CN114567827A

CN114567827A - Method for determining transmission time delay of passive optical network

Info

Publication number: CN114567827A
Application number: CN202011358520.1A
Authority: CN
Inventors: 宋显辉; 张伦; 龚瑞
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-11-27
Filing date: 2020-11-27
Publication date: 2022-05-31
Also published as: WO2022111045A1

Abstract

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, and the time synchronization message includes the first time stamp; the ONU sets the time of the second module to the time identified by the first time stamp; the ONU according to the first module time and the first time stamp The second module time determines the first time difference, and the first time difference is equal to the transmission delay of the time synchronization message from the OLT to the second module. Through this method, 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 a balanced delay, which avoids the impact of windowing on other ONUs' services and reduces windowing. Delay caused by ranging.

Description

Method for determining transmission time delay of passive optical network

Technical Field

The present disclosure relates to the field of Optical communications, and in particular, to a method and an apparatus for ranging in a Passive Optical Network (PON) system.

Background

Passive Optical Network (PON) technology is a point-to-multipoint Optical fiber access technology. The 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 with a plurality of ONUs through the ODN.

All the ONUs under one PON port of the OLT adopt a time division multiplexing mode, and uplink data is sent to the OLT through the ODN at the time designated by the OLT. The OLT must accurately measure the distance between each ONU and the OLT through ranging (ranging) in order to control the timing at which each ONU transmits upstream data. The OLT needs to open a window in the ranging process, namely the Quiet Zone suspends the uplink sending channels of other ONUs. Since the OLT does not authorize other ONUs to send upstream data during the windowing, a transmission delay may be incurred for traffic data transmitted by other ONUs.

At present, more and more service scenes provide a technical requirement of low time delay for a PON system, such as a 5G service scene, an Optical Transport Network (OTN) dedicated line service scene, and the like. How to reduce the service delay caused by windowing ranging becomes a technical problem to be solved urgently.

Disclosure of Invention

The application provides a method for determining transmission delay of a PON system, and a device and a system for realizing the method.

In a first aspect, the present application provides a method for determining a passive optical network PON transmission delay. The optical network unit ONU comprises a first module and a second module, wherein the first module communicates with the OLT through a first optical distribution network ODN, and the second module communicates with the OLT through a second ODN; the time synchronization between the first module and the OLT is completed; the second module receives a time synchronization message sent by the OLT, wherein the time synchronization message comprises a first time stamp which identifies the OLT time when the counter value of the OLT is K; when the counter value of the second module is K, the ONU sets the time of the second module as the time identified by the first timestamp; and the ONU determines the first time difference according to the first module time and the second module time, wherein the first time difference is equal to the difference value of the second module time and the OLT time at the same time, and the first time difference is equal to the transmission time delay of the time synchronization message from the OLT to the second module. By the method of the first aspect, the second module of the ONU does not need to perform windowing ranging, and can obtain the transmission delay from the OLT to the ONU, thereby obtaining the equalization delay. The second module can complete the registration on-line process more quickly because windowing distance measurement is not needed; because windowing is not needed, and uplink sending channels of other ONUs do not need to be suspended, the service influence on other ONUs can be reduced; similarly, the second modules of other ONUs do not need to perform windowing ranging, and the service impact on the ONU is also reduced. When the service transmitted by the second module is a real-time service or a delay sensitive service, the delay caused by 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 a superframe count value K of the LT, and the time identified by the first timestamp is the OLT time when the superframe counter value of the OLT is equal to the time of the OLT at the moment K; and when the superframe counter value of the second module is equal to K, the ONU sets the time of the second module as 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 method comprises the steps that a first module sends a first message to a second module, the first message comprises a sending timestamp, the first module sends the first message at the time when the sending timestamp is the time of the first module, the second module adds a receiving timestamp in the first message when receiving the first message, and the second module receives the first message at the time when the receiving timestamp is the time of the second module; the ONU determines a second time difference, wherein the second time difference is the difference value between the receiving time stamp and the sending time stamp; and the ONU determines a first time difference according to the second time difference and the Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time delay of the communication between the first module and the second module through the Ethernet link.

In a possible implementation manner of the first aspect, the ONU determines the equalization delay of the second module in communication with the OLT according to the first time difference, for example, determines the equalization delay EqD2 of the second module in communication with the OLT according to the following calculation formula:

EqD2＝Teqd-RspTime2-(dt/(n1/(n1+n2))),

wherein Teqd is the zero-distance equivalent time delay, RspTime2 is the response time length 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 refractive index of the uplink light communicated between the ONU and the OLT.

In a possible implementation manner of the first aspect, after determining the equalization delay of the communication between the second module and the OLT, the ONU waits for at least a duration corresponding to the equalization delay after processing the request of the OLT, and then sends the uplink packet to the OLT.

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

In a second aspect, the present application provides a PON system device. The device comprises a first module and a second module; the first module is used for completing ranging and time synchronization with an Optical Line Terminal (OLT) through a first Optical Distribution Network (ODN); a second module, configured to receive, through a second ODN, a time synchronization message sent by an OLT, where the time synchronization message includes a first timestamp, and the first timestamp identifies an OLT time at which a counter value of the OLT is K times; when the counter value of the second module is K, setting the time of the second module as the time identified by the first timestamp; and determining a first time difference, wherein the first time difference is equal to the difference between the time of the second module and the time of the OLT at the same time, 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 a superframe count value K of the OLT, and the time identified by the first timestamp is the time of the OLT when the superframe counter value of the OLT reaches K; and the second module is further configured to set the second module time to 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 a time when the first packet is sent by the first module at the time of the first module; the second module is further used for adding a receiving timestamp in the first message when the first message is received, wherein the receiving timestamp is the time of the second module at the moment when the second module receives the first message; determining a second time difference, wherein the second time difference is the difference value between the receiving time stamp and the sending time stamp; and determining a first time difference according to the second time difference and the Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time 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 an equalization delay of the second module in communication with the OLT according to the first time difference, for example, determine an equalization delay EqD2 of the second module in communication with the OLT according to the following calculation formula:

EqD2＝Teqd-RspTime2-(dt/(n1/(n1+n2))),

wherein Teqd is the zero-distance equivalent time delay, RspTime2 is the response time length 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 uplink light communicated between the second module and the OLT.

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

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

In a possible implementation manner of the second aspect, the first module includes a processor, a memory, a PON Media Access Control (MAC) chip, a transceiver, and a time control module, and the second module also includes a processor, a memory, a PON Media Access Control (MAC) chip, a transceiver, and a time control module; the first module processor is used for controlling the first module to finish ranging and time synchronization, the first module PON MAC chip is used for finishing data forwarding with the OLT under the control of the first module processor, the first module transceiver is used for communicating with the OLT through the first ODN, and the first module time control module is used for controlling the first module time; the second module transceiver is used for communicating with the OLT through a second ODN, the PON MAC chip of the second module is used for completing data transceiving with the OLT under the control of the second module processor, the second module processor is used for processing the received time synchronization message, when the counter value of the second module is K, the time of the second module is set as the time marked by the first timestamp, and the time control module of the second module is used for controlling the time of the second module according to the setting of the second module processor; the second module processor is further configured to determine a first time difference based on 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 are intercommunicated through an ethernet link; the first module processor is also used for sending a 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 message to the second module processor for processing; the second module processor is also used for adding a receiving timestamp in the first message, wherein the receiving timestamp is the time of the second module at the moment when the second module receives the first message; determining a second time difference, wherein the second time difference is the difference value of the receiving time stamp and the sending time stamp; and determining a first time difference according to the second time difference and the Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time 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 an equilibrium delay of the second module in communication with the OLT according to the ONU response time length, the zero-distance equivalent delay, and the first time difference.

In a third aspect, the present application provides a PON communication system, which includes an OLT and the ONU according to the first or second aspect.

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

Drawings

Fig. 1 is a schematic diagram of a PON system according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram illustrating a principle of ranging of a PON system according to an embodiment of the present disclosure;

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

fig. 4 is a schematic diagram of time synchronization of a PON system according to 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 Description

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

The technical solution of the embodiment of the present application may be applied to various passive optical network systems, for example, a next-generation PON (NG-PON), an NG-PON1, an NG-PON2, a gigabit-capable PON (GPON), a 10 gigabit-per-second PON (10 gigabit-per-second PON, XG-PON), a symmetric 10 gigabit-per-second passive optical network (10 gigabit-symmetric passive optical network, XGs-PON), an Ethernet PON (Ethernet PON, EPON), a 10 gigabit-per-second PON (10 gigabit-per-second PON, 10G-EPON), a next-generation EPON (next-generation PON, NG-EPON), a wavelength division multiplexing (wavelength-division multiplexing, WDM) PON, a time division multiplexing (time-wavelength-division multiplexing, WDM) PON, a time division multiplexing (WDM-wavelength-division multiplexing, WDM) PON, a WDM-wavelength division multiplexing (WDM-wavelength-division multiplexing, WDM-PON, WDM-wavelength division multiplexing (WDM-wavelength-division multiplexing, WDM) PON, WDM-node (WDM-node, and WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, WDM-node, and node, asynchronous transfer mode PONs (APONs), Broadband PONs (BPONs), and the like, as well as 25gigabit per second PONs (25G-PONs), 50gigabit per second PONs (50G-PONs), 100gigabit per second PONs (100G-PONs), 25gigabit per second EPONs (25gigabit per second, 25G-EPONs), 50gigabit per second EPONs (50gigabit per second, 50G-EPONs), 100gigabit per second EPONs (100gigabit per second, 100G-EPONs), and other rates of GPONs, EPONs, and the like.

Fig. 1 is a schematic diagram of an architecture of a PON system, and as shown in fig. 1, the PON system 100 includes at least one OLT 110, at least one ODN 120, and a plurality of ONUs 130. The OLT 110 provides a network side interface for the PON system 100, and the ONU130 provides a user side interface for the PON system 100, and is connected to the ODN 120. If ONU130 directly provides the user port function, it is called Optical Network Terminal (ONT). For convenience of description, the ONU130 mentioned below refers to an ONT that can directly provide a user port function and an ONU that provides a user side interface. The ODN 120 is a network composed of optical fibers and passive optical splitting devices, and is used for connecting the OLT 110 device and the ONU130 device, and for distributing or multiplexing data signals between the OLT 110 and the ONU 130.

In the PON system 100, a direction from the OLT 110 to the ONUs 130 is defined as a downstream direction, and a direction from the ONUs 130 to the OLT 110 is defined as an upstream direction. In the downlink direction, the OLT 110 broadcasts downlink data to a plurality of ONUs 130 managed by the OLT 110 in a Time Division Multiplexing (TDM) manner, and each ONU130 only receives data carrying its own identifier; in the uplink direction, the ONUs 130 communicate with the OLT 110 in a Time Division Multiple Access (TDMA) manner, and each ONU130 transmits uplink data according to the Time domain resource allocated to it by the OLT 110. With the above mechanism, the downstream optical signal transmitted by the OLT 110 is a continuous optical signal, and the upstream optical signal transmitted by the ONU130 is a burst optical signal.

The OLT 110 is typically located in a Central Office (CO), and may collectively manage at least one ONU130 and transmit data between the ONU130 and an upper network. In particular, the OLT 110 may act as an intermediary between the ONUs 130 and the upper Network (e.g., the Internet, a Public Switched Telephone Network (PSTN)), forwarding data received from the upper Network to the ONUs 130, and forwarding data received from the ONUs 130 to the upper Network, the particular configuration of the OLT 110 may vary depending on the particular type of PON system 100. for example, in one embodiment, the OLT 110 may include a transmitter configured to transmit downstream continuous optical signals to the ONUs 130 and a receiver configured to receive upstream optical burst signals from the ONUs 130, wherein the downstream optical signals and the upstream optical signals may be transmitted through the ODN 120, although embodiments of the invention are not limited in this respect.

The ONUs 130 may be distributively located at customer-side locations (e.g., customer premises). The ONU130 may be a network device for communicating with the OLT 110 and a user, in particular, the ONU130 may act as an intermediary between the OLT 110 and the user, e.g. the ONU130 may forward data received from the OLT 110 to the user and forward data received from the user to the OLT 110.

The ODN 120 may be a data distribution network and 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 component, and in particular, the optical fiber, optical coupler, optical splitter, or other device may be a component that does not require power support when distributing data signals between the OLT 110 and the ONUs 130. Specifically, taking an optical Splitter (Splitter) as an example, the optical Splitter may be connected to the OLT 110 through a trunk optical fiber and connected to the ONUs 130 through a plurality of branch optical fibers, respectively, so as to implement a point-to-multipoint connection between the OLT 110 and the ONUs 130. Additionally, in other embodiments, the ODN 120 may also include one or more processing devices, such as optical amplifiers or Relay devices (Relay devices). In addition, the ODN 120 may specifically extend from the OLT 110 to multiple ONUs 130, but may also be configured in 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 unequal, the transmission time of optical signals on the optical fiber is different, and the time when the optical signals reach the ONUs is different. Meanwhile, the Round Trip Delay (RTD) of the OLT and the ONU also varies with time and environment. In order to ensure that the upstream data sent by each ONU to the OLT is inserted into a specified time slot after the ODN fibers are merged, and the specified time slot does not collide with each other and the gap is not too large, the OLT must accurately measure the distance between each ONU and the OLT through ranging (ranging) so as to control the time when each ONU sends the upstream data. The OLT starts a ranging function when the ONU registers for the first time, obtains the RTD of the round trip Delay of the ONU, calculates the physical distance of each ONU, and specifies an appropriate Equalization Delay (EqD) parameter according to the physical distance of the ONU. The OLT needs to open a window in the ranging process, namely the Quiet Zone suspends the uplink sending channels of other ONUs. The OLT assigns the EqD to the ONUs to synchronize data frames sent by the ONUs, so that collision cannot be generated on the optical splitter when each ONU sends data. All ONUs are at the same logic distance, and data can be sent in corresponding time slots, so that collision and collision of uplink cells are avoided.

The ranging of the GPON is completed in the ONU registration stage, and when the ONU receives an SN request message sent by the OLT, the ONU returns an SN response message after waiting for a certain response time. After receiving the response message and verifying that the response message is legal, the OLT allocates an ONU-ID to the ONU, and the ONU enters a ranging state after receiving the allocated ONU-ID.

The principle of the OLT calculating and assigning the equalization delay is shown in fig. 2. Assuming that the OLT sends a ranging request to an ONU at time T1 while commanding other ONUs to stop sending upstream traffic, a ranging window is opened in the upstream time slot for this ONU to use. The ONU receives the ranging request at time T2, performs internal processing, and then transmits an upstream frame in response to the ranging request at time T3, and the OLT receives the upstream frame in response to the ranging request at time T4. Then the OLT can calculate the RTD of the ONU according to T4 and T1. The zero-distance equivalent delay Teqd in fig. 1 is a value set by the OLT according to the farthest optical fiber length, and is greater than or equal to the RTD of the ONU farthest in logical distance. In order to ensure that the uplink data phases of all ONUs connected to the same PON interface of the OLT are the same, the OLT allocates an EqD to all ONUs under the same PON interface of the OLT according to the following principle, wherein i represents an ONU number:

Teqd＝RTD(i)+EqD(i) (1)

EqD(i)＝Teqd-RTD(i) (2)

after the subsequent ONU processes the request of the OLT, the subsequent ONU needs to wait for the EqD time and then sends the uplink data or the uplink frame, so that the uplink data phases of all the ONUs under the same PON port of the OLT can be ensured to be the same.

Based on the eqd (i) determined by the ranging process, time synchronization is also required between the OLT and the ONU. It should be noted that, each PON module in the ONU and each PON module in the OLT are respectively timed by a time control module, and when time synchronization is not performed, the time of the ONU and the time of the OLT may be different at the same time, and even the time between the PON modules in the ONU may be different. A well understood example is that at the same time, beijing time is 18 points and london time is 10 points. Therefore, similar descriptions of ONU time or OLT time, etc. are used in this application to indicate the timing of different devices or modules.

The ITU g.984.3 standard defines a time synchronization scheme. In the scheme, an OLT sends a time synchronization message to an ith ONU, wherein the time synchronization message carries a time stamp Tsend (i) of the OLT, the ith ONU calculates and obtains the transmission delay of the time synchronization message according to EqD (i) after receiving the time synchronization message, and the local time Trecv (i) of the ONU is set as the transmission delay of the Tsend (i) + time synchronization message, namely

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

Wherein, eqd (i) is the determined equalization delay after the i-th ONU measures the distance, rsptime (i) is the response duration of the i-th ONU (as shown in fig. 1, duration T3-T2), nd is the refractive index of the downstream wavelength, and nu is the refractive index of the upstream wavelength, and (Teqd-eqd (i) -rsptime (i) (nd/(nd + nu)) is the transmission delay of the time synchronization message calculated according to eqd (i).

It should be understood by those skilled in the art that, for the sake of emphasis, the ranging and time synchronization procedures described in the embodiments of the present application may be outlined for some message procedures; in a specific implementation, the time synchronization message sent by the OLT may further carry a superframe count value of the OLT corresponding to the time tsend (i), and after the ith 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, the local time trecv (i) of the ONU is set to the transmission delay of the tsend (i) + time synchronization message.

Fig. 3 is a system architecture suitable for use in 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 ONU130 in fig. 1, respectively. In fig. 3, each ONU comprises 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 comprises two PON modules, OLT-PON-0 and OLT-PON-1, wherein the ONU-PON-0 communicates with the OLT-PON-0 through ODN-0, and the ONU-PON-1 communicates with the OLT-PON-1 through ODN-1. And the two PON modules of the ONU are respectively registered in the PON modules of the connected OLT, namely the ONU-PON-0 is registered in the OLT-PON-0 through ODN-0, and the ONU-PON-1 is registered in the OLT-PON-1 through ODN-1. The ONU-PON-0 and the ONU-PON-1 correspond to two virtual ONUs and communicate with the OLT through different ODNs. When one ONU needs to measure the distance, the OLT sends a distance measurement request to the ONU and also commands other ONUs to stop sending the upstream service, so that the distance measurement process affects the real-time performance of the services transmitted by the ONU performing the distance measurement and other ONUs. Since the ONU-PON-0 and the ONU-PON-1 communicate with the OLT through different ODN networks, in the prior art, the OLT needs to perform ranging for the ONU-PON-0 and the ONU-PON-1, respectively. Namely, each PON module of each ONU needs to perform ranging, and the problem of delay caused by ranging is more prominent.

In order to solve the problem of time delay caused by windowing ranging, the present application provides a ranging scheme without windowing, and the scheme can be applied to a PON network architecture as shown in fig. 3. The ranging scheme proposed in the present application is described below based on fig. 4. Fig. 4 is a timing diagram of communication between the OLT and the ONUs. The horizontal axis corresponding to the OLT represents the time axis of the OLT; the horizontal axis corresponding to the ONU-PON-0 represents the time axis of the ONU-PON-0; the horizontal axis corresponding to the ONU-PON-1 represents the time axis of the ONU-PON-1. The ONU-PON-0 is one of the PON modules of any one of the ONUs in FIG. 3, and the ONU-PON-1 is the other PON module of the ONU. The OLT comprises 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 described in fig. 3.

Step 1, after the ONU is powered on, the ONU-PON-0 completes the distance measurement and time synchronization with the OLT-PON-0. The time maintained on the ONU-PON-0 is consistent with the time of the OLT-PON-0. The ONU-PON-0 and the OLT-PON-0 can perform ranging and time synchronization according to the ITU standard definition method. If it is assumed that the OLT-PON-0 sends a time synchronization message to the ONU-PON-0, the time synchronization message carries a timestamp of Ts0 time, and the ONU-PON-0 receives the time synchronization message after a certain transmission delay (e.g. dt0), as shown in formula (3),

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

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

The ONU-PON-0 completes time synchronization with the OLT-PON-0 based on dt0 and Ts0 in the time synchronization message, and at the time of Tr0, the ONU-PON-0 time and the OLT-PON-0 time are Ts0+ dt 0; wherein at the time of Tr0, the superframe count value of the ONU-PON-0 is the same as the superframe count value of the OLT-PON-0 in the time synchronization message.

It should be noted that Ts0 in fig. 4 refers not to the timestamp of the time when OLT-PON-0 sends the time synchronization message, but to the timestamp carried in the time synchronization message sent by OLT-PON-0; tr0 does not refer to a time stamp of the time when the ONU-PON-0 receives the time synchronization message, but a time stamp of the time when the ONU-PON-0 completes the time synchronization message (e.g., Tr0 corresponds to the time when the superframe count value of the ONU-PON-0 is equal to the superframe count value in the time synchronization message).

And 2, the OLT sends a time synchronization message to the ONU-PON-1 through the OLT-PON-1, wherein the time synchronization message carries a time stamp Ts1 of the OLT-PON-1. After the transmission delay of dt1, the ONU-PON-1 receives a time synchronization message issued by the OLT, records a timestamp Ts1 contained in the synchronization message, and performs subsequent timing or time maintenance by taking Ts1 as a reference; specifically, at the time when the superframe count value of the ONU-PON-1 is the same as the superframe count value of the OLT-PON-1 in the time synchronization message, such as Tr1, the ONU-PON-1 sets the ONU-PON-1 time to Ts1, and the OLT-PON-1 time is Ts1+ dt 1. Therefore, the ONU-PON-1 does not really complete the time synchronization with the OLT-PON-1, and at the same time, a difference dt1 exists between the ONU-PON-1 time and the OLT time. Since the ONU-PON-0 completes time synchronization with the OLT (the OLT-PON-0 and the OLT-PON-1 are time synchronized), the difference between the ONU-PON-0 time and the ONU-PON-1 time at the same time is dt 1. It should be noted that Ts0 and Ts1 are not temporally consecutive. The OLT may send a time synchronization message to the ONU-PON-0 or to the ONU-PON-1, and in any case, after the time synchronization message is processed by the ONU-PON-0 and the ONU-PON-1 according to the steps 1 and 2, the time difference between the ONU-PON-0 time and the ONU-PON-1 time is dt1, that is, the time difference is dt at the same time

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

As described 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)

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

It can be seen from formula 7 that dt1 and EqD (1) have a certain equivalent relationship, and if dt1 can be known, EqD (1) can be obtained by calculation through formula 6; namely, the EqD (1) can be obtained without a windowing distance measurement method, and the time delay of on-line registration of the ONU-PON-1 is greatly reduced.

It should be noted that Ts1 in fig. 4 refers not to the timestamp of the time when OLT-PON-1 sends the time synchronization message, but refers to the timestamp carried in the time synchronization message sent by OLT-PON-1; tr1 does not refer to a time stamp of the time when the ONU-PON-1 receives the time synchronization message, but refers to a time stamp of the time when the ONU-PON-1 completes the time synchronization message.

And 3, the ONU-PON-0 sends 1588 messages to the ONU-PON-1. 1588, which refers to clock synchronization protocol standard defined by IEEE 1588 protocol, aims to precisely synchronize clocks which are distributed and run independently in a system; 1588 the message refers to a time synchronization message conforming to this protocol. The 1588 message sent by the ONU-PON-0 comprises a sending timestamp which is used for indicating the time of sending the 1588 message and the ONU-PON-0 time Ts 2. And writing a receiving time stamp in the 1588 message after the ONU-PON-1 receives the 1588 message, wherein the receiving time stamp is used for indicating the moment of receiving the 1588 message and the time Tr2 of the ONU-PON-1. According to the formula 6, the time Ts2 when the ONU-PON-0 sends the 1588 message, and the local time of the ONU-PON-1 should be Ts2-dt 1. Assuming that the transmission time of the 1588 message transmitted from the ONU-PON-0 to the ONU-PON-1 is dt2, the difference between the receiving timestamp and the transmitting timestamp can be expressed by the following formula

Ts2-Tr2＝Ts2-(Ts2-dt1+dt2)＝dt1-dt2 (8)

Dt2 is an ethernet link delay or ethernet link transmission time between two modules of an ONU-PON-0 and an ONU-PON-1 inside the ONU, and may be preset in the ONU software in advance. Therefore, the ONT can calculate dt1 according to the receiving timestamp and the sending timestamp in the 1588 message, and further obtain EqD (1). And the subsequent ONU-PON-1 takes the EqD (1) as the balanced time delay for communicating with the OLT, namely waiting for at least the time length corresponding to the EqD (1) before sending the uplink message. It should be noted that, the ethernet link time delay between the ONU-PON-0 and ONU-PON-1 can be measured in advance by 1588 time synchronization protocol; for example, the ONU-PON-0 and the ONU-PON-1 firstly complete time synchronization, then the ONU-PON-0 sends 1588 messages to the ONU-PON-1, the ONU-PON-0 and the ONU-PON-1 write sending or receiving time stamps in the sent or received 1588 messages, the ONU calculates the difference value between the receiving time stamp of the ONU-PON-1 and the sending time stamp of the ONU-PON-0, and the difference value is the Ethernet link delay. It should be further noted that, after the ONU-PON-1 determines the equalization delay, the ONU-PON-1 also needs to modify the local maintenance time to ensure time synchronization with the OLT; the ONU-PON-1 can modify the local time through dt1, and can also complete time synchronization with the ONU-PON-0 or the OLT through a time synchronization flow again.

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, and those skilled in the art will understand that the time difference between the ONU-PON-0 time and the ONU-PON-1 time may also be obtained by other methods. For example, the ONU-PON-0 and the ONU-PON-1 report the current time at the same time, or the ONU-PON-0 time and the ONU-PON-1 time are acquired by an interrupt triggering mode.

It can be seen that, by the method described in fig. 4, the ONU-PON-1 can obtain the transmission delay dt1 from the OLT to the ONU without performing windowing ranging, and further obtain the equalization delay EqD (1). The ONU-PON-1 module of the ONU1 does not need to be windowed for ranging, the ONU-PON-1 can more quickly finish the registration on-line process, and the uplink sending channels of other ONUs do not need to be paused because the windowing is not needed, thereby reducing the service influence on other ONUs; similarly, the ONU-PON-1 modules of other ONUs do not need to perform windowing ranging, and the traffic impact on the ONU-PON-1 module of the ONU1 is also reduced. When the service transmitted by the ONU-PON-1 module is real-time service or delay sensitive service, the delay caused by windowing and ranging is avoided.

The windowing-free ranging scheme can reduce time delay of PON network service transmission. Two PON modules in an ONU communicate with the OLT through different ODNs (or called different channels, a first channel and a second channel) respectively: the OLT completes the ranging of the ONTs in the first channel (e.g., ODN-0), and the second channel (e.g., ODN-1) does not need to perform windowing ranging. The first channel is a communication channel needing distance measurement, 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 and the like; the second channel is a communication channel without ranging, and the communication of the second channel can be based on communication protocols such as GPON, XG-PON, XGS-PON, TWDM-PON, EPON, 10G EPON and the like.

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, which correspond to the ONU-PON-0 and the ONU-PON-1 in the above embodiments, respectively, for example, the first module 501 corresponds to the ONU-PON-0, and the second module 502 corresponds to the ONU-PON-1. The first module 501 includes modules such as a processor 5011, a memory 5012, a PON Media Access Control (MAC) chip 5013, a transceiver 5014, a time control chip 5015, and an ethernet MAC chip 5016. Similarly, the second module 502 includes a processor 5021, a memory 5022, a PON Media Access Control (MAC) chip 5023, a transceiver 5024, a time control module 5025 and an ethernet MAC chip 5026.

The

processors

5011 and 5021 may adopt a general Central Processing Unit (CPU), a microprocessor, an application specific integrated circuit ASIC, or at least one integrated circuit for executing related programs, the

processors

5011 and 5021 control the first module and the second module to complete the business logic in the above embodiments, as shown in step 1, the processor 5011 determines Ts0+ dt0 as the absolute time of receiving the synchronization message, and sets the absolute time to the time control module 5015, and the time control module 5015 performs subsequent time maintenance of the first module based on the absolute time; in step 2, the processor 5021 determines Ts1, sets Ts1 to the time control module 5025, and the time control module 5025 performs subsequent time maintenance of the second module based on the time; in step 3, the processor 5025 obtains the sending timestamp and the receiving timestamp of the 1588 message, and calculates and determines the balanced delay of the second module according to a formula 7 and a formula 8.

The

memories

5012 and 5022 may be Read Only Memories (ROMs), static Memory devices, dynamic Memory devices, or Random Access Memories (RAMs). The

memories

5012 and 5022 may store an operating system and other application programs. When the technical solution provided by the embodiment of the present invention is implemented by software or firmware, program codes for implementing the technical solution provided by the embodiment 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 responsible for forwarding PON user plane data with the OLT under the control of the

processors

5011 and 5021, respectively. The

PON MAC chips

5013 and 5023 may include a physical coding sublayer and a MAC control sublayer.

In an embodiment, the memory 5012 may be included within the processor 5011 and the memory 5022 may be included within the processor 5021. In another embodiment, the processor 5011 and the memory 5012 are two separate structures and the processor 5021 and the memory 5022 are two separate structures.

In an embodiment, processor 5011 and processor 5021 are two separate processors and

memories

5012 and 5022 are two separate memories. In another embodiment, processor 5011 and processor 5021 are physically the same processor and

memory

5012 and 5022 are physically the same memory.

In one embodiment, the processor 5011 and the MAC chip 5013 may be two separate structures, and the processor 5021 and the MAC chip 5023 may be two separate structures. In another embodiment, the MAC chip 5013 may be included in the processor 5013, and the MAC chip 5023 may be included in the processor 5023.

Transceivers

5014 and 5024 may include optical transmitters and/or optical receivers. The optical transmitter may be used to transmit optical signals and the optical receiver may be used to receive optical signals. The light emitter may be implemented by a light emitting device such as a gas laser, a solid laser, a liquid laser, a semiconductor laser, a direct modulation laser, or the like. The optical receiver may be implemented by a photodetector, such as a photodetector or a photodiode (e.g., an avalanche diode), etc. The

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 a transceiver 5014 and the second module 502 communicates with the OLT through a transceiver 5024.

The

time control

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

Ethernet MACs

5016 and 5026 are responsible for ethernet interworking between the first module and the second module, and the processor may be directly connected to the ethernet MACs or may be connected to the ethernet MACs through a repeater. As in step 3, the processor 5011 of the first module sends 1588 message to the first module through the ethernet MAC5016, and the ethernet MAC 5026 of the second module receives the 1588 message and then sends the processor 5021 to process the message.

The ONU shown in fig. 5 executes the method for determining the equalization delay without ranging as described above, and the beneficial effects brought by the method are not described herein again.

The present invention further provides a PON system, which comprises the optical line terminal OLT 110 and at least one ONU130, wherein the ONU130 has the structure and function shown in fig. 5. The ONU130 comprises two PON modules and the OLT also comprises two PON modules. As shown in fig. 3, the two PON modules of the ONU130 are connected to the two PON modules of the OLT 110 through different ODNs.

Finally, it should be noted that, as will be understood by those skilled in the art, the time synchronization described in the present application may have a certain synchronization error or clock error or time error; as shown in step 1 of fig. 4, the time synchronization between the first module of the ONU and the OLT does not indicate that the clock of the first module of the ONU and the clock of the OLT are completely error-free, and there may be an error in a certain range, such as an error in the order of microseconds, between the two clocks.

In the above embodiments, the implementation may be wholly or partially realized by software, hardware, firmware, or any combination thereof. When implemented in software, may 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 loaded and executed on a computer, cause the processes or functions described in accordance with the embodiments of the invention to occur, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a network of computers, or other programmable device. The computer instructions may be stored in a computer readable storage medium or transmitted from one computer readable storage medium to another, for example, from one website site, computer, server, or data center to another website site, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, Digital Subscriber Line (DSL)) or wireless (e.g., 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, etc., that incorporates one or more of the available media. The usable medium may be a magnetic medium (e.g., floppy Disk, hard Disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., Solid State Disk (SSD)), among others.

Claims

1. A method for determining the transmission delay of a Passive Optical Network (PON) is characterized by comprising the following steps,

a first module of an optical network unit ONU communicates with the OLT through a first optical distribution network ODN, and the time of the first module is synchronous with the time of the OLT;

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

when the counter value of the second module is K, the ONU sets the time of the second module as the time identified by the first timestamp;

and the ONU determines the first time difference according to the first module time and the second module time, wherein the first time difference is equal to the difference value between the second module time and the OLT time at the same time, and 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 of 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 an OLT time when the superframe counter value of the OLT equals K times; and when the superframe counter value of the second module is equal to K, the ONU sets the time of the second module as 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, specifically comprising:

the first module sends a first message to the second module, wherein the first message comprises a sending timestamp, the sending timestamp is the time of the first module at the time when the first module sends the first message, the second module adds a receiving timestamp in the first message when receiving the first message, and the receiving timestamp is the time of the second module at the time when the second module receives the first message;

the ONU determines a second time difference, wherein the second time difference is the difference value of the receiving time stamp and the sending time stamp;

and the ONU determines a first time difference according to the second time difference and Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time delay of communication between the first module and the second module through the Ethernet link.

4. The method according to any of claims 1-3, wherein the ONU determines an equalization delay for the second module to communicate with the OLT based on the first time difference.

5. The method of claim 4, wherein the ONU determines the equalization delay EqD2 of the second module communicating with the OLT according to the following calculation formula:

EqD2＝Teqd-RspTime2-(dt/(n1/(n1+n2))),

wherein Teqd is a zero-distance equivalent time delay, RspTime2 is a response time length of the ONU, dt is the first time difference, n1 is a refractive index of downlink light for communication between the OLT and the ONU, and n2 is a refractive index of uplink light for communication between the ONU and the OLT.

6. The method according to claim 4 or 5, wherein the ONU determines an equalized time delay for the second module to communicate with the OLT, the method further comprising,

and after processing the request of the OLT, the second module at least waits for the time length corresponding to the balanced delay and then sends an uplink message to the OLT.

7. The method of claim 3, further comprising the ONU measuring and calculating Ethernet link delay between the first module and the second module according to 1588 time synchronization protocol.

8. PON network device, characterized in that it comprises a first module and a second module,

the first module is used for completing ranging and time synchronization with an Optical Line Terminal (OLT) through a first Optical Distribution Network (ODN);

the second module is configured to receive, through a second ODN, a time synchronization message sent by the OLT, where the time synchronization message includes a first timestamp, and the first timestamp identifies an OLT time at which a counter value of the OLT is K times; when the counter value of the second module is K, setting the time of the second module as the time identified by the first timestamp; determining a first time difference, where the first time difference is equal to a difference between the time of the second module and the time of the OLT at the same time, and the first time difference is equal to a transmission delay of the time synchronization message from the OLT to the second module.

9. The apparatus of 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 an OLT time when the superframe counter value of the OLT equals K times; the second module is further configured to set the second module time to the time identified by the first timestamp when the superframe counter value of the second module is equal to K.

10. The apparatus according to claim 8 or 9,

the first module is further configured to send a first message to the second module, where the first message includes a sending timestamp, and the sending timestamp is a time when the first module sends the first message at the first module time;

the second module is further configured to add a receiving timestamp to the first packet when the first packet is received, where the receiving timestamp is a time when the second module receives the first packet at the time; determining a second time difference, wherein the second time difference is a difference value between the receiving time stamp and the sending time stamp; and determining a first time difference according to the second time difference and the Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time delay of communication between the first module and the second module through the Ethernet link.

11. The apparatus of any of claims 8-10, wherein the second module is further configured to determine an equalization delay for the second module to communicate with the OLT according to the first time difference.

12. The apparatus of claim 11, wherein the second module determines an equalization delay EqD2 for the second module to communicate with the OLT according to the following calculation:

EqD2＝Teqd-RspTime2-(dt/(n1/(n1+n2))),

wherein Teqd is a zero-distance equivalent time delay, RspTime2 is a response time length of the second module, dt is the first time difference, n1 is a refractive index of downlink light for communication between the OLT and the ONU, and n2 is a refractive index of uplink light for communication between the second module and the OLT.

13. The apparatus according to claim 11 or 12, wherein the second module is further configured to wait for at least a duration corresponding to the equalization delay after processing the request of the OLT, and then send an uplink packet to the OLT.

14. The apparatus of claim 9, wherein the second module measures ethernet link delay between the first module and the second module according to 1588 time synchronization protocol.

15. The apparatus of any of claims 8-14, wherein the first module comprises a processor, a memory, a PON Media Access Control (MAC) chip, a transceiver, and a time control module, and wherein the second module also comprises a processor, a memory, a PON Media Access Control (MAC) chip, a transceiver, and a time control module;

the first module processor is configured to control the first module to complete ranging and time synchronization, the first module PON MAC chip is configured to complete data forwarding with the OLT under control of the first module processor, 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 configured to communicate with the OLT through the second ODN, the second module PON MAC chip is configured to complete data transceiving with the OLT under control of the second module processor, the second module processor is configured to process the received time synchronization message, when a counter value of the second module is K, the second module time is set as the time identified by the first timestamp, and 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 based on the first module time and the second module time.

16. The apparatus of claim 15, wherein the first module further comprises an ethernet MAC chip and the second module further comprises an ethernet MAC chip, wherein the first module ethernet MAC chip and the second module ethernet MAC chip communicate via 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 used for forwarding the first message to the second module processor for processing;

the second module processor is further configured to add a receiving timestamp to the first packet, where the receiving timestamp is a time at which the second module receives the first packet at the second module time; determining a second time difference, wherein the second time difference is a difference value between the receiving time stamp and the sending time stamp; and determining a first time difference according to the second time difference and the Ethernet link time delay, wherein the first time difference is the sum of the second time difference and the Ethernet link time delay, and the Ethernet link time delay is the time delay of communication between the first module and the second module through the Ethernet link.

17. The apparatus of claim 15 or 16, wherein the second module processor is further configured to determine an equalized delay for the second module to communicate with the OLT according to an ONU response time duration, a zero-distance equivalent delay, and the first time difference.

18. A passive optical network, PON, system comprising an ONU and an OLT, the ONU being configured to perform the method of any of claims 1-6 to determine an equalization delay for communication with the OLT.

19. A computer-readable storage medium comprising instructions that, when executed on a computer, cause the computer to perform the method of any 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 one of claims 1 to 7.