HK1188045B - Optical line terminal olt - Google Patents

Abstract

The invention discloses a passive optical fiber plant analysis. In a first aspect, the method and apparatus of the present disclosure can be used to periodically and/or intermittently place one or more ONUs attached to a PON in a power savings mode so that an OTDR test can be performed. While in the power savings mode, the ONUs temporarily suspend their transmitter function and power down their upstream lasers. In a second aspect, the method and apparatus of the present disclosure can be used to coordinate the performance of OTDR during one or more periodic or intermittent discovery slots used to detect and register ONUs recently connected to the PON. Because new ONUs are infrequently connected to the PON and ONUs already registered are not permitted to transmit during the discovery windows, OTDR can be performed during these windows without impacting, to a great degree, the normal operation of the PON.

Description

Optical line terminal OLT

Technical Field

The present application relates generally to analysis of fiber optic equipment and, more particularly, to analysis of passive fiber optic equipment using Optical Time Domain Reflectometry (OTDR).

Background

To keep pace with increasing voice, data, and video traffic, in many areas, network operators upgrade existing access networks by deploying optical fiber deep into the last mile to shorten the length of existing copper and coaxial networks. Among different competitive optical network technologies, Passive Optical Networks (PONs) have become one of the favored options for next-generation access networks. With large bandwidth optical fibers, PONs can provide bandwidth intensive voice, data, and video services.

However, the large bandwidth of PONs increases the need to provide a high level of network reliability. For example, because PONs have the potential to transport large amounts of data, a single failed optical connector or fiber may disrupt a large number of services running through the network. Therefore, network reliability is an extremely important issue for PON operators.

Addressing an interruption in a PON includes locating and identifying the source of the interruption. Optical Time Domain Reflectometry (OTDR) is in this case often used to locate and potentially identify the source of an interruption, such as a fibre fault or break. OTDR is an optical measurement technique used to analyze the attenuation (i.e., optical loss) of an optical fiber. The technique specifically involves injecting short laser pulses into a fiber optic device and measuring the backscatter and reflection of light over time. The backscattered and reflected light characteristics may then be analyzed to determine the location of any fiber faults/breaks or splice losses.

Although OTDR devices can be used to locate and potentially identify the source of an interruption in a PON, the effectiveness of these devices is often suppressed by the noise of other devices on the PON. For example, an Optical Network Unit (ONU) attached to a PON leaks optical power even when not transmitting. The leakage power generates noise that can affect the quality of the OTDR measurements. In addition, the use of OTDR devices typically generates and/or requires interruption of the operation of the PON itself.

Disclosure of Invention

According to an aspect of the present invention, there is provided an optical line terminal, OLT, configured to perform optical time domain reflection, OTDR, for locating an interrupt in a passive optical network, PON, the OLT comprising: a PON controller configured to transmit a power-saving start command to an Optical Network Unit (ONU) through the PON to place the ONU in a power-saving mode; and an OTDR module configured to inject pulses into the PON and to analyze signals reflected back from the injected pulses through the PON to locate interrupts in the PON, wherein the OTDR module injects pulses into the PON after receiving an indication that the ONU has accepted the power saving initiation command and is in power saving mode.

Preferably, the OTDR module is further configured to analyse reflected signals to identify the source of an interruption in the PON.

Preferably, the source of the interruption is at least one of a faulty connector, a faulty splitter, and a fiber break or macrobend.

Preferably, the PON controller is further configured to receive an acknowledgement message from the ONU indicating that the ONU has accepted the power-saving start command.

Preferably, when the ONU is in power-save mode, an upstream laser of the ONU is powered down to reduce optical power leakage onto the PON.

Preferably, the ONU remains registered with the PON while in the power saving mode and after terminating the power saving mode.

Preferably, the OLT further comprises an optical transceiver configured to inject the pulses into the PON under the direction of the OTDR module. Wherein the pulse is injected into the PON at a wavelength of 1,490nm, 1,550nm, 1650nm, or 1310nm by the optical transceiver.

Preferably, the PON controller is further configured to transmit a termination command to the ONU over the PON to terminate the power saving mode of operation at the ONU.

Preferably, the PON controller is further configured to provide an indication to the OTDR module when a discovery slot occurs. Wherein the OTDR module injects the pulse into the PON based on the indication to inject the pulse into the PON during a discovery time slot. Wherein the discovery time slot is used to detect an ONU that is newly connected to the PON.

According to another aspect of the present invention, there is provided an optical line terminal, OLT, configured to perform optical time domain reflection, OTDR, for locating an interrupt in a passive optical network, PON, the OLT comprising: an OTDR module configured to inject pulses into the PON and analyze signals reflected back from the injected pulses through the PON to locate disruptions in the PON; and a PON controller configured to provide an indication to the OTDR module of when a discovery time slot occurs, wherein the OTDR module injects the pulse into the PON based on the indication to inject the pulse into the PON during a discovery time slot, wherein the discovery time slot is used to detect an optical network unit, ONU, that is newly connected to the PON.

Preferably, the PON controller is further configured to transmit a discovery GATE message including a start time of the discovery slot over the PON.

Preferably, the OTDR module is further configured to discard a result of analyzing a reflected signal from the injection pulse if the ONU responds to finding a time slot.

Preferably, the OLT further comprises: an optical transceiver configured to inject the pulse into the PON under direction of the OTDR module. Wherein the pulse is injected into the PON at a wavelength of 1,490nm, 1,550nm, 1650nm, or 1310nm by the optical transceiver.

Preferably, the PON controller is further configured to transmit a power-saving initiation command to an ONU over the PON to place the ONU in a power-saving mode.

Preferably, the OTDR module is further configured to inject the pulse into the PON after receiving an indication that the ONU has accepted the power saving start command and is in power saving mode.

Preferably, the OTDR module is further configured to use the round trip time associated with an ONU to interpret the result of analyzing the reflected signal.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments.

Fig. 1 shows an exemplary PON according to an embodiment of the present invention.

Fig. 2 illustrates data transmitted upstream through a PON according to a non-contention based medium access protocol (non-contention based access system) according to an embodiment of the present invention.

Fig. 3 shows an exemplary block diagram of an OLT according to an embodiment of the present invention.

Fig. 4 shows a flow diagram of a method of periodically and/or intermittently placing one or more ONUs attached to a PON in a power saving mode so that OTDR can be performed, according to an embodiment of the invention.

FIG. 5 illustrates an exemplary computer system that can be used to implement various aspects of the present invention.

Embodiments of the present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is generally indicated by the leftmost digit(s) in the corresponding reference number.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the invention. It will be apparent, however, to one skilled in the art that embodiments, including structures, systems, and methods, may be practiced without these specific details. The descriptions and representations herein are the means used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

I. Overview

The present invention relates to methods and arrangements to improve the quality of OTDR measurements in a PON and/or the impact of performing these measurements on the normal operation of the PON.

As briefly mentioned above, a PON may include many attached devices, such as ONUs, that leak optical power onto the PON even when not actively transmitting. The noise introduced on the PON by these leaking devices may negatively affect the quality of the measurements made by the OTDR device. Thus, in a first aspect, the method and apparatus of the present invention may be used to periodically or intermittently place one or more ONUs attached to a PON in a power saving mode so that OTDR may be performed.

Typically, the power saving mode is specified in a number of PON standards, such as the ITU-T Gigabit Passive Optical Network (GPON) standard and the IEEE Ethernet Passive optical network interworking Service (SIEPON) standard. While in power save mode, the ONU temporarily suspends its transmitter function and powers off its upstream laser. This reduces the optical power that leaks from those devices onto the PON. Importantly, the ONU is not de-registered from the PON because it is placed in the power saving mode, which helps to reduce the overall impact of placing the ONU in the power saving mode to perform OTDR on the normal operation of the PON.

In a second aspect, the methods and apparatus of the present invention may be used to adjust the performance of OTDR during one or more periodic or intermittent discovery slots used to detect and register ONUs recently connected to a PON. Since new ONUs are rarely connected to the PON and registered ONUs are not allowed to transmit during discovery time slots, OTDR may be performed during these time slots without largely affecting the normal operation of the PON.

These and other aspects of the invention are described in the following sections.

II. Exemplary operating Environment

Fig. 1 illustrates an exemplary PON100 in which embodiments of the present invention may be implemented. As shown in fig. 1, a PON100 communicatively couples a central office (central office)110 to a single home unit (SFU)120 and a multi-dwelling unit (MDU)130 (i.e., a structure that houses two or more residential or commercial units). The transmission within the PON100 is specifically performed between an Optical Line Terminal (OLT) at the central office 110 and Optical Network Units (ONUs) at the SFUs 120 and the MDUs 130 over optical fibers spanning the distance between the central office 110 and the SFUs 120 and the MDUs 130. The OLT of the central office 110 couples the PON100 at its end to a service network (not shown), which may be a metro or core network, for example. Additionally, the ONUs at the SFU120 and the MDU130 further couple the PON100 at their ends to a home network or a business network (also not shown).

The overall network architecture shown in fig. 1 allows end-user devices coupled to a home network or business network within the SFU120 and MDU130 to send and receive data to and from a serving network through the PON 100. Wavelength Division Multiplexing (WDM) can be used to transmit downstream traffic over one wavelength and upstream traffic over another wavelength. For example, multiple PON standards use the same basic wavelength scheme: a wavelength of 1,490 nanometers (nm) for downstream flow, and a wavelength of 1,310nm for upstream flow. 1,550nm wavelength is also commonly used for selective overlay services, such as RF video.

As further shown in fig. 1, the portion of the PON100 closest to the central office 110 is commonly referred to as a feed area 150. The region includes one or more feeder cables each having a plurality of optical fibers. Passive optical splitter/combiner 140 can be used to split the individual fibers of the feeder cable into a plurality of distributed fibers belonging to a second portion of PON100, which portion is commonly referred to as a distribution region 160. The distributed fiber is then split into a plurality of drop fibers (dropfibers) that extend to the SFUs 120 and the MDUs 130 using an additional passive optical splitter/combiner 140. The drop fiber belongs to the third and final part of the PON100, which part is commonly referred to as the drop area (drop) 170.

In existing access networks, distribution area 160 and/or lead-in area 170 are deployed using copper cables and/or coaxial cables. By extending the optical cable deep into the access network, up to home, building, roadside, etc., the PON100 can provide bandwidth-intensive voice, data, and video services that existing access networks cannot handle. As shown in fig. 1, the remaining portion of the network between the central office 110 and the end-user devices at the SFU120 and MDU130, which are potentially not optically connected, are within the local area network range of these locations (i.e., within the metal area 180). With such short copper and/or coaxial wiring distances, current local area network technologies typically provide sufficient bandwidth.

It should be noted that the PON100 illustrates only one exemplary PON and fiber distribution topology (i.e., a tree topology) in which embodiments of the present invention may be implemented. Other fiber distribution topologies in which embodiments of the present invention may be implemented include other point-to-multipoint topologies, ring topologies, mesh topologies, and the like.

In operation of the access network shown in fig. 1, signals transmitted downstream through the OLT at the central office 110 over three portions of the PON100 are split by the passive optical splitter/combiner 140 and received by the ONUs at the SFUs 120 and MDUs 130. Thus, downstream transmitted signals are thus broadcast to all ONUs. Conversely, signals transmitted upstream through ONUs at the SFU120 and MDU130 on three sections of the PON100 are combined together by a passive optical splitter/combiner 140 and received by the OLT at the central office 110.

To prevent collisions in the upstream direction and to share the upstream capacity of the PON100 fairly, the OLT at the central office 110 and the ONUs at the SFUs 120 and MDUs 130 implement some form of arbitration mechanism. For example, PONs implement a non-contention based medium access protocol that allows each ONU to access the shared medium at limited time intervals to transmit data upstream. The finite time interval is commonly referred to as a time slot.

Fig. 2 shows an example of data sent upstream over a PON according to a non-contention based medium access protocol. In fig. 2, each ONU1-N is synchronized to a common timing reference and is assigned a time slot for upstream transmission of one or more data packets to the OLT. More specifically, each ONU1-N buffers data packets received from an attached end user (or users) and bursts one or more buffered data packets upstream to the OLT upon arrival of its assigned time slot. For example, ONU1 receives two data packets from attached user 1, buffers the two data packets, and transmits the two data packets upstream in bursts during the first time slot assigned to ONU 1. ONU2 receives a single packet from attached user 2, buffers this packet, and transmits this packet upstream in bursts during the second time slot assigned to ONU 2. As can be seen from fig. 2, the time slots are allocated to the ONUs such that they do not overlap in time, thereby preventing upstream collisions.

In addition to simply allocating time slots so that they do not overlap in time, the exact method of when and how much capacity is granted to a particular ONU in a non-contention based medium access protocol can have a tremendous impact on the performance of the PON. In most PONs, each ONU is dynamically allocated a time slot of varying capacity based on the instantaneous value of the ONU buffered data (i.e. according to a Dynamic Bandwidth Allocation (DBA) scheme).

In a PON implementing a DBA scheme, the OLT is responsible for assigning an upstream grant (or time slot) to each ONU. An ONU defers its upstream transmissions until authorization is received by the OLT. To receive the grant, the ONU generates and transmits an upstream message, called a REPORT message, to the OLT informing the OLT of the status of its respective upstream queues. The OLT uses this information sent from each ONU requesting upstream bandwidth to generate and transmit GATE messages to the ONUs. Each GATE message typically assigns upstream transmission grants to ONUs based on its upstream bandwidth requirements and other ONUs' upstream bandwidth requirements, etc.

However, because the ONUs are located at different locations from the OLT, the time taken for a signal to be sent out upstream from each ONU before reaching the OLT is different due to fiber delay. It is therefore important to establish a common timing reference between the OLT and the ONUs to account for the different fibre delays so that when an ONU signal arrives at the OLT it reaches or is very close to the time at which the OLT intends to receive the signal. This prevents collisions in the upstream direction. The timing reference between the OLT and the ONUs may be established through a process called ranging (typically performed in a discovery process).

The discovery process is used by the OLT to detect and register ONUs recently connected to the PON by knowing their respective round-trip delays and MAC addresses. To perform the discovery process, the OLT periodically or intermittently transmits a discovery GATE message including time information of a local time of the OLT and a start time of a discovery slot to the ONUs.

The unregistered ONUs may respond to the discovery GATE message by setting their local time (as determined by their local clock) to the time information contained in the discovery GATE message. The ONU may transmit a REGISTER _ REQUEST message when the local clock of the unregistered ONU reaches the start time of the discovery slot (also contained in the discovery GATE message). The REGISTER _ REQUEST message may include the MAC address of the ONU and time information indicating the local time of the ONU at the time when the REGISTER _ REQUEST is transmitted.

When the OLT receives the REGISTER _ REQUEST message from the ONU, the MAC address of the ONU and the Round Trip Time (RTT) of the ONU can be known. The RTT may be specifically calculated as a difference between the time when the REGISTER REQUEST message is received at the OLT and the time information contained in the REGISTER REQUEST message. The RTT time may be stored for each registered ONU and may be used to adjust the time at which data frames are to be transmitted from the ONU (as indicated by the OLT). Collisions may occur because more than one unregistered ONU may respond during a discovery slot. However, no conflict typically occurs. Indeed, in many cases, no ONU responds to the discovery slot.

Referring now to fig. 3, there is illustrated an exemplary high-level block diagram of an OLT300 that may implement embodiments of the present invention. OLT300 includes a Service Network Interface (SNI)305, an optional classifier 310, an upstream queue module 315, a downstream queue module 320, a PON controller 325, an optical transceiver 330, and an Optical Time Domain Reflectometry (OTDR) module 335 for performing OTDR.

In the upstream direction, the optical transceiver 330 receives optical signals transmitted from the ONUs through the PON. Data in the form of data packets is recovered from the optical signal and provided to the PON controller 325 in an electronic format. The PON controller 325 accepts and analyzes the data packets and, based on the contents of the data packets, potentially passes the data packets to the upstream queue module 315 for buffering. Packets buffered in the upstream queue module 315 are sequentially transmitted to the serving network via the SNI 305.

In the downstream direction, data packets of data to be transmitted over the PON to the ONUs are initially received from the serving network via the SNI 305. Classifier 310 (optionally included in OLT 300) classifies packets into priority classes based on the type of content they carry. For example, data packets carrying voice or video data may be classified into priority classes characterized by small transmission delays (e.g., high priority classes), while data packets carrying data other than voice or video may be classified into priority classes characterized by requiring only best effort transmission (e.g., low priority classes).

Assuming that classifier 310 is included in OLT300, downstream queue module 320 may include a plurality of downstream queues, each having a respective assigned priority. Classifier 310 may insert a packet received from a serving network via SNI305 into one of a plurality of downstream queues having a specified priority corresponding to a priority level of the packet. Once removed from the downstream queue, the data packets are typically sent downstream through a PON coupled to OLT300 using PON controller 325 and optical transceiver 330.

As briefly described above, the channel capacity of a PON, such as a PON coupled to OLT300, is typically shared by multiple ONUs in the upstream direction. As a result, upstream transmissions from each ONU attached to the PON are arbitrated to avoid collisions. OLT300 is configured to perform this arbitration by assigning grants (also referred to as time slots) to the ONUs. In this scheme, the ONU delays upstream data transmission until a grant is received from OLT 300. To receive the grant, the ONU generates and transmits an upstream message, called a REPORT message informing the OLT300 of the different statuses of the upstream queue, to the OLT 300. OLT300 may use this information sent from one or more ONUs requesting upstream bandwidth to generate and transmit GATE messages to the ONUs. Each GATE message typically assigns an upstream transmission grant to an ONU based on, for example, its upstream bandwidth requirements and the upstream bandwidth requirements of other ONUs.

In OLT300, PON controller 325 may be configured to process the received REPORT message and generate an appropriate GATE message in response. In addition, the PON controller 325 may also be configured to perform the above-described discovery process used to detect and register the ONUs by knowing the respective round-trip delays and MAC addresses of recent connections to the PON.

III, first aspect of the invention

In a first aspect, the present invention relates to a method and apparatus for periodically and/or intermittently placing one or more ONUs attached to a PON in a power saving mode so that OTDR can be performed. The first aspect is described below with reference to an exemplary OLT300 shown in fig. 3. It should be noted, however, that the methods and apparatus of the present invention may be implemented in other OLTs, as will be appreciated by those of ordinary skill in the art.

Typically, a PON may include many attached devices, such as ONUs, that leak optical power onto the PON even when not actively transmitting. The noise introduced on the PON by these leaking devices may negatively impact the quality of the measurements analyzed by OTDR module 335 shown in fig. 3. For example, because OTDR involves measuring very weak power backscattering and reflections of light received through an optical fiber, any additional noise on the fiber may affect the quality of the results from analyzing the measured backscattering and reflected light.

Accordingly, OTDR module 335 may periodically and/or intermittently place one or more ONUs connected to a PON in which OLT300 operates in a power saving mode so that OTDR tests may be performed. Typically, the power saving mode is specified in a number of PON standards, such as the ITU-T GPON standard and the IEEESIEPON standard. While in power save mode, the ONUs temporarily suspend their transmitter functions and power down their upstream lasers. This reduces the optical power that leaks from those devices onto the PON. Importantly, the ONU is typically not logged out because it was placed in the power saving mode, which helps to reduce the overall impact of placing the ONU in the power saving mode to perform OTDR on the normal operation of the PON.

OTDR module 335 may signal PON controller 325 via OTDR timing/control signals 340 to send a command to one or more ONUs to temporarily enter a power-save mode by disabling their transmitter function and powering down their upstream lasers. For example, in a PON configured to operate in accordance with the SIEPON standard, the PON controller 325 may send a power saving initiation command, commonly referred to as sleep all, to one or more ONUs. In response, when one or more ONUs accept the power saving initiation command, a message, commonly referred to as a sleep ack, may be returned. Once PON controller 325 receives a sleep ack message (or some equivalent message) from all or part of one or more ONUs, PON controller 325 may signal OTDR module 335 via OTDR timing/control signal 340 to begin an OTDR test.

OTDR module 335 may begin an OTDR test by sending a pulse or pulse pattern to optical transceiver 330 via OTDR test signal 345. The optical transceiver 330 may then inject a pulse or pulse pattern into the PON. Pulses are injected at the same wavelength (e.g., 1,490nm or 1,550nm wavelength) for normal downstream traffic, the same wavelength (e.g., 1310nm wavelength) for upstream traffic, or other out-of-band wavelengths.

The optical transceiver 330 may further sample the resulting backscatter and reflection of light from the injected pulse or pulse pattern. The sampled backscattered and reflected light may be passed to the OTDR module 335 for analysis as a function of time to locate and potentially identify the source of the interruption, such as an unclean/damaged/misaligned connector or splitter or fiber break/macrobend. The results of this analysis may be provided as output from OLT300 via OTDR result signal 355.

Once the backscatter and reflection of light is sampled, the PON controller 325 may optionally send a command to one or more ONUs to terminate the power saving mode. OTDR module 335 may send a signal to PON controller 325 via OTDR timing/control signal 340 when a termination command may be sent.

It should be noted that in other embodiments, one or more ONUs may simply be forced down or reset by the OLT to have their lasers disabled. However, this may have the negative effect of deregistering the ONU from the PON, which greatly affects the service.

Fig. 4 shows a flowchart 400 of a method for periodically and/or intermittently placing one or more ONUs attached to a PON in a power saving mode so that OTDR can be performed, according to an embodiment of the invention. The method of flowchart 400 may be implemented by OLT300 shown in fig. 3. However, it should be noted that the method may be implemented by other systems and components. It should also be noted that certain steps of flowchart 400 need not occur in the order shown in fig. 4.

The method of flowchart 400 begins at step 402. In step 402, a command is sent to one or more ONUs on the PON to instruct the ONUs to temporarily enter a power-saving mode. For example, in a PON configured to operate in accordance with the SIEPON standard, a power saving initiation command (commonly referred to as sleep all) may be sent to one or more ONUs to instruct the ONUs to temporarily enter a power saving mode.

In a determination step 404, it is determined whether a sleep confirmation message (or some equivalent message) has been received from all or part of one or more ONUs. If a sleep confirmation message (or some equivalent message) is received from all or part of one or more ONUs, flow diagram 400 proceeds to step 406. Otherwise, the flowchart 400 remains in step 404.

In step 406, an OTDR test is initiated and a pulse or pulse pattern is injected into the PON. Pulses are injected at the same wavelength (e.g., 1,490nm or 1,550nm wavelength) for normal downstream traffic, the same wavelength (e.g., 1310nm wavelength) for upstream traffic, or other out-of-band wavelengths.

In step 408, the backscatter and reflection of light resulting from the injected pulse or pulse pattern can be measured and analyzed as a function of time to locate and potentially identify the source of the interruption, such as an unclean/damaged/misaligned connector or splitter or fiber break/macrobend.

In step 410, the analysis results may be output. For example, the analysis may be output to a display or a file for storage.

In step 412, a command may be sent to one or more ONUs to terminate the power saving mode.

IV, second aspect of the invention

In a second aspect, the present invention relates to a method and apparatus for adjusting the performance of OTDR tests during one or more periodic or intermittent discovery slots of a discovery process performed in a PON. A second aspect is described below with reference to an exemplary OLT300 shown in fig. 3. However, it should be noted that the method and apparatus of the present invention may be implemented in other OLTs, as would be understood by one of ordinary skill in the art.

As described above, the discovery process is used to detect and register ONUs recently connected to the PON by knowing their respective round trip delays and MAC addresses. To perform the discovery process, the PON controller 325 of the OLT300 periodically or intermittently transmits a discovery GATE message including time information of a local time of the OLT300 and a start time of a discovery slot to the ONUs.

The unregistered ONUs may respond to the discovery GATE message by setting their local time (as determined by their local clock) to the time information contained in the discovery GATE message. The ONU may transmit a REGISTER _ REQUEST message when the local clock of the unregistered ONU reaches the start time of the discovery slot (also included in the discovery GATE message). The REGISTER _ REQUEST message may include a MAC address of the ONU and time information indicating a local time of the ONU at the time of transmitting the REGISTER _ REQUEST message.

When OLT300 receives a REGISTER _ REQUEST message from an ONU, it can know the MAC address of the ONU and the Round Trip Time (RTT) of the ONU. The RTT may specifically be calculated as a difference between the time at which the REPORT message is received at OLT300 and the time information contained in the REPORT message. The RTT may be stored for each registered ONU and may be used to adjust the time of data frames to be transmitted from the ONU (as indicated by the OLT).

Collisions may occur because more than one unregistered ONU may respond to a discovery slot. However, no conflict typically occurs. Indeed, in many cases, no ONU responds to the discovery slot. Accordingly, OTDR module 335 may leverage these time periods to perform OTDR testing when there are potentially no devices transmitting over the PON. This helps to reduce the impact of performing OTDR tests on the normal operation of the PON.

For example, in one embodiment, OTDR module 335 may receive an indication of the occurrence of a discovery slot from PON controller 325 via OTDR timing/control signals 340. OTDR module 335 may then begin an OTDR test by sending a pulse or pulse pattern to optical receiver 330 via OTDR test signal 345. The optical transceiver 330 may then inject a pulse or pulse pattern into the PON. Pulses are injected at the same wavelength (e.g., 1,490nm or 1,550nm wavelength) for normal downstream traffic, the same wavelength (e.g., 1310nm wavelength) for upstream traffic, or other out-of-band wavelengths.

The optical transceiver 330 may further sample the backscatter and reflection of light produced by the injected pulse or pulse pattern. The sampled backscattered and reflected light may be passed to the OTDR module 335 for analysis as a function of time to locate and potentially identify the source of the interruption, such as an unclean/damaged/misaligned connector or splitter or fiber break/macrobend. The results of this analysis may be provided as output from OLT300 via OTDR result signal 355.

If an unregistered ONU attempts to register during a discovery slot, the sampled light backscatter and reflection can be corrupted and can simply be discarded by OTDR module 335.

It should be noted that OTDR testing requires a large number of samples to balance the noise. Thus, to obtain results in a fast manner, the rate at which discovery slots are made available to the PON may be increased by the PON controller 325. For example, in many PONs, discovery slots are typically made available approximately every second. This typical rate can be increased (e.g. to 1000 discovery slots per second) to obtain OTDR test results in a faster manner.

It should also be noted that the second aspect of the invention may be used with the first aspect of the invention described in the previous section. For example, one or more ONUs may be placed in a power saving mode, and after all or a portion of the one or more ONUs are in the power saving mode, an OTDR test may be performed by OTDR module 335 during a discovery slot.

V, other aspects of the invention

In another aspect, the methods and apparatus of the present invention may use the measured RTT for ONUs on the PON to associate the ONUs with a particular reflectance value measured by OTDR module 335. As described above, after injecting a pulse or pulse pattern into the PON during OTDR testing, the optical transceiver 330 may sample the backscatter and reflection of the generated light. The sampled backscatter and reflection of light may be passed to OTDR module 335 for analysis. More specifically, OTDR module 335 may analyze the sample as a function of time. Because the RTTs associated with ONUs are measured when the ONUs register with the PON (as described above), one or more registered ONUs may be further plotted against samples or associated with these samples based on the respective RTTs to help interpret the results of the OTDR test.

In yet another aspect, the methods and apparatus of the present invention may perform an admittance test (as opposed to a reflection test). In this case, the admittance is measured by having the selected ONU inject a pulse or pulse pattern into the PON and measuring the admittance of the pulse or pulse pattern at OLT 300. This has the advantage of allowing analysis of a single upstream path from a selected ONU to OLT 300. In one embodiment, the pulses or pulse patterns may be scheduled for transmission from a selected ONU. For example, the pulses or pulse patterns may be scheduled by OLT300 for injection into the PON by a selected ONU during a discovery time slot used in the discovery process.

VI, implementation of an exemplary computer System

It will be apparent to those skilled in the relevant art that various elements and features of the invention, as described herein, may be implemented in hardware using analog and/or digital circuitry, or in software using one or more general purpose or special purpose processors executing instructions, or in a combination of hardware and software.

For completeness, the following description of a general-purpose computer system is provided. Embodiments of the present invention may be implemented in hardware, or in a combination of software and hardware. Thus, embodiments of the invention may be implemented in the context of a computer system or other processing system. An example of such a computer system 500 is shown in fig. 5. One or more of the modules depicted in fig. 3 may execute on one or more different computer systems 500. Further, each of the steps of the flow chart depicted in fig. 4 may be implemented on one or more different computer systems 500.

Computer system 500 includes one or more processors, such as a processor 504. The processor 504 may be a special purpose processor or a general purpose digital signal processor. The processor 504 is connected to a communication facility 502 (e.g., a bus or network). Various software implementations are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art how to implement the invention using other computer systems and/or computer structures.

Computer system 500 also includes a main memory 506, preferably Random Access Memory (RAM), and may also include a secondary memory 508. For example, the secondary memory 508 may include a hard disk drive 510 and/or a removable storage drive 512, representing a floppy diskette drive, a magnetic tape drive, a compact disk drive, etc. The removable storage drive 512 reads from and/or writes to a removable storage unit 516 in a well known manner. Removable storage unit 516 represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive 512. One skilled in the relevant art will appreciate that removable storage unit 516 includes a computer usable storage medium having stored therein computer software and/or data.

In alternative implementations, secondary memory 508 may include other similar means for allowing computer programs or other instructions to be loaded into computer system 500. Such means may include, for example, a removable storage unit 518 and an interface 514. Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, a thumb drive (thumb drive) and USB port, and other removable storage units 518 and interfaces 514 which allow software and data to be transferred from the removable storage unit 518 to computer system 500.

Computer system 500 may also include a communications interface 520. Communications interface 520 allows software and data to be transferred between computer system 500 and peripheral devices. Examples of communications interface 520 may include a modem, a network interface (such as an ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface 520 are in the form of signals which may be electrical, electromagnetic, optical or other signals capable of being received by communications interface 520. These signals are provided to communications interface 520 via a communications path 522. Communication path 522 carries signals and is implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link, or other communication channels.

As described herein, the terms "computer program medium" and "computer-readable medium" are used to generally refer to tangible storage media such as removable storage units 516 and 518 or a hard disk installed in hard disk drive 510. These computer program products are means for providing software to computer system 500.

Computer programs (also called computer control logic) are stored in main memory 506 and/or secondary memory 508. Computer programs may also be received via communications interface 520. Such computer programs, when executed, enable computer system 500 to implement the present invention as discussed herein. In particular, the computer programs, when executed, enable the processor 504 to implement processes of the present invention, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system 500. When the present invention is implemented using software, the software may be stored in a computer program product and loaded into computer system 500 using removable storage device 512, interface 514, hard drive 512, or communications interface 520.

In another embodiment, the features of the present invention are implemented primarily in hardware using hardware components such as Application Specific Integrated Circuits (ASICs) and gate arrays. It will also be apparent to one skilled in the relevant art that hardware state machines are implemented to perform the functions described herein.

VII, conclusion

The present invention has been described above with the aid of functional components illustrating specified functions and relationships thereof. The scope of the functional building blocks is arbitrarily defined herein for convenience of description. The optional scope may be defined so long as the specified functions and relationships thereof are appropriately performed.

Claims (10)

1. An optical line termination, OLT, configured to perform optical time domain reflection, OTDR, for locating an interruption in a passive optical network, PON, the OLT comprising:

a PON controller configured to transmit a power-saving start command to an Optical Network Unit (ONU) through the PON to place the ONU in a power-saving mode; and

an OTDR module configured to inject pulses into the PON and analyze signals reflected back from the injected pulses through the PON to locate disruptions in the PON,

wherein the OTDR module injects a pulse into the PON after receiving an indication that the ONU has accepted the power saving start command and is in a power saving mode.

2. The OLT of claim 1, wherein the OTDR module is further configured to analyze reflected signals to identify a source of an interruption in the PON.

3. The OLT of claim 1, wherein a source of the interruption is at least one of a faulty connector, a faulty splitter, and a fiber break or macrobend.

4. The OLT of claim 1, wherein the PON controller is further configured to receive an acknowledgement message from the ONU indicating that the ONU has accepted the power saving initiation command.

5. The OLT of claim 1, wherein an upstream laser of the ONU is powered down to reduce optical power leakage onto the PON when the ONU is in a power save mode.

6. An optical line termination, OLT, configured to perform optical time domain reflection, OTDR, for locating an interruption in a passive optical network, PON, the OLT comprising:

an OTDR module configured to inject pulses into the PON and analyze signals reflected back from the injected pulses through the PON to locate disruptions in the PON; and

a PON controller configured to provide an indication to the OTDR module of when a discovery slot occurred,

wherein the OTDR module injects the pulses into the PON based on the indication to inject the pulses into the PON during a discovery time slot,

wherein the discovery time slot is used to detect an optical network unit, ONU, that is newly connected to the PON.

7. The OLT of claim 6, wherein the PON controller is further configured to transmit a discovery GATE message over the PON that includes a start time of the discovery slot.

8. The OLT of claim 6, wherein the OTDR module is further configured to discard results of analyzing a reflected signal from the injection pulse if an ONU responds to finding a time slot.

9. The OLT of claim 6, further comprising:

an optical transceiver configured to inject the pulse into the PON under direction of the OTDR module.

10. The OLT of claim 9, wherein the pulse is injected into the PON at a wavelength of 1,490nm, 1,550nm, 1650nm, or 1310nm by the optical transceiver.