An optical line terminal (olt) for performing in-band and out-band otdr measurements

Optical line terminal for performing in-band and out-of-band OTDR testing

AN OPTICAL LINE TERMINAL (OLT) FOR PERFORMING IN-BAND AND OUT-BAND OTDR MEASUREMENTS

The present invention mainly relates to a passive optical network (PON), and more specifically, to an optical network unit ( ONU).

A passive optical network (PON) includes an optical line terminal (OLD) that connects multiple optical network units (ONU) in a point-to-multipoint network. New standards have been developed to define different types of PONs, each for a different purpose. For example, various different PON types known in related fields include broadband PON (BPON), Ethernet PON (EPON), 10 Gigabit Ethernet PON (10G-EPON), Gigabit PON (GPON), 10 Gigabit PON ( XG-PON), and other PONs.

An example diagram of a typical PON 100 is schematically shown in FIG. 1. The PON 100 includes N ONUs 120-1 to 120-N (collectively referred to as ONU 120) connected to the PLT 130 through a passive optical splitter 140 and optical fibers. In GPON, for example, the GPON encapsulation method (GEM) is used to implement traffic data transmission on two optical wavelengths, where one wavelength is used in the downstream direction and the other wavelength is used in the upstream direction. Therefore, the downstream transmission from the OLT 130 is broadcast to all ONUs 120. Each ONU 120 filters its respective data according to a pre-allocated label (for example, GEM port-ID in GPON). Splitter 140 is a 1 to N splitter, for example, capable of distributing traffic between a single PLT 130 and N ONU 120.

In most PON architectures, the upstream transmission is in the TDMA-based access The ONUs 120 are shared and controlled by the OLT 130. TDMA requires the OLT 130 to first discover the ONU and measure the round-trip time of the ONU before allowing coordinated access to the uplink. To this end, the OLT 130 tries to determine the range between the terminal units (ie, the ONU 120) during the ranging state to at least find the RTT between the OLT 130 and each ONU 120. In order to coordinate the TDMA-based access of all ONUs 120 sharing the uplink, the RTT of each ONU 120 is necessary. During the normal operation mode, the distance between the OLT 130 and the ONU 120 may change over time due to the temperature change of the optical fiber link (which causes the signal propagation time on the optical fiber to change). Therefore, the OLT 130 continuously measures RTT and adjusts the TDMA scheme of each ONU accordingly.

As schematically shown in FIG. 2, for example, an OLT 200 operable in GPON or XG-PON includes an electrical module (electrical module) 210 and an optical module 220. The electrical module is used to process the received upstream burst signal and generate the downstream signal. The electrical module 210 usually includes a network processor and a media access control (MAC) adapter, where the media access control adapter is designed to process and process upstream signals and downstream signals according to respective PON standards.

The optical module 220 is implemented as a small form-factor pluggable (SFP) transceiver in most cases, which receives the optical burst signal sent from the ONU and transmits the continuous optical signal to the ONU. The reception and transmission of signals are carried out through two different wavelengths. For example, in GPON, in the downstream direction, the optical module 220 generates optical signals from 1480nm to 1500nm (called 15XY), and receives optical signals between 1260nm and 1360nm in the upstream direction (also known as GPON 13XY).

The optical module 220 includes a laser driving diode 221 coupled to a transmission laser diode, and the transmission laser diode generates an optical signal based on the electrical signal provided by the laser diode driver 221. The module 220 also includes a limiting amplifier 222 coupled to a receiving diode, and the receiving diode generates a current proportional to the light amount of the light input burst signal. The limiting amplifier 222 generates two current levels indicating whether the received burst signal is a logic value of '1' or '0'.

The receiver/transmitter optical components (ie, photodiodes and laser diodes) are implemented as a bidirectional optical subassembly (BoSa) module 223, which can transmit and receive high-rate optical signals. The optical module 220 also includes a controller 224, which communicates with the electrical module 210 through an I2C interface, and performs tasks related to the calibration and monitoring of the transceiver.

The OLT supplier usually develops and manufactures the electrical module 210 of the OLT, where the optical module 220 is usually an off-the-shelf transceiver, such as SFP, XFP, and so on. Therefore, the interface between the electrical module 210 and the optical module 220 is a standard interface compatible with any type of SFP transceiver. As shown in FIG. 2, the interface includes wires for receiving (RX) data, transmitting (TX) data, TX enable signal, RX reset signal, and for connecting the electrical module 210 and the controller. I2C between 224. The I2C interface is a relatively slow serial interface with a data rate of 4Mb/sec. In contrast, the RX data and TX data interfaces are high-speed interfaces, where the data rate of the signal on these interfaces is used as the data rate of the PON (for example, 1Gb/sec in GPON).

In some PON configurations, dedicated ONUs are connected to the PON to perform maintenance and service availability applications. For example, a dedicated ONU can be used as part of the protection mechanism. Other examples include, dedicated ONUs can be used to perform optical time domain reflectometry (OTDR) analysis in a PON, measure RTT values, detect optical failures, and so on. Examples of using dedicated ONUs in PON can be found in co-pending U.S. Patent Application Nos. 12/648,885 and 13/189,935 assigned to the co-assignee, the contents of which are incorporated herein by reference.

Optical faults and the location of optical faults in the PON can be detected with an optical time domain reflectometer (OTDR). The principle of OTDR involves injecting a string of light pulses into the fiber at one end of the fiber under test and also extracting light scattered (Rayleigh backscatter) or reflected back from a point along the fiber from the same end of the fiber. The intensity of the return signal is measured and integrated as a function of time, and can be plotted as a function of fiber length. The results can be analyzed to determine the length of the fiber, total attenuation, optical failures (such as breaks), and to measure optical return loss.

OTDR measurement can use out-of-band, intra-band, or dedicated wavelength technology in PON implement. Out-of-band testing requires stopping the normal operation of the network and verifying the fiber with external OTDR tools. This can be performed with, for example, wavelengths and test pulses that are independent, independent, and different from other wavelengths used to transmit customer service traffic.

When the network is valid, perform the intra-frequency OTDR test. However, this test requires a dedicated OTDR test signal. The OTDR test signal used in the traditional intra-frequency OTDR scheme is AM or FM adjusted. However, such signals can only be transmitted during the PON test period, during which data signals cannot be transmitted to the ONU. Other OTDR solutions use dedicated upstream wavelengths to measure the reflection of optical fibers.

These OTDR technologies are implemented using external test devices. The external test devices can be dedicated optical units or OTDR tools connected to the PON and suitable for performing OTDR measurements.

In the traditional solution, the dedicated ONU is connected to the OLT through an optical fiber (which can be a dedicated optical fiber, PON optical fiber, or a combination thereof). Therefore, the ODTR measurement performed with a dedicated ONU should consider the delay induced by the optical fiber connecting the OLT and the ONU. The induced delay is usually determined by the ranging process.

In addition, the dedicated ONU should be within a small optical distance from the OLT. However, this is not always the case in systems used to detect optical failures. As an example, the system discussed in Application 13/189,935, in which the OLT connects dedicated ONUs (ie parallel ONUs) through splitters and dedicated optical fibers to form an optical link for signal transmission to facilitate fault detection.

Certain embodiments of the invention include an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform OTDR measurements. The OLT includes: an electrical module for generating continuous downstream signals and processing the received upstream burst signals according to the PON communication protocol; used for transmitting continuous optical signals of the first wavelength and receiving optical upstream burst signals of the second wavelength , And an optical module for transmitting the optical uplink burst signal of the third wavelength, wherein the optical module further includes an optical network unit (ONU) that is electrically coupled to the optical module and the electrical module. ), Among them, the optical network unit (ONU) traffic processing module is configured to simulate an optical network unit among multiple PON optical network units (ONUs) and generate an analysis mode for optical uplink burst signal transmission as a third wavelength ( analysis pattern) and the analysis pattern received in the optical upstream burst signal (optical upstream burst signal) of the second wavelength to perform OTDR measurement; and used in electrical modules and optical The interface of the interface connection between the modules.

Certain embodiments of the present invention also include an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform in-frequency OTDR measurements. The OLT includes: electrical modules for generating continuous downstream signals and processing the received upstream burst signals according to the PON communication protocol; used for transmitting continuous optical signals of the first wavelength and receiving optical upstream burst signals of the second wavelength , And an optical module for transmitting the optical uplink burst signal of the second wavelength, wherein the optical module further includes an optical network unit (ONU) flow processing module electrically coupled to the optical module and the electrical module, wherein the optical network The ONU traffic processing module is configured to simulate an optical network unit among multiple PON optical network units (ONUs), generate an analysis mode that will be used as an optical uplink burst signal transmission of the second wavelength, and analyze The analysis mode received in the optical upstream burst signal to facilitate OTDR measurement. The first wavelength and the second wavelength are the wavelengths defined in the PON communication protocol; and used for the interface connection between the electrical module and the optical module Interface.

Certain embodiments of the present invention also include an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform in-frequency OTDR measurements. The OLT includes: electrical modules for generating continuous downstream signals and processing the received upstream burst signals according to the PON communication protocol; used for transmitting continuous optical signals of the first wavelength and receiving optical upstream burst signals of the second wavelength , And an optical module for transmitting the optical uplink burst signal of the second wavelength, wherein the optical module further includes an optical network unit (ONU) flow processing module electrically coupled to the optical module and the electrical module, wherein the optical network The ONU traffic processing module is configured to simulate an optical network unit among multiple PON optical network units (ONUs), generate an analysis mode that will be used as an optical uplink burst signal transmission of the second wavelength, and analyze The analysis mode received in the optical uplink burst signal for easy execution For OTDR measurement, the first wavelength and the second wavelength are the wavelengths defined in the PON communication protocol; and the interface used for the interface connection between the electrical module and the optical module.

One aspect of the present invention relates to an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform OTDR measurements, including: an electrical module for communication according to the PON The protocol generates continuous downstream signals and processes the received upstream burst signals; optical modules are used to transmit continuous optical signals of the first wavelength, receive optical upstream burst signals of the second wavelength, and transmit optical upstream signals of the third wavelength Burst signal; wherein the optical module further includes an optical network unit (ONU) traffic processing module electrically coupled to the optical module and the electrical module, wherein the ONU traffic processing module is It is configured to simulate one of a plurality of optical network units (ONUs) of the PON, generate an analysis mode to be used as the optical uplink burst signal transmission of the third wavelength, and analyze the optical uplink burst of the second wavelength The analysis mode received in the signal is sent to perform the OTDR measurement; and an interface is used for the interface connection between the electrical module and the optical module.

In the above-mentioned OLT, preferably, the optical module further includes: a photonic component module including a first laser diode operable at the first wavelength, a second photodiode operable at the second wavelength, and A third laser diode operable at the third wavelength, wherein the first wavelength and the second wavelength are wavelengths defined in the PON communication protocol; a laser driver is coupled to the first A laser diode; a limiting amplifier, coupled to the second photodiode; a burst laser driver, coupled to the third laser diode; a controller, coupled to the I2C line of the interface; signal switching Unit, coupled to the limiting amplifier and activated by the ONU traffic processing module to relay the received uplink signal to the electrical module; and a signal splitter, coupled to the transmission data of the interface And provide repeated signals of continuous downstream signals generated by the electrical module to the ONU traffic processing module.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further coupled to the output end of the limiting amplifier to receive the respective repeated bursts of the received burst signals. Signal.

In the above-mentioned OLT, it is preferable that the generated analysis mode is a high-rate data mode including a low-rate component.

In the above-mentioned OLT, it is preferable that the OTDR measurement is an intra-frequency OTDR measurement.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further configured to: encapsulate the generated analysis mode in an upstream data frame complying with the communication protocol of the PON, wherein the upstream data frame serves as the Transmit the optical uplink burst signal of the third wavelength; receive the uplink data frame including the analysis mode, wherein the uplink data frame is included in the received optical uplink burst signal of the second wavelength; and transfer the generated The analysis mode of and the received analysis mode are autocorrelated, where the autocorrelation result represents the intra-frequency OTDR measurement.

In the above-mentioned OLT, it is preferable that the abnormal events of the respective autocorrelation results indicate a failure in the optical path of the PON, and the occurrence time of these events indicates the location of the failure in the optical path.

In the above-mentioned OLT, preferably, the second wavelength is equal to the third wavelength, and the third wavelength is a wavelength used by a plurality of ONUs for uplink communication.

In the above-mentioned OLT, it is preferable that the received analysis mode represents the reflection from the optical path of the PON, and the optical path includes the optical fiber and the optical element in the PON.

In the above-mentioned OLT, preferably, the OTDR measurement is an out-of-band OTDR measurement.

In the above-mentioned OLT, it is preferable that the optical module further includes a third photodiode for receiving the optical upstream burst signal of the third wavelength, wherein the third wavelength is a dedicated undefined communication protocol of the PON wavelength.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further configured to: encapsulate the generated analysis pattern in an upstream data frame, wherein the upstream data frame is transmitted as an optical upstream signal of the third wavelength ; Receiving an uplink data frame including the analysis mode, wherein the uplink data frame is included in the received optical uplink signal of the third wavelength; and the generated analysis mode and the received analysis mode from Correlation, where the autocorrelation result represents the out-of-band OTDR measurement.

In the above-mentioned OLT, it is preferable that the upstream signal of the third wavelength is any one of a continuous optical signal and a burst optical signal.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further configured to: generate a graph including the autocorrelation result; and compare the generated graph with the normal state of the optical path of the PON to detect Failure in the light path.

In the above-mentioned OLT, preferably detected faults include at least one of the following: damaged fiber, fiber bend, poor splice, dirty connector, and light cut.

In the above-mentioned OLT, preferably, the electrical module is configured to allocate uplink time slots for the ONU traffic processing module to transmit uplink burst signals.

In the above-mentioned OLT, it is preferable that the interface is a small form-factor pluggable (SFP) interface.

In the above-mentioned OLT, preferably the PON is any one of the following: Ethernet PON (EPON), 10 Gigabit Ethernet PON (10G-EPON), Gigabit PON (GPON), and 10 Gigabit PON (XG-PON) .

Another aspect of the present invention relates to an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform intra-frequency OTDR measurements, including: an electrical module for The PON communication protocol generates continuous downstream signals and processes the received upstream burst signals; optical modules are used to transmit continuous optical signals of the first wavelength, receive optical upstream burst signals of the second wavelength, and transmit the second wavelength The optical upstream burst signal; wherein, the optical module further includes an optical network unit (ONU) traffic processing module electrically coupled to the optical module and the electrical module, wherein the ONU traffic processing The module is configured to simulate one of a plurality of optical network units (ONUs) of the PON, generate an analysis mode to be transmitted as an optical uplink burst signal of the second wavelength, and analyze the optical uplink burst The analysis mode received in the signal is used to perform OTDR measurement, the first wavelength and the second wavelength are the wavelengths defined in the PON communication protocol; Interface connection between groups.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further configured to: encapsulate the generated analysis pattern in the upstream which complies with the communication protocol of the PON In the data frame, the uplink data frame is transmitted as an optical uplink burst signal of the second wavelength; the uplink data frame including the analysis mode is received, and the uplink data frame is included in the received In the optical uplink burst signal of the second wavelength; and autocorrelate the generated analysis mode and the received analysis mode, wherein the autocorrelation result represents the intra-frequency OTDR measurement.

Yet another aspect of the present invention relates to an optical line terminal (OTL) operable in a passive optical network (PON) and configured to perform out-of-band OTDR measurements, including: an electrical module for The communication protocol generates continuous downstream signals and processes the received upstream burst signals; optical modules are used to transmit continuous optical signals of the first wavelength, receive optical upstream burst signals of the second wavelength, and transmit the analysis of the third wavelength The optical uplink burst signal and the analysis optical uplink burst signal receiving the third wavelength; wherein, the optical module further includes an optical network unit (ONU) electrically coupled to the optical module and the electrical module ) A traffic processing module, wherein the ONU traffic processing module is configured to simulate one of a plurality of optical network units (ONUs) of the PON to generate an analysis optical upstream burst signal to be used as the third wavelength The analysis mode of transmission and the analysis mode received in the analysis optical upstream burst signal to perform OTDR measurement, wherein the third wavelength is a dedicated wavelength that is not defined in the PON communication protocol; and an interface for Interface connection between the electrical module and the optical module.

In the above-mentioned OLT, it is preferable that the ONU traffic processing module is further configured to: encapsulate the generated analysis pattern in an upstream data frame, wherein the upstream data frame is used as an analysis optical upstream signal of the third wavelength Transmission, the upstream data frame does not comply with the PON communication protocol, wherein the upstream signal of the third wavelength is any one of a continuous optical signal and a burst optical signal; receiving the upstream data signal including the analysis mode Frame, wherein the uplink data frame is included in the received analysis optical uplink signal of the third wavelength; and the generated analysis mode is autocorrelated with the received analysis mode, wherein the autocorrelation result represents the out-of-band OTDR measurement.

<p>100Passive Optical Network (PON)</p><p>120-1~120-NOptical Network Unit (ONU)</p><p>130Optical Line Terminal (OLT)</p><p>140Passive Optical Splitter</p><p>200Optical Line Terminal (OLT)</p><p>210Electrical Module</p><p>220Optical Module</p><p>221Laser Driver</p><p>222Limiting Amplifier</p><p>223Optical Subassembly (BoSa) Module</p><p>224controller</p><p>300Optical Line Terminal (OLT)</p><p>310Electrical Module</p><p>320Optical Module</p><p>321Laser Driver</p><p>322Limiting Amplifier</p><p>323controller</p><p>324Photonic Assembly (OSA) Module</p><p>325Signal Splitter</p><p>326burst laser driver</p><p>327Signal switching</p><p>330Standard interface</p><p>340ONU Traffic Processing Module</p><p>328Continuous receiver</p><p>400Passive Optical Network (PON)</p><p>410Fiber</p><p>420-1~420-NOptical Network Unit (ONU)</p><p>500Sample flow chart</p><p>S510~S570Sample flowchart</p><p>S610~S670Sample flowchart</p><p>710Curve</p><p>720curve graph</p><p>730Curve graph</p>

The subject matter of the present invention is specifically pointed out and clearly claimed in the scope of patent application at the conclusion of the specification. With reference to the accompanying drawings, the foregoing and other features and advantages of the present invention will be apparent from the following detailed description.

Figure 1 is a schematic diagram of a PON.

Figure 2 is a block diagram of a traditional OLT.

Figure 3A is a block diagram of an OLT designed to perform ONU functions and intra-frequency OTDR measurements according to one embodiment.

Figure 3B is a block diagram of an OLT designed to perform ONU functions and out-of-band OTDR measurements according to one embodiment.

Fig. 4 is a schematic diagram of a PON for describing different embodiments of the present invention.

FIG. 5 is a flowchart showing a method for performing intra-frequency OTDR using the OLT shown in FIG. 3A according to an embodiment.

FIG. 6 is a flowchart showing a method for performing out-of-band OTDR using the OLT shown in FIG. 3B according to an embodiment.

Figures 7A and 7B show graphs of the power of the reconditioning signal over time generated by an embodiment of the present invention.

It should be noted that the disclosed embodiments are merely examples of the many advantageous uses of the innovative technology herein. Generally, the statements made in the specification of the present disclosure are not necessarily limiting any aspect of the different claimed inventions. Moreover, certain statements can be applied to certain inventive features but not to other inventive features. Generally, unless explicitly specified otherwise, singular elements may be plural elements, and vice versa, without loss of generality. In the drawings, similar reference numerals refer to similar parts throughout the multiple figures.

Figure 3 shows an exemplary and non-limiting diagram of an optical line terminal (OLT) 300 constructed in accordance with one embodiment. The OLT 300 includes an electrical module 310 and an optical module 320 connected to each other through a standard interface 330.

The interface 330 provides connections for transmitting (TX) signals, receiving (RX) signals, TX enable signals for activating transmission to the ONU, and interfaces for resetting current burst signals. Connectivity of the received RX reset signal and control (I2C) signal. As described above, the interface 330 provides standard connectivity compatible with different types of SFPs or other standard transceivers that can operate in the OLT.

The electrical module 310 processes the received uplink signal and generates the downlink signal. The electrical module 310 generally includes a network processor and a PON MAC adapter designed to process and process upstream signals and downstream signals according to respective PON standards. In one embodiment, the electrical module 310 processes PON upstream and downstream traffic compatible with at least any one of EPON, 10G-EPON, GPON, and XG-PON. In the downstream direction, continuous signals are sent to all ONUs connected to the PON in the form of GEM frames in GPON or XGEM frames in XG-PON, for example. Each ONU filters its own data according to a pre-allocated label (for example, GEM port-ID in GPON). The electrical module 310 allocates a time slot for each ONU, and the ONU can send data to the OLT in the time slot. The reception of data in the upstream direction is the reception of burst signals sent from the ONU.

The optical module 320 receives the upstream optical burst signal sent from the ONU, and transmits the downstream continuous optical signal to the ONU. These downlink/uplink signals are received and transmitted through two different wavelengths. For example, in GPON, in the downstream direction, the optical module 320 generates an optical signal with a wavelength of 15XY, and receives an optical signal with a wavelength of 13XY in the upstream direction.

The optical module 320 includes a laser driving diode 321 and a limiting amplifier (Amp) driver 322 respectively coupled to a transmit laser diode and a receiving photodiode. The functions of the laser driver 321 and the amplifier 322 are described above based on FIG. 2. The controller 323 communicates with the electrical module 310 through an I2C interface, and performs tasks related to the calibration and monitoring of the transceiver.

According to the embodiment, the light transmitting element and the light receiving element coupled to the laser driving diode 321 and the limiting amplifier 322 are part of the photonic assembly (OSA) module 324. In one embodiment, the OSA module 324 is a triplexer.

According to this embodiment, in addition to a pair of transmission/reception optical elements, the OSA module Group 324 also includes transmission laser diodes, hereinafter "ONU-TX-laser diodes" (not shown) used to transmit burst optical signals at the wavelength used by the ONU in the PON downstream. As a non-limiting example, in the GPON implementation of the OLT 300, the OSA module 324 includes a transmission laser diode for transmitting signals with a wavelength of 15XY, a receiving photodiode for receiving optical signals with a wavelength of 13XY, and a photodiode for transmitting 13XY ONU-TX-laser diodes for wavelength signals. The ONU-TX-laser diode is driven by a burst laser driver 326. The burst laser driver 326 generates two current signals: bias and modulation. The bias current determines the '0' level optical power of the burst signal generated by the ONU traffic processing module 340, and the modulation current determines the '1' level optical power of the burst signal generated by the ONU traffic processing module 340.

According to another embodiment, the OSA module 324 is a quad-plexer including four optical elements, two laser diodes and two photodiodes. The first pair of transmitting/receiving optical elements and the second pair of transmitting/receiving optical elements operating at the wavelength of the OLT (the example provided above) are used to transmit/receive signals from the ONU traffic processing module 340. The wavelength of the second pair of transmission/reception optical elements may be a wavelength defined for upstream communication through the ONU in the PON or a dedicated wavelength not defined by the respective PON communication protocol. A pair of transmission/reception optical elements includes a laser diode and a photodiode, respectively.

According to different embodiments disclosed herein, integrated in the optical module 320 of the OLT 300 is the ONU traffic processing module 340, which is coupled to the signal splitter 335 for receiving signals to be transmitted to the PON. The ONU traffic processing module 340 is further connected to the output end of the limiting amplifier 322 so as to provide the module 340 with duplicate samples of the received burst signal. In an embodiment, the module 340 can also be connected to the signal switching unit 327 to directly transmit the burst signal to the OLT electrical module 310 and through the PON. If the RX data of the electrical module 310 comes from the PON or the module 340, the selection is based on the burst enable signal asserted by the ONU traffic processing module 340.

The ONU traffic processing module 340 is configured as any other ONU in the PON. In other words, the ONU traffic processing module 340 is assigned a unique ONU-ID to which downstream traffic can be directed. Moreover, the OLT 300 can allocate time slots to the ONU traffic processing module 340 by virtue of the electrical module 310 for transmitting upstream data.

The ONU traffic processing module 340 is electrically connected to the OLT 300. Therefore, the data transmitted by the OLT 300 is not received through the optical fiber of the PON, but is received at the module 340 through the signal splitter 325. Therefore, the optical distance between the ONU traffic processing module 340 and the OLT 300 is actually zero because the distance is determined by the electrical path between the module 310 and the module 340.

The ONU traffic processing module 340 includes a data packet processor and a PON MAC adapter (neither shown). The data packet processor generally performs PON processing tasks, such as filtering, forwarding-and-learning, flow classification, data packet classification, data packet queuing and shaping, data packet reassembly, and so on.

Because the module 340 is not connected to the user device, the packet processor only processes the downstream data stream, that is, the data sent from the OLT. In an embodiment, the data processor of the module 340 is configured to generate a set of predefined data patterns, which can be sent to the PON through the OSA module 324, and finally received by the OLT 300. The data patterns generated and sent in this way are used in various maintenance and service availability applications, including but not limited to PON protection, optical fault detection using OTDR measurement, RTT measurement, and so on. In other embodiments, the module 340 may be configured to respond to communications from the OLT with data packets.

The PON MAC adapter included in the ONU traffic processing module 340 processes the downstream traffic according to the type of the PON network. In an embodiment, the PON MAC adapter of the module 340 handles GPON or XG-PON traffic. In this configuration, the PON MAC adapter supports multiple traffic containers (T-CONT). T-CONT is a virtual upstream channel, and its bandwidth is authorized by the electrical module 310 of the OLT. A single T-CONT can be assigned to ONU, Class of Service (CoS), or logical ONU. The PON MAC switch keeps the T-CONT queue as the number of T-CONTs, and periodically requests data packets to fill a specific T-CONT queue.

The ONU traffic processing module 340 included in the optical module 320 is used as a dedicated ONU. However, unlike the traditional solution, the optical ONU traffic processing module 340 is electrically connected to the OLT 300 without passing through an optical fiber. Therefore, there is no need to use optical filters and create dedicated optical links, so when such dedicated ONUs are needed, the improved OLT 300 simplifies the layout of the PON. The improved OLT 300 further simplifies the processing of various maintenance and service availability application programs. The maintenance and service availability application programs can be executed by a dedicated ONU (that is, the ONU traffic processing module 340).

The ONU traffic processing module 340 may be implemented as an integrated circuit (IC), an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA) integrated in the optical module 320. In an exemplary embodiment, the ONU traffic processing module 340 can be implemented as the enhanced PON processor described in US Patent 7,643,753 or the PON processing with programmable data path described in the co-pending US Patent Application No. 12/821,931 The two are jointly assigned to the same assignee as the assignee of this application, so their content is incorporated herein by reference. According to an exemplary embodiment, when a dedicated ONU is used, the microprocessor and/or network processor may be adapted to perform maintenance and service availability applications.

It should be noted that the ONU traffic processing module 340 is integrated in the OLT optical module 320 to provide a standardized fast communication channel to the optical module 320 without changing the standard interface 330. The communication channel is realized by sending the downlink data to the module 340 through the PON or through the signal switching unit 327 and receiving the response signal generated by the module 340. The communication channel complies with the PON communication protocol. As described above, in this communication channel, signals used in processing related to testing the performance of PON and OLT, detection of optical faults, RTT measurement, OTDR measurement, etc. can be transmitted. Moreover, all such processes and their signals are transmitted by using the standard communication protocol of PON.

According to embodiments of the present invention, the improved OLT 300 can be used to perform intra-frequency and out-of-frequency OTDR measurements. The intra-frequency OTDR is executed by the following signal, which is generated by the ONU traffic processing module 340 and transmitted through the wavelength used by other ONUs in the PON. The back reflection signal is received at the OLT 300 and processed by the module 340.

In another embodiment, as shown in FIG. 3B, the LOT 300 is in its quadruplexer configuration, that is, the OSA module is a quadruplexer. This configuration is used to perform out-of-band OTDR for generating analysis signals transmitted on dedicated wavelengths. Also at the dedicated wavelength, the ONU traffic processing module 340 receives the reflected signal via the continuous receiver 328 to facilitate OTDR measurement. According to the embodiments disclosed herein, both in-band and out-of-band OTDR technologies can perform OTDR measurement without terminating the operation of the PON.

To implement the OTDR technology, connect the OLT 300 in the PON 400 as shown in FIG. 4. It should be noted that the OLT 300 is used as the OLT of the PON 400. The OLT 300 may be implemented as discussed in connection with FIGS. 3A and 3B. In other words, the OLT 300 performs all tasks defined by the various communication protocols of the PON. These tasks include at least allocating time slots for transmission data of ONUs 420-1 to 420-N, receiving and processing upstream burst data from ONUs 420-1 to 420-N, and generating downstream data and sending it to ONUs. In addition, the OLT 300 controls the ONU traffic processing module 340 as described above. The OTDR measurement can be used to detect a fault at any position in the optical path (for example, optical path 410) passing through the splitter 430 between the OLT 300 and each of the ONUs 420-1 to 420-N. The detected faults may include at least fiber damage, fiber bending, poor splices, dirty connectors, fiber cuts, and so on.

FIG. 5 is a non-limiting example flowchart 500 showing a method for performing intra-frequency OTDR using an OLT 300 according to an embodiment of the present invention. In S510, one or more time slots are allocated for the transmission of the analysis mode of the ONU traffic processing module 340.

In S520, the analysis mode is generated by the ONU traffic processing module 340. According to one embodiment, the analysis mode is a low-rate data mode including high-frequency components. The analysis mode meets the communication requirements of the PON, but can be analyzed to determine the above-mentioned faults and the location of the faults in the optical path. For example, if the OLT 300 is installed in the PON, the analysis mode maintains the continuous same number (CID) requirement of GPON, for example, CID&lt;72 bits, and the transmission rate of this mode is the allowable upstream data rate in GPON.

In an exemplary embodiment, the creation of the analysis mode includes the use of low-rate multiple The term (low rate polynomial) generates the data pattern, and the full rate repeating bits function is applied to the data pattern to generate the first bit sequence, and the first bit sequence is generated by the scrambler polynomial. A first bit-wise-xor operation is performed between the second bit sequence to generate an analysis bit sequence, and a second bit-wise-xor operation is performed between the analysis bit sequence and the third bit sequence generated by the scrambler. The bitwise operation generates an analysis pattern. For a detailed discussion of the analysis patterns used, see the co-pending application 13/189,935 cited above.

In S530, the generated analysis pattern is encapsulated in a data frame sent from the ONU module 340 to the OLT 300 in the upstream direction. For example, in GPON, the generated analysis pattern can be included in one or more upstream GEM frames.

In S540, the uplink data frame is transmitted to the optical fiber 410 through the OSA module 324. The wavelength used by the upstream data frame for upstream transmission in other ONUs of the PON (for example, ONU 420-1 to 420-N) is sent as an optical burst signal. For example, in GPON, the wavelength used is 13XY.

In S550, the upstream optical signal (partially carrying analysis feedback) is received in the OLT 300 that receives the photodiode of the OSA module 324 at the wavelength used for the upstream communication of the ONU. The received optical signal is reflected from the optical fiber 410 or sent back at one end of the optical fiber 410. The upstream signal received at the output end of the limiting amplifier 322 is also input to the ONU traffic processing module 340.

In S560, the ONU traffic processing module 340 analyzes the received upstream signal in order to perform OTDR measurement, which can be used to detect the fault of the optical path between the OLT 300 and the ONU 420 and the precise location of the fault. The fault location can be determined at any point of the optical fiber 410 (for example, 120 meters from the OLT 300) and any position of the optical element (for example, optical connector, splitter, etc.) in the optical path.

It should be noted that the traffic processing module 340 can receive the upstream burst signals sent by all ONUs 420-1 to 420-N. However, for OTDR measurement, only the received signal carrying the analysis mode is analyzed.

According to an exemplary embodiment, the analysis is performed using a time-shifted autocorrelation function between the received signal including the analysis pattern and the generated copy of the analysis pattern. This analysis is repeated for the N necessary bit-shifts. The number of bit shifts N represents the distance from the OTDR for which the signal is being analyzed, where the signal is shifted by 1 relative to other signals representing all possible measurement delays of the PON. The parameter N is a configurable parameter that can determine the resolution of the OTDR measurement. In order to provide higher resolution, the generated analysis mode should be a transmitter with a higher mode rate.

As a non-limiting example, the autocorrelation processing used during signal analysis can be defined as follows: AutoCorrelation(Ti){analog amount}=sum of((RX_AP bit-wise-xor(analog GEN_AP(Ti)))with quantization of n bits, where n&gt;1

Among them, RX_AP is the received analysis mode, and GEN_AP is the generated analysis mode. AutoCorrelation is a vector with the length of the optical path. Each element of the vector is the value of the correlation amount between the transmitted mode and the received mode, where the correlation bit delay represents the measured distance. The value of AutoCorrelation(Ti) can represent the condition that the light path is at the point C*Ti/2 (C is the speed of light in the fiber).

The measured autocorrelation at any Ti represents the reflected power from the position of the respective i-th shift in the optical path. According to one embodiment, the value of the autocorrelation function at time Ti can be compared with a value indicating the normal or acceptable behavior of the position on the optical path (respective time Ti), and any deviation is a fault indication. It should be noted that the measured correlation (correlation) represents a value (i.e., reflected power) that is higher or lower than the standard indicating different failures in the optical path. For example, a higher reflected power value can indicate fiber damage/breakage, while a lower than standard reflection value indicates attenuation in the fiber due to, for example, bending, poor splicing, direct-connect connectors, or fiber cuts.

In S570, a graph representing the autocorrelation result is generated. The autocorrelation function result represents the OTDR measurement. Any abnormal results in the autocorrelation graph are obvious in the graph (for example, as spikes) and indicate a fault in the light path. Abnormal knot The result can be a function of noise, speed change, and frequency of the associated graph.

Since the analysis is performed by the ONU traffic processing module 340, which is responsible for sending the analysis pattern and receiving the pattern reflected by the PON, there is no need to perform any ranging processing as part of the OTDR processing. Therefore, the disclosed embodiment simplifies the execution of the OTDR measurement in the PON intermediate frequency. It should be noted that the OLT 300 may perform ranging processing when needed. However, for OTDR measurement according to the teachings disclosed herein, the ranging process does not need to be performed.

In the above-described embodiment, the analysis of the received mode (for example, S570 and S580) for performing OTDR measurement is performed by the ONU traffic processing module 340. In another embodiment, the electrical module 310 of the OLT 300 or a computing processor configured to perform time shift correction may be used to perform such analysis. According to an embodiment, the module 340 provides the generated analysis mode through the signal switching unit 327. Later, the analysis mode is autocorrelated with the received burst signal including the mode analysis (generated and sent by the module 340 through the OSA 324). The autocorrelation can be performed as described above.

It should be noted that because the optical path between the ONU traffic processing module 340 and the electrical module 310 is almost zero, there is no optical delay that should be determined or considered when performing an OTDR measurement.

FIG. 6 is a non-limiting example flowchart 600 showing a method for performing out-of-band OTDR measurement using the OLT 300 according to an embodiment of the present invention. According to this embodiment, the OSA 324 is a quadruplexer as shown in FIG. 3, and the OSA supports other wavelengths (hereinafter referred to as dedicated wavelengths) that are not defined in the various communication protocol standards of the PON. For example, the dedicated wavelength in the PON will not be selected in the range of 13XY and 15XY. The value of the dedicated wavelength may be a function of the cost of manufacturing OSA 324. In order to support a dedicated wavelength, the OSA 324 includes a layer diode for transmitting optical signals and a photodiode for receiving signals modulated at the dedicated wavelength. In addition, the optical module 320 includes a continuous receiver 328.

In S610, the ONU traffic processing module 340 is set to perform out-of-band OTDR testing quantity. The module 340 can also be configured to perform OTDR. This can be performed on demand or at predetermined intervals. These settings can be completed by the PON operator. In S620, the analysis mode is generated by the ONU traffic processing module 340. As mentioned above, the analysis mode is a low-rate data mode. It should be noted that in the case of out-of-band OTDR, high-frequency components are not required because dedicated receivers and transmitters are used to receive/transmit signals at dedicated wavelengths.

In S630, the generated analysis pattern is transmitted to the optical fiber 410 via the OSA module 324 at a dedicated wavelength as an optical uplink burst signal. At S640, the receiving photodiode in the OSA module 324 associated with the dedicated wavelength receives the upstream burst optical signal (partially carrying the analysis mode) in the OLT 300. The received optical signal is reflected from the optical fiber 410. In S650, the uplink signal received at the output end of the continuous receiver 328 is also input to the ONU traffic processing module 340. In addition, the ONU traffic processing module 340 locally analyzes the signal received at the dedicated wavelength.

In S660, the ONU traffic processing module 340 analyzes the received upstream burst signal to facilitate OTDR measurement. As mentioned above, these measurements can be used to detect faults in the optical path between OLT 300 and ONU 420, and the precise location of these faults. The execution of the analysis is described in detail above.

At S670, a graph showing the result of the autocorrelation function is generated. The autocorrelation function result represents the OTDR measurement. Any non-autocorrelation results are obvious on the graph (for example, as spikes) and indicate a malfunction in the optical path.

It should be noted that the network operator can configure the ONU traffic processing module 340 with respect to the operation mode for performing OTDR measurement.

The intra-frequency and out-of-frequency OTDR measurements disclosed herein can be based on the autocorrelation results of the two generated analysis modes and the received (reflected) analysis mode. The fault can be determined by generating a graph representing the results of the autocorrelation. Examples are shown in Figures 7A and 7B.

Fig. 7A shows graphs 710 and 720, graphs 710 and 720 are examples of possible normal autocorrelations of received analysis patterns and generated analysis patterns. Figure 7B depicts the_fThe graph 730 of the spike signal. This indicates a fault in the optical path, which may be the result of a bad adapter that returns part of the power, for example. The location of the fault is (C*T_f)/2, f=0, 1,...N-1. Examples of other faults that can be detected include cat fibers, flattened fibers, fiber bends, dirty connections, and so on.

The various different embodiments disclosed herein can be implemented as hardware, firmware, software, and any combination thereof. Moreover, the software is preferably implemented as an application program tangibly embodied in a program storage unit or a computer-readable medium. The application program can be loaded into and executed by a machine including any suitable structure. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units ("CPU"), memory, and input/output interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be part of the microinstruction code or part of the application program, or may be a combination of them, and they may be executed by the CPU, regardless of whether the computer or processor is explicitly shown. In addition, various other peripheral units can be connected to the computer platform, such as an additional data storage unit and a printing unit.

All the examples and conditional language detailed in this article are for teaching purposes to help readers understand the principles and concepts of the present invention contributed by the inventors to improve the prior art, and should be construed as not limited to these detailed examples and conditions. Moreover, all the statements of the principles, aspects and embodiments of the present invention and specific examples thereof described herein are intended to simultaneously cover the structurally and functionally equivalent features of the present invention. In addition, these equivalent features include currently known equivalent features and equivalent features formed in the future, that is, any elements developed that perform the same function independently of the structure.