Measuring fiber asymmetry

Abstract

A method for obtaining an asymmetry metric between optical fibers of a forward path and a reverse path to synchronize clocks of optical nodes connected by an asymmetric optical fiber path is provided. The method comprises: receiving a first optical signal transmitted on a first optical fiber and a second optical signal transmitted on a second optical fiber from a first optical network device at a first arrival time and a second arrival time; and calculating a first time difference between the second arrival time and the first arrival time. The method further comprises determining an asymmetry metric between the first optical fiber and the second optical fiber based on the first time difference and a second time difference: the second time difference being the difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

Description

Technical Field

[0001] The present disclosure relates to optical networks. Background Art

[0002] Optical networks are commonly used to transmit data. Wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) technologies can be used to transmit data using optical signals over common or shared optical fibers (sometimes referred to as optical links). In these technologies, the clocks at corresponding network elements, nodes, and / or devices are synchronized. To ensure clock synchronization, network elements include Global Positioning System (GPS) receivers and external GPS antennas for receiving accurate time information. External interference from the environment can introduce errors in clock synchronization via the GPS receiver and GPS antenna.

[0003] Another method for synchronizing clocks is to use the Precision Time Protocol (PTP), defined by the Institute of Electrical and Electronics Engineers (IEEE) 1588v2 standard, to distribute time-of-day (TOD) information. The IEEE 1588v2 standard defines the synchronization and distribution of time-of-day from a master clock at a master node to one or more slave clocks at a slave node, a remote slave client, or another master node. In PTP, clocks are synchronized across a packet-switched network. Synchronization is achieved using data packets sent and received in a session between the master and slave clocks. Due to the delay in signal propagation through the physical medium (fiber), messages are received "some time later." This propagation delay is an error that needs to be calculated and compensated for when synchronizing clocks. PTP calculates the round-trip delay between the master and slave clocks. The delay, or latency, between the master node and the slave node(s) is assumed to be half the round-trip delay. Therefore, the PTP calculation assumes that the fiber in the forward and reverse paths is symmetrical. If the fiber is asymmetrical, the PTP calculation introduces errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 is a block diagram illustrating an optical network according to an example embodiment, the optical network including first and second optical nodes configured to measure a propagation delay of an optical signal sent through a first optical fiber of a forward path.

[0005] Figure 2 is a diagram showing a method according to an example embodiment Figure 1 A block diagram of an optical network, wherein a first optical node and a second optical node are configured to measure a propagation delay of an optical signal sent through a second optical fiber in a reverse path.

[0006] Figure 3 is a diagram illustrating a method for obtaining a propagation delay of an optical signal transmitted through a first optical fiber in a forward path and through a second optical fiber in a reverse path, according to an example embodiment.

[0007] Figure 4 is a flow chart generally depicting a method for determining path asymmetry between a first optical fiber in a forward path and a second optical fiber in a reverse path in an optical network, according to an example embodiment.

[0008] Figure 5 is a hardware block diagram of a device configured to perform techniques for determining fiber asymmetry to synchronize clocks of optical nodes in an optical network, according to various example embodiments. DETAILED DESCRIPTION

[0009] Overview

[0010] Briefly, in one embodiment, methods for measuring the asymmetry of the path lengths of optical fibers on forward and return paths are provided. In these methods, a second optical network device receives a first optical signal transmitted on a first optical fiber from a first optical network device at a first arrival time, and also receives a second optical signal transmitted on a second optical fiber from the first optical network device at a second arrival time. The second optical network device calculates a first time difference between the second arrival time of the second optical signal and the first arrival time of the first optical signal. The second optical network device determines an asymmetry measure between the first optical fiber and the second optical fiber based on the first time difference and a second time difference, the second time difference being the difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

[0011] Exemplary embodiments

[0012] Service providers may want next-generation networks (e.g., fifth-generation (5G) mobile networks) to not rely on the Global Navigation Satellite System (GNSS), as GNSS signals are susceptible to interference and errors. Next-generation networks use and rely on accurate network synchronization. For example, new systems are increasing the resolution of timestamp transmission accuracy to comply with the Class C profile specified in International Telecommunication Union (ITU) G.8273.2, "Timing Characteristics of Telecom Boundary Clocks and Telecom Time Slave Clocks" (October 2018), which limits the constant time error of each optical network node to + / - 10 nanoseconds.

[0013] For next-generation networks, service providers can use a timing distribution model based on the IEEE 1588v2 protocol, provided that the asymmetry between the lengths of the forward and reverse fiber paths can be adjusted. The techniques proposed in this paper combine the round-trip delay calculation supported by IEEE 1588v2's PTP with the calculated asymmetry between the forward and reverse fiber paths to reduce errors in clock synchronization between communicating optical nodes. In one form, an optical switch is deployed in each optical node. The optical switch is capable of switching the propagation direction of optical signals between the forward and reverse paths. Thus, a first optical network device sends a packet to a second optical network device over two optical fibers and calculates the asymmetry between the forward and reverse fiber paths based on the difference between the packet's transmission and arrival times. Based on the fiber asymmetry, the time offset value can be adjusted when calculating the round-trip delay using the PTP protocol, allowing for high-precision clock synchronization. These techniques improve the resolution of the asymmetry measurement to the resolution at which optical network devices insert and extract timestamp data packets, i.e., a resolution of less than 1 nanosecond (with an accuracy of less than 40 cm of fiber).

[0014] Even if fiber asymmetry itself doesn't affect the accuracy of signal processing at a given node, the accuracy of the PTP distribution can be affected, as each meter of asymmetry can introduce an error of 2.5 nanoseconds. Because network deployments can have several meters of uncontrolled path asymmetry due to patch panels and fiber patches, the proposed technique can measure fiber asymmetry and adjust the PTP measurement accordingly.

[0015] Using PTP on a bidirectional optical service channel (OSC) is an alternative method for measuring fiber asymmetry. Since PTP is transmitted on only one fiber in a bidirectional OSC, there is no path asymmetry. However, deploying bidirectional OSC in an optical network is less than ideal, and separate fibers for each path may be preferable. In one example embodiment, asymmetry is measured without the use of an optical time domain reflectometer (OTDR) integrated into the node, which can be expensive and inaccurate.

[0016] In various exemplary embodiments, the timestamp mechanism available with IEEE 1588v2 PTP transport is used in conjunction with optical switches to calculate fiber asymmetry. The resolution of the asymmetry metric is based on the resolution of digital equipment inserting / extracting timestamps, which is less than 1 nanosecond (for fiber lengths less than 40 cm).

[0017] In another exemplary embodiment, when optical network devices are connected without amplification, PTP is transmitted on a single channel (wavelength). This single channel can also be used for data traffic. In this case, the optical network devices do not use OSC. Therefore, an optical switch is deployed before the full line or interface, as detailed below.

[0018] Now refer to Figure 1 , Figure 1 A block diagram depicting an optical network 100 is shown, according to an example embodiment, including first and second optical nodes (e.g., a master node and a slave node, respectively) configured to measure a propagation delay of an optical signal sent through a first optical fiber of a forward path between the first and second optical nodes. Figure 2 A similar arrangement of the optical network 100 is shown in , where the first optical node and the second optical node are configured to measure the propagation delay of an optical signal sent through a second optical fiber of a reverse path between the first optical node and the second optical node.

[0019] The optical network 100 can use WDM or DWDM technology. Figure 1 In FIG, the optical network 100 includes a forward path (FP) optical fiber 102 and a reverse path (RP) optical fiber 104 connected between a master node 110 and a slave node 130. The optical network 100 may include a plurality of nodes, and the number of nodes depends on the specific configuration of the optical network 100 and is not limited to Figure 1 Example shown.

[0020] FP fiber 102 and RP fiber 104 provide bidirectional communication between master node 110 and slave node 130. FP fiber 102 supports at least one optical communication channel from master node 110 to slave node 130. RP fiber 104 supports at least one optical communication channel from slave node 130 to master node 110. FP fiber 102 can occupy the same wavelength as RP fiber 104, i.e., frequency synchronized or frequency locked. The length of FP fiber 102 can be different from the length of RP fiber 104, e.g., Figure 1 Because the FP fiber 102 and the RP fiber 104 can have different lengths, the paths associated with the FP fiber 102 and the RP fiber 104 can be considered asymmetric.

[0021] The master node 110 and the slave node 130 are optical network elements or devices (nodes), such as optical transponders, which are connected to each other via the FP optical fiber 102 and the RP optical fiber 104. The master node 110 includes a master clock 112, a first optical supervisory channel component (OSC) 114, a first optical transmitter 116, a first optical receiver 118, a first optical switch 120, and a first controller 122 including a processor and a memory. The slave node 130 includes a slave clock 132, a second OSC 134, a second optical transmitter 136, a second optical receiver 138, a second optical switch 140, and a second controller 142 including a processor and a memory.

[0022] Optical transmitters 116 and 136 each include a transmitter module and a transmitter digital signal processor (DSP), which are not shown. Optical receivers 118 and 138 each include a receiver module and a receiver DSP, which are not shown. The transmitter module and the receiver module may be optical pluggable modules configured to transmit and receive optical signals, respectively. The DSP processes the electrical signals by performing various signal processing operations. The first optical switch 120 and the second optical switch 140 may be crossbar switches. The first optical switch 120 may be arranged between the FP fiber 102 and the RP fiber 104 and the first optical transmitter 116 and the first optical receiver 118. Similarly, the second optical switch 140 may be arranged between the FP fiber 102 and the RP fiber 104 and the second optical transmitter 136 and the second optical receiver 138. This arrangement allows for the direction of optical signal propagation on either the FP fiber 102 or the RP fiber 104 to be changed, as described below. The first controller 122 and the second controller 142 control the components of the corresponding optical network element.

[0023] exist Figure 1 In the exemplary embodiment shown, first optical transmitter 116 and first optical receiver 118 are part of first OSC 114, and second optical transmitter 136 and second optical receiver 138 are part of second OSC 134. That is, optical network 100 may be an optically amplified metropolitan area network. In a metropolitan area network, wavelengths or optical channels carrying customer traffic are amplified by optical amplifiers (e.g., erbium-doped fiber amplifiers) placed along the way. Because the asymmetry introduced by the presence of various optical amplifiers can be difficult to track, PTP packets are transmitted out-of-band via an optical service channel (OSC). The OSC is a control channel that does not pass through any optical amplifiers and is regenerated at each optical network element.

[0024] In yet another exemplary embodiment, the first optical transmitter 116 and the first optical receiver 118 can be part of a line card or a customer traffic interface. Similarly, the second optical transmitter 136 and the second optical receiver 138 can be part of a line card or a customer traffic interface. In this case, the optical network 100 can be a backhaul network that connects two remote sites in a mobile access application without requiring any amplification along the way. Since no amplifiers are deployed, only a single channel or wavelength can be sufficient to transmit both customer / data traffic and control data. The optical network 100 deployed without the first OSC 114 and the second OSC 134 uses the channel used for customer / data traffic to transmit packets for the technical purposes presented herein. The optical network 100 can be deployed to support coherent optical applications.

[0025] exist Figure 1In the embodiment, the master node 110 generates a first optical signal 103. The first optical signal 103 is transmitted from the master node 110 to the slave node 130 over the FP optical fiber 102. The first optical switch 120 connects the first optical transmitter 116 to the FP optical fiber 102, and the second optical switch 140 connects the second optical receiver 138 to the FP optical fiber 102, thereby propagating the first optical signal 103 from the master node 110 to the slave node 130 over the FP optical fiber 102.

[0026] Now refer to Figure 2 , Figure 2 An optical network 100 is shown according to an example embodiment, wherein a first optical node and a second optical node are configured to measure a propagation delay of an optical signal sent through an RP optical fiber 104 . Figure 2 Depicts the Figure 1 For the sake of brevity, detailed descriptions of the same network components are omitted.

[0027] exist Figure 2 , optical switches 120 and 140 are switched. As a result, first optical transmitter 116 is connected to RP optical fiber 104 via the cross-connect function of first optical switch 120, and second optical receiver 138 is connected to RP optical fiber 104 via the cross-connect function of second optical switch 140. Second optical signal 105 propagates from master node 110 to slave node 130 via RP optical fiber 104.

[0028] In the example embodiment, the following reference is used Figure 3 To explain the techniques presented herein in more detail, the master clock 112 and the slave clock 132 are synchronized to have the same TOD.

[0029] Figure 3 is a diagram illustrating a method 300 for obtaining a propagation delay of an optical signal transmitted through a first optical fiber in a forward path and a second optical fiber in a reverse path according to an example embodiment. Figure 1 and Figure 2 For use Figure 3 Description. Figure 3 Depicts the Figure 1 At least some of the same network components are omitted for the sake of brevity. Figure 3 The first OSC 114 and the second OSC 134 are depicted, but according to another exemplary embodiment, the first OSC 114 and the second OSC 134 may be omitted.

[0030] Figure 3 The master node 110 and the slave node 130 are depicted as being connected via the FP optical fiber 102 and the RP optical fiber 104. The master node 110 transmits a first optical signal 103 ( Figure 1) sends the first packet to the slave node 130, and transmits the first packet to the slave node 130 via the RP optical fiber 104 with the second optical signal 105 ( Figure 2 )Send the second packet.

[0031] For example, the master node 110 and the slave node 130 are frequency locked via Synchronous Ethernet (SyncE) signaling. Synchronous Ethernet is an ITU-T standard for computer networks that facilitates the transmission of clock signals over the Ethernet physical layer. The signal is traceable to an external clock. The master clock 112 of the master node 110 is set to time T. The slave clock 132 of the slave node 130 is set to time T'. The offset between the time of day (TOD) of the master clock 112 and the slave clock 132 is unknown, so T' = T + Δτ, where Δτ is the unknown offset between the two clocks 112 and 132. In an exemplary embodiment, path asymmetry is calculated based on the difference in flight time between the FP fiber 102 and the RP fiber 104, as described below. Path asymmetry is independent of the time error between the two nodes (i.e., the unknown offset (Δτ)).

[0032] At 302, the master node 110 sends a first packet to the slave node 130 via the FP optical fiber 102 in a first optical signal 103 at time T1. At 304, when the first packet is received by the slave node 130, the slave node 130 timestamps the first arrival time T2' of the first packet. First arrival time T2'=T1+T FF +Δτ, where T FF is the propagation delay of the first optical signal 103 on the FP optical fiber 102 , ie, the forward flight time. The slave node 130 stores the first arrival time T2 ′ counted by the slave clock 132 in the second controller 142 .

[0033] Next, at 306a, the first optical switch 120 is switched in the master node 110, and at 306b, the second optical switch 140 is switched in the slave node 130. In this manner, the master node 110 and the slave node 130 are configured to reverse the propagation direction of the optical signal, such that the master node 110 transmits the second packet via the RP optical fiber 104, rather than the master node 110 receiving the optical signal from the slave node 130 on the RP optical fiber 104.

[0034] Specifically, at 308, the master node 110 sends the second packet to the slave node 130 via the RP optical fiber 104 using the second optical signal 105 at time T3. At 310, when the second packet is received by the slave node 130, the slave node 130 times the second arrival time T4' of the second packet. The second arrival time T4'=T3+T FR +Δτ, where T FRis the propagation delay of the second optical signal 105 on the RP optical fiber 104 , ie, the reverse flight time. The slave node 130 stores the second arrival time T4 ′ counted by the slave clock 132 in the second controller 142 .

[0035] At 312a, the master node 110 calculates a first time difference (Δ). The first time difference is the difference between the second transmission time T3 of the second packet and the first transmission time T1 of the first packet (Δ=T3-T1).

[0036] At 312b, a second time difference (Δ') is calculated from the node 130. The second time difference is the difference between the second arrival time T4' and the first arrival time T2' (Δ'=T4'-T2').

[0037] At 314, the slave node 130 determines the path asymmetry between the FP fiber 102 and the RP fiber 104 based on the first time difference (Δ) and the second time difference (Δ′). or skew. Path asymmetry is the difference between the first time difference and the second time difference (Δ'-Δ). Path asymmetry is the forward flight time (T FF ) and reverse flight time (T FR ) and is independent of the unknown offset (Δτ). That is:

[0038]

[0039]

[0040] As described above, one meter of fiber introduces a 5 nanosecond delay. This can cause skew between the fibers, which can introduce an offset in the TOD difference. For example, asymmetry in one meter of fiber can introduce an error of 2.5 nanoseconds, which is comparable to a Class C profile with a constant time error limit of + / - 10 nanoseconds. In an exemplary embodiment, the asymmetry is taken into account when synchronizing the clocks of a first node and a second node communicating with each other, thereby avoiding additional time errors.

[0041] PTP packet exchange can be used to synchronize the master clock 112 and the slave clock 132, but based on the calculated path asymmetry According to an example embodiment, based on the estimated path asymmetry The exact propagation delay can be factored into the clock synchronization. The TOD of the slave clock 132 is set to the time of the master clock 112 adjusted by the offset. Thus, the TOD of the master clock 112 (T) received by the slave node 130 will be adjusted by the offset, which accounts for the asymmetry of the fiber (T'=T+offset), where the offset value or propagation delay takes into account or includes the estimated path asymmetry. In short, the path asymmetry between the FP fiber 102 and the RP fiber 104 is obtained. And this value is inserted into the PTP protocol by proportionally adjusting the offset when setting the TOD of the slave clock 132 .

[0042] Although Figure 3 It is described that the master node 110 determines the first time difference (Δ) at 312a and the slave node 130 determines the second time difference (Δ') at 312b, but this is only an example. According to another exemplary embodiment, the second time difference (Δ') may be provided by the slave node 130 to the master node 110, and the master node 110 may then calculate the path asymmetry. According to another exemplary embodiment, the first optical signal may include a first message including a first transmission time (T1), and the second optical signal may include a second message including a second transmission time (T2). Thus, the slave node 130 may calculate a first time difference (Δ) and a second time difference (Δ') between the transmission times of the two packets.

[0043] An exemplary embodiment involves measuring fiber asymmetry using an optical switch inserted into an optical node to reverse the direction of signal propagation on one of two optical fibers connected between a first optical node and a second optical node. Packets are sent at specific times, and the arrival times of the packets are measured (using PTP packets sent via an OSC or traffic channel, depending on the specific network deployment). Propagation delay is determined based on the packet's send and arrival times. Fiber asymmetry is determined based on the difference between the send delays of the two fibers.

[0044] Now go to Figure 4 According to an example embodiment, a flow chart of a method 400 is now described for determining path asymmetry between a first optical fiber in a forward path and a second optical fiber in a reverse path in an optical network. The method 400 is performed by an optical network device, such as a master node 110 or a slave node 130, as shown in FIG. Figures 1 to 3 shown.

[0045] At 402 , a second optical network device receives a first optical signal sent on a first optical fiber from a first optical network device at a first arrival time.

[0046] At 404 , the second optical network device receives a second optical signal sent on a second optical fiber from the first optical network device at a second arrival time.

[0047] At 406 , the second optical network device calculates a first time difference between a second arrival time of the second optical signal and a first arrival time of the first optical signal.

[0048] At 408 , the second optical network device determines an asymmetry metric between the first optical fiber and the second optical fiber based on the first time difference and the second time difference, wherein the second time difference is a difference between a first transmission time when the first optical network device transmits the first optical signal and a second transmission time when the first optical network device transmits the second optical signal.

[0049] The method 400 may further include: receiving, from the first optical network device through the second optical network device, the second time difference calculated by the first optical network device.

[0050] In method 400, operation 408 of determining an asymmetry metric between the first optical fiber and the second optical fiber may include calculating, by the second optical network device, a path difference based on a difference between the first time difference and the second time difference, wherein the path difference represents the asymmetry metric.

[0051] In method 400, operation 404 of receiving a second optical signal may include switching, by the second optical network device, transmitting to the first optical network device on the second optical fiber to receiving the second optical signal from the first optical network device via the second optical fiber.

[0052] In one form, the method 400 may further include: before the first optical network device transmits the first optical signal and the second optical signal, frequency synchronizing a first clock of the first optical network device with a second clock of the second optical network device.

[0053] The method 400 may further include converting, by the second optical network device, the asymmetry metric into a time offset, and adjusting, by the second optical network device, a time reference of the second optical network device based on the time offset.

[0054] In one form, the operation of adjusting the time reference may include adjusting an offset value based on the asymmetry metric when calculating a round-trip delay based on a timing protocol between the first optical fiber and the second optical fiber. The method 400 may also include synchronizing a second clock of the second optical network device with a first clock of the first optical network device using the timing protocol and the offset value.

[0055] According to one or more exemplary embodiments, the operation 402 of receiving a first optical signal may include receiving, by a second optical network device, the first optical signal transmitted on a first optical fiber via an optical service channel, and the operation 404 of receiving a second optical signal may include receiving, by the second optical network device, the second optical signal transmitted on a second optical fiber via the optical service channel.

[0056] According to yet other exemplary embodiments, the operation 402 of receiving a first optical signal may include receiving, by the second optical network device, a first optical signal transmitted at a first wavelength for transmitting traffic data, and the operation 404 of receiving a second optical signal may include receiving, by the second optical network device, a second optical signal transmitted at the first wavelength, the first wavelength being used to transmit traffic data from the second optical network device to the first optical network device.

[0057] In method 400, operation 402 of receiving a first optical signal may include receiving, by the second optical network device, the first optical signal transmitted via a data channel used to transmit data traffic from the first optical network device to the second optical network device. Similarly, operation 404 of receiving a second optical signal may include receiving, by the second optical network device, the second optical signal transmitted via a data channel used to transmit data traffic from the second optical network device to the first optical network device.

[0058] As described above, the first optical signal may include a first message having a first transmission time, and the second optical signal may include a second message having a second transmission time.

[0059] Figure 5 is a hardware block diagram illustrating a computing device 500 according to an example embodiment, which can execute the Figures 1 to 4 The computing device 500 performs the above-mentioned Figures 1 to 4 The functions of the master node 110 or the slave node 130.

[0060] It should be realized that Figure 5 This merely provides an illustration of one embodiment and is not intended to limit the environments in which different embodiments may be implemented. Many modifications to the depicted environments are possible.

[0061] As shown, computing device 500 includes bus 512, which provides communication between computer processor(s) 514, memory 516, persistent storage 518, communication unit 520, and input / output (I / O) interface(s) 522. Bus 512 can be implemented using any architecture designed to pass data and / or control information between a processor (e.g., a microprocessor, a communications and network processor, etc.), system memory, peripheral devices, and any other hardware components within the system. For example, bus 512 can be implemented using one or more buses.

[0062] Memory 516 and persistent storage 518 are computer-readable storage media. In the depicted embodiment, memory 516 includes random access memory (RAM) 524 and cache 526. In general, memory 516 can include any suitable volatile or non-volatile computer-readable storage media. Instructions for control logic 525 can be stored in memory 516 or persistent storage 518 for execution by processor(s) 514.

[0063] The control logic 525 includes instructions that, when executed by the computer processor(s) 514, cause the computing device 500 to perform one or more of the methods described herein, including determining an asymmetry metric between a first optical fiber and a second optical fiber based on a first time difference and a second time difference, the first time difference being derived from arrival times of the first optical signal and the second optical signal propagating through the two different optical fibers, and the second time difference being derived from transmission times of the first optical signal and the second optical signal. The control logic 525 can be stored in the memory 516 or the persistent storage device 518 for execution by the computer processor(s) 514.

[0064] One or more programs may be stored in persistent storage 518 for execution by one or more corresponding computer processors 514 via one or more memories in memory 516. Persistent storage 518 may be a magnetic disk drive, a solid-state hard drive, a semiconductor memory device, read-only memory (ROM), erasable programmable read-only memory (EPROM), flash memory, or any other computer-readable storage medium capable of storing program instructions or digital information.

[0065] The media used by persistent storage 518 may also be removable. For example, a removable hard drive may be used for persistent storage 518. Other examples include optical and magnetic disks that are inserted into a drive to be converted to another computer-readable storage medium (also part of persistent storage 518), thumb drives, and smart cards.

[0066] Communications unit 520, in these examples, provides for communications with other data processing systems or devices. Communications unit 520, in these examples, includes one or more network interface cards. Communications unit 520 may provide communications using either or both physical and wireless communications links.

[0067] Input / output interface(s) 522 may allow for input and output of data with other devices that may be connected to computing device 500. For example, I / O interface 522 may provide a connection to external devices 528, such as a keyboard, keypad, touch screen, and / or some other suitable input device. External devices 528 may also include portable computer-readable storage media, such as database systems, thumb drives, portable optical or magnetic disks, and memory cards.

[0068] Software and data used to practice the embodiments may be stored on such portable computer-readable storage media and loaded onto persistent storage 518 via I / O interface(s) 522. I / O interface(s) 522 may also connect to display 530. Display 530 provides a mechanism for displaying data to a user and may be, for example, a computer monitor.

[0069] The programs described herein are identified based on the applications in which they are implemented in specific embodiments. However, it should be appreciated that any specific program nomenclature herein is used for convenience only, and thus the embodiments should not be limited to use in any specific application identified and / or implied by such nomenclature.

[0070] Data related to the operations described herein may be stored in any conventional or other data structure (e.g., files, arrays, lists, stacks, queues, records, etc.) and may be stored in any desired storage unit (e.g., databases, data or other repositories, queues, etc.). Data transmitted between entities may include any desired format and arrangement and may include any number, size, and type of fields to store the data. The definition and data model of any data set may indicate the overall structure in any desired manner (e.g., computer-related language, graphical representation, list, etc.).

[0071] The present embodiment may employ any number of any type of user interface (e.g., a graphical user interface (GUI), a command line, a prompt, etc.) to obtain or provide information, wherein the interface may include any information arranged in any manner. The interface may include any number of any type of input or driver mechanisms (e.g., buttons, icons, fields, boxes, links, etc.) disposed in any location to input / display information and initiate desired actions via any suitable input device (e.g., a mouse, a keyboard, etc.). The interface screens may include any suitable drivers (e.g., links, tabs, etc.) for navigating between screens in any manner.

[0072] The environment of this embodiment can include any number of computers or other processing systems (e.g., client or end-user systems, server systems, etc.) and databases or other repositories arranged in any desired manner, wherein this embodiment can be applied to any desired type of computing environment (e.g., cloud computing, client-server, network computing, mainframe, stand-alone system, etc.). The computers or other processing systems used in this embodiment can be implemented by any number of any personal or other type of computers or processing systems (e.g., desktops, laptops, PDAs, mobile devices, etc.) and can include any commercial operating system and any combination of commercial software and custom software (e.g., machine learning software, etc.). These systems can include any type of display and input device (e.g., keyboard, mouse, voice recognition device, etc.) for inputting and / or viewing information.

[0073] It should be understood that the software of the present embodiment can be implemented in any desired computer language and can be developed by a person of ordinary skill in the computer arts based on the functional descriptions contained in the specification and the flowcharts shown in the accompanying drawings. In addition, any reference herein to software that performs various functions generally refers to a computer system or processor that performs these functions under the control of the software. The computer system of the present embodiment can alternatively be implemented by any type of hardware and / or other processing circuitry.

[0074] Each element described herein can be coupled to and / or interact with each other via an interface and / or any other suitable connection (wired or wireless) that provides a feasible communication path. The interconnections, interfaces, and variations thereof discussed herein can be used to provide connections between elements in a system and / or can be used to provide communication, interaction, operations, etc. between directly or indirectly connected elements in a system. Any combination of interfaces can be provided for the elements described herein to facilitate the operations discussed for the various embodiments described herein.

[0075] The various functions of a computer or other processing system can be distributed in any manner among any number of software and / or hardware modules or units, processing or computer systems and / or circuits, wherein the computers or processing systems can be located locally or remotely from each other and communicate via any suitable communication medium (e.g., LAN, WAN, intranet, Internet, hard wiring, modem connection, wireless, etc.). For example, the functions of the present embodiment can be distributed in any manner among various end-user / client and server systems and / or any other intermediate processing devices. The software and / or algorithms described above and shown in the flowcharts can be modified in any manner to achieve the functions described herein. Furthermore, the functions in the flowcharts or descriptions can be performed in any order to achieve the desired operations.

[0076] The software of this embodiment may be made available on non-transitory computer-usable media (e.g., magnetic or optical media, magneto-optical media, floppy disks, CD-ROMs, DVDs, memory devices, etc.) on a fixed or portable program product apparatus or device for use with a stand-alone system or with systems connected via a network or other communications medium.

[0077] The communication network can be implemented by any number of any type of communication networks (e.g., LAN, WAN, Internet, intranet, virtual private network (VPN), etc.). The computer or other processing system of the present embodiment can include any conventional or other communication device that communicates on the network via any conventional or other protocol. The computer or other processing system can access the network using any type of connection (e.g., wired, wireless, etc.). The local communication medium can be implemented by any suitable communication medium (e.g., local area network (LAN), hard wiring, wireless link, intranet, etc.).

[0078] In another exemplary embodiment, the apparatus is an optical network device. The apparatus includes a communication interface, a memory configured to store executable instructions, and a processor coupled to the communication interface and the memory. The processor is configured to perform operations including: receiving, via the communication interface, a first optical signal transmitted on a first optical fiber from a first optical network device at a first arrival time, and receiving, via the communication interface, a second optical signal transmitted on a second optical fiber from the first optical network device at a second arrival time. The processor is further configured to perform operations including: calculating a first time difference between a second arrival time of the second optical signal and a first arrival time of the first optical signal, and determining an asymmetry measure between the first optical fiber and the second optical fiber based on the first time difference and a second time difference, the second time difference being a difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

[0079] The processor may be further configured to perform operations including: receiving a second time difference calculated by the first optical network device from the first optical network device via the communication interface.

[0080] In one form, the processor may be further configured to determine an asymmetry measure between the first optical fiber and the second optical fiber by calculating a path difference based on a difference between the first time difference and the second time difference. The path difference may represent the asymmetry measure.

[0081] In one or more exemplary embodiments, the apparatus may further include a switch configured to switch transmission to the first optical network device over the second optical fiber to reception of the second optical signal from the first optical network device via the second optical fiber.

[0082] According to one or more exemplary embodiments, the processor may be further configured to perform operations including: frequency synchronizing a first clock of the first optical network device with a second clock of the apparatus before the first optical network device sends the first optical signal and the second optical signal.

[0083] The processor may be further configured to perform operations including converting the asymmetry measure into a time offset value, and adjusting a time reference of the apparatus based on the time offset value.

[0084] In another form, the processor may be configured to adjust the time reference by adjusting an offset value based on the asymmetry measure when calculating a round trip delay based on a timing protocol between the first optical fiber and the second optical fiber.

[0085] The processor may be further configured to perform operations including synchronizing a second clock of the apparatus with a first clock of the first optical network device using the timing protocol and the offset value.

[0086] The processor may be configured to receive a first optical signal by receiving, via the communication interface, a first optical signal transmitted on a first optical fiber via an optical service channel. Furthermore, the processor may be configured to receive a second optical signal by receiving, via the communication interface, a second optical signal transmitted on a second optical fiber via the optical service channel.

[0087] In another form, the processor may be configured to receive a first optical signal by receiving, via a communication interface, a first optical signal transmitted at a first wavelength for transmitting traffic data, and to receive a second optical signal by receiving, via the communication interface, a second optical signal transmitted at the first wavelength for transmitting traffic data from the apparatus to the first optical network device.

[0088] The processor may be configured to receive the first optical signal by receiving, via the communication interface, a first optical signal transmitted through a data channel for transmitting data traffic from the first optical network device to the apparatus. Furthermore, the processor may be configured to receive the second optical signal by receiving, via the communication interface, a second optical signal transmitted through a data channel for transmitting data traffic from the apparatus to the first optical network device.

[0089] According to one or more exemplary embodiments, the first optical signal includes a first message having a first transmission time, and the second optical signal includes a second message having a second transmission time.

[0090] In another exemplary embodiment, one or more non-transitory computer-readable storage media are encoded with instructions. When executed by a processor, the instructions cause the processor to perform operations including receiving a first optical signal transmitted over a first optical fiber from a first optical network device at a first arrival time, and receiving a second optical signal transmitted over a second optical fiber from the first optical network device at a second arrival time. The operations further include calculating a first time difference between the second arrival time of the second optical signal and the first arrival time of the first optical signal, and determining an asymmetry measure between the first optical fiber and the second optical fiber based on the first time difference and the second time difference, the second time difference being a difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

[0091] The instructions may further cause the processor to perform additional operations including: receiving, from the first optical network device, a second time difference calculated by the first optical network device.

[0092] In one form, the instructions may cause the processor to determine an asymmetry measure between the first optical fiber and the second optical fiber by calculating a path difference based on a difference between the first time difference and the second time difference.The path difference may represent the asymmetry measure.

[0093] The instructions may cause the processor to receive the second optical signal by switching from transmitting on the second optical fiber to the first optical network device to receiving the second optical signal from the first optical network device via the second optical fiber.

[0094] The instructions may further cause the processor to perform additional operations, including: frequency synchronizing a first clock of the first optical network device with a second clock of the second optical network device before the first optical network device sends the first optical signal and the second optical signal.

[0095] The instructions may further cause the processor to perform additional operations including converting the asymmetry metric into a time offset value, and adjusting a time reference of the second optical network device based on the time offset value.

[0096] The instructions may further cause the processor to adjust a time reference by adjusting an offset value based on the asymmetry metric when calculating a round trip delay based on a timing protocol between the first optical fiber and the second optical fiber.

[0097] The instructions may further cause the processor to perform additional operations including synchronizing a second clock of the second optical network device with a first clock of the first optical network device using the timing protocol and the offset value.

[0098] The instructions may further cause the processor to receive a first optical signal by receiving a first optical signal sent on a first optical fiber via an optical service channel, and receive a second optical signal by receiving a second optical signal sent on a second optical fiber via an optical service channel.

[0099] The instructions may further cause the processor to perform the following operations: receive a first optical signal by receiving a first optical signal transmitted at a first wavelength for transmitting traffic data; and receive a second optical signal by receiving a second optical signal transmitted at the first wavelength, the first wavelength being used to transmit traffic data from the second optical network device to the first optical network device.

[0100] The instructions may further cause the processor to perform the following operations: receiving a first optical signal by receiving a first optical signal sent through a data channel for sending data traffic from the first optical network device; and receiving a second optical signal by receiving a second optical signal sent through a data channel for sending traffic data to the first optical network device.

[0101] According to one or more exemplary embodiments, the first optical signal may include a first message including a first transmission time, and the second optical signal may include a second message including a second transmission time.

[0102] The proposed embodiments may be in various other forms, for example, a system or a computer program product. The computer program product may include a computer-readable storage medium having computer-readable program instructions thereon for causing a processor to perform various aspects described herein.

[0103] A computer-readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of computer-readable storage media includes the following: a portable computer floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device (such as a punched card or a raised structure in a groove with instructions recorded thereon), and any suitable combination of the foregoing. The computer-readable storage medium used herein should not itself be interpreted as a temporary signal, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated through a waveguide or other transmission medium (for example, a light pulse through a fiber optic cable), or an electrical signal transmitted by a wire.

[0104] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to a corresponding computing / processing device, or downloaded to an external computer or external storage device via a network (e.g., the Internet, a local area network, a wide area network, and / or a wireless network). The network can include copper transmission cables, fiber optic transmission fibers, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in a computer-readable storage medium within the corresponding computing / processing device.

[0105] The computer-readable program instructions for performing the operation of the present embodiment can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, the configuration data of integrated circuit or source code or the object code written in any combination of one or more programming languages, these programming languages ​​include object-oriented programming languages ​​(such as Python, C++ etc.) and process programming languages ​​(such as " C " programming language or similar programming languages).Computer-readable program instructions can be performed completely on the user's computer, partly on the user's computer, as an independent software package, partly on the user's computer and partly on a remote computer, or completely on a remote computer or server.In the latter case, the remote computer can be connected to the user's computer by any type of network including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (such as, by using the Internet of an Internet service provider).In certain embodiments, the electronic circuit including, for example, programmable logic circuit, field programmable gate array (FPGA) or programmable logic array (PLA) can perform computer-readable program instructions with personalized electronic circuit by utilizing the state information of computer-readable program instructions, to perform various aspects as described herein.

[0106] Various aspects of the present embodiments are described herein with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to the embodiments. It is to be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0107] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device for producing a machine, so that the instructions executed by the processor of the computer or other programmable data processing device create a module for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium, which can direct the computer, programmable data processing device, and / or other equipment to operate in a specific manner, so that the computer-readable storage medium having the instructions stored therein includes an article of manufacture, which includes instructions for implementing various aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0108] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other device to produce a computer-implemented process, so that the instructions executed on the computer, other programmable apparatus, or other device implement the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0109] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality and operation of possible implementations of the systems, methods and computer program products according to various embodiments. In this regard, each box in the flowchart or block diagram can represent a module, segment or portion of an instruction, which includes one or more executable instructions for implementing (one or more) specified logical functions. In some alternative embodiments, the functions marked in the box may appear outside the order marked in the figure. For example, two boxes shown in succession can actually be executed substantially simultaneously, or the boxes can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart illustration, and the combination of boxes in the block diagram and / or flowchart illustration, can be implemented by a system based on special-purpose hardware that performs a specific function or action or performs a combination of special-purpose hardware and computer instructions.

[0110] The description of various embodiments has been provided for the purpose of illustration and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was selected to best explain the principles of the embodiments, practical applications, or technical improvements over technologies found in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for an optical network, comprising: receiving, by the second optical network device, a first optical signal sent on the first optical fiber from the first optical network device at a first arrival time; receiving, by the second optical network device, a second optical signal sent on a second optical fiber from the first optical network device at a second arrival time, wherein the second optical fiber is a reverse path optical fiber configured to send the optical signal from the second optical network device to the first optical network device; calculating, by the second optical network device, a first time difference between a second arrival time of the second optical signal and a first arrival time of the first optical signal; as well as An asymmetry metric between the first optical fiber and the second optical fiber is determined by the second optical network device based on the first time difference and a second time difference, where the second time difference is a difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

2. The method according to claim 1, further comprising: The second time difference calculated by the first optical network device is received from the first optical network device through the second optical network device.

3. The method according to claim 2, wherein: Determining an asymmetry metric between the first optical fiber and the second optical fiber includes: A path difference is calculated by the second optical network device based on a difference between the first time difference and the second time difference, wherein the path difference represents the asymmetry metric.

4. The method according to any one of claims 1 to 3, wherein Receiving the second optical signal includes: The second optical network device switches the transmission of the second optical signal to the first optical network device over the second optical fiber to the reception of the second optical signal from the first optical network device via the second optical fiber.

5. The method according to any one of claims 1 to 3, further comprising: Before the first optical network device sends the first optical signal and the second optical signal, a first clock of the first optical network device is frequency synchronized with a second clock of the second optical network device.

6. The method according to any one of claims 1 to 3, further comprising: converting the asymmetry metric into a time offset value by the second optical network device; as well as The time reference of the second optical network device is adjusted based on the time offset value by the second optical network device.

7. The method according to claim 6, wherein: Adjusting the time base includes: When calculating a round trip delay based on a timing protocol between the first optical fiber and the second optical fiber, an offset value is adjusted based on the asymmetry metric.

8. The method according to claim 7, further comprising: The second clock of the second optical network device is synchronized with the first clock of the first optical network device using the timing protocol and the offset value.

9. The method according to any one of claims 1 to 3, wherein: Receiving the first optical signal includes receiving, by the second optical network device, the first optical signal transmitted on the first optical fiber via an optical service channel; and Receiving the second optical signal includes receiving, by the second optical network device, the second optical signal sent on the second optical fiber via the optical service channel.

10. The method according to any one of claims 1 to 3, wherein: Receiving the first optical signal includes receiving, by the second optical network device, the first optical signal transmitted at a first wavelength for transmitting traffic data; and Receiving the second optical signal includes receiving, through the second optical network device, the second optical signal sent at the first wavelength, where the first wavelength is used to send traffic data from the second optical network device to the first optical network device.

11. The method according to any one of claims 1 to 3, wherein: Receiving the first optical signal comprises receiving, by the second optical network device, the first optical signal sent over a data channel used to send data traffic from the first optical network device to the second optical network device; and Receiving the second optical signal includes receiving, by the second optical network device, the second optical signal sent through the data channel used to send data traffic from the second optical network device to the first optical network device.

12. The method according to any one of claims 1 to 3, wherein The first optical signal includes a first message including the first transmission time, and the second optical signal includes a second message including the second transmission time.

13. A device for an optical network, comprising: Communication interface; a memory configured to store executable instructions; as well as a processor coupled to the communication interface and the memory and configured to perform the following operations, including: receiving, via the communication interface, a first optical signal sent on a first optical fiber from a first optical network device at a first arrival time; receiving, via the communication interface, from the first optical network device a second optical signal sent on a second optical fiber at a second arrival time, wherein the second optical fiber is a reverse path optical fiber configured to send optical signals from the second optical network device to the first optical network device; calculating a first time difference between a second arrival time of the second optical signal and a first arrival time of the first optical signal; and An asymmetry metric between the first optical fiber and the second optical fiber is determined based on the first time difference and a second time difference, wherein the second time difference is a difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

14. The device according to claim 13, wherein The processor is further configured to perform the following operations, including: A second time difference calculated by the first optical network device is received from the first optical network device via the communication interface.

15. The device according to claim 14, wherein The processor is configured to perform an operation of determining an asymmetry measure between the first optical fiber and the second optical fiber by: A path difference is calculated based on a difference between the first time difference and the second time difference, wherein the path difference represents the asymmetry measure.

16. The apparatus according to any one of claims 13 to 15, further comprising: A switch switches the optical signal transmitted to the first optical network device over the second optical fiber to the optical signal received from the first optical network device over the second optical fiber.

17. The device according to any one of claims 13 to 15, wherein The processor is further configured to perform the following operations, including: Before the first optical network device sends the first optical signal and the second optical signal, a first clock of the first optical network device is frequency synchronized with a second clock of the apparatus.

18. The device according to any one of claims 13 to 15, wherein The processor is further configured to perform the following operations, including: converting the asymmetry measure into a time offset value; and A time base of the device is adjusted based on the time offset value.

19. One or more non-transitory computer-readable storage media encoded with instructions that, when executed by a processor, cause the processor to perform the following operations, including: receiving a first optical signal sent on a first optical fiber from a first optical network device at a first arrival time; receiving, from the first optical network device at a second arrival time, a second optical signal sent on a second optical fiber, wherein the second optical fiber is a reverse path optical fiber configured to send optical signals from the second optical network device to the first optical network device; calculating a first time difference between a second arrival time of the second optical signal and a first arrival time of the first optical signal; as well as An asymmetry metric between the first optical fiber and the second optical fiber is determined based on the first time difference and a second time difference, wherein the second time difference is a difference between a first transmission time of the first optical signal by the first optical network device and a second transmission time of the second optical signal by the first optical network device.

20. The one or more non-transitory computer-readable storage media encoded with instructions of claim 19, wherein: The instructions further cause the processor to perform the following additional operations, including: The second time difference calculated by the first optical network device is received from the first optical network device.

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