Method, system and device for protecting long-reach passive optical network

A method, system and device for protecting a Long Reach Passive Optical Network (LR-PON) system are provided. The Electrical Relay (E-R) device receives the optical signal transmitted on two fiber transmission paths by the Optical Line Terminal (OLT) or Optical Network Unit (ONU) on one side, performs optical-to-electrical (O/E) conversion, signal regeneration, and electrical-to-optical (E/O) conversion for the optical signal, and sends the signal to the ONU or the OLT on the other side through the two fiber transmission paths. Through backup of the fiber transmission path, an LR-PON system protection method is provided to improve the reliability of the LR-PON system. The method, system, and device for protecting the LR-PON system under the present invention all support and are compatible with the existing functions of all devices in the existing LR-PON system.

FIELD OF THE INVENTION

The present invention relates to a Passive Optical Network (PON) technology, and in particular, to a method, system and device for protecting a Long-Reach PON (LR-PON).

BACKGROUND OF THE INVENTION

With the emergence of new services such as Video On Demand (VOD), high definition television, and online gaming, the bandwidth required by users is increasing. The development of Fiber To The Home (FTTH) ensures the last mile bandwidth of the access network. The PON technology is one of the most widely applied FTTH technologies currently.

FIG. 1shows a network architecture of a traditional PON in the conventional art. As shown inFIG. 1, in which a PON system is composed of an Optical Line Terminal (OLT), an Optical Network Unit (ONU), an optical splitter, and an Optical Distribution Network (ODN). The OLT is connected to the optical splitter through a trunk fiber, and the ONU is connected to the optical splitter through a branch fiber. The trunk fiber, optical splitter, and branch fiber constitute an ODN. The direction from the OLT to the ONU is the downstream direction, and the direction from the ONU to the OLT is the upstream direction.

The conventional art provides a PON system protection model to avoid PON system failures.FIG. 2shows a Gigabit-PON (GPON) system backup model in the conventional art. In the backup model shown inFIG. 2, both the ONU and the OLT have two ODN interfaces in addition to the ODN backup. This protection model may have four protection modes.FIG. 3ais a type-A protection mode, which provides backup only for the trunk fiber between the OLT and the optical splitter.FIG. 3bshows a type-B protection mode, which provides backup for both the trunk fiber and the OLT.FIG. 3cshows a type-C protection mode, which provides backup for the OLT, the trunk fiber, the optical splitter, the branch fibers, and all ONUs.FIG. 3dshows a type-D protection mode, which provides backup for the OLT, the trunk fiber, the optical splitter, the branch fibers, and some ONUs. Table 1 shows the characteristics of the four protection modes. In practice, a proper protection mode may be selected according to the actual requirements and the characteristics of the four protection modes.

In a traditional PON system, few ONUs are connected to the OLT through the optical splitter, and the coverage radius is small. Consequently, in the traditional network structure, the quantity of OLTs is large, and the location areas are remote and distributed, thus bringing inconvenience of management and maintenance. With the emergence of the next-generation optical access network, the LR-PON system is proposed. Because the all optical long-reach technology is difficult to implement and costly, the solution characterised by Electrical Relay (E-R)-based long-reach regenerator comes forth.FIG. 4shows a structure of an LR-PON system implemented through an E-R device in the conventional art. As shown inFIG. 4, an E-R device is set between the optical splitter and the OLT, and a traditional ODN is divided into two ODNs, namely, ODN1and OND2inFIG. 4. The E-R device regenerates the signal, namely, performs Reamplifying, Reshaping, Retiming (3R) for the signal, thus reducing the signal defect as a result of long reach of the OLT in an LR-PON system in the transmission.FIG. 5shows a structure of an E-R device in the conventional art. As shown inFIG. 5, the E-R device includes an optical-to-electrical converting unit (O/E unit)501, a signal regenerating unit502, and an electrical-to-optical converting unit (E/O unit)503. The O/E unit501is configured to receive the downstream optical signal from the OLT, or receive the upstream optical signal from the ONU, and convert the received optical signal into an electrical signal. The signal regenerating unit502is configured to perform 3R processing for the converted electrical signal from the O/E unit501. The E/O unit503is configured to convert the electrical signal processed by the signal regenerating unit502into an optical signal, and send the signal.

An active E-R device is introduced into the LR-PON, thus increasing instability of the LR-PON system. The optical transmission path is extended from 20 km to 100 km, and the failure probability of the long-reach fiber path is increased. After the coverage is widened, more services are affected once a failure occurs. Therefore, the LR-PON system needs protection urgently. However, no protection method is available for protecting the LR-PON system at present.

SUMMARY OF THE INVENTION

A method, system, and device for protecting an LR-PON system are provided in embodiments of the present invention to improve reliability of the LR-PON system.

An LR-PON protection system is provided. The system includes an OLT, an E-R device, and an ONU.

The OLT is configured to: send an optical signal to the E-R device through two fiber transmission paths, and receive the optical signal from the E-R device through the two fiber transmission paths.

The E-R device is configured to: receive the optical signal from the OLT or ONU on one side; perform O/E conversion, signal regeneration, and E/O conversion for the optical signal; and send the signal to the ONU or OLT on the other side.

The ONU is configured to: receive the optical signal from the E-R device through two fiber transmission paths, and send the optical signal to the E-R device through the two fiber transmission paths.

An LR-PON protection method is provided. The method includes: (1) by an E-R device, obtaining optical signals transmitted through two fiber transmission paths on one side, and performing O/E conversion for the optical signals transmitted through the two paths; (2) selecting an electrical signal on one path among the converted electrical signals on the two paths; and (3) performing signal regeneration for the selected electrical signal, performing E/O conversion for the regenerated electrical signal, and sending the converted optical signal through two fiber transmission paths on the other side.

An E-R device is provided. The E-R device includes: two O/E units, an automatic switching unit, a signal regenerating unit, and two E/O units.

Each O/E unit is configured to: receive an optical signal sent along a fiber transmission path connected to the O/E unit, and perform O/E conversion for the optical signal to obtain an electrical signal.

The automatic switching unit is configured to select an electrical signal on one path among the electrical signals transmitted on two paths and obtained from the two O/E units.

The signal regenerating unit is configured to: perform signal regeneration for the electrical signal selected by the automatic switching unit, and send the regenerated electrical signal to the two E/O units.

Each E/O unit is configured to: convert the electrical signal sent by the signal regenerating unit into an optical signal, and send the optical signal through a fiber transmission path connected to the E/O unit.

It can be seen from the foregoing technical solution that: In the method, system and device for protecting the LR-PON system, the E-R device receives an optical signal from the OLT or ONU through two fiber transmission paths on one side, performs O/E conversion, signal regeneration and E/O conversion for the optical signal, and sends the signal to the ONU or OLT through two fiber transmission paths on the other side. Through backup of the fiber transmission path, an LR-PON system protection method, which is unavailable in the conventional art, is provided in the embodiments of the present invention to improve the LR-PON system reliability. The method, system, and device for protecting the LR-PON system under the present invention all support and are compatible with the existing functions of all devices in the existing LR-PON system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To make the technical solution, objectives and merits of the present invention clearer, the following describes the present invention in detail with reference to accompanying drawings and exemplary embodiments.

The method provided in an embodiment of the present invention includes: using two fibers for backup in an ODN on both sides of an E-R device in an LR-PON system.

According to this method, the fibers in the ODN on both sides of the E-R device can be used for backup, or two E-R devices are used for backup, or a dual-optical-interface E-R device is used for backup.

The method provided in this embodiment may employ four types of protection:

Type A: Two fibers, a single OLT, a single ONU, and a single optical splitter are applied. This protection type is subdivided into the following three types:

Type A-I: Only the fibers in the ODN on both sides of the E-R device are backed up.FIG. 6ashows an LR-PON system under type A-I protection according to an embodiment of the present invention. A downstream signal sent from the OLT or an upstream signal sent from the ONU is transmitted on two fibers. Therefore, once one fiber fails, the signal is still transmitted between the OLT and the ONU reliably. This protection mode is the most cost-efficient one.

In this protection mode, the E-R device may be capable of detecting signal defects and may also be incapable of detecting signal defects. If the E-R device is incapable of detecting signal defects, the E-R device performs O/E conversion for the received optical signal, performs 3R processing, and performs E/O conversion for the signal, and then sends the signal to the ONU or OLT through two fibers on the other side. The defect detection, defect decision and signal selection performed by the ONU or OLT over the received signal are based on conventional and well-known devices, and are not described further.

If the E-R device is capable of signal detection, the E-R device performs defect detection for the received signal. If the signal is detected as defective, the E-R device returns an alarm indication signal to the transmitter-side OLT or ONU which sends the signal, and may also insert an alarm indication signal into the signal sent to the receiver-side ONU or OLT to facilitate fault analysis and locating.

Type A-II: The E-R device and the fibers in the ODN on both sides of the E-R device are backed up. That is, two E-R devices and two fibers are applied. As shown inFIG. 6b, the E-R device1and the fibers on both sides of the E-R device1as well as the E-R device2and the fibers on both sides of the E-R device2make up two independent transmission paths. An upstream signal or downstream signal may be transmitted on the two transmission paths. The E-R device may be capable of signal detection and may also be incapable of detecting signal defects.

If the E-R device is incapable of signal detection, the signal sent from the OLT or ONU is transmitted on the two transmission paths simultaneously. The receiver-side ONU or OLT selects a non-defective signal transmitted through one of the two fiber paths, and discards the signal transmitted through the other path.

If the E-R device is capable of signal detection, the E-R device performs defect detection for the received signal. If the signal is detected as defective, the E-R device returns an alarm indication signal to the transmitter-side OLT or ONU which sends the signal, and may also insert an alarm indication signal into the signal sent to the receiver-side ONU or OLT to facilitate fault analysis and locating, and may further assist the OLT or ONU in determining and selecting a non-defective transmission path for transmitting and receiving data.

Type A-III: The fibers in the ODN on both sides of the E-R device are backed up, and a dual-optical-interface E-R device is applied. As shown inFIG. 6c, two fiber transmission paths share an E-R device through different optical interfaces. The signal sent by the transmitter-side OLT or ONU is transmitted to the E-R device through two fiber paths in an ODN. Through two ODN receiving interfaces, the E-R device receives the signal transmitted along the two fiber paths respectively, selects the signal transmitted from one of the paths, and performs 3R processing for the signal. Afterward, the E-R device sends the signal to two fiber paths in another ODN through two ODN transmitting interfaces. The receiver-side ONU or OLT selects a non-defective signal transmitted through one of the two fiber paths, and discards the signal transmitted through the other path.

Type B: Two fibers, two OLTs, a single ONU, and a single optical splitter are applied. This protection type is subdivided into the following two types:

Type B-I: The E-R device and the fibers in the ODN on both sides of the E-R device are backed up. That is, two E-R devices and two fibers are applied. As shown inFIG. 7a, the E-R device1and the fibers on both sides of the E-R device1make up an independent transmission path, which is connected to the ODN interface1of the OLT; the E-R device2and the fibers on both sides of the E-R device2make up another independent transmission path, which is connected to the ODN interface2of the OLT. Both the upstream signal and the downstream signal can be transmitted on the two transmission paths. The E-R device may be capable of signal detection and may also be incapable of detecting signal defects.

If the E-R device is incapable of signal detection, the signal sent from the OLT or ONU is transmitted on the two transmission paths simultaneously. The receiver-side ONU or OLT selects a non-defective signal transmitted through one of the two fiber paths, and discards the signal transmitted through the other path.

If the E-R device is capable of signal detection, the E-R device performs defect detection for the received signal. If the signal is detected as defective, the E-R device returns an alarm indication signal to the transmitter-side OLT or ONU which sends the signal, and may also insert an alarm indication signal into the signal sent to the receiver-side ONU or OLT to facilitate fault analysis and locating, and may further assist the OLT or ONU in determining and selecting a non-defective transmission path for transmitting and receiving data.

Type B-II: The fibers in the ODN on both sides of the E-R device are backed up, and a dual-optical-interface E-R device is applied. As shown inFIG. 7b, the OLT is connected to two fiber transmission paths through two ODN interfaces. The two fiber transmission paths share an E-R device through different optical interfaces. The signal sent by the transmitter-side OLT or ONU is transmitted to the E-R device through two fiber paths in an ODN. Through two ODN receiving interfaces, the E-R device receives the signals transmitted along the two fiber paths respectively, selects the signal transmitted from one of the paths, and performs 3R processing for the signal. Afterward, the E-R device sends the signal to two fiber paths in another ODN through two ODN transmitting interfaces. The receiver-side ONU or OLT selects a non-defective signal transmitted through one of the two fiber paths, and discards the signal transmitted through the other path.

Type C: Two fibers, two OLTs, two ONUs, and two optical splitters are applied. This protection type is subdivided into the following two types:

Type C-I: The E-R device and the fibers in the ODN on both sides of the E-R device are backed up. That is, two E-R devices and two fibers are applied. As shown inFIG. 8a, the E-R device1and the fibers on both sides of the E-R device1make up an independent transmission path. One end of this transmission path is connected to the ODN interface1of the OLT, and the other end is connected to the ODN interface1of each ONU through the optical splitter1. The E-R device2and the fibers on both sides of the E-R device2make up another independent transmission path, and one end of this transmission path is connected to the ODN interface2of the OLT, and the other end is connected to the ODN interface2of each ONU through the optical splitter2. Both the upstream signal and the downstream signal can be transmitted on the two transmission paths. The signal processing performed by the E-R device in the signal transmission process is the same as that in Type A-II and Type B-I above, and is not described further.

Type C-II: The fibers in the ODN on both sides of the E-R device are backed up, and a dual-optical-interface E-R device is applied. As shown inFIG. 8b, the OLT is connected to two fiber transmission paths through two ODN interfaces. The two fiber transmission paths share an E-R device through different optical interfaces. Likewise, the two ODN interfaces of the ONU are connected to two fiber transmission paths through two optical splitters. The two fiber transmission paths share an E-R device through different optical interfaces. The signal processing performed by the E-R device in the signal transmission process is the same as that in Type A-III and Type B-II above, and is not described further.

Type D: Two fibers, two OLTs, partially two ONUs, and two groups of optical splitters are applied. This protection type is subdivided into the following two types:

Type D-I: The E-R device and the fibers in the ODN on both sides of the E-R device are backed up. That is, two E-R devices and two fibers are applied. As shown inFIG. 9a, the E-R device1and the fibers on both sides of the E-R device1make up an independent transmission path, and one end of this transmission path is connected to the ODN interface1of the OLT, and the other end is connected through the optical splitter1to the ODN interface1of the ONU which has a backup ODN interface and to the ODN interface of other ONUs without any backup ODN interface. The E-R device2and the fibers on both sides of the E-R device2make up another independent transmission path, and one end of this transmission path is connected to the ODN interface2of the OLT, and the other end is connected through the optical splitter2to the ODN interface2of the ONU which has a backup ODN interface. Both the upstream signal and the downstream signal can be transmitted on the two transmission paths. The signal processing performed by the E-R device in the signal transmission process is the same as that in Type A-II, Type B-I, and Type C-I above, and is not described further.

Type D-II: The fibers in the ODN on both sides of the E-R device are backed up, and a dual-optical-interface E-R device is applied. As shown inFIG. 9b, the OLT is connected to two fiber transmission paths through two ODN interfaces. The two fiber transmission paths share an E-R device through different optical interfaces. Likewise, the two ODN interfaces of the ONU with a backup ODN interface are connected to two fiber transmission paths through two optical splitters; and the ONU without any backup ODN interface is connected to the two fiber transmission paths through one optical splitter. The two fiber transmission paths share an E-R device through different optical interfaces. The signal processing performed by the E-R device in the signal transmission process is the same as that in Type A-III, Type B-II, and Type C-II above, and is not described further.

All the protection types described above are compatible with the ODN interface of traditional ONUs and OLTs, and with the switching function of the traditional ONUs and OLTs. Table 2 is a summary of the characteristics of the four protection types.

In Type A-I, Type A-II, Type B-I, Type C-I and Type D-I above, the E-R device may be capable of signal detection or not.

If the E-R device is incapable of signal detection, the E-R device structure shown inFIG. 5may be adopted. In this case, the E-R device performs O/E conversion for the received optical signal only, performs 3R processing for the converted electrical signal, converts the processed electrical signal into an optical signal, and sends the signal out.

If the E-R device is capable of signal detection, the E-R device obtains the downstream optical signal sent from the OLT or obtains the upstream optical signal sent from the ONU, and detects the received optical signal to check whether loss of signal (LOS) occurs; if LOS occurs, the E-R device returns a LOS alarm indication signal to the OLT or ONU which sends the optical signal. The E-R device may further obtains the electrical signal after O/E conversion, performs frame alignment for the data frame in the obtained electrical signal to judge whether loss of frame (LOF) occurs in the electrical signal. If LOF occurs, the E-R device returns a LOF alarm indication signal to the OLT or ONU which sends the optical signal. The E-R device may further perform data check for the aligned data frame, and judge whether SF or SD occurs in the electrical signal according to the data check result. If SF or SD occurs, the E-R device returns an alarm indication signal of SF or SD to the OLT or ONU which sends the optical signal.

In the foregoing process, the alarm indication signal is returned to the transmitter-side OLT or ONU for the transmitter-side OLT or ONU to know the failure on the transmission path between the OLT/ONU and the E-R device, and facilitate the OLT or ONU to locate the failure and/or assist in switching the transmission path. Besides, if SF or SD is detected, the E-R device may further insert an alarm indication signal into the signal sent to the receiver-side ONU or OLT. This alarm indication signal assists the receiver-side ONU or OLT in determining and selecting the non-defective signal and discarding the defective signal.

In this case, the structure of the E-R device capable of signal detection is shown inFIG. 10.FIG. 10shows a structure of an E-R device according to an embodiment of the present invention. The E-R device includes an O/E unit101, a signal regenerating unit102, an E/O unit103, a detecting unit104, and an alarm unit105.

The O/E unit101is configured to: receive an optical signal from the ONU or OLT, and convert the received optical signal into an electrical signal.

The signal regenerating unit102is configured to perform 3R processing for the converted electrical signal from the O/E unit101.

The E/O unit103is configured to: convert the electrical signal processed by the signal regenerating unit102into an optical signal, and send the optical signal to the receiver-side OLT or ONU.

The detecting unit104is configured to: obtain the optical signal sent by the ONU or OLT from the O/E unit101, detect whether LOS occurs in the optical signal, and send an alarm notification to the alarm unit105if LOS occurs.

The alarm unit105is configured to return an alarm indication signal to the OLT or ONU which sends the optical signal after receiving the alarm notification from the detecting unit104; or further configured to insert an alarm indication signal into the signal processed by the signal regenerating unit102after receiving the alarm notification from the detecting unit104.

The detecting unit104is further configured to: detect whether LOF occurs in the signal processed by the signal regenerating unit102, and send an alarm notification to the alarm unit105if LOF occurs; and further configured to: detect whether SF or SD occurs in the signal, and send an alarm notification to the alarm unit105if SF or SD occurs.

The Type A-III, Type B-II, Type C-II, and Type D-II E-R devices are detailed below. The Type A-III, Type B-II, Type C-II and Type D-II E-R devices are dual-optical-interface E-R devices. Each of such E-R devices includes two O/E units and two E/O units. The two O/E units are connected to two fiber transmission paths and receive signals from the OLT or ONU; and the two E/O units are connected to the two fiber transmission paths and send processed signals to the ONU or OLT.

The method for implementing LR-PON system protection through the dual-optical-interface E-R device includes the following: The E-R device obtains optical signals transmitted through two fiber transmission paths on one side, and performs O/E conversion for the optical signals transmitted through the two paths; selects an electrical signal on one path among the converted electrical signals on the two paths; and performs 3R processing for the selected electrical signal, performs E/O conversion for the processed electrical signal, and sends the converted optical signal through two fiber transmission paths on the other side. In the foregoing method, the LR-PON system is protected through a mechanism of “sending a signal on two paths and receiving a signal on only one path selectively” (hereinafter referred to as a “dual sending and selective receiving” mechanism).

The signals on the two paths are detected, and an electrical signal on one path is selected among the converted electrical signals on the two paths. The selected electrical signal may be the electrical signal of better quality, or the electrical signal selected randomly. The signal may be selected in two methods. The two selection methods are detailed below through two embodiments.

FIG. 11is a flowchart of a first method for implementing LR-PON protection through a dual-optical-interface E-R device according to an embodiment of the present invention. As shown inFIG. 11, the method includes the following steps:

Step1101: The E-R device obtains optical signals transmitted through two paths by the OLT or ONU on one side, and performs O/E conversion for the optical signals on both paths to obtain electrical signals transmitted on the two paths.

Step1102: The E-R device detects whether LOS occurs in the converted electrical signal. If LOS occurs on one path, the process proceeds to step1103; if LOS doesn't occur in either of the two paths, the process proceeds to step1104; and, if both paths involve LOS, the process proceeds to step1109.

In this step, the detection about whether any optical signal is lost on the two paths may include: detecting the optical power of the optical signal on either path to check whether the voltage or current of any electrical signal after O/E conversion is lower than a preset threshold of voltage or current; and, if yes, determining that this path involves LOS.

Besides, in this step, after detecting that a path involves LOS, the E-R device determines that this path has failed, and may return a LOS alarm indication signal to the OLT or ONU which sends the signal. If the signal is an upstream signal, the E-R device may return an alarm indication signal of upstream LOS to the ONU; and, if the signal is a downstream signal, the E-R device may return an alarm indication signal of downstream LOS to the OLT. The E-R device may insert an alarm indication signal into the 3R-processed signal, and send the signal to the ONU or OLT which receives the signal. If the signal is an upstream signal, the E-R device may insert an alarm indication signal of upstream LOS and send the signal to the OLT; and, if the signal is a downstream signal, the E-R device may insert an alarm indication signal of downstream LOS and send the signal to the ONU.

Step1103: The E-R device selects the converted electrical signal on the path that does not involve LOS, and the process proceeds to step1111.

Step1104: The E-R device obtains electrical signals on the two paths after O/E conversion, and detects whether LOF occurs in the electrical signals on the two paths. If LOF occurs on one path, the process proceeds to step1105; if neither path involves LOF, the process proceeds to step1106; and, if both paths involve LOF, the process proceeds to step1109.

In this step, the detection about whether LOF occurs in the electrical signals may be performed through frame alignment of the converted electrical signals.

Besides, in this step, after detecting that a path involves LOF, the E-R device may return a LOF alarm indication signal to the OLT or ONU which sends the signal. If the signal is an upstream signal, the E-R device may return an alarm indication signal of upstream LOF to the ONU; and, if the signal is a downstream signal, the E-R device may return an alarm indication signal of downstream LOF to the OLT. The E-R device may insert a LOF alarm indication signal into the 3R-processed signal, and send the signal to the ONU or OLT which receives the signal. If the signal is an upstream signal, the E-R device may insert an alarm indication signal of upstream LOF and send the signal to the OLT; and, if the signal is a downstream signal, the E-R device may insert an alarm indication signal of downstream LOF and send the signal to the ONU.

Step1105: The E-R device selects the electrical signal on a path that does not involve LOF, and then the process proceeds to step1111.

Step1106: The E-R device detects whether SF exist in the electrical signals on the two paths after O/E conversion. If SF occurs in the electrical signal on one path, the process proceeds to step1107; if SF occur in the electrical signal on both paths, the process proceeds to step1109; and, if SF does not occur in either of the electrical signals on the two paths, the process proceeds to step1108.

The detection of SF of the electrical signal after O/E conversion in this step may include: performing data check for the frame-aligned electrical signal, counting the bit error rate according to the data check result, judging whether the bit error rate is higher than a preset SF threshold, and determining that SF occurs in the electrical signal if the bit error rate is higher than the preset SF threshold.

Besides, in this step, after detecting that a path involves SF, the E-R device may return a SF alarm indication signal to the OLT or ONU which sends the signal. If the signal is an upstream signal, the E-R device may return an alarm indication signal of upstream SF to the ONU; and, if the signal is a downstream signal, the E-R device may return an alarm indication signal of downstream SF to the OLT. The E-R device may insert an alarm indication signal into the 3R-processed signal, and send the signal to the ONU or OLT which receives the signal. If the signal is an upstream signal, the E-R device may insert an alarm indication signal of upstream SF and send the signal to the OLT; and, if the signal is a downstream signal, the E-R device may insert an alarm indication signal of downstream SF and send the signal to the ONU.

Step1107: The E-R device selects the electrical signal on a path that does not involve SF, and then the process proceeds to step1111.

Step1108: The E-R device detects whether SD occur in the electrical signals on the two paths after O/E conversion. If SD occurs in the electrical signal on one path, the process proceeds to step1110; if SD occurs on both paths or on neither path, the process proceeds to step1109.

The detection of SD of the electrical signal after O/E conversion in this step may include: performing data check for the frame-aligned electrical signal, counting the bit error rate according to the data check result, judging whether the bit error rate is higher than a preset SD threshold, and determining that SD occurs in the electrical signal if the bit error rate is higher than the preset SD threshold.

Besides, in this step, after detecting that a path involves SD, the E-R device may return a SD alarm indication signal to the OLT or ONU which sends the signal. If the signal is an upstream signal, the E-R device may return an alarm indication signal of upstream SD to the ONU; and, if the signal is a downstream signal, the E-R device may return an alarm indication signal of downstream SD to the OLT. The E-R device may insert an alarm indication signal into the 3R-processed signal, and send the signal to the ONU or OLT which receives the signal. If the signal is an upstream signal, the E-R device may insert an alarm indication signal of upstream SD and send the signal to the OLT; and, if the signal is a downstream signal, the E-R device may insert an alarm indication signal of downstream SD and send the signal to the ONU.

Step1109: The E-R device selects the electrical signal on either path, and then the process proceeds to step1111.

Step1110: The E-R device selects the electrical signal on a path that does not involve SD.

Step1111: The E-R device performs 3R processing for the selected electrical signal, and sends the signal to two E/O interfaces for E/O conversion. After E/O conversion, the E-R device sends the converted optical signal through two fiber transmission paths on the other side.

Table 3 shows the corresponding true value decision in the flow shown inFIG. 11. In this table, LOS represents loss of signal; LOF represents loss of frame; SF represents signal failure; SD represents signal degrade; A represents one fiber transmission path; B represents the other fiber transmission path; 1 means a defect is detected; 0 means that no defect is detected; and X is a random value.

TABLE 3LOS_ALOS_BLOF_ALOF_BSF_ASF_BSD_ASD_BSelection Result10XXXXXXB is selected01XXXXXXA is selected11XXXXXXEither path isselected0010XXXXB is selected0001XXXXA is selected0011XXXXEither path isselected000010XXB is selected000001XXA is selected000011XXEither path isselected00000010B is selected00000001A is selected00000011Either path isselected00000000Either path isselected

FIG. 12is a flowchart of a second method for implementing LR-PON protection through a dual-optical-interface E-R device according to an embodiment of the present invention. As shown inFIG. 12, the method includes the following steps:

Step1201: The E-R device obtains optical signals transmitted through two transmission paths by the OLT or ONU on one side, and performs O/E conversion for the optical signals on both paths to obtain electrical signals transmitted on the two paths.

Step1202: The E-R device selects the electrical signal on either path (which is regarded as the first path). The E-R device detects whether LOS occurs in the electrical signal on the first path; if LOS occurs in the electrical signal on the first path, the process proceeds to step1203; and, if LOS does not occur in the electrical signal on the first path, the process proceeds to step1204.

In this step, the electrical signal on either path is selected, where the selected electrical signal may be on a path selected randomly or selected beforehand.

Step1203: The E-R device selects the electrical signal on the other path (which is regarded as the second path), and then the process proceeds to step1211.

Step1204: The E-R device judges whether LOF occurs in the electrical signal on the first path; if LOF occurs in the electrical signal on the first path, the process proceeds to step1205; and, if LOF does not occur in the electrical signal on the first path, the process proceeds to step1206.

Step1205: The E-R device judges whether LOS occurs in the electrical signal on the second path; if LOS occurs in the electrical signal on the second path, the E-R device still selects the electrical signal on the first path, and then the process proceeds to step1211; and, if LOS does not occur in the electrical signal on the second path, the E-R device selects the electrical signal on the second path, and then the process proceeds to step1211.

In this embodiment, the detection result about the electrical signal on either path may be stored. The E-R device may judge whether LOS occurs in the electrical signal on the second path in this step according to the stored detection result about the second path; or, perform LOS detection for the electrical signal on the second path, and then make judgment according to the detection result.

Step1206: The E-R device detects whether SF occurs in the optical signal on the first path; if SF does not occur in the optical signal on the first path, the process proceeds to step1207; and, if SF does not occur in the optical signal on the first path, the process proceeds to step1208.

Step1207: The E-R device judges whether LOS or LOF occurs in the electrical signal on the second path; if LOS or LOF occurs in the electrical signal on the second path, the E-R device selects the electrical signal on the first path, and then the process proceeds to step1211; and, if LOS or LOF does not occur in the electrical signal on the second path, the E-R device selects the electrical signal on the second path, and then the process proceeds to step1211.

The E-R device may judge whether LOS or LOF occurs in the electrical signal on the second path according to the stored detection result about the second path; or, detect LOS or LOF of the electrical signal on the second path, and then make judgment according to the detection result.

Step1208: The E-R device detects whether SD occurs in the optical signal on the first path; if SD occurs in the optical signal on the first path, the process proceeds to step1209; and, if SD does not occur in the optical signal on the first path, the process proceeds to step1210.

Step1209: The E-R device judges whether LOS, LOF or SF occurs in the electrical signal on the second path; if LOS, LOF or SF occurs in the electrical signal on the second path, the E-R device selects the electrical signal on the first path, and then the process proceeds to step1211; and, if LOS, LOF or SF does not occur in the electrical signal on the second path, the E-R device selects the electrical signal on the second path, and then the process proceeds to step1211.

The E-R device may judge whether LOS, LOF or SF occurs in the electrical signal on the second path according to the stored detection result about the second path; or, detect LOS, LOF or SF of the electrical signal on the second path, and then make judgment according to the detection result.

Step1210: The E-R device selects the electrical signal on the first path.

Step1211: The E-R device performs 3R processing for the selected electrical signal, and sends the signal to two E/O interfaces for E/O conversion. After E/O conversion, the E-R device sends the converted optical signal through two fiber transmission paths on the other side.

The mode of detecting LOS, LOF, SF or SD, and the mode of sending an alarm after detecting LOS, LOF, SF or SD in the flow shown inFIG. 12are the same as those inFIG. 11, and are described further.

Table 4 shows the corresponding true value decision in the flow shown inFIG. 12. In this table, LOS represents loss of signal; LOF represents loss of frame; SF represents signal failure; SD represents signal degrade; A represents one fiber transmission path; B represents the other fiber transmission path; 1 means a defect is detected; 0 means that no defect is detected; X is a random value; and the suffix h represents the detection result about the signal on the other path, which may be the result of the previous detection stored in the storing unit.

It is evident thatFIG. 11differs fromFIG. 12in that: In the flow shown inFIG. 11, the signals on the two paths are detected separately, and then the better one is selected according to the detection result and then sent out through two transmission paths; in the flow shown inFIG. 12, the signal on one path is detected, and, if the signal on this path is defective, switching is performed to detect the signal on the second path, and finally the better one is selected according to the detection result and then sent out through two transmission paths. In the flow shown inFIG. 11, the signals on the two paths are detected separately, and then the better one is selected according to the detection result, and therefore, the detection, judgment, and automatic switching are quick. In the flow shown inFIG. 12, the selection is performed before detection, and only one signal path needs to be detected, which is more cost-efficient.

Besides, a complete method flow is given inFIG. 11andFIG. 12. In practice, only LOS of the electrical signal may be detected; or LOS and LOF may be detected; or LOS, LOF, SF and SD may be detected. The order of severity of the defects is: LOS>LOF>SF>SD.

FIG. 13shows a structure of a dual-optical-interface E-R device according to an embodiment of the present invention. As shown inFIG. 13, the E-R device may include: two O/E units1300, an automatic switching unit1310, a signal regenerating unit1320, and two E/O units1330.

Each O/E unit1300is configured to: receive an optical signal sent along a fiber transmission path connected to the O/E unit, and perform O/E conversion for the optical signal to obtain an electrical signal.

The automatic switching unit1310is configured to select the electrical signal on one path among the electrical signals transmitted on two paths and obtained from the two O/E units1300.

The signal regenerating unit1320is configured to: perform 3R processing for the electrical signal selected by the automatic switching unit1310, and send the processed electrical signal to the two E/O units1330.

Each E/O unit1330is configured to: convert the electrical signal sent by the signal regenerating unit1320into an optical signal, and send the optical signal through a fiber transmission path connected to the E/O unit.

The automatic switching unit1310may include: (1) a first LOS detecting unit1311, configured to detect LOS of the converted electrical signal from one of the O/E units; (2) a second LOS detecting unit1312, configured to detect LOS of the converted electrical signal from the other O/E unit; (3) a deciding unit1313, configured to decide whether LOS occurs in the electrical signal on only one path according to the detection results of the first LOS detecting unit1311and the second LOS detecting unit1312; and (4) a selecting unit1314, configured to select the electrical signal on the path that does not involve LOS when the deciding unit1313decides that LOS occurs in the electrical signal on only one path.

If the detection involves only LOS and no other defects are detected, the selecting unit1314is further configured to select the electrical signal on either path when the deciding unit1313decides that LOS occurs on both paths or on neither path.

The automatic switching unit1310may further include: (1) a first LOF detecting unit1315, configured to detect LOF of the electrical signal on one of the paths when the deciding unit1313decides that LOS occurs in the electrical signal on neither path; and (2) a second LOF detecting unit1316, configured to detect LOF of the electrical signal on the other path when the deciding unit1313decides that LOS occurs in the electrical signal on neither path.

The first LOF detecting unit1315and the second LOF detecting unit1316may be frame aligning units.

The deciding unit1313may be further configured to decide whether LOF occurs in the electrical signal on only one path according to the detection results of the first LOF detecting unit1315and the second LOF detecting unit1316.

The selecting unit1314is further configured to select the electrical signal on the path that does not involve LOF when the deciding unit1313decides that LOF occurs in the electrical signal on only one path.

If the detection involves only LOS and LOF without detecting other defects, the selecting unit1314is further configured to select the electrical signal on either path when the deciding unit1313decides that LOF occurs on both paths or on neither path.

The automatic switching unit1310may further include: (1) a first SF detecting unit1317, configured to detect SF of the electrical signal on one of the paths when the deciding unit1313decides that LOF occurs in the electrical signal on neither path; and (2) a second SF detecting unit1318, configured to detect SF of the electrical signal on the other path when the deciding unit1313decides that LOF occurs in the electrical signal on neither path.

The first SF detecting unit1317and the second SF detecting unit1318may be data checking units.

The deciding unit1313may be further configured to decide whether SF occurs in the electrical signal on only one path according to the detection results of the first SF detecting unit1317and the second SF detecting unit1318.

The selecting unit1314may be further configured to select the electrical signal on the path that does not involve SF when the deciding unit1313decides that SF occurs in the electrical signal on only one path.

If the detection involves only LOS, LOF and SF without detecting other defects, the selecting unit1314is further configured to select the electrical signal on either path when the deciding unit1313decides that SF occurs on both paths or on neither path.

If the detection needs to involve SD, the automatic switching unit1310may further include: (1) a first SD detecting unit1324, configured to detect SD of the electrical signal on one of the paths when the deciding unit1313decides that SF occurs in the electrical signal on neither path; and (2) a second SD detecting unit1325, configured to detect SD of the electrical signal on the other path when the deciding unit1313decides that SF occurs in the electrical signal on neither path.

The deciding unit1313is further configured to decide whether SD occurs in the electrical signal on only one path according to the detection results of the first SD detecting unit1324and the second SD detecting unit1325.

The selecting unit1314is further configured to: select the electrical signal on the path that does not involve SD when the deciding unit1313decides that SD occurs in the electrical signal on only one path; and select the electrical signal on either path when SD occurs in the electrical signals on both paths or on neither path.

The automatic switching unit1310may further include: a LOS alarm unit1319, configured to return a LOS alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves LOS when LOS is detected by the first LOS detecting unit1311or the second LOS detecting unit1312; and/or insert a LOS alarm indication signal into the same-direction downstream signal on the path that involves LOS.

The automatic switching unit1310may further include: a LOF alarm unit1321, configured to return a LOF alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves LOF when LOF is detected by the first LOF detecting unit1315or the second LOF detecting unit1316; and/or insert a LOF alarm indication signal into the same-direction downstream signal on the path that involves LOF.

The automatic switching unit1310may further include: a SF alarm unit1322, configured to return a SF alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves SF when SF is detected by the first SF detecting unit1317or the second SF detecting unit1318; and/or insert a SF alarm indication signal into the same-direction downstream signal on the path that involves SF.

The automatic switching unit1310may further include: a SD alarm unit1323, configured to return a SD alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves SD when SD is detected by the first SD detecting unit1324or the second SD detecting unit1325; and/or insert a SD alarm indication signal into the same-direction downstream signal on the path that involves SD.

The LOS alarm unit1319, the LOF alarm unit1321, the SF alarm unit1322, and the SD alarm unit1323may be set independently of the automatic switching unit1310.

FIG. 14shows another structure of the automatic switching unit1310. This automatic switching unit1310may include: (1) a selecting unit1401, configured to select the electrical signal on either path (which is regarded as the first path) after conversion is performed by two O/E units; (2) a LOS detecting unit1402, configured to detect LOS of the electrical signal on the first path selected by the selecting unit1401; and (3) a deciding unit1403, configured to decide whether LOS occurs in the electrical the signal on the first path according to the detection result of the LOS detecting unit1402.

The selecting unit1401is further configured to select the electrical signal on the other path (which is regarded as the second path) when the deciding unit1403decides that LOS occurs in the electrical signal on the first path.

The E-R device may further include a storing unit1400, which is configured to store the detection result about the electrical signal on either path.

The automatic switching unit1310may further include a LOF detecting unit1404, which is configured to detect LOF of the electrical signal on the first path when the deciding unit1403decides that no LOS occurs in the electrical signal on the first path.

The LOF detecting unit1404may be a frame aligning unit.

The deciding unit1403is further configured to: judge whether LOF occurs in the electrical signal on a path according to the detection result of the LOF detecting unit1404, and judge whether LOS occurs in the electrical signal on the second path according to the detection result about the electrical signal on the second path stored in the storing unit1400or according to the detection result obtained after the electrical signal on the second path is sent to the LOS detecting unit1402for detection.

The selecting unit1401is configured to: select the electrical signal on the first path when the deciding unit1403decides that LOF occurs in the electrical signal on the first path and LOS occurs in the electrical signal on the second path; and select the electrical signal on the second path when the deciding unit1403decides that LOF occurs in the electrical signal on the first path but no LOS occurs in the electrical signal on the second path.

The automatic switching unit1310may further include a frame failure detecting unit1405, which is configured to detect SF of the electrical signal on the first path when the deciding unit1403decides that no LOF occurs in the electrical signal on the first path.

The SF detecting unit1405may be a data checking unit.

The deciding unit1403is further configured to: judge whether SF occurs in the electrical signal on the first path according to the detection result of the SF detecting unit1405, and, if yes, judge whether LOS or LOF occurs in the electrical signal on the second path according to the detection result about the electrical signal on the second path stored in the storing unit1400or according to the detection result obtained after the electrical signal on the second path is sent to the LOS detecting unit1402and/or the LOF detecting unit1404for detection.

The selecting unit1401is configured to: select the electrical signal on the first path when the deciding unit1403decides that SF occurs in the electrical signal on the first path and LOS or LOF occurs in the electrical signal on the second path; and select the electrical signal on the second path when the deciding unit1403decides that SF occurs in the electrical signal on the first path but no LOS or LOF occurs in the electrical signal on the second path.

The automatic switching unit1310may further include a SD detecting unit1410, which is configured to detect SD of the electrical signal on the first path when the deciding unit1403decides that no SF occurs in the electrical signal on the first path.

The deciding unit1403is further configured to: judge whether SD occurs in the electrical signal on the first path according to the detection result of the SD detecting unit1410, and, if yes, judge whether LOS, LOF or SF occurs in the electrical signal on the second path according to the detection result about the electrical signal on the second path stored in the storing unit1400or according to the detection result obtained after the electrical signal on the second path is sent to the LOS detecting unit1402and/or the LOF detecting unit1404and/or SF detecting unit1405for detection.

The selecting unit1401is further configured to: select the electrical signal on the first path when the deciding unit1403decides that SD occurs in the electrical signal on the first path and LOS, LOF or SF occurs in the electrical signal on the second path; and select the electrical signal on the second path when the deciding unit1403decides that SD occurs in the electrical signal on the first path but no LOS, LOF or SF occurs in the electrical signal on the second path.

The automatic switching unit1310may further include: a LOS alarm unit1406, configured to: return a LOS alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves LOS when LOS is detected by the LOS detecting unit1402; and/or insert a LOS alarm indication signal into the same-direction downstream signal on the path that involves LOS.

The automatic switching unit1310may further include: a LOF alarm unit1407, configured to: return a LOF alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves LOF when LOF is detected by the LOF detecting unit1404; and/or insert a LOF alarm indication signal into the same-direction downstream signal on the path that involves LOF.

The automatic switching unit1310may further include: a SF alarm unit1408, configured to: return a SF alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves SF when SF is detected by the SF detecting unit1405; and/or insert a SF alarm indication signal into the same-direction downstream signal on the path that involves SF.

The E-R device1310further includes: a SD alarm unit1409, configured to return a SD alarm indication signal to the transmitter-side OLT or ONU along a transmission path reverse to the path that involves SD when SD is detected by the SD detecting unit1410; and/or insert a SD alarm indication signal into the same-direction downstream signal on the path that involves SD.

The LOS alarm unit1406, the LOF alarm unit1407, the SF alarm unit1408, and the SD alarm unit1409may be set independently of the automatic switching unit1310.

The system shown inFIG. 13corresponds to the flow shown inFIG. 11, and the system shown inFIG. 14corresponds to the flow shown inFIG. 12. The systems in FIG.13andFIG. 14show that two detecting units are set inFIG. 13to detect signals on two paths respectively, and therefore, the detection, judging and automatic switching are quick. Only one detecting unit is set inFIG. 14, and thus the equipment cost is low.

The foregoing technical solution shows that: In the method, system and device for protecting the LR-PON system, the E-R device receives an optical signal from the OLT or ONU through two fiber transmission paths on one side, performs O/E conversion, signal regeneration and E/O conversion for the optical signal, and sends the signal to the ONU or OLT through two fiber transmission paths on the other side. Through backup of the fiber transmission path, an LR-PON system protection method is provided to improve the reliability of the LR-PON system. The method, system, and device for protecting the LR-PON system under the present invention all support and are compatible with the existing functions of all devices in the existing LR-PON system. Moreover, multiple protection types are provided herein to meet different requirements and application scenarios.

A dual-optical-interface E-R device is provided herein to reduce probability of failures that occur in the LR-PON system after multiple fiber sections fail or a new E-R device is added. Two solutions are provided herein, and the user may select one of the solutions according to different switching performance requirements and equipment costs. The E-R device under the present invention is compatible with the existing PON system, and supports the automatic switching and failure location functions of the existing OLT or ONU.

Although the invention has been described through some exemplary embodiments, the invention is not limited to such embodiments. It is apparent that those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. The invention is intended to cover the modifications and variations provided that they fall in the scope of protection defined by the following claims or their equivalents.