WO2022111045A1 - Method for determining transmission delay of passive optical network - Google Patents

Abstract

Provided is a method for determining the transmission delay of a passive optical network (PON). An optical network unit (ONU) comprises a first module and a second module, the first module communicating with an optical line terminal (OLT) by means of a first optical distribution network (ODN), the second module communicating with said OLT by means of a second ODN; the first module time completes synchronization with the OLT; the second module receives a time synchronization message from said OLT, a first time stamp being comprised in the time synchronization message; the ONU sets the second module time to the time identified by the first time stamp; the ONU determines the first time difference according to the first module time and the second module time, the first time difference being equal to the transmission delay of the time synchronization message from the OLT to the second module. By means of the method, the second module of the ONU does not require open-window ranging to obtain the transmission delay from the OLT to the ONU, and thus obtain a balanced time delay, avoiding the service impact of an open window on other ONUs, reducing the time delay caused by open-window ranging.

Description

A method for determining the transmission delay of passive optical network

This application claims the priority of the Chinese patent application with the application number 202011358520.1 and the application title "Method for Determining the Transmission Delay of a Passive Optical Network" filed with the State Intellectual Property Office of China on November 27, 2020, the entire contents of which are by reference Incorporated in this application.

technical field

The present application relates to the field of optical communication, and more particularly, to a method and device related to ranging in a passive optical network (Passive Optical Network, PON) system.

Background technique

Passive Optical Network (PON) technology is a point-to-multipoint fiber access technology. A PON system may include an Optical Line Terminal (OLT), an Optical Distribution Network (ODN), and at least one Optical Network Unit (ONU). The OLT is connected to multiple ONUs through the ODN.

All ONUs under a PON port of the OLT use time division multiplexing, and at the time specified by the OLT, send upstream data to the OLT through the ODN. The OLT must accurately measure the distance between each ONU and the OLT through ranging, so as to control the moment when each ONU sends uplink data. In the process of ranging, the OLT needs to open the window, that is, the Quiet Zone, and suspend the upstream transmission channels of other ONUs. Since the OLT does not authorize other ONUs to send uplink data during the windowing period, it will cause a transmission delay to the service data transmitted by other ONUs.

At present, more and more business scenarios put forward low-latency technical requirements for PON systems, such as 5G business scenarios and optical transport network (OTN) private line business scenarios. How to reduce the service delay caused by window opening and ranging has become a technical problem to be solved urgently.

SUMMARY OF THE INVENTION

The present application proposes a method for determining the transmission delay of a PON system, and a device and system for implementing the method.

In a first aspect, the present application proposes a method for determining the transmission delay of a passive optical network PON. The optical network unit ONU includes a first module and a second module, the first module communicates with the OLT through the first optical distribution network ODN, and the second module communicates with the OLT through the second ODN; the first module completes the communication with the OLT in time. Time synchronization; the second module receives the time synchronization message sent by the OLT, the time synchronization message includes a first time stamp, and the first time stamp identifies the counter value of the OLT as the OLT time at time K; the counter value of the second module is K When the ONU sets the second module time as the time marked by the first time stamp; the ONU determines the first time difference according to the first module time and the second module time, and the first time difference is equal to the second module time and the OLT time at the same moment The first time difference is equal to the transmission delay of the time synchronization message from the OLT to the second module. Through the method described in the first aspect, the second module of the ONU can obtain the transmission delay from the OLT to the ONU without performing windowing and ranging, and then obtain the balanced delay. Because there is no need to open the window for ranging, the second module can complete the registration and online process faster; because there is no need to open the window, it does not need to suspend the upstream transmission channels of other ONUs, so the service impact on other ONUs can be reduced; The second module of the ONU also does not need to perform windowing and ranging, which also reduces the business impact on the ONU. When the service transmitted by the second module is a real-time service or a delay-sensitive service, the delay caused by the windowing and ranging is avoided.

In a possible implementation manner of the first aspect, the time synchronization message received by the second module further includes the superframe count value K of the LT, and the time identified by the first timestamp is the superframe counter value of the OLT equal to K OLT time at the moment; when the superframe counter value of the second module is equal to K, the ONU sets the time of the second module to the time identified by the first timestamp.

In a possible implementation manner of the first aspect, the ONU determines the first time difference through an Ethernet packet between the first module and the second module; the first module sends a first packet to the second module, and the first packet includes Sending timestamp, when the sending timestamp is the time of the first module, the time when the first module sends the first packet, the second module adds a receiving timestamp to the first packet when receiving the first packet, and receives The time stamp is the time when the second module receives the first message under the time of the second module; the ONU determines the second time difference, which is the difference between the receiving time stamp and the sending time stamp; The first time difference is determined by the road delay, and the first time difference is the sum of the second time difference and the Ethernet link delay, and the Ethernet link delay is the communication time between the first module and the second module through the Ethernet link. extension.

In a possible implementation manner of the first aspect, the ONU determines the equalization delay of the communication between the second module and the OLT according to the first time difference, such as determining the equalization delay EqD2 of the communication between the second module and the OLT according to the following calculation formula:

EqD2=Teqd-RspTime2-(dt/(n1/(n1+n2))),

Among them, Teqd is zero distance equivalent delay, RspTime2 is the ONU response time, dt is the first time difference, n1 is the refractive index of the downstream light communicated between the OLT and the ONU, and n2 is the upstream light communicated between the ONU and the OLT. refractive index.

In a possible implementation manner of the first aspect, after the ONU determines the equalization delay for communication between the second module and the OLT, the second module waits at least for the equalization delay after processing the OLT request. time, and then send an upstream packet to the OLT.

In a possible implementation manner of the first aspect, the ONU measures the Ethernet link delay between the first module and the second module according to the 1588 time synchronization protocol.

In a second aspect, the present application provides a PON system device. The device includes a first module and a second module; the first module is used to complete ranging and time synchronization with the optical line terminal OLT through the first ODN; the second module is used to receive the time synchronization sent by the OLT through the second ODN message, the time synchronization message includes a first time stamp, and the first time stamp identifies that the counter value of the OLT is the OLT time at time K; when the counter value of the second module is K, the second module time is set to the first time. A time marked by a timestamp; determine the first time difference, the first time difference is equal to the difference between the second module time and the OLT time at the same moment, and the first time difference is equal to the transmission delay of the time synchronization message from the OLT to the second module.

In a possible implementation manner of the second aspect, the time synchronization message received by the second module further includes the superframe count value K of the OLT, and the time identified by the first timestamp is the time when the superframe counter value of the OLT reaches K OLT time; the second module is further configured to set the second module time as the time identified by the first timestamp when the superframe counter value of the second module is equal to K.

In a possible implementation manner of the second aspect, the first module is further configured to send a first packet to the second module, where the first packet includes a sending timestamp, and the sending timestamp is the time of the first module, and the first packet The time when the first module sends the first packet; the second module is further configured to add a receiving timestamp to the first packet when receiving the first packet, and when the receiving timestamp is the time of the second module, the second module receives The time at the moment of the first packet; the second time difference is determined, and the second time difference is the difference between the receiving timestamp and the sending timestamp; the first time difference is determined according to the second time difference and the Ethernet link delay, and the first time difference is the second time difference The sum of the Ethernet link delay, the Ethernet link delay is the delay of communication between the first module and the second module through the Ethernet link.

In a possible implementation manner of the second aspect, the second module is further configured to determine the equalization delay of the communication between the second module and the OLT according to the first time difference, such as determining the equalization delay of the communication between the second module and the OLT according to the following calculation formula Delay EqD2:

EqD2=Teqd-RspTime2-(dt/(n1/(n1+n2))),

Among them, Teqd is zero distance equivalent delay, RspTime2 is the response time of the second module, dt is the first time difference, n1 is the refractive index of the downlink light communicated between the OLT and the ONU, and n2 is the communication between the second module and the OLT. the refractive index of the upstream light.

In a possible implementation manner of the second aspect, the second module is further configured to, after processing the request of the OLT, at least wait for a duration corresponding to the equalization delay, and then send an uplink message to the LT.

In a possible implementation manner of the second aspect, the second module measures the Ethernet link delay between the first module and the second module according to the 1588 time synchronization protocol.

In a possible implementation manner of the second aspect, the first module includes a processor, a memory, a PON medium access control (MAC) chip, a transceiver and a time control module, and the second module also includes a processor, Memory, PON media access control (medium access control, MAC) chip, transceiver and time control module; the first module processor is used to control the first module to complete ranging and time synchronization, and the first module PON MAC chip is used for the first module. Under the control of the module processor, data forwarding with the OLT is completed, the first module transceiver is used to communicate with the OLT through the first ODN, the first module time control module is used to control the first module time; the second module transceiver is used for The second ODN communicates with the OLT, the second module PON MAC chip is used to complete the data transmission and reception with the OLT under the control of the second module processor, and the second module processor is used for receiving the time synchronization message. Processing, when the counter value of the second module is K, the second module time is set to the time marked by the first time stamp, and the second module time control module is used to control the second module time according to the setting of the second module processor ; The second module processor is further configured to determine the first time difference according to the first module time and the second module time.

In a possible implementation manner of the second aspect, the first module further includes an Ethernet MAC chip, the second module further includes an Ethernet MAC chip, and the first module Ethernet MAC chip and the second module Ethernet MAC chip communicate with each other through an Ethernet link; The first module processor is further configured to send the first packet to the second module Ethernet MAC chip through the first module Ethernet MAC chip; the second module Ethernet MAC chip is configured to forward the first packet to the second module processor for processing; The second module processor is further configured to add a receiving time stamp to the first message, where the receiving time stamp is the time when the second module receives the first message under the time of the second module; determining the second time difference, the first The second time difference is the difference between the receiving time stamp and the sending time stamp; the first time difference is determined according to the second time difference and the Ethernet link delay, and the first time difference is the sum of the second time difference and the Ethernet link delay. The delay is the delay of communication between the first module and the second module through the Ethernet link.

In a possible implementation manner of the second aspect, the second module processor is further configured to determine the balance of the communication between the second module and the OLT according to the ONU response time, the zero-distance equivalent delay and the first time difference time delay.

In a third aspect, the present application provides a PON communication system, where the PON system includes an OLT and the ONU described in the first or second aspect.

In a fourth aspect, the present application provides a computer-readable storage medium comprising instructions that, when executed on a computer, cause the computer to perform the method of the first aspect.

In a fifth aspect, the present application provides a computer program product comprising instructions which, when run on a computer, cause the computer to perform the method of the first aspect.

Description of drawings

1 is a schematic diagram of a PON system architecture provided by an embodiment of the present application;

FIG. 2 is a schematic diagram of the ranging principle of a PON system provided by an embodiment of the present application;

3 is a schematic diagram of the networking structure of a PON system according to an embodiment of the present application;

4 is a schematic diagram of time synchronization of a PON system provided by an embodiment of the present application;

FIG. 5 is a schematic structural diagram of an ONU device according to an embodiment of the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

The technical solutions of the embodiments of the present application can be applied to various passive optical network systems, for example, next-generation PON (NG-PON), NG-PON1, NG-PON2, gigabit-capable PON (next-generation PON, NG-PON) PON, GPON), 10 gigabit per second PON (10 gigabit per second PON, XG-PON), symmetric 10 gigabit passive optical network (10-gigabit-capable symmetric passive optical network, XGS-PON), Ethernet PON ( Ethernet PON, EPON), 10 gigabit per second EPON (10 gigabit per second EPON, 10G-EPON), next-generation EPON (next-generation EPON, NG-EPON), wavelength-division multiplexing (wavelength-division multiplexing, WDM) PON , Time-and wavelength-division multiplexing (TWDM) PON, point-to-point (P2P) WDM PON (P2P-WDM PON), asynchronous transfer mode PON (asynchronous transfer mode PON, APON) ), broadband PON (broadband PON, BPON), etc., and 25 gigabit per second PON (25 gigabit per second PON, 25G-PON), 50 gigabit per second PON (50 gigabit per second PON, 50G-PON) , 100 gigabit per second PON (100 gigabit per second PON, 100G-PON), 25 gigabit per second EPON (25 gigabit per second EPON, 25G-EPON), 50 gigabit per second EPON (50 gigabit per second EPON, 50G-EPON), 100 gigabit per second EPON (100 gigabit per second EPON, 100G-EPON), and other rates of GPON, EPON, etc.

FIG. 1 is a schematic diagram of a PON system architecture. As shown in FIG. 1 , the PON system 100 includes at least one OLT 110 , at least one ODN 120 and multiple ONUs 130 . The OLT 110 provides a network-side interface for the PON system 100, and the ONU 130 provides a user-side interface for the PON system 100 and is connected to the ODN 120. If the ONU 130 directly provides the user port function, it is called an optical network terminal (Optical Network Terminal, ONT). For ease of description, the ONU 130 mentioned below collectively refers to an ONT that can directly provide a user port function and an ONU that provides a user side interface. ODN 120 is a network composed of optical fibers and passive optical splitting devices, used to connect OLT 110 equipment and ONU 130 equipment, and used to distribute or multiplex data signals between OLT 110 and ONU 130.

In the PON system 100, the direction from the OLT 110 to the ONU 130 is defined as the downstream direction, and the direction from the ONU 130 to the OLT 110 is defined as the upstream direction. In the downstream direction, the OLT 110 adopts the time division multiplexing (Time Division Multiplexing, TDM) method to broadcast the downstream data to the multiple ONUs 130 managed by the OLT 110, and each ONU 130 only receives the data carrying its own identification; Each ONU 130 communicates with the OLT 110 in a time division multiple access (Time Division Multiple Access, TDMA) manner, and each ONU 130 sends uplink data according to the time domain resources allocated by the OLT 110. Using the above mechanism, the downlink optical signal sent by the OLT 110 is a continuous optical signal, and the uplink optical signal sent by the ONU 130 is a burst optical signal.

The OLT 110 is usually located in a central office (Central Office, CO), can manage at least one ONU 130 uniformly, and transmit data between the ONU 130 and the upper-layer network. Specifically, the OLT 110 can act as a medium between the ONU 130 and the upper-layer network (such as the Internet, a public switched telephone network (PSTN), and forward the data received from the upper-layer network to the ONU 130, And forward the data received from ONU 130 to the upper layer network. The specific structural configuration of the OLT 110 may vary depending on the specific type of the PON system 100, for example, in one embodiment, the OLT 110 may include transmitting The transmitter and the receiver, the transmitter is used to send the downlink continuous optical signal to the ONU 130, and the receiver is used to receive the uplink burst optical signal from the ONU 130, wherein the downlink optical signal and the uplink optical signal can be carried out through the ODN 120. transmission, but the embodiment of the present invention is not limited thereto.

The ONUs 130 may be distributed in user-side locations (such as customer premises). The ONU 130 may be a network device for communicating with the OLT 110 and the user, specifically, the ONU 130 may act as an intermediary between the OLT 110 and the user, for example, the ONU 130 may receive data from the OLT 110 Forwarding to the user, and forwarding of data received from the user to the OLT 110.

The ODN 120 may be a data distribution network, which may include optical fibers, optical couplers, optical splitters, or other devices. In one embodiment, the optical fiber, optical coupler, optical splitter or other device may be a passive optical device, specifically, the optical fiber, optical coupler, optical splitter or other device may be between the OLT 110 and the ONU 130 devices that do not require power supply when distributing data signals between Specifically, taking an optical splitter (Splitter) as an example, the optical splitter can be connected to the OLT 110 through a trunk fiber, and connected to a plurality of ONUs 130 through a plurality of branch fibers respectively, thereby realizing the OLT 110 and the ONU 130. point-to-multipoint connections. In addition, in other embodiments, the ODN 120 may further include one or more processing devices, for example, an optical amplifier or a relay device (Relay device). In addition, the ODN 120 may specifically extend from the OLT 110 to multiple ONUs 130, but may also be configured into any other point-to-multipoint structure, and the embodiment of the present invention is not limited thereto.

For the OLT, the logical distances from different ONUs to the OLT are not equal, the transmission time of the optical signal on the optical fiber is different, and the time when it reaches each ONU is different. At the same time, the round trip delay (Round Trip Delay, RTD) between the OLT and the ONU also changes with time and the environment. In order to ensure that the uplink data sent by each ONU to the OLT is inserted into the designated time slot after the ODN fiber is converged, and there is no collision with each other and the gap is not too large, the OLT must measure the distance between each ONU and the OLT through ranging (ranging). The distance between them can be accurately measured in order to control the time when each ONU sends the uplink data. The OLT will start the ranging function when the ONU registers for the first time, obtain the RTD of the round-trip delay of the ONU, calculate the physical distance of each ONU, and specify the appropriate equalization delay (Equalization Delay, EqD) parameter according to the physical distance of the ONU . In the process of ranging, the OLT needs to open the window, that is, the Quiet Zone, and suspend the upstream transmission channels of other ONUs. By specifying EqD for the ONU, the OLT synchronizes the data frames sent by each ONU to ensure that each ONU will not cause conflict on the optical splitter when sending data. Quite all the ONUs are in the same logical distance, and it is enough to send data in the corresponding time slot, so as to avoid collision and collision of upstream cells.

The ranging of GPON is completed in the ONU registration phase. When the ONU receives the SN request message sent by the OLT, the ONU returns an SN response message after waiting for a certain response time. After receiving the reply message and verifying the validity, the OLT assigns an ONU-ID to the ONU, and the ONU enters the ranging state after receiving the assigned ONU-ID.

The principle of the OLT calculating and distributing the equalization delay is shown in Figure 2. It is assumed that the OLT sends a ranging request to the ONU at time T1, and at the same time commands other ONUs to stop sending uplink services, and opens a ranging window in the uplink time slot for this ONU to use. The ONU receives the ranging request at time T2, and after internal processing, sends an uplink frame responding to the ranging request at time T3, and the OLT receives the uplink frame responding to the ranging request at time T4. Then the OLT can calculate and obtain the RTD of the ONU according to T4 and T1. The zero-distance equivalent delay Teqd in Figure 1 is a value set by the OLT according to the length of the farthest optical fiber, which is greater than or equal to the RTD of the ONU with the farthest logical distance. To ensure that the upstream data phases of all ONUs connected to the same PON interface of the OLT are the same, the OLT allocates EqD to all ONUs connected to the same PON interface of the OLT according to the following principles, where i represents the ONU number:

Teqd=RTD(i)+EqD(i) (1)

EqD(i)=Teqd-RTD(i) (2)

After the subsequent ONU processes the request of the OLT, it must wait for the EqD time before sending the upstream data or upstream frame, which can ensure that the upstream data phase of all ONUs under the same PON port of the OLT is the same.

Based on the EqD(i) determined in the ranging process, time synchronization is also required between the OLT and the ONU. First of all, it should be noted that each PON module in the ONU and the time control module in the OLT respectively have time control modules. In the case of no time synchronization, the time of the ONU and the time of the OLT may be different at the same moment, and even the ONU may be different. The time may also be different between the PON modules inside. A well-understood example is that at the same time, Beijing time is 18:00 and London time is 10:00. Therefore, similar descriptions such as ONU time or OLT time are used in this application to represent the timing of different devices or modules.

The ITU G.984.3 standard defines a time synchronization scheme. In this scheme, the OLT sends a time synchronization message to the ith ONU, which carries the timestamp Tsend(i) of the OLT. After receiving the time synchronization message, the ith ONU calculates and obtains the transmission of the time synchronization message according to EqD(i). Delay, set the local time Trecv(i) of the ONU to Tsend(i) + the transmission delay of the time synchronization message, that is

Trecv(i)=Tsend(i)+(Teqd-EqD(i)-RspTime(i))*(nd/(nd+nu))    (3)

Among them, EqD(i) is the equalization delay determined by the i-th ONU after ranging, RspTime(i) is the response time of the i-th ONU (the duration of T3-T2 in Figure 1), and nd is the downlink wavelength Refractive index, nu is the refractive index of the upstream wavelength, (Teqd-EqD(i)-RspTime(i))*(nd/(nd+nu)) is the transmission delay of the time synchronization message obtained by calculating EqD(i).

It should be understood by those skilled in the art that, in order to highlight the key points, the ranging and time synchronization processes described in the embodiments of this application may briefly describe some message processes; for example, in the specific implementation, the time synchronization message sent by the OLT It can also carry the superframe count value of the OLT corresponding to the time Tsend(i). After the i-th ONU receives the time synchronization message, when the superframe count value of the ONU is equal to the superframe count value of the OLT in the time synchronization message , and set the local time Trecv(i) of the ONU as Tsend(i) + the transmission delay of the time synchronization message.

FIG. 3 is a system architecture applicable to various embodiments of the present application. The system architecture shown in FIG. 3 is a further refinement of the system architecture shown in FIG. 1 . The OLT, ODN and ONU shown in FIG. 3 are specific embodiments of the OLT 110, ODN 120 and ONU 130 in FIG. 1, respectively. In Figure 3, each ONU includes two PON modules, ONU-PON-0 and ONU-PON-1, and ONU-PON-0 and ONU-PON-1 communicate with the OLT through different ODNs respectively; the OLT also includes two PON module, OLT-PON-0 and OLT-PON-1, ONU-PON-0 communicates with OLT-PON-0 through ODN-0, and ONU-PON-1 communicates with OLT-PON-1 through ODN-1. The two PON modules of the ONU are registered in the PON module of the connected OLT respectively, that is, ONU-PON-0 is registered in OLT-PON-0 through ODN-0, and ONU-PON-1 is registered in OLT-PON through ODN-1 -1 for registration. ONU-PON-0 and ONU-PON-1 are equivalent to two virtual ONUs, which communicate with the OLT through different ODNs. When an ONU needs ranging, the OLT sends a ranging request to the ONU, and also orders other ONUs to stop sending uplink services. Therefore, the ranging process will affect the real-time performance of the ranging ONU and the services transmitted by other ONUs. influences. Since ONU-PON-0 and ONU-PON-1 communicate with the OLT through different ODN networks, in the prior art, the OLT needs to perform ranging on ONU-PON-0 and ONU-PON-1 respectively. That is, each PON module of each ONU needs to perform ranging, and the delay problem caused by ranging will be more prominent.

In order to solve the time delay problem caused by windowed ranging, the present application proposes a ranging solution that does not require windowing, and the solution can be applied to the PON network architecture as shown in FIG. 3 . The following describes the ranging solution proposed by the present application based on FIG. 4 . FIG. 4 is a sequence diagram of communication between the OLT and the ONU. The horizontal axis corresponding to OLT represents the time axis of OLT; the horizontal axis corresponding to ONU-PON-0 represents the time axis of ONU-PON-0; the horizontal axis corresponding to ONU-PON-1 represents the time axis of ONU-PON-1 axis. ONU-PON-0 is one of the PON modules of any ONU in FIG. 3 , and ONU-PON-1 is another PON module of the ONU. The OLT includes two PON modules, OLT-PON-0 and OLT-PON-1. The connection relationship between each PON module of the ONU and each PON module of the OLT is as shown in FIG. 3 .

Step 1. After ONU is powered on, ONU-PON-0 completes ranging and time synchronization with OLT-PON-0. The maintenance time on ONU-PON-0 is the same as the time on OLT-PON-0. ONU-PON-0 and OLT-PON-0 can perform ranging and time synchronization according to the methods defined by ITU standards. For example, suppose that OLT-PON-0 sends a time synchronization message to ONU-PON-0, the time synchronization message carries the time stamp of Ts0, and ONU-PON-0 receives the time synchronization message after a certain transmission delay (such as dt0). , according to formula (3), it can be known that,

dt0=(Teqd-EqD(0)-RspTime(0))*(nd/(nd+nu))    (4)

Among them, EqD(0) is the equalization delay corresponding to ONU-PON-0, and RspTime(0) is the response time of ONU-PON-0.

ONU-PON-0 completes time synchronization with OLT-PON-0 based on dt0 and Ts0 in the time synchronization message. At Tr0 time, ONU-PON-0 time and OLT-PON-0 time are both Ts0+dt0; where Tr0 At the moment, the superframe count value of ONU-PON-0 is the same as the superframe count value of OLT-PON-0 in the time synchronization message.

It should be noted that Ts0 in Figure 4 does not refer to the time stamp when the time synchronization message is sent by OLT-PON-0, but refers to the time stamp carried in the time synchronization message sent by OLT-PON-0; Tr0 does not refer to the ONU- The timestamp when PON-0 receives the time synchronization message, but the timestamp when ONU-PON-0 completes the time synchronization message (for example, the superframe count value of Tr0 corresponding to ONU-PON-0 is equal to the superframe count value in the time synchronization message. time).

Step 2: The OLT sends a time synchronization message to the ONU-PON-1 through the OLT-PON-1, and the time synchronization message carries the time stamp Ts1 of the OLT-PON-1. After the transmission delay of dt1, the ONU-PON-1 receives the time synchronization message sent by the OLT, records the time stamp Ts1 contained in the synchronization message, and performs subsequent timing or time maintenance based on Ts1; When the superframe count value of ONU-PON-1 is the same as the superframe count value of OLT-PON-1 in the time synchronization message, such as time Tr1, ONU-PON-1 sets the time of ONU-PON-1 to Ts1, At this time, the time of OLT-PON-1 is Ts1+dt1. Therefore, ONU-PON-1 does not really complete the time synchronization with OLT-PON-1. At the same time, there is a difference dt1 between ONU-PON-1 time and OLT time. Since ONU-PON-0 has completed the time synchronization with OLT (OLT-PON-0 and OLT-PON-1 time synchronization), therefore, at the same time, the difference between ONU-PON-0 time and ONU-PON-1 time The value is also dt1. It should be noted that Ts0 and Ts1 are in no particular order in time. The OLT can first send a time synchronization message to ONU-PON-0, or it can first send a time synchronization message to ONU-PON-1. In either case, the two modules of ONU-PON-0 and ONU-PON-1 follow step 1 After processing the time synchronization message with step 2, the time difference between ONU-PON-0 time and ONU-PON-1 time is dt1, that is, at the same time

ONU-PON-0 time-ONU-PON-1 time=dt1 (6)

As mentioned in step 1, the specific value of dt1 can be expressed by the following formula

dt1=(Teqd-EqD(1)-RspTime(1))*(nd/(nd+nu))    (7)

Among them, EqD(1) is the equalization delay corresponding to ONU-PON-1, and RspTime(1) is the response time of ONU-PON-1.

It can be seen from Equation 7 that dt1 and EqD(1) have a certain equivalent relationship. If dt1 can be known, EqD(1) can be calculated by Equation 6; Knowing EqD(1) greatly reduces the time delay of ONU-PON-1 online registration.

It should be noted that Ts1 in Figure 4 does not refer to the time stamp at the time when OLT-PON-1 sends the time synchronization message, but refers to the time stamp carried in the time synchronization message sent by OLT-PON-1; Tr1 does not refer to ONU- The time stamp of the time when PON-1 receives the time synchronization message is the time stamp of the time when ONU-PON-1 completes the time synchronization message.

Step 3. ONU-PON-0 sends a 1588 message to ONU-PON-1. The so-called 1588 refers to the clock synchronization protocol standard defined by the IEEE 1588 protocol. The purpose of this standard is to accurately synchronize the scattered and independent clocks in the system; the 1588 message refers to the time synchronization message that conforms to this protocol. The 1588 message sent by the ONU-PON-0 includes a sending time stamp, and the sending time stamp is used to indicate the time when the 1588 message was sent, and the ONU-PON-0 time Ts2. After receiving the 1588 message, ONU-PON-1 writes a reception time stamp in the 1588 message, and the reception time stamp is used to indicate the time of receiving the 1588 message, the ONU-PON-1 time Tr2. According to formula 6, the time Ts2 when ONU-PON-0 sends the 1588 message, the local time of ONU-PON-1 should be Ts2-dt1. Assuming that the transmission time of 1588 packets sent from ONU-PON-0 to ONU-PON-1 is dt2, the difference between the receiving timestamp and the sending timestamp can be expressed by the following formula

Ts2-Tr2=Ts2-(Ts2-dt1+dt2)=dt1-dt2 (8)

Among them, dt2 is the Ethernet link delay or the Ethernet link transmission time between the ONU-PON-0 and ONU-PON-1 modules inside the ONU, which can be preset in the ONU software in advance. Therefore, the ONT can calculate and obtain dt1 according to the receiving timestamp and sending timestamp in the 1588 packet, and further obtain EqD(1). The subsequent ONU-PON-1 takes EqD(1) as the equalization delay for communication with the OLT, that is, waits at least the time corresponding to EqD(1) before sending the upstream message. It should be noted that the Ethernet link delay between ONU-PON-0 and ONU-PON-1 can be calculated in advance through the 1588 time synchronization protocol; for example, ONU-PON-0 and ONU-PON-1 first complete the time delay After synchronization, ONU-PON-0 sends a 1588 message to ONU-PON-1. ONU-PON-0 and ONU-PON-1 write the sent or received timestamp in the sent or received 1588 message, and the ONU calculates The difference between the receiving timestamp of ONU-PON-1 and the sending timestamp of ONU-PON-0 is the Ethernet link delay. It should also be noted that after ONU-PON-1 determines the equalization delay, ONU-PON-1 also needs to modify the local maintenance time to ensure time synchronization with the OLT; ONU-PON-1 can modify the local time through dt1, and also Time synchronization with ONU-PON-0 or OLT can be completed again through the time synchronization process.

In FIG. 4, the time difference dt1 between the ONU-PON-0 time and the ONU-PON-1 time is obtained by sending an Ethernet message. Those skilled in the art can understand that the ONU-PON-0 time and the ONU-PON-0 time can also be obtained in other ways. The time difference between ONU-PON-1 time. For example, let ONU-PON-0 and ONU-PON-1 report the current time at the same time, or obtain ONU-PON-0 time and ONU-PON-1 time by means of interrupt triggering.

It can be seen that, through the method described in FIG. 4 , ONU-PON-1 can obtain the transmission delay dt1 from the OLT to the ONU without performing windowing and ranging, and then obtain the equalization delay EqD(1). The ONU-PON-1 module of ONU1 does not need to open the window for distance measurement, and the ONU-PON-1 can complete the registration and online process faster. Since it does not need to open the window, it does not need to suspend the upstream transmission channels of other ONUs, so it can reduce the need for other ONUs. The service impact of the ONU; similarly, the ONU-PON-1 modules of other ONUs do not need to perform windowing and ranging, which also reduces the business impact on the ONU-PON-1 module of the ONU1. When the business transmitted by the ONU-PON-1 module is a real-time business or a delay-sensitive business, the delay caused by windowing and ranging is avoided.

The window-free ranging solution proposed in this application can reduce the time delay of PON network service transmission. The two PON modules in the ONU communicate with the OLT through different ODNs (or called different channels, the first channel and the second channel) respectively: the OLT completes the ONT measurement in the first channel (such as ODN-0). The second channel (such as ODN-1) does not need to perform windowing ranging. The first channel is a communication channel that needs ranging, and the communication of the first channel can be based on communication protocols such as GPON, XG-PON, XGS-PON, TWDM-PON, EPON, 10G EPON; the second channel does not require ranging The communication channel of the second channel can be based on communication protocols such as GPON, XG-PON, XGS-PON, TWDM-PON, EPON, and 10G EPON.

The present invention also provides a network device, which is the ONU shown in FIG. 3 .

As shown in FIG. 5 , the network device 500 includes two modules, a first module 501 and a second module 502 , respectively corresponding to ONU-PON-0 and ONU-PON-1 in the above embodiment, such as the first module 501 corresponding to ONU-PON-0, the second module 502 corresponds to ONU-PON-1. The first module 501 includes a processor 5011, a memory 5012, a PON medium access control (MAC) chip 5013, a transceiver 5014, a time control 5015 and an Ethernet MAC chip 5016 and other modules. Similarly, the second module 502 includes a processor 5021, a memory 5022, a PON medium access control (MAC) chip 5023, a transceiver 5024, a time control module 5025, an Ethernet MAC chip 5026 and other modules.

The processors 5011 and 5021 can use a general-purpose central processing unit (Central Processing Unit, CPU), a microprocessor, an application-specific integrated circuit ASIC, or at least one integrated circuit for executing related programs, and the processor 5011 and the processor 5021 control The first module and the second module complete the business logic in the above embodiment, as in step 1, the processor 5011 determines that Ts0+dt0 is the absolute time of receiving the synchronization message, and sets the absolute time to the time control module 5015, The time control module 5015 uses this time as the benchmark to perform the subsequent time maintenance of the first module; in step 2, the processor 5021 determines Ts1, and sets Ts1 to the time control module 5025, and the time control module 5025 uses this time as the benchmark to perform the first module. Subsequent time maintenance of the second module; in step 3, the processor 5025 obtains the sending time stamp and the receiving time stamp of the 1588 message, and calculates and determines the balanced delay of the second module according to formula 7 and formula 8.

The memories 5012 and 5022 may be read only memories (Read Only Memory, ROM), static storage devices, dynamic storage devices, or random access memory (Random Access Memory, RAM). Memories 5012 and 5022 may store operating systems and other applications. When implementing the technical solutions provided by the embodiments of the present invention through software or firmware, program codes for implementing the technical solutions provided by the embodiments of the present invention are stored in the memories 5012 and 5022 and executed by the processors 5011 and 5021 .

The PON MAC chips 5013 and 5023 are respectively under the control of the processors 5011 and 5021, and are responsible for the PON user plane data forwarding with the OLT. The PON MAC chips 5013 and 5023 may include a physical coding sublayer and a MAC control sublayer.

In one embodiment, the processor 5011 may include a memory 5012, and the processor 5021 may include a memory 5022. In another embodiment, the processor 5011 and the memory 5012 are two independent structures, and the processor 5021 and the memory 5022 are two independent structures.

In one embodiment, processor 5011 and processor 5021 are two independent processors, and memories 5012 and 5022 are two independent memories. In another embodiment, the processor 5011 and the processor 5021 are physically the same processor, and the memories 5012 and 5022 are physically the same memory.

In one embodiment, the processor 5011 and the MAC chip 5013 may be two independent structures, and the processor 5021 and the MAC chip 5023 may be two independent structures. In another embodiment, the processor 5013 may include a MAC chip 5013, and the processor 5023 may include a MAC chip 5023.

Transceivers 5014 and 5024 may include optical transmitters and/or optical receivers. Optical transmitters can be used to transmit optical signals, and optical receivers can be used to receive optical signals. The light transmitter can be realized by a light-emitting device, such as a gas laser, a solid-state laser, a liquid laser, a semiconductor laser, a directly modulated laser, and the like. The optical receiver may be implemented by a photodetector, such as a photodetector or a photodiode (eg, an avalanche diode) or the like. Transceivers 5014 and 5024 may also include digital-to-analog converters and analog-to-digital converters. The first module 501 communicates with the OLT through the transceiver 5014 , and the second module 502 communicates with the OLT through the transceiver 5024 .

The time control modules 5015 and 5025 are respectively responsible for the time control of the first module and the second module, and perform timing and time maintenance according to the time set by the processor.

The Ethernet MACs 5016 and 5026 are responsible for the Ethernet intercommunication between the first module and the second module. The processor can be directly connected to the Ethernet MAC, or can be connected to the Ethernet MAC through a repeater. As in step 3, the processor 5011 of the first module sends the 1588 message to the first module through the Ethernet MAC 5016, and the Ethernet MAC 5026 of the second module sends the processor 5021 to process the 1588 message after receiving the 1588 message.

The ONU shown in FIG. 5 implements the above-mentioned method of avoiding ranging and determining the equalized delay, and the beneficial effects brought by it will not be repeated here.

The present invention also provides a PON system, which includes the above-mentioned optical line terminal OLT 110 and at least one ONU 130, wherein the ONU 130 has the structure and function as shown in 5. The ONU 130 includes two PON modules, and the OLT also includes two PON modules. The connection relationship between the OLT 110 and the ONU 130 is shown in Figure 3, and the two PON modules of the ONU 130 are respectively connected to the two PON modules of the OLT 110 through different ODNs.

Finally, it should be noted that those skilled in the art should understand that the time synchronization described in this application may have certain synchronization errors or clock errors or time errors; Synchronization does not mean that the clock of the first module of the ONU and the clock of the OLT are completely error-free, and the clocks between the two may have errors within a certain range, such as a microsecond-level error.

In the above-mentioned embodiments, it may be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented in software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer may be a general purpose computer, special purpose computer, computer network, or other programmable device. The computer instructions may be stored in or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions may be downloaded from a website site, computer, server, or data center Transmission to another website site, computer, server, or data center is by wire (eg, coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (eg, infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, a data center, or the like that includes an integration of one or more available media. The usable media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g. DVD), or semiconductor media (e.g. Solid State Disk (SSD)), among others.

Claims (20)

1. A method for determining the transmission delay of a passive optical network PON, comprising:

   The first module of the optical network unit ONU communicates with the OLT through the first optical distribution network ODN, and the time of the first module is synchronized with the time of the OLT;

   The second module of the ONU receives the time synchronization message sent by the OLT, the second module communicates with the OLT through the second ODN, the time synchronization message includes a first time stamp, and the first time stamp The counter value that identifies the OLT is the OLT time at time K;

   When the counter value of the second module is K, the ONU sets the second module time to the time of the first time stamp;

   The ONU determines the first time difference according to the first module time and the second module time, and the first time difference is equal to the difference between the second module time and the OLT time at the same moment, and the The first time difference is equal to the transmission delay of the time synchronization message from the OLT to the second module.
2. The method according to claim 1, wherein the time synchronization message received by the second module further includes a superframe count value K of the OLT, and the time identified by the first timestamp is the time of the OLT. The value of the superframe counter is equal to the OLT time at time K; when the value of the superframe counter of the second module is equal to K, the ONU sets the time of the second module to the time identified by the first timestamp.
3. The method according to claim 1 or 2, wherein the ONU determines the first time difference according to the first module time and the second module time, which specifically includes:

   The first module sends a first message to the second module, the first message includes a sending time stamp, and the sending time stamp is the time of the first module, and the first module sends the The time at the time of the first packet, the second module adds a reception timestamp to the first packet when receiving the first packet, and the reception timestamp is the time of the second module, so the time when the second module receives the first message;

   The ONU determines a second time difference, and the second time difference is the difference between the receiving timestamp and the sending timestamp;

   The ONU determines the first time difference according to the second time difference and the Ethernet link delay, where the first time difference is the sum of the second time difference and the Ethernet link delay. The delay is the delay of communication between the first module and the second module through the Ethernet link.
4. The method according to any one of claims 1-3, wherein the method further comprises: the ONU determining, according to the first time difference, an equalization delay for communication between the second module and the OLT.
5. The method according to claim 4, wherein the ONU determines the equalization delay EqD2 of the communication between the second module and the OLT according to the following calculation formula:

   EqD2=Teqd-RspTime2-(dt/(n1/(n1+n2))),

   Wherein, Teqd is zero distance equivalent time delay, RspTime2 is the response time of the ONU, dt is the first time difference, n1 is the refractive index of the downlink light communicated between the OLT and the ONU, and n2 is the The refractive index of the upstream light communicated between the ONU and the OLT.
6. The method according to claim 4 or 5, wherein after the ONU determines the equalization delay of the communication between the second module and the OLT, the method further comprises:

   After processing the request of the OLT, the second module waits at least for a duration corresponding to the equalization delay, and then sends an uplink message to the OLT.
7. The method according to claim 3, characterized in that, the method further comprises: measuring, by the ONU, an Ethernet link delay between the first module and the second module according to a 1588 time synchronization protocol.
8. A PON network device is characterized by comprising a first module and a second module,

   The first module is used to complete ranging and time synchronization with the optical line terminal OLT through the first ODN;

   The second module is configured to receive the time synchronization message sent by the OLT through the second ODN, where the time synchronization message includes a first time stamp, and the first time stamp identifies the counter value of the OLT as time K When the counter value of the second module is K, the second module time is set to the time identified by the first time stamp; the first time difference is determined, and the first time difference is equal to the time at the same time. The difference between the time of the second module and the time of the OLT, and the first time difference is equal to the transmission delay of the time synchronization message from the OLT to the second module.
9. The apparatus according to claim 8, wherein the time synchronization message received by the second module further includes a superframe count value K of the OLT, and the time identified by the first timestamp is the time of the OLT. The superframe counter value is equal to the OLT time at time K; the second module is further configured to set the second module time as the first timestamp when the superframe counter value of the second module is equal to K identified time.
10. The device according to claim 8 or 9, characterized in that,

    The first module is further configured to send a first message to the second module, where the first message includes a sending time stamp, and the sending time stamp is the time of the first module when the first message is sent. the time when the module sends the first message;

    The second module is further configured to add a reception timestamp to the first packet when receiving the first packet, where the reception timestamp is the time of the second module, the second module the time when the first packet is received; determine a second time difference, where the second time difference is the difference between the receiving timestamp and the sending timestamp; determine the first time difference according to the second time difference and the Ethernet link delay Time difference, the first time difference is the sum of the second time difference and the Ethernet link delay, and the Ethernet link delay is the Ethernet link between the first module and the second module. delay in communicating.
11. The apparatus according to any one of claims 8-10, wherein the second module is further configured to determine the equalization delay of the communication between the second module and the OLT according to the first time difference.
12. The device according to claim 11, wherein the second module determines the equalization delay EqD2 of the communication between the second module and the OLT according to the following calculation formula:

    EqD2=Teqd-RspTime2-(dt/(n1/(n1+n2))),

    Wherein, Teqd is zero distance equivalent delay, RspTime2 is the response time of the second module, dt is the first time difference, n1 is the refractive index of the downlink light communicated between the OLT and the ONU, and n2 is The refractive index of the upstream light communicated between the second module and the OLT.
13. The apparatus according to claim 11 or 12, wherein the second module is further configured to, after processing the request of the OLT, at least wait for a duration corresponding to the equalization delay, and then send the request to the OLT. The OLT sends upstream packets.
14. The device according to claim 9, wherein the second module measures the Ethernet link delay between the first module and the second module according to a 1588 time synchronization protocol.
15. The device according to any one of claims 8-14, wherein the first module comprises a processor, a memory, a PON medium access control (MAC) chip, a transceiver and a time control module, and the The second module also includes a processor, a memory, a PON medium access control (MAC) chip, a transceiver and a time control module;

    The first module processor is used to control the first module to complete ranging and time synchronization, and the first module PON MAC chip is used to complete the communication with the OLT under the control of the first module processor. data forwarding, the first module transceiver is configured to communicate with the OLT through the first ODN, and the first module time control module is configured to control the first module time;

    The second module transceiver is used to communicate with the OLT through the second ODN, and the second module PON MAC chip is used to complete data with the OLT under the control of the second module processor. Send and receive, the second module processor is used to process the received time synchronization message, and when the counter value of the second module is K, the second module time is set to the first timestamp The identified time, the second module time control module is configured to control the second module time according to the setting of the second module processor;

    The second module processor is further configured to determine the first time difference according to the first module time and the second module time.
16. The device according to claim 15, wherein the first module further comprises an Ethernet MAC chip, the second module further comprises an Ethernet MAC chip, the first module Ethernet MAC chip and the second module Ethernet MAC chips communicate with each other through the Ethernet link;

    The first module processor is further configured to send the first message to the second module Ethernet MAC chip through the first module Ethernet MAC chip;

    The second module Ethernet MAC chip is used for forwarding the first packet to the second module processor for processing;

    The second module processor is further configured to add a reception time stamp to the first message, where the reception time stamp is the time of the second module, and the second module receives the first message the time of the moment; determine the second time difference, the second time difference is the difference between the receiving timestamp and the sending timestamp; determine the first time difference according to the second time difference and the Ethernet link delay, the first time difference is the sum of the second time difference and the Ethernet link delay, where the Ethernet link delay is the delay for communication between the first module and the second module through the Ethernet link.
17. The apparatus according to claim 15 or 16, wherein the second module processor is further configured to determine the difference between the second module and the second module according to the ONU response time, the zero-distance equivalent delay and the first time difference Equalization delay of the OLT communication.
18. A passive optical network PON system, comprising an ONU and an OLT, the ONU is configured to execute the method according to any one of claims 1-6, so as to determine an equalized delay in communication with the OLT.
19. A computer-readable storage medium comprising instructions which, when run on a computer, cause the computer to perform the method of any one of claims 1-7.
20. A computer program product comprising instructions which, when run on a computer, cause the computer to perform the method of any of claims 1-7.

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