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CN102377481B - Distance-finding method in a kind of EPON and system - Google Patents

Distance-finding method in a kind of EPON and system Download PDF

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Publication number
CN102377481B
CN102377481B CN201010257115.0A CN201010257115A CN102377481B CN 102377481 B CN102377481 B CN 102377481B CN 201010257115 A CN201010257115 A CN 201010257115A CN 102377481 B CN102377481 B CN 102377481B
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olt
onu
time
standby
main
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CN102377481A (en
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张伟良
耿丹
何苑凌
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ZTE Corp
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ZTE Corp
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Priority to PCT/CN2011/071838 priority patent/WO2012019458A1/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Small-Scale Networks (AREA)
  • Optical Communication System (AREA)

Abstract

The invention discloses the distance-finding method in a kind of EPON, the method comprises: the information of current in running order optical network unit (ONU), when normally working, is sent to spare OLT by primary optical line terminal (OLT); Spare OLT is found range to the dynamic realtime of ONU to be measured according to the information realization of described ONU.The invention also discloses the ranging system in a kind of EPON, information transmitting unit is used for primary OLT when normally working, and the information of current in running order ONU is sent to spare OLT.Adopt method and system of the present invention, spare OLT can be realized each ONU dynamic realtime is found range.

Description

Ranging method and system in passive optical network
Technical Field
The present invention relates to the field of communications, and in particular, to a method and a system for ranging in a Passive Optical Network (PON).
Background
Gigabit-capable passive optical network (GPON) technology and Ethernet Passive Optical Network (EPON) are two important technical branches in the PON family, and similar to other PON technologies, GPON and EPON are also passive optical access technologies that employ point-to-multipoint topologies.
As shown in fig. 1, a PON system comprises an Optical Line Terminal (OLT) on an office side, an Optical Network Unit (ONU) on a subscriber side, and an Optical Distribution Network (ODN), and generally adopts a point-to-multipoint network structure. The ODN is composed of single-mode optical fibers, optical splitters, optical connectors, and other passive optical devices, and provides an optical transmission medium for physical connection between the OLT and the ONUs.
In a PON system, a broadcast method is adopted for data transmission in a downstream direction, i.e., a direction from an OLT to an ONU, each ONU receives all frames, an ONU of the GPON system acquires its own frame according to an ONU-ID (ONU-ID), a gigabit passive optical network encapsulation method port ID (GEM-port ID), and an Allocation ID (Allocation-ID), and an ONU of the EPON system acquires its own frame according to a Logical Link ID (LLID) and a physical ID of the ONU. For data transmission in the upstream direction, i.e. from ONU to OLT, each ONU should transmit upstream data in the time slot it has been arranged for itself by the OLT, since each ONU needs to share the transmission medium. The distances between each ONU and the OLT are different, and in order to prevent uplink data sent by each ONU from reaching the OLT at the same time, the OLT needs to measure the distance of the ONU in the registration activation stage.
In the related art of the existing ONU ranging, the GPON system adopts the following stepsThe method carries out ranging on the ONU: the OLT firstly determines the farthest distance L of the ONU supported by the OLT from the OLT, and the OLT measures the value RTD of the loop delay (RTD) of the ONU at the LmaxAnd according to the RTDmaxDetermining a value eqD for the maximum equalization delay (eqD) for all ONUsmaxWhen an ONU is accessed into the PON system, the ONU enters a registration activation stage after being powered on, when the ONU enters a ranging stage of the registration activation stage, the OLT ranges the ONU, and the OLT measures the RTD of the ONUiThereby obtaining the EqD of the ONUiValue of (EqD)i＝EqDmax-RTDi) OLT converts the above EqDiThe value of the data is sent to the corresponding ONU, the ONU adjusts a clock for sending the data according to the balanced time delay sent by the OLT so as to realize uplink transmission synchronization, and the ONU enters a working state; the EPON system adopts the following method to measure the distance of the ONU: the OLT sends a Multi-point control protocol data unit (MPCPDU) named as a Gate (Gate) with a time stamp (time-stamp) of T0 to the ONU at a time T0, the OLT records a value at a time T0, the ONU receives the MPCPDU named as the Gate, extracts the value T0 of the time stamp and updates a value of a local counter to T0, the ONU sends an MPCPDU named as a Report (Report) with a time stamp of T1 at a time T1 in response to the MPCDU named as the Gate sent by the OLT, the OLT receives the content sent by the ONU at a time T2, the OLT records values of the T1 and the T2, and the OLT calculates an RTT value of the ONU, wherein the RTT is T2-T1. After the OLT in the EPON calculates the RTT for the ONU, the OLT sends an MPCPDU named Gate to the ONU, and if the OLT desires to receive data of the ONU at time T1, for example, the start time of the MPCPDU named Gate is T0 — T1-RTT.
In addition, in order to consider reliability, the PON system provides a protection method, that is, a trunk fiber protection, as shown in fig. 2, protects a trunk fiber between the OLT and the ODN, and provides a redundant trunk fiber and a corresponding redundant OLT, where OLT0 and OLT1 shown in fig. 2 are active and standby with each other, one trunk fiber and the corresponding OLT operate normally, and the other trunk fiber and the corresponding OLT are in a standby state, and when the active trunk fiber or the active OLT fails, protection is switched, and the standby trunk fiber and the standby OLT become the active trunk fiber and the active OLT.
Because the main OLT and the standby OLT use the same wavelength downstream, the standby OLT cannot dynamically measure the distance of each ONU in real time under the condition that the main OLT normally operates, for example: if the main OLT and the standby OLT both send downlink frames to the ONUs, because the same wavelength is used, the ONUs cannot recognize whether the currently received downlink frame is sent by the main OLT or the standby OLT, so that an error occurs when the downlink frame responds, and because the main OLT and the standby OLT can both receive the uplink frame sent when the ONUs respond, the ONUs send the uplink frame to the main OLT at the same time when the main OLT and the standby OLT respond to the downlink frame sent by the standby OLT, the OLT may receive the uplink data of the two ONUs at the same time, so that the OLT cannot correctly analyze the uplink data.
In summary, with the prior art, when the active OLT and the standby OLT both send downlink frames to the ONUs with the same wavelength to request ranging, the uplink data sent by the ONUs in response to ranging of the standby OLT may collide with the uplink data sent by other ONUs, and actually, with the prior art, the standby OLT cannot dynamically perform ranging on each ONU in real time, so that when the standby OLT is used as the active OLT after protection switching, each ONU needs to be re-measured to normally operate, which often takes a long time, and cannot guarantee the quality of service (QoS) of the service. At present, no unified and effective scheme is available for realizing dynamic real-time ranging of each ONU by the standby OLT.
Disclosure of Invention
In view of the above, the main objective of the present invention is to provide a ranging method and system in a PON, which can implement dynamic real-time ranging of each ONU by a standby OLT.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a method of ranging in a passive optical network, the method comprising: when a main Optical Line Terminal (OLT) works normally, sending information of an Optical Network Unit (ONU) in a working state to a standby OLT; and the standby OLT realizes dynamic real-time ranging of the ONU to be measured according to the information of the ONU.
Wherein, the method also comprises: and after the standby OLT is switched to the main OLT, allocating an uplink time slot to the ONU to be tested according to the information of the ONU.
Wherein, allocating the uplink timeslot specifically includes: and allocating uplink time slots for part of the ONUs to be tested or allocating uplink time slots for all the ONUs to be tested.
The ONU information specifically includes: the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
The identity information carried by the ONU to be tested specifically includes: the serial number of the ONU, or the media access control address of the ONU.
The identity information allocated to the ONU to be tested specifically includes: an ONU identification of the ONU, or a logical link identification of the ONU.
The implementation of the dynamic real-time ranging of the ONU to be measured specifically includes any one of the following modes:
the first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the standby OLT receives the uplink frame sent by the ONU to be measured, the standby OLT realizes the distance measurement of the ONU to be measured;
the second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the ONU to be tested receives the uplink frame, the standby OLT realizes the distance measurement of the ONU to be tested;
the third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time of sending the uplink frame by the ONU to be measured received by the main OLT and the standby OLT and the time of sending the downlink frame by the main OLT; and the main OLT sends the ranging result to the standby OLT.
A ranging system in a passive optical network, the system comprising: an information transmitting unit and a ranging unit; wherein,
the information sending unit is used for sending the information of the ONU in the current working state to the standby OLT when the main OLT works normally;
and the ranging unit is used for realizing dynamic real-time ranging of the ONU to be measured by the standby OLT according to the information of the ONU.
The system also comprises a distribution unit, which is used for distributing uplink time slots to the ONU to be tested according to the information of the ONU after the standby OLT is switched to the main OLT; when the uplink time slot is allocated, allocating the uplink time slot for part of the ONUs to be detected or allocating the uplink time slot for all the ONUs in the ONUs to be detected.
The ONU information specifically includes: the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
The distance measurement unit is further configured to implement dynamic real-time distance measurement on the ONU to be measured by any one of the following manners;
the first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the standby OLT receives the uplink frame sent by the ONU to be measured, the standby OLT realizes the distance measurement of the ONU to be measured;
the second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the ONU to be tested receives the uplink frame, the standby OLT realizes the distance measurement of the ONU to be tested;
the third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time of sending the uplink frame by the ONU to be measured received by the main OLT and the standby OLT and the time of sending the downlink frame by the main OLT; and the main OLT sends the ranging result to the standby OLT.
When the main OLT works normally, the information of the ONU currently in the working state is sent to the standby OLT; and the standby OLT realizes dynamic real-time ranging of the ONU to be measured according to the information of the ONU.
By adopting the invention, when the main OLT works normally, the standby OLT realizes dynamic real-time ranging on the ONU to be measured in advance, and the standby OLT does not need to perform ranging again when the standby OLT is used as the main OLT after protection switching, so that the problem that the QoS is influenced by the normal work of each ONU only by performing ranging again when the standby OLT is used as the main OLT after protection switching in the prior art can be avoided, the switching time is reduced, and the QoS of the system bearing service is ensured.
Drawings
FIG. 1 is a diagram illustrating the structure of a PON in the prior art;
FIG. 2 is a diagram of a prior art PON system architecture including a trunk fiber;
FIG. 3 is a flow chart illustrating an implementation of an embodiment of the method of the present invention.
Detailed Description
The basic idea of the invention is: when the main OLT works normally, the information of the ONU in the working state at present is sent to the standby OLT; and the standby OLT realizes dynamic real-time ranging of the ONU to be measured according to the information of the ONU.
The following describes the embodiments in further detail with reference to the accompanying drawings.
An example of a ranging method in a PON is shown in fig. 3, which includes the following steps:
step 100, when the main OLT works normally, the information of the ONU currently in working state is sent to the standby OLT.
And 200, the standby OLT realizes dynamic real-time ranging of the ONU to be measured according to the information of the ONU.
Here, the specific processing procedure of step 200 may be: and the standby OLT acquires the ONU to be tested according to the information of the ONU, and finishes dynamic real-time ranging on the ONU to be tested under the condition that the main OLT works normally and the standby OLT does not send downlink frames to the ONU to be tested.
Here, the ONU to be tested refers to an ONU currently in a working state, and details are not described here.
Further, after the standby OLT is switched to the active OLT, an uplink time slot is allocated to the ONU to be tested according to the information of the ONU. Wherein, uplink time slots can be allocated to part or all of the ONUs to be tested.
Further, the information of the ONU includes: and the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
Further, the identity information carried by the ONU to be tested includes, but is not limited to, a serial number of the ONU, or a Media Access Control (MAC) address of the ONU.
Further, the identity information assigned to the ONU to be tested includes, but is not limited to, an ONU-ID of the ONU, or an LLID of the ONU.
Further, the step of the standby OLT completing the dynamic real-time ranging of the ONU to be measured specifically includes any one of the following manners:
the first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; and the standby OLT realizes the ranging of the ONU to be measured according to the time when the main OLT sends the downlink frame and the time when the standby OLT receives the uplink frame sent by the ONU to be measured.
The second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; and the standby OLT realizes the ranging of the ONU to be measured according to the time of sending the downlink frame by the main OLT and the time of receiving the uplink frame sent by the ONU to be measured.
The third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time for the main OLT to send the uplink frame and the time for the main OLT to send the downlink frame, which are received by the main OLT and the standby OLT; and the main OLT sends the ranging result to the standby OLT.
Further, time synchronization is maintained between the active OLT and the standby OLT.
The invention is illustrated below.
The first embodiment is as follows: an application scenario of the EPON embodiment, the above-described manner one, and the above-described manner two.
In an EPON system, the main steps of protection switching for protecting a trunk fiber shown in fig. 2 include:
step 101: the standby OLT and the main OLT keep time synchronization through a communication channel between the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a convergence switching device which is commonly connected with the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a common network management system. And the main OLT sends the MAC address and the LLID of the ONU in the working state to the standby OLT.
Step 102: the main OLT sends an MPCDU with a time-stamp of T0 and named Gate to the ONU at the time of T0, the standby OLT monitors the MPCDU sent by the main OLT, or the main OLT sends the time T0 for sending the Gate to the standby OLT, and the standby OLT records the value at the time of T0.
Step 103: after receiving the MPCPDU named Gate, the ONU extracts the time stamp value T0 and updates the local counter value to T0, and sends an MPCPDU named Report (Report) with time stamp T1 at time T1 in response to the MPCPDU named Gate sent by the OLT.
Step 104: the standby OLT monitors that the main OLT receives the content sent by the ONU at the time of T2, or the main OLT sends the time T2 for receiving the content to the standby OLT, the standby OLT receives the content sent by the ONU at the time of T2 ', and the standby OLT records the values of T2 and T2'.
Step 105: the standby OLT calculates the RTT between the ONU and the standby OLT, and the RTT is (T2-T1) -2 × (T2-T2 ') -2 × T2' -T1-T2. The standby OLT stores the value of the RTT.
Step 106: when protection switching occurs, the standby OLT becomes the main OLT, all the ONUs in the working state before protection switching directly enter the working state, and the main OLT directly allocates uplink time slots to the ONUs.
Example two: and in an application scenario of the EPON embodiment in the third manner.
In an EPON system, the main steps of protection switching for protecting a trunk fiber shown in fig. 2 include:
step 201: the standby OLT and the main OLT keep time synchronization through a communication channel between the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a convergence switching device which is commonly connected with the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a common network management system. And the main OLT sends the MAC address and the LLID of the ONU in the working state to the standby OLT.
Step 202: the active OLT sends an MPCPDU named Gate with time-stamp (time-stamp) of T0 to the ONU at time T0, and the active OLT records the value at time T0.
Step 203: after receiving the MPCPDU named Gate, the ONU extracts the time stamp value T0 and updates the local counter value to T0, and sends an MPCPDU named Report (Report) with time stamp T1 at time T1 in response to the MPCPDU named Gate sent by the OLT.
Step 204: the main OLT receives the content sent by the ONU at the time T2, and the standby OLT receives the content sent by the ONU at the time T2 'and sends the value of T2' to the main OLT.
Step 205: the main OLT records the values of T1, T2 and T2 ', calculates the value of RTT between the ONU and the standby OLT, and sets RTT (T2-T1) -2 × (T2-T2 ') -2 × T2 ' -T1-T2. And the main OLT sends the RTT between the standby OLT and the ONU to the standby OLT.
Step 206: and the standby OLT receives and stores the RTT value sent by the main OLT. When protection switching occurs, the standby OLT becomes the main OLT, all the ONUs in the working state before protection switching directly enter the working state, and the main OLT directly allocates uplink time slots to the ONUs.
Example three: GPON embodiment, application scenario of the above-described manner one.
In a GPON system, the main steps of protection switching for protecting a trunk fiber shown in fig. 2 include:
step 301: the standby OLT and the main OLT keep time synchronization through a communication channel between the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a convergence switching device which is commonly connected with the standby OLT and the main OLT, or the standby OLT and the main OLT keep time synchronization with a common network management system. The main OLT sends the serial number and ONU-ID of the ONU in working state to the standby OLT, and the main OLT sends the maximum EqD value EqD of the main channelmax master modeAnd the EqD measured on the main channel by each ONU in the working state is sent to the standby OLT.
Step 302: the standby OLT monitors that the main OLT sends a Ranging Request (Ranging _ Request) to the ONU in the working state, the Ranging Request is bandwidth allocation (the starting time is StartTime, the ending time is StopTime), and the standby OLT records the time point T of the main OLT sending the Ranging Request1。
Step 303: after receiving the ranging request, the ONU has a fixed response time (assumed to be T)resp) And responding to the ranging response after waiting for the time of the corresponding EqD and the StartTime allocated by the ranging request, wherein the sent message is a Serial _ Number _ ONU message.
Step 304: the standby OLT monitors the receiving time T when the main OLT receives the ranging response sent by the ONU2And the standby OLT records the T2And recording the receiving time T when the self receives the ranging response sent by the ONU3The spare OLT calculates the EqD value EqD between itself and the ONUFor standbyComprises the following steps:
EqDfor standby＝EqDmax master mode-(T2-T1)+EqD+StartTime-(1+iDownstream/iUplink is carried out)×(T3-T2)-(EqDmax for standby-EqDmax master mode)；
Wherein, EqDmax for standbyThe maximum EqD value of the spare channel, the EqD is the measured time value of the EqD on the main channel by the ONU in the working state, iUplink is carried outFor the refractive index of the light traveling up in the fiber, iDownstreamIs the refractive index of the downstream light in the fiber.
Step 305: the spare OLT calculates the EqD value EqD of the ONU on the spare channel obtained in step 304For standbySending the data to the main OLT, and the main OLT transmits the EqDFor standbyAnd sending the data to the corresponding ONU.
Step 306: the ONU receives the EqD sent by the active OLT in step 305For standbyThereafter, the EqD is storedFor standbyThe value of (c).
Step 307: after the protection switching is switched, the standby OLT becomes a main OLT, the main OLT informs all the ONUs in the working state before the protection switching to switch the EqD value of the standby channel to the main channel and directly enters the working state, and the main OLT allocates an uplink time slot to the ONUs.
In this embodiment, the standby OLT performs ranging on the ONU in the working state, and in other embodiments, the standby OLT may also perform ranging on the ONU in the ranging state during the registration activation process, and for this situation, in step 301, the active OLT allocates itself to the value T of the pre-allocation delay of the ONU in the ranging state during the registration activation processpreSends it to the standby OLT with T in step 304preInstead of EqD.
A ranging system in a PON, the system comprising: an information transmitting unit and a ranging unit; the information sending unit is used for sending the information of the ONU currently in the working state to the standby OLT when the main OLT works normally. And the ranging unit is used for realizing dynamic real-time ranging of the ONU to be measured by the standby OLT according to the information of the ONU. And the ONU to be tested is the ONU which is currently in a working state.
The system also comprises a distribution unit, wherein the distribution unit is used for distributing an uplink time slot to the ONU to be tested according to the information of the ONU after the standby OLT is switched to the main OLT; when the uplink time slot is allocated, allocating the uplink time slot for part of the ONUs to be detected or allocating the uplink time slot for all the ONUs in the ONUs to be detected.
Here, the information of the ONU specifically includes: the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
Here, the ranging unit is further configured to implement dynamic real-time ranging on the ONU to be measured in any one of the following manners.
The first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; and the standby OLT realizes the ranging of the ONU to be measured according to the time when the main OLT sends the downlink frame and the time when the standby OLT receives the uplink frame sent by the ONU to be measured.
The second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; and the standby OLT realizes the ranging of the ONU to be measured according to the time of sending the downlink frame by the main OLT and the time of receiving the uplink frame sent by the ONU to be measured.
The third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time for the main OLT to send the uplink frame and the time for the main OLT to send the downlink frame, which are received by the main OLT and the standby OLT; and the main OLT sends the ranging result to the standby OLT.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims (9)

1. A method for ranging in a passive optical network, the method comprising: when a main Optical Line Terminal (OLT) works normally, sending information of an Optical Network Unit (ONU) in a working state to a standby OLT; the standby OLT realizes dynamic real-time ranging of the ONU to be measured according to the information of the ONU;
the implementation of the dynamic real-time ranging of the to-be-measured ONU specifically includes any one of the following modes:
the first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the standby OLT receives the uplink frame sent by the ONU to be measured, the standby OLT realizes the distance measurement of the ONU to be measured;
the second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the ONU to be tested receives the uplink frame, the standby OLT realizes the distance measurement of the ONU to be tested;
the third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time of sending the uplink frame by the ONU to be measured received by the main OLT and the standby OLT and the time of sending the downlink frame by the main OLT; the main OLT sends a ranging result to the standby OLT;
the method further comprises the following steps:
calculating by the standby OLT or the main OLT to obtain the RTT (2 × T2' -T1-T2) between the ONU to be measured and the standby OLT; wherein, T1 is the time when the main OLT sends the downlink frame, T2 is the time when the main OLT receives the uplink frame sent by the ONU to be tested, and T2' is the time when the standby OLT receives the uplink frame sent by the ONU to be tested.
2. The method of claim 1, further comprising: and after the standby OLT is switched to the main OLT, allocating an uplink time slot to the ONU to be tested according to the information of the ONU.
3. The method of claim 2, wherein allocating uplink timeslots specifically comprises: and allocating uplink time slots for part of the ONUs to be tested or allocating uplink time slots for all the ONUs to be tested.
4. The method according to any of claims 1 to 3, wherein the information of the ONU specifically comprises: the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
5. The method according to claim 4, wherein the identity information carried by the ONU to be tested specifically comprises: the serial number of the ONU, or the media access control address of the ONU.
6. The method according to claim 4, wherein the identity information allocated to the ONU to be tested specifically includes: an ONU identification of the ONU, or a logical link identification of the ONU.
7. A ranging system in a passive optical network, the system comprising: an information transmitting unit and a ranging unit; wherein,
the information sending unit is used for sending the information of the ONU in the current working state to the standby OLT when the main OLT works normally;
the ranging unit is used for realizing dynamic real-time ranging of the ONU to be measured by the standby OLT according to the information of the ONU;
the distance measurement unit is further used for realizing dynamic real-time distance measurement of the ONU to be measured by adopting any one of the following modes;
the first method is as follows: the standby OLT monitors a downlink frame sent by the main OLT and records the time of sending the downlink frame by the main OLT; the standby OLT monitors an uplink frame sent by the ONU to be tested and records the time when the standby OLT receives the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the standby OLT receives the uplink frame sent by the ONU to be measured, the standby OLT realizes the distance measurement of the ONU to be measured;
the second method comprises the following steps: the main OLT sends the time for sending the downlink frame to the standby OLT; the standby OLT records the time of receiving the uplink frame sent by the ONU to be tested; according to the time that the main OLT sends the downlink frame and the time that the ONU to be tested receives the uplink frame, the standby OLT realizes the distance measurement of the ONU to be tested;
the third method comprises the following steps: the standby OLT sends the time for receiving the uplink frame sent by the ONU to be tested to the main OLT; the main OLT realizes ranging between the standby OLT and the ONU to be measured according to the time of sending the uplink frame by the ONU to be measured received by the main OLT and the standby OLT and the time of sending the downlink frame by the main OLT; the main OLT sends a ranging result to the standby OLT;
the ranging unit is further used for calculating to obtain RTT (2 × T2' -T1-T2) between the ONU to be measured and the standby OLT by the standby OLT or the main OLT; wherein, T1 is the time when the main OLT sends the downlink frame, T2 is the time when the main OLT receives the uplink frame sent by the ONU to be tested, and T2' is the time when the standby OLT receives the uplink frame sent by the ONU to be tested.
8. The system according to claim 7, further comprising an allocation unit, configured to allocate an upstream timeslot to the ONU to be tested according to the information of the ONU after the standby OLT switches to the active OLT; when the uplink time slot is allocated, allocating the uplink time slot for part of the ONUs to be detected or allocating the uplink time slot for all the ONUs in the ONUs to be detected.
9. The system according to claim 7 or 8, wherein the information of the ONU specifically comprises: the identity information carried by the ONU to be tested and the identity information distributed to the ONU to be tested by the main OLT.
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