽不能有效地统计复用。 采用较小的分配周期，可以减小时间片间隔，缩短时间片调度时延。但是由于每个时间片的突发开销固定，要保证合理的带宽利用率在减小带宽分配周期需要配套建设OLT下ONU数量，比如把DBA(Dynamic Bandwidth Assignment，动态带宽分配)分配周期改为125us的1/4可以把ONU数量控制在8个以内。
其中，开放安静窗口用于OLT发现、测距ONU，属于OLT和ONU之间通道连接初始化带来的开销。为了发现位于距OLT相差最大20KM的ONU，必须要打开有200微秒的安静窗口，这期间正常工作的ONU不能与OLT进行通常的通信。另一方面，为了实现快速发现ONU，OLT需周期性地开放安静窗口，以发现ONU。由于该安静窗口用于待注册激活的ONU发送上行信号，而其他已经完成注册激活的正常工作的ONU不能在安静窗口发送上行信号，那么如果正常工作的ONU正好在安静窗口开始时有上行数据要发送，则必须要等待安静窗口结束之后才有机会发送上行数据，这种情况下，正常工作的ONU发送的上行数据将可能造成最大200微秒的时延。在预先知道ONU信息和光纤距离的情况下可以去掉发现和测试过程以消除开窗引起的延时。
因此，通过减少ONU数量、缩短光纤距离、采用固定带宽分配、消除测距开窗可以使无源光网络满足移动承载低时延的要求。但是传统的FTTH业务希望分光比大，接入范围大，带宽统计复用效率高，开通方便。满足低时延要求的无源光网络的光分配网与注册机制和传统的FTTH无源光网络有较大差别，要在同一个无源光网络中同时承载低时延业务和传统的FTTH业务，需要解决两者之间的矛盾。
图3为本申请一实施例提供的一种光线路终端OLT的结构示意图。如图3所示，该OLT包括：
基础波长通道单元和对应的扩展波长通道单元；
所述基础波长通道单元，用于支持基础波长通道，在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从 基础波长通道切换为对应的扩展波长通道；
所述扩展波长通道单元，用于支持一个或多个扩展波长通道，在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；
所述ONU支持基础波长通道和扩展波长通道的切换。
其中，所述OLT还包括：分波器；
所述基础波长通道单元包括：基础通道媒体访问控制MAC模块和对应的基础通道光模块；
所述扩展波长通道单元包括：一个或多个扩展通道MAC模块和对应的一个或多个扩展通道光模块，一个扩展通道MAC模块对应一个扩展通道光模块；
多个光模块分别对应不同的波长；所述基础通道光模块与所述分波器相连，支持基础波长通道；一个或多个扩展通道光模块与所述分波器相连，支持一个或多个扩展波长通道。
其中，所述扩展波长通道上采用固定带宽或者小的带宽分配周期。
其中，所述扩展波长通道单元，还用于在所述扩展波长通道上根据所述基础波长通道的测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，调整所述ONU的均衡时延值EqD。
图4为本申请一实施例提供的一种光网络单元ONU的结构示意图。如图4所示，该ONU包括：
媒体访问控制MAC模块和对应的光模块；
所述光模块包括两个或两个以上的子光模块，子光模块分别对应不同的波长；所述MAC模块与第一子光模块连接支持基础波长通道，所述MAC模块与其他子光模块连接支持一个或多个扩展波长通道。
图5为本申请一实施例提供的一种光网络单元ONU的结构示意图。如图5所示，该ONU包括：
媒体访问控制MAC模块和对应的光模块；
所述光模块为波长可调光模块，所述波长可调光模块对应不同的波长；所述MAC模块与所述光模块连接支持基础波长通道和扩展波长通道的切换。
图6为本申请一实施例提供的一种无源光网络PON系统的结构示意图。如图6所示，该PON系统包括：
光线路终端OLT、光分配网络ODN和光网络单元ONU；
所述OLT支持基础波长通道和一个或多个扩展波长通道；所述ONU支持基础波长通道和扩展波长通道的切换；
所述OLT通过所述ODN连接所述ONU，所述ODN支持承载基础波长通道信号和扩展波长通道信号；
所述OLT用于在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输。
其中，所述OLT还用于在所述扩展波长通道上根据所述基础波长通道的测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，调整所述ONU的均衡时延值EqD。
图7为本申请另一实施例提供的一种无源光网络PON系统的结构示意图。如图7所示，该PON系统包括：
光线路终端OLT、光分配网络ODN和光网络单元ONU。
其中，OLT支持基础波长通道和扩展波长通道，在基础波长通道上进行完成所有ONU发现和测距以及普通ONU的业务传输，在扩展波长通道上进行低时延ONU业务的传输。
具体而言，OLT上下行分别支持多个不同波长的通道，其中一个为基础波长通道，一个或者一个以上扩展波长通道，通过软件配置控制基础波长通 道和扩展波长通道的分组关系，即基础波长通道与扩展波长通道的对应关系。
其中，ONU分普通ONU和低时延ONU，普通ONU使用基础波长通道承载普通业务。低时延ONU支持基础波长通道和扩展波长通道切换，在基础波长通道上ONU发现和测距、在扩展波长通道上支持低时延业务。
如图7所示，本实施例中，OLT上下行分别支持一个基础波长通道和对应的一个扩展波长通道为例；其中ONU均为低时延ONU。
具体而言，低时延ONU支持光模块接收和发送波长切换或者调谐，ONU不同时间可以选择工作在基础波长通道或者扩展波长通道。
其中，ODN采用功率分光器实现点到多点拓扑连接。
具体而言，支持在同一个ODN中同时承载基础波长通道和扩展波长通道信号。
其中，基础波长通道独立完成普通ONU的发现和测距以及业务的传输，基础波长通道和扩展波长通道配合实现低时延ONU的发现和测距以及低延时业务传输。
具体而言，在基础波长通道进行ONU发现和测距，基础波长通道上测距结果同步到扩展波长通道，扩展波长通道根据基础波长通道测距结果和两个通道的波长特性对计算对应扩展波长通道的往返时间从而得到ONU的测距，扩展波长通道不进行ONU发现和测距过程以消除开窗引起的时延。
其中，在扩展波长通道上可以采用固定带宽和较小的带宽分配周期实现进一步降低时延，扩展波长通道上采用固定带宽和较小的带宽分配周期不会影响基础PON通道上ONU的带宽。
另外，在基础波长通道可以兼容普通ONU接入和普通业务承载，基础波长通道上ONU数量不会影响扩展波长通道上ONU的时延。
本申请实施例提供的技术方案，采用基础波长通道和扩展波长通道组合的PON系统，实现在普通PON网络基础上扩展支持低时延业务。
图8为本申请另一实施例提供的一种无源光网络PON系统的结构示意图。
本实施例中，该PON系统包括：光线路终端OLT、光分配网络ODN和光网络单元ONU。
其中，OLT上下行分别支持两个或者两个以上不同波长的通道，图8中以支持两个通道，即一个普通波长通道和对应的一个扩展波长通道进行显示，仅为示例性说明，并不构成对本申请实施例的限制。例如也可以支持两个以上的通道，比如一个普通波长通道和对应的一个以上的扩展波长通道。
其中，ONU支持光模块接收和发送波长切换或者调谐。
具体而言，在ONU侧可以接入普通ONU和低时延ONU，不管是普通ONU还是低时延ONU都只有一个MAC。低时延ONU采用波长可切换或者波长可调谐光模块，也可以使用多个独立的光模块对应多个扩展波长通道，
其中，一个ONU同时只能选择一个波长通道工作。对于ONU采用波长可切换或者波长可调谐光模块的情况，光模块虽然支持多个波长，但是同一时间只支持一个波长，通过波长切换开关或者波长调谐机制控制光模块工作在特定波长。对于ONU使用多个独立的光模块对应多个扩展波长通道，通过控制光模块的开关控制同一时间只有对应指定波长光模块处于工作状态。
其中，ODN可以采用分光器实现点到多点拓扑连接。
本实施例中，在原有PON架构基础上，增加一个或者多个扩展波长通道。在OLT侧多个通道对应多个MAC(Media Access Control，媒体访问控制)模块，其中一个MAC模块对应基础PON通道，其他一个或者多个MAC模块对应一个或多个扩展波长通道。OLT可以采用多个光模块配合外部分波合波器将多个通道信号复用到同一个ODN中，也可以采用在光模块内部进行多个波长通道的复用。例如，如图8所示，OLT包括：PON OLT基础通道MAC模块111、PON OLT扩展通道MAC模块112、PON OLT基础通道光模块121、PON OLT扩展通道光模块122；低时延ONU-1包括：PON ONU MAC模块和PON ONU波长可调光模块。其他ONU也可以设置为普通ONU或者低时延ONU。其中，122可以有多个分别对应不同波长，121、122、分光器13三部分可以集成到一个光模块实体中(内置分波器，支持多个波长通道)。对应的122有多个时，PON ONU波长可调光模块也需要对应支持多个波长。
低时延ONU在注册阶段和工作阶段采用不同波长，分别对应基础波长通 道和扩展波长通道。低时延ONU在掉线状态和注册过程中工作在基础波长通道，在完成发现和测距后根据ONU能力和OLT配置情况由OLT确定是否将该ONU切换到扩展波长通道。在扩展波长通道中不再进行发现过程，而是根据在基础波长通道获取的ONU标识信息和测距结果进行工作。例如，基础波长通道上测距结果同步到扩展波长通道，扩展波长通道根据基础波长通道测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，得到扩展通道上的ONU测距。由于在扩展波长通道上不进行发现和测距过程，可以避免发现和测距窗口引入的时延。
其中，在基础波长通道中可以进行普通ONU注册和测距以及普通业务的传输；低时延ONU也可以兼容普通ONU进行普通业务的传输。
另外，具体PON技术制式可以有不同选择，例如但不限于：GPON(Gigabit-Capable PON，吉比特无源光网络)、XGPON(增强的无源光网咯)、XGSPON(增强的下一代无源光网路)或者EPON(以太网无源光网络，Ethernet Passive Optical Network)、10GEPON。
本实施例以GPON制式为例说明基础波长通道和扩展波长通道配合实现低时延ONU具体注册和业务传输过程，包括：
在基础波长通道上进行ONU发现和注册：
1.1，OLT在基础波长通道上定期开放安静窗口，并发送SN(Serial Number，序列号)请求；
1.2，当有新的ONU需要上线时或者ONU掉线后，该ONU在基础波长通道等待OLT开放的安静窗口并捕捉到SN请求，然后在安静窗口内竞争发送SN；
1.3，OLT在基础波长通道上获取新ONU的SN；
1.4，OLT在基础波长通道上给ONU分配ONU-ID标识，并继续开放测距窗口，并向该ONU发送测距请求；
1.5，ONU在基础波长通道上发送测距响应；
1.6，OLT获取测距响应，计算出基础波长通道的测距结果发送给ONU；
1.7，OLT和ONU间建立OMCC通道；
1.8，OLT获取ONU对扩展波长通道的支持能力；
1.9，OLT根据ONU对扩展波长通道的支持能力和OLT上对该ONU的配置决定是否将该ONU切换到扩展波长通道上，如果不需要切换则在基础波长通道上按普通ONU进行工作，如果需要切换到扩展波长通道上则继续以下步骤：
其中，OLT可以向ONU发送获取是否支持扩展波长通道的消息，根据ONU的响应消息确定是否支持扩展波长通道。OLT上可以配置ONU承载普通业务或者低时延业务。OLT向ONU查询是否支持扩展波长通道的消息可以采用PLOAM((Physical layer Operation Administration and Maintenance，物理层操作维护管理)消息或者OMCI(光网络单元管理控制接口，ONU Management and Control Interface)消息。
2.0，OLT将该ONU标识和测距信息从基础波长通道同步到对应的扩展波长通道；
2.1，OLT在基础PON通道上通知ONU切换波长通道，ONU接收到切换命令后调整光模块接收和发送波长到指定的扩展波长通道对应的波长；
其中，OLT通知ONU切换波长，可以采用OMCI(光网络单元管理控制接口，ONU Management and Control Interface)消息，也可以采用PLOAM(Physical Layer Operations,Administration and Maintenance物理层操作管理和维护)消息。
2.2，OLT在扩展波长通道上对切换到扩展波长通道的ONU进行EqD调整；
其中，由于不同波长的光信号在同样长度的光纤内传播的时间不同，以基础波长通道计算的EqD(均衡时延值，Equalization Delay)作为扩展通道的EqD初始值，后面再在扩展波长通道上根据OLT接收ONU上行信息对齐情况进行调整。
2.3，OLT和ONU在扩展波长通道完成OMCC建链后进行带宽分配和业务传输。
其中，在扩展波长通道上可以采用固定带宽和较小的带宽分配周期实现进一步降低时延，扩展波长通道上采用固定带宽和较小的带宽分配周期不会 影响基础PON通道上ONU的带宽。
本实施例中，在扩展波长通道上无需执行ONU发现、ONU测距过程，而是直接进入工作状态；ONU掉线恢复到初始状态时波长切换到基础波长通道对应的波长。
其他PON技术制式的注册过程，与上述GPON过程类似，仅在具体交互消息存在差别。例如，对GPON来说使用PLOAM消息和OMCI消息进行注册过程交互和控制，如果采用EPON则使用MPCP(Multi-Point Control Protocol，多点控制协议)报文和OAM报文配合进行注册交互和控制。
图9为本申请另一实施例提供的一种无源光网络PON系统的结构示意图。
本实施例中，该PON系统包括：光线路终端OLT、分光器Splitter和光网络单元ONU-1、ONU-2、ONU-3。
其中，ONU-1和ONU-2对应普通FTTH业务，ONU-3对应低时延业务，OLT PON MAC-1对应基础波长通道，OLT PON MAC-2对应扩展波长通道。即ONU-1和ONU-2为普通ONU，ONU-3为低时延ONU。
其中，OLT包括PON MAC-1和MAC-2以及分别与PON MAC-1和MAC-2连接的光模块。该光模块内置分波器，支持基础波长通道和扩展波长通道。
在OLT上配置PON MAC-1和MAC-2的分组关系(对应关系)，MAC-2不启用定期开窗机制，按普通模式配置ONU-1和ONU-2，在配置ONU-3时指定低时延业务。在ONU-1和ONU-2在OLT PON MAC-1上按标准的XGSPON标准流程进行注册和进行业务传送，ONU-3在OLT PON MAC-1上先进行发现和注册后切换到OLT PON MAC-2上进行业务传送。
本实施例中，ONU-3注册到开始业务传送的过程，包括：
1、ONU-3在OLT PON MAC-1上进行ONU发现和注册，包括：
1.1，OLT在PON MAC-1上定期开放安静窗口，并发送SN请求；
1.2，ONU-3在基础波长通道使用波长下行1577nm/上行1270nm等待OLT PON MAC-1发出的SN请求消息，然后在安静窗口内竞争发送SN消息；
1.3，OLT在PON MAC-1上获取ONU-3的SN；
1.4，OLT在PON MAC-1上给ONU-3分配ONU-ID，继续开放测距窗口并向该ONU发送测距请求；
1.5，ONU-3在基础波长通道上发送测距响应消息；
1.6，OLT PON MAC-1获取测距响应消息，计算出基础PON通道的测距结果发送给ONU-3；
1.7，OLT PON MAC-1和ONU-3间在基础波长通道上建立OMCC通道；
1.8，OLT获取ONU-3对扩展波长通道的支持能力；
2、OLT根据ONU-3支持扩展波长通道同时在OLT对该ONU配置了低时延模式决定是否将该ONU切换到扩展波长通道上，继续以下步骤：
2.1，OLT将该ONU-3的标识和测距信息从PON MAC-1同步到PON MAC-2；
2.2，OLT在PON MAC-1上给ONU-3发消息通知该ONU从基础波长通道使用波长下行1577nm/上行1270nm切换到扩展波长通道使用的波长下行1490nm/上行1310nm，ONU-3接收到切换命令后调整光模块接收和发送波长到波长下行1490nm/上行1310nm；
2.3，OLT在PON MAC-2上对ONU-3进行EqD(均衡延时参数，Equalization Delay)调整；
其中，在PON MAC-2上监控ONU-3上行信号到达时间，如果偏离超出一定门限则对EqD进行调整。
2.4，OLT PON MAC-2和ONU-3在扩展波长通道完成OMCC建链后进行带宽分配和业务传输。
其中，在扩展波长通道上可以采用固定带宽和较小的带宽分配周期实现进一步降低时延，扩展通道上采用固定带宽和较小的带宽分配周期不会影响基础PON通道上ONU的带宽。
图10为本申请另一实施例提供的一种无源光网络PON系统的结构示意 图。
本实施例中，该PON系统包括：光线路终端OLT、分光器Splitter和光网络单元ONU-1、ONU-2、ONU-3。
其中，OLT包括MAC-1和MAC-2，分别与MAC-1和MAC-2连接的光模块-1、光模块-2，以及分别与光模块-1、光模块-2连接的WM(wavelength division multiplexer，波分复用器)。
具体而言，一个光模块连接一个MAC接口，MAC模块工作在XGSPON模式，光模块可以有不同波长光模块，其中一种使用波长下行1577nm/上行1270nm(对应标准的XGSPON波长)用于基础波长通道，其他使用TWDM-PON(Time and Wavelength Division Multiplexed Passive Optical Network，时分复用无源光网络)波长用于扩展波长通道。不同波长的单通道OLT光模块配合外置波分复用器WM实现基础波长通道加扩展波长通道。如果PON口下需要支持低时延业务，在ODN网络OLT侧增加分波合波器，将两个或者多个不同波长的OLT光模块通过分波合波器连到同一个ODN(分光器Splitter)，分光器Splitter下同时挂接普通ONU和低时延ONU，对低时延ONU开通低时延业务。当ODN分支数够用而带宽不满足新增ONU或者带宽扩展要求时，新增不同波长的OLT PON口链接到同一个ODN中进行扩容。
本实施例中，ONU-1和ONU-2对应普通FTTH业务，ONU-3对应低时延业务。即ONU-1和ONU-2为普通ONU，ONU-3为低时延ONU。
OLT MAC-1和光模块-1对应基础波长通道，OLT MAC-2和光模块-2对应扩展波长通道。光模块-1工作波长下行1577nm/上行1270nm，光模块-2工作波长下行1596nm/上行1528nm。
在OLT上配置MAC-1和MAC-2的分组关系，MAC-2不启用定期开窗机制，按普通模式配置ONU-1和ONU-2，在配置ONU-3时指定低时延业务。在ONU-1和ONU-2在OLT PON MAC-1上按标准的XGSPON标准流程进行注册和进行业务传送，ONU-3在OLT PON MAC-1上先进行发现和注册后切换到OLT PON MAC-2上进行业务传送。
本实施例中，ONU-3注册到开始业务传送的过程，包括：
1，ONU-3在OLT PON MAC-1上进行ONU发现和注册，包括：
1.1，OLT在PON MAC-1上定期开放安静窗口，并发送SN请求；
1.2，ONU-3在基础波长通道使用波长下行1577nm/上行1270nm等待OLT PON MAC-1发出的SN请求消息，然后在安静窗口内竞争发送SN消息；
1.3，OLT在PON MAC-1上获取ONU-3的SN；
1.4，OLT在PON MAC-1上给ONU-3分配ONU-ID，继续开放测距窗口并向该ONU发送测距请求；
1.5，ONU-3在基础波长通道上发送测距响应消息；
1.6，OLT PON MAC-1获取测距响应消息，计算出基础波长通道的测距结果发送给ONU-3；
1.7，OLT PON MAC-1和ONU-3间在基础波长通道上建立OMCC通道；
1.8，OLT获取ONU-3对扩展波长通道的支持能力；
2，OLT根据ONU-3支持扩展波长通道同时在OLT对该ONU配置了低时延模式决定是否将该ONU切换到扩展波长通道上，继续以下步骤：
2.1，OLT将该ONU-3的标识和测距信息从PON MAC-1同步到PON MAC-2；
2.2，OLT在PON MAC-1上给ONU-3发消息通知该ONU从基础波长通道使用波长下行1577nm/上行1270nm切换到扩展波长通道使用的波长下行1596nm/上行1528nm，ONU-3接收到切换命令后调整光模块接收和发送波长到波长下行1596nm/上行1528nm；
2.3，OLT在PON MAC-2上对ONU-3进行EqD调整；
其中，在PON MAC-2上监控ONU-3上行信号到达时间，如果偏离超出一定门限则对EqD进行调整。
2.4，OLT PON MAC-2和ONU-3在扩展波长通道完成OMCC建链后进行带宽分配和业务传输。
其中，在扩展波长通道上可以采用固定带宽和较小的带宽分配周期实现进一步降低时延，扩展通道上采用固定带宽和较小的带宽分配周期不会影响基础PON通道上ONU的带宽。
图11为本申请一实施例提供的一种降低无源光网络上行时延的方法的流程示意图。如图11所示，该方法包括：
步骤1101，光线路终端OLT在基础波长通道上实现光网络单元ONU的发现和测距；
步骤1102，在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；
步骤1103，在所述扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；
所述OLT支持基础波长通道和一个或多个扩展波长通道，所述ONU支持基础波长通道和扩展波长通道的切换。
其中，所述扩展波长通道上采用固定带宽或者小的带宽分配周期。
其中，该方法还包括：
所述OLT在所述扩展波长通道上根据所述基础波长通道的测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，调整所述ONU的均衡时延值EqD。
图12为本申请另一实施例提供的一种降低无源光网络上行时延的方法的流程示意图。如图12所示，该方法包括：
步骤1201，光网络单元ONU在基础波长通道上向光线路终端OLT进行注册；
步骤1202，在基础波长通道上与所述OLT建立第一OMCC通道，通过所述第一OMCC通道接收所述OLT的通知，从所述基础波长通道切换为扩展波长通道；
步骤1203，在所述扩展波长通道上与所述OLT建立第二OMCC通道进 行低时延业务的传输。
本申请实施例提供的技术方案，具有如下技术效果：
1，性能提升；在扩展PON通道取消发现和测距窗口，通过扩展通道传输低时延业务，大大降低时延；
2，兼容性；兼容普通ONU，继续用普通ONU承载普通业务，避免由于部分低时延业务引起普通业务使用终端成本增加；
3、可扩展性。可以在已有普通业务接入的ODN中根据低时延业务的需求增加扩展PON通道，避免新增ODN网络和改造ODN网络。同一个ODN网络中基础PON通道和扩展PON通道上ONU业务独立，基础PON通道上ONU数量不会影响扩展PON通道上ONU的时延，扩展通道上采用固定带宽和较小的带宽分配周期不会影响基础PON通道上ONU的带宽。
本领域普通技术人员可以理解，上文中所公开方法中的全部或某些步骤、系统、装置中的功能模块/单元可以被实施为软件、固件、硬件及其适当的组合。在硬件实施方式中，在以上描述中提及的功能模块/单元之间的划分不一定对应于物理组件的划分；例如，一个物理组件可以具有多个功能，或者一个功能或步骤可以由若干物理组件合作执行。某些组件或所有组件可以被实施为由处理器，如数字信号处理器或微处理器执行的软件，或者被实施为硬件，或者被实施为集成电路，如专用集成电路。这样的软件可以分布在计算机可读介质上，计算机可读介质可以包括计算机存储介质(或非暂时性介质)和通信介质(或暂时性介质)。如本领域普通技术人员公知的，术语计算机存储介质包括在用于存储信息(诸如计算机可读指令、数据结构、程序模块或其他数据)的任何方法或技术中实施的易失性和非易失性、可移除和不可移除介质。计算机存储介质包括但不限于RAM、ROM、EEPROM、闪存或其他存储器技术、CD-ROM、数字多功能盘(DVD)或其他光盘存储、磁盒、磁带、磁盘存储或其他磁存储装置、或者可以用于存储期望的信息并且可以被计算机访问的任何其他的介质。此外，本领域普通技术人员公知的是，通信介质通常包含计算机可读指令、数据结构、程序模块或者诸如载波或其他 传输机制之类的调制数据信号中的其他数据，并且可包括任何信息递送介质。

Claims (10)

  1. 一种光线路终端OLT，包括：
    基础波长通道单元和对应的扩展波长通道单元；
    所述基础波长通道单元，用于支持基础波长通道，在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；
    所述扩展波长通道单元，用于支持一个或多个扩展波长通道，在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；
    所述ONU支持基础波长通道和扩展波长通道的切换。
  2. 根据权利要求1所述的OLT，其中，所述OLT还包括：分波器；
    所述基础波长通道单元包括：基础通道媒体访问控制MAC模块和对应的基础通道光模块；
    所述扩展波长通道单元包括：一个或多个扩展通道MAC模块和对应的一个或多个扩展通道光模块，一个扩展通道MAC模块对应一个扩展通道光模块；
    多个光模块分别对应不同的波长；所述基础通道光模块与所述分波器相连，支持基础波长通道；一个或多个扩展通道光模块与所述分波器相连，支持一个或多个扩展波长通道。
  3. 根据权利要求1所述的OLT，其中，
    所述扩展波长通道上采用固定带宽或者小的带宽分配周期。
  4. 根据权利要求1所述的OLT，其中，
    所述扩展波长通道单元，还用于在所述扩展波长通道上根据所述基础波长通道的测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，调整所述ONU的均衡时延值EqD。
  5. 一种光网络单元ONU，包括：
    媒体访问控制MAC模块和对应的光模块；
    所述光模块包括两个或两个以上的子光模块，子光模块分别对应不同的波长；所述MAC模块与第一子光模块连接支持基础波长通道，所述MAC模块与其他子光模块连接支持一个或多个扩展波长通道；
    或者，所述光模块为波长可调光模块，所述波长可调光模块对应不同的波长；所述MAC模块与所述光模块连接支持基础波长通道和扩展波长通道的切换。
  6. 一种无源光网络PON系统，包括：
    光线路终端OLT、光分配网络ODN和光网络单元ONU；
    所述OLT支持基础波长通道和对应的一个或多个扩展波长通道；所述ONU支持基础波长通道和扩展波长通道的切换；
    所述OLT通过所述ODN连接所述ONU，所述ODN支持承载基础波长通道信号和扩展波长通道信号；
    所述OLT用于在所述基础波长通道上实现光网络单元ONU的发现和测距；还用于在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；在扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输。
  7. 一种降低无源光网络上行时延的方法，包括：
    光线路终端OLT在基础波长通道上实现光网络单元ONU的发现和测距；
    在所述基础波长通道上与所述ONU建立第一ONU管理与控制信道OMCC通道，当所述ONU支持扩展波长通道且配置为低时延模式时，通过所述第一OMCC通道通知所述ONU从所述基础波长通道切换为扩展波长通道；
    在所述扩展波长通道上与所述ONU建立第二OMCC通道进行低时延业务的传输；
    所述OLT支持基础波长通道和一个或多个扩展波长通道，所述ONU支持基础波长通道和扩展波长通道的切换。
  8. 根据权利要求7所述的方法，其中，
    所述扩展波长通道上采用固定带宽或者小的带宽分配周期。
  9. 根据权利要求7所述的方法，其中，该方法还包括：
    所述OLT在所述扩展波长通道上根据所述基础波长通道的测距结果和两个通道的波长特性计算对应扩展波长通道的往返时间，调整所述ONU的均衡时延值EqD。
  10. 一种降低无源光网络上行时延的方法，包括：
    光网络单元ONU在基础波长通道上向光线路终端OLT进行注册；
    在基础波长通道上与所述OLT建立第一OMCC通道，通过所述第一OMCC通道接收所述OLT的通知，从所述基础波长通道切换为扩展波长通道；
    在所述扩展波长通道上与所述OLT建立第二OMCC通道进行低时延业务的传输。
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