Abstract:
A method, system and apparatus for managing alarms in a Long Reach Passive Optical Network (LR-PON) system are disclosed. The method includes: obtaining a PON signal from an Optical Line Terminal (OLT) or an Optical Network Unit (ONU) on one side; checking whether the obtained PON signal fails; and notifying the ONU or the OLT on the other side if the PON signal fails. The method, system and apparatus under the present invention monitor the LR-PON transmission quality and process various alarm indications raised in the LR-PON signal monitoring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2008/072461, filed on Sep. 23, 2008, which claims the benefit of Chinese Patent Application No. 200710163635.3, filed on Oct. 15, 2007, both of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a Passive Optical Network (PON) technology, and in particular, to a method, system and apparatus for managing alarms in a Long-Reach PON (LR-PON) system. 
     BACKGROUND OF THE INVENTION 
     Currently, with the emergence of the services such as Video on Demand (VOD), High-Definition Television (HDTV) and online gaming, telecom users raise higher and higher requirements on network bandwidth. Driven by such requirements, the Fiber to the Home (FTTH) technology that ensures the “last mile” access network is developing rapidly, and especially, the PON technology is applied widely. 
       FIG. 1  shows a structure of a traditional PON system. A traditional PON system is composed of an Optical Line Terminal (OLT), more than one Optical Network Unit (ONU), and an Optical Distribution Network (ODN) that connects the ONU to the OLT. The ODN includes a passive optical splitter for distributing optical power, a feed fiber between the passive optical splitter and the OLT, and a branch fiber between the passive optical splitter and the ONU. In a traditional PON system, the OLT covers the ONUs that are not over 20 km away. 
     Monitoring and maintenance of a traditional PON system are illustrated in  FIG. 2 .  FIG. 2  shows alarm links in a PON system in the prior art. The PON system provides three types of Operations, Administration and Maintenance (OAM) channels: embedded OAM, Physical Layer OAM (PLOAM), and Operation and Maintenance Center (OMC). In  FIG. 2 , the Bit Interleaved Parity (BIP) and Remote Defect Indication (RDI) messages are transmitted through embedded OAM bits or bytes, and the Remote Error Indication (REI) and Deactivate (DACT) messages are transmitted in the form of PLOAM messages. 
     In a traditional PON system, the OLT is interconnected with the ONU directly through an optical splitter. As shown in  FIG. 2 , in both the upstream and the downstream directions, failure detection is performed for fiber links and reported by raising alarms such as Loss of Signal (LOS) alarms and Loss of Frame (LOF) alarms; and data transmission performance is detected through BIP check and reported by raising alarms such as Signal Degrade (SD) alarms and Signal Fail (SF) alarms. The result of performance monitoring in the downstream direction is returned to the OLT through RDI and REI messages to facilitate the OLT check and failure locating. 
     With the emergence of the next-generation optical access network, the LR-PON is proposed. The LR-PON needs to reach farther and enable the OLT to cover the ONUs 100 km away.  FIG. 3  shows a structure of an LR-PON system in the prior art. As shown in  FIG. 3 , the LR-PON includes an OLT, a regenerator, more than one ONU, and an ODN 1  and an ODN 2  which are located on both sides of the regenerator. The ODN 1  connects the regenerator to the OLT, and includes a feed fiber. The ODN 2  connects the regenerator to the ONU, and includes: a passive optical splitter, a feed fiber between the passive optical splitter and the regenerator, and a branch fiber between the passive optical splitter and the ONU. By adding a regenerator in the LR-PON system, the OLT in the LR-PON system covers the ONUs up to 100 km away. Through an Electrical Relay (E-R) regenerator in the prior art, the coverage of the PON can be extended in E-R mode. 
     Although the E-R regenerator extends the coverage of the PON and enables the OLT to cover ONUs as far as required, long-distance fiber failures may arise after the fiber transmission distance is extended from 20 km to 100 km. The active E-R device introduced into the PON also reduces the stability and reliability of the device in the system. The E-R regenerator on the feed fiber divides the Fiber path into two sections, which increases the complexity of fast failure locating. The existing PON system provides complete monitoring and maintenance functions and specifies various alarm indications, performance events and management operations between the OLT and the ONU in detail, but such functions are applicable only to the scenarios where the OLT interworks with the ONU directly through optical signals in the traditional PON system. In the E-R LR-PON application, the E-R regenerator does not perform necessary monitoring or processing for the PON signals. Previous alarm indications and maintenance functions are transmitted transparently, and the failures of the intermediate nodes cannot be analyzed or located. Therefore, the existing E-R LR-PON solution does not monitor the LR-PON signals, and does not put forward various alarm indications raised in the LR-PON signal monitoring or the corresponding processing method. 
     SUMMARY OF THE INVENTION 
     A method for managing alarms in an LR-PON system is provided in an embodiment of the present invention to monitor the LR-PON transmission quality and to process various alarm indications raised in the LR-PON signal monitoring. 
     A system for managing alarms in an LR-PON system is provided in an embodiment of the present invention to monitor the LR-PON transmission quality and to process various alarm indications raised in the LR-PON signal monitoring. 
     An E-R regenerator is provided in an embodiment of the present invention to monitor the LR-PON transmission quality and to raise alarms for different failures. 
     The technical solution under the present invention is implemented in the following way: 
     A method for managing alarms in an LR-PON system includes: 
     obtaining a PON signal from an OLT or an ONU on one side; checking whether the obtained PON signal fails; and notifying the ONU or the OLT on the other side if the PON signal fails. 
     A system for managing alarms in an LR-PON system includes: 
     a first PON apparatus, adapted to send a PON signal to an E-R regenerator; 
     the E-R regenerator, adapted to: obtain the PON signal from the first PON apparatus, check whether the obtained PON signal fails, and notify a second PON apparatus if the PON signal fails; and 
     the second PON apparatus, adapted to: judge and locate the failure according to the received notification and take a corresponding action. 
     An E-R regenerator includes: 
     a detecting module, adapted to: check whether a PON signal from a first PON apparatus fails, and notify an alarm module to send an alarm to a second PON apparatus if the PON signal fails; and 
     the alarm module, adapted to send an alarm to the second PON apparatus according to the received notification. 
     Through the method, system and apparatus disclosed herein, the alarm detection function is added in the E-R regenerator, and the detected alarm signal is transmitted to the OLT or ONU, so that the OLT can analyze, judge and locate the failure and can distinguish the alarm level, thus facilitating device maintenance. In this way, the LR-PON transmission quality is monitored, and various alarm indications in the LR-PON signal monitoring are processed properly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a structure of a traditional PON system; 
         FIG. 2  shows alarm links in a PON system in the prior art; 
         FIG. 3  shows a structure of an LR-PON system in the prior art; 
         FIG. 4  shows alarm links according to a first embodiment of the present invention; 
         FIG. 5  shows alarm links according to a second embodiment of the present invention; 
         FIG. 6  shows a structure of an upstream frame in a GPON according to an embodiment of the present invention; 
         FIG. 7  shows alarm links according to a third embodiment of the present invention; 
         FIG. 8  shows an UpStream BandWidth Map (US BW Map) structure in a Physical Control Block downstream (PCBd) overhead field in a GPON according to an embodiment of the present invention; 
         FIG. 9  shows alarm links according to a fourth embodiment of the present invention; 
         FIG. 10  shows a structure of an E-R regenerator according to the first embodiment of the present invention; 
         FIG. 11  shows a structure of an E-R regenerator according to the second embodiment of the present invention; 
         FIG. 12  shows a structure of an E-R regenerator according to the third embodiment of the present invention; and 
         FIG. 13  shows a structure of an E-R regenerator according to the fourth embodiment of the present invention. 
     
    
    
     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. 
     A method for managing alarms in an LR-PON system is provided in an embodiment of the present invention. The method includes: 
     obtaining a PON signal from an OLT or an ONU on one side; checking whether the obtained PON signal fails; and notifying the ONU or the OLT on the other side if the PON signal fails. 
     The method may further include: 
     by the ONU or the OLT on the other side, judging and locating the failure according to the received notification and taking a corresponding action. 
     In the following embodiment, alarm detection is added in the E-R regenerator. After detecting an alarm, the E-R regenerator generates an alarm signal, and sends the generated alarm signal to the ONU or the OLT, so that the ONU or the OLT on the other side knows that the obtained signal fails. To facilitate failure analysis and alarm management of the OLT, the traditional ONU and OLT need to be modified. Table 1 shows failure judgment and locating performed by the OLT for various alarm signals in this embodiment. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 New 
                   
                   
                   
               
               
                   
                 Alarm 
                 Alarm or 
               
               
                   
                 Check 
                 Existing 
                 Failure 
                   
                 Failure 
               
               
                 Alarm Type 
                 Point 
                 Alarm 
                 Analysis 
                 Failure Path 
                 Type 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 RDI 
                 Remote 
                 The 
                 Existing 
                 If RDI = 0, no 
                 If RDI = 0 and 
                 When both 
               
               
                   
                 (ONU) 
                 ONU 
                 alarm 
                 defect exists in 
                 RDIu = 0, data is 
                 failure 
               
               
                   
                 received 
                 detects 
                   
                 the data on the 
                 normal on the 
                 detection 
               
               
                   
                 downstream 
                 the alarm 
                   
                 whole 
                 whole downstream 
                 and 
               
               
                   
                 data defect 
                 and sends 
                   
                 downstream path 
                 path from the OLT 
                 performance 
               
               
                   
                 indication 
                 it back to 
                   
                 from the OLT to 
                 to the ONU; 
                 monitoring 
               
               
                   
                   
                 the OLT. 
                   
                 the ONU; 
                 If RDI = 1 and 
                 are 
               
               
                   
                   
                   
                   
                 If RDI = 1, a 
                 RDIu = 0, a defect 
                 available in 
               
               
                   
                   
                   
                   
                 defect exists in 
                 exists on the 
                 the E-R, the 
               
               
                   
                   
                   
                   
                 the data on the 
                 downstream path 
                 combination 
               
               
                   
                   
                   
                   
                 downstream path 
                 from the E-R to the 
                 of RDI and 
               
               
                   
                   
                   
                   
                 from the OLT to 
                 ONU; 
                 RDIu 
               
               
                   
                   
                   
                   
                 the ONU. 
                 If RDI = 1 and 
                 indicates 
               
               
                 RDIu 
                 Remote 
                 OLT 
                 New 
                 If RDIu = 0, no 
                 RDIu = 1, a defect 
                 only a 
               
               
                   
                 (E-R) 
                   
                 alarm 
                 defect exists in 
                 exists on the 
                 performance 
               
               
                   
                 received 
                   
                   
                 the data on the 
                 downstream path 
                 defect. 
               
               
                   
                 downstream 
                   
                   
                 downstream path 
                 from the OLT to 
               
               
                   
                 data defect 
                   
                   
                 from the OLT to 
                 the E-R, or a defect 
               
               
                   
                 indication 
                   
                   
                 the E-R; 
                 also exists on the 
               
               
                   
                   
                   
                   
                 If RDIu = 1, a 
                 downstream path 
               
               
                   
                   
                   
                   
                 defect exists in 
                 from the E-R to the 
               
               
                   
                   
                   
                   
                 the data on the 
                 ONU; 
               
               
                   
                   
                   
                   
                 downstream path 
                 If RDI = 0 and 
               
               
                   
                   
                   
                   
                 from the OLT to 
                 RDIu = 1, it is a 
               
               
                   
                   
                   
                   
                 the E-R. 
                 mistaken report. 
               
               
                   
                 Remote 
                 OLT 
                 New 
                 An LOS or LOF 
                 Downstream 
                 When only 
               
               
                   
                 (E-R) 
                   
                 alarm 
                 alarm exists in 
                 direction from the 
                 failure 
               
               
                   
                 received 
                   
                   
                 the downstream 
                 OLT to the E-R. 
                 detection is 
               
               
                   
                 downstream 
                   
                   
                 data received by 
                   
                 available, 
               
               
                   
                 data failure 
                   
                   
                 the E-R from the 
                   
                 this alarm 
               
               
                   
                 indication 
                   
                   
                 OLT. 
                   
                 indicates a 
               
               
                   
                   
                   
                   
                   
                   
                 major 
               
               
                   
                   
                   
                   
                   
                   
                 alarm. 
               
               
                 AISd back- 
                 Alarm 
                 The 
                 New 
                 An LOS or LOF 
                 Downstream 
                 Major 
               
               
                 transmitted 
                 inserted by 
                 ONU 
                 alarm 
                 alarm exists in 
                 direction from the 
                 alarm. 
               
               
                 alarm 
                 E-R to ONU 
                 detects 
                   
                 the downstream 
                 OLT to the E-R. 
               
               
                   
                   
                 the alarm 
                   
                 data received by 
               
               
                   
                   
                 and sends 
                   
                 the E-R from the 
               
               
                   
                   
                 it back to 
                   
                 OLT. 
               
               
                   
                   
                 the OLT. 
               
               
                 SDi/ 
                 Upstream 
                 OLT 
                 Existing 
                 If SDi = 0 and 
                 If SDi = 0 and 
                 When both 
               
               
                 SFi 
                 signal 
                   
                 alarm 
                 SFi = 0, no defect 
                 SFi = 0, and 
                 failure 
               
               
                   
                 degrade/ 
                   
                   
                 exists in the data 
                 RDId = 0, data is 
                 detection 
               
               
                   
                 failure alarm 
                   
                   
                 on the whole 
                 normal on the 
                 and 
               
               
                   
                   
                   
                   
                 upstream path 
                 whole upstream 
                 performance 
               
               
                   
                   
                   
                   
                 from the ONU to 
                 path from the ONU 
                 monitoring 
               
               
                   
                   
                   
                   
                 the OLT; 
                 to the OLT; 
                 are 
               
               
                   
                   
                   
                   
                 If SDi = 1 or 
                 If SDi = 1 or SFi = 1, 
                 available in 
               
               
                   
                   
                   
                   
                 SFi = 1, a defect 
                 and RDId = 0, a 
                 the E-R, the 
               
               
                   
                   
                   
                   
                 exists in the data 
                 defect exists on the 
                 combination 
               
               
                   
                   
                   
                   
                 on the upstream 
                 upstream path from 
                 of SDi/SFi 
               
               
                   
                   
                   
                   
                 path from the 
                 the E-R to the 
                 and RDId 
               
               
                   
                   
                   
                   
                 ONU to the 
                 OLT; 
                 indicates 
               
               
                   
                   
                   
                   
                 OLT. 
                 If SDi = 1 or SFi = 1, 
                 only a 
               
               
                 RDId 
                 Remote 
                 The 
                 New 
                 If RDId = 0, no 
                 and RDId = 1, a 
                 performance 
               
               
                 back- 
                 (E-R) 
                 ONU 
                 alarm 
                 defect exists in 
                 defect exists on the 
                 defect. 
               
               
                 transmitted 
                 received 
                 detects 
                   
                 the data on the 
                 upstream path from 
               
               
                 alarm 
                 ONU 
                 the alarm 
                   
                 upstream path 
                 the ONU to the 
               
               
                   
                 upstream 
                 and sends 
                   
                 from the ONU to 
                 E-R; or, a defect 
               
               
                   
                 data defect 
                 it back to 
                   
                 the E-R; 
                 also exists on the 
               
               
                   
                 indication 
                 the OLT. 
                   
                 If RDId = 1, 
                 upstream path from 
               
               
                   
                   
                   
                   
                 defects exist in 
                 the E-R to the 
               
               
                   
                   
                   
                   
                 the data on the 
                 OLT; 
               
               
                   
                   
                   
                   
                 upstream path 
                 If SDi = 0 and 
               
               
                   
                   
                   
                   
                 from the ONU to 
                 SFi = 0, and 
               
               
                   
                   
                   
                   
                 the E-R 
                 RDId = 1, it is a 
               
               
                   
                   
                   
                   
                   
                 mistaken report. 
               
               
                   
                 Remote 
                 The 
                 New 
                 An LOS or LOSi 
                 Upstream direction 
                 When only 
               
               
                   
                 (E-R) 
                 ONU 
                 alarm 
                 or LOFi alarm 
                 from the ONU to 
                 failure 
               
               
                   
                 received 
                 detects 
                   
                 exists in the 
                 the E-R. 
                 detection is 
               
               
                   
                 ONU 
                 the alarm 
                   
                 upstream data 
                   
                 available, 
               
               
                   
                 upstream 
                 and sends 
                   
                 received by the 
                   
                 this alarm 
               
               
                   
                 data failure 
                 it back to 
                   
                 E-R. 
                   
                 indicates a 
               
               
                   
                 indication 
                 the OLT. 
                   
                   
                   
                 major 
               
               
                   
                   
                   
                   
                   
                   
                 alarm. 
               
               
                 LOS 
                 Loss of 
                 OLT 
                 Existing 
                 Loss of signal 
                 Upstream direction 
                 Major 
               
               
                   
                 signal 
                   
                 alarm 
                 occurs in the 
                 from the E-R to the 
                 alarm. 
               
               
                   
                   
                   
                   
                 whole upstream 
                 OLT. 
               
               
                   
                   
                   
                   
                 data stream 
               
               
                   
                   
                   
                   
                 received by the 
               
               
                   
                   
                   
                   
                 OLT. 
               
               
                 AISu 
                 Alarm 
                 OLT 
                 New 
                 Loss of signal 
                 Upstream direction 
                 Major 
               
               
                   
                 inserted by 
                   
                 alarm 
                 occurs in the 
                 from the ONU to 
                 alarm. 
               
               
                   
                 E-R to OLT 
                   
                   
                 whole upstream 
                 the E-R. 
               
               
                   
                   
                   
                   
                 data stream 
               
               
                   
                   
                   
                   
                 received by the 
               
               
                   
                   
                   
                   
                 E-R. 
               
               
                 LOSi/ 
                 Loss of 
                 OLT 
                 Existing 
                 Loss of signal or 
                 Upstream direction 
                 Major 
               
               
                 LOFi 
                 signal or 
                   
                 alarm 
                 frame occurs in 
                 from the E-R to the 
                 alarm. 
               
               
                   
                 frame of 
                   
                   
                 the data of ONU i   
                 OLT. 
               
               
                   
                 ONU i  in the 
                   
                   
                 received in the 
               
               
                   
                 upstream 
                   
                   
                 upstream 
               
               
                   
                 direction 
                   
                   
                 direction by the 
               
               
                   
                   
                   
                   
                 OLT. 
               
               
                 AISi 
                 Alarm 
                 OLT 
                 New 
                 Loss of signal 
                 Upstream direction 
                 Major 
               
               
                   
                 inserted by 
                   
                 alarm 
                 and loss of frame 
                 from ONU i  to the 
                 alarm. 
               
               
                   
                 E-R to ONU i   
                   
                   
                 occur in the data 
                 E-R. 
               
               
                   
                   
                   
                   
                 of ONU i   
               
               
                   
                   
                   
                   
                 received in the 
               
               
                   
                   
                   
                   
                 upstream 
               
               
                   
                   
                   
                   
                 direction by the 
               
               
                   
                   
                   
                   
                 E-R. 
               
               
                   
               
             
          
         
       
     
     After receiving the alarm signal, the OLT determines which side of the fiber path fails and the type of the failure according to the method of failure judgment and locating shown in Table 1. 
     After receiving the alarm signal, the OLT or the ONU needs to take a corresponding action to process the alarm signal. Table 2 shows how an OLT processes a new alarm signal, and Table 3 shows how an ONU processes a new alarm signal according to an embodiment of the present invention. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Alarm Type 
                 Detection Conditions 
                 Actions 
                 Cancellation Conditions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 AISu 
                 Alarm frame 
                 A data stream compliant 
                 Suppress the 
                 A data stream 
               
               
                   
                 inserted for 
                 with the AISu alarm frame 
                 LOSi, LOFi, 
                 incompliant with 
               
               
                   
                 the whole 
                 format is detected. 
                 and AISi 
                 the AISu alarm 
               
               
                   
                 upstream 
                   
                 alarms. 
                 frame format is 
               
               
                   
                 data stream 
                   
                   
                 detected. 
               
               
                 AISi 
                 Alarm frame 
                 For the data frame of 
                 Suppress the 
                 For the data frame 
               
               
                   
                 inserted for 
                 ONU i , a data stream 
                 LOFi alarm. 
                 of ONU i , a data 
               
               
                   
                 ONU i   
                 compliant with the AISi 
                   
                 stream incompliant 
               
               
                   
                   
                 alarm frame format is 
                   
                 with the AISi alarm 
               
               
                   
                   
                 detected. 
                   
                 frame format is 
               
               
                   
                   
                   
                   
                 detected. 
               
               
                 RDIu 
                 Remote 
                 When the value of the 
                 Recover the 
                 The value of RDIu is 0. 
               
               
                   
                 defect 
                 physical overhead area 
                 downstream 
               
               
                   
                 indication 
                 RDIu of the upstream data 
                 interface 
               
               
                   
                   
                 frame of the ONU is 1, it 
                 processing 
               
               
                   
                   
                 indicates that a defect exists 
                 unit of the 
               
               
                   
                   
                 in the data sent by the OLT 
                 OLT. 
               
               
                   
                   
                 to the E-R regenerator in 
               
               
                   
                   
                 the downstream direction. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Cancellation 
               
               
                 Alarm Type 
                 Detection Conditions 
                 Actions 
                 Conditions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 AISd 
                 Alarm 
                 A data stream compliant 
                 Suppress the 
                 A data stream 
               
               
                   
                 inserted for 
                 with the AISd alarm frame 
                 LOF alarm. 
                 incompliant with 
               
               
                   
                 all ONUs in 
                 format is detected. It 
                   
                 the AISd alarm 
               
               
                   
                 the 
                 indicates that the failure 
                   
                 frame format is 
               
               
                   
                 downstream 
                 occurs on the path from the 
                   
                 detected. 
               
               
                   
                 direction 
                 OLT to the E-R regenerator 
               
               
                   
                   
                 in the downstream direction. 
               
               
                 RDId 
                 Remote 
                 When the value of the 
                 Recover the 
                 The value of RDId 
               
               
                   
                 defect 
                 physical overhead area 
                 upstream 
                 is 0. 
               
               
                   
                 indication 
                 RDId of the downstream 
                 interface 
               
               
                   
                   
                 data frame of the OLT is 1, 
                 processing 
               
               
                   
                   
                 it indicates that a defect 
                 unit of the 
               
               
                   
                   
                 exists in the data sent by 
                 ONU. 
               
               
                   
                   
                 the ONU to the E-R 
               
               
                   
                   
                 regenerator in the upstream 
               
               
                   
                   
                 direction. 
               
               
                   
               
             
          
         
       
     
     First Embodiment 
       FIG. 4  shows alarm links according to the first embodiment of the present invention. In this embodiment, alarm detection functions are added only to the E-R generator, and the ONU and the OLT remain unchanged. 
     Downstream Direction: 
     After detecting an LOS or LOF alarm, the E-R regenerator switches off the transmitting laser in the downstream direction, so that the ONU detects the LOS alarm in the downstream direction. The subsequent processing is the same as that in the prior art; that is, the ONU determines that an LOS failure occurs on the downstream path from the E-R regenerator to the ONU. After knowing that the LOS alarm and the LOF alarm are cleared, the E-R regenerator switches on the transmitting laser in the downstream direction again. 
     Upstream Direction: 
     After detecting the LOS alarm, the E-R regenerator switches off the transmitting laser in the upstream direction, so that the OLT detects the LOS alarm in the upstream direction. The subsequent processing is the same as that in the prior art. After knowing that the LOS alarm is cleared, the E-R regenerator switches on the transmitting laser in the upstream direction again. 
     The E-R regenerator performs detection and frame alignment for the electrical signal which is obtained through optical-to-electrical (O/E) conversion of the PON upstream optical signal from the ONU, and judges whether LOS or LOF occurs in the upstream data sent by the ONU. If LOS or LOF occurs in the upstream data sent by the ONU, the E-R regenerator transmits the LOSi alarm to the OLT transparently so that the OLT detects the LOSi alarm. The subsequent processing on the OLT is the same as that in the prior art. 
     Evidently, the solution under the present invention is simple, and is compatible with the existing functions of the ONU and the OLT in the prior art. 
     Second Embodiment 
       FIG. 5  shows alarm links according to the second embodiment of the present invention. The features that make this embodiment different from the first embodiment are as follows: An alarm back-transmission function is added to the E-R regenerator; the OLT can detect and process three additional types of alarms to facilitate failure judgment and locating; and the ONU remains unchanged. 
     Downstream Direction: 
     After detecting the LOS and LOF alarms, the E-R regenerator switches off the transmitting laser in the downstream direction, the details of which are the same as those of the first embodiment and are provided further. 
     After detecting the LOS and LOF alarms, the E-R regenerator sends the set third-type downstream Alarm Indication Signal (AIS) back to the OLT. Here the third-type downstream AIS is an RDIu alarm. 
     As shown in Table 1, after receiving the RDIu alarm, the OLT determines that a failure leading to LOS or LOF occurs on the downstream path from the OLT to the E-R regenerator. As shown in Table 2, a recovery operation is performed for the downstream interface processing unit of the OLT. 
     In the foregoing step, the E-R regenerator may send back the RDIu through idle bits in a PON upstream frame.  FIG. 6  shows a structure of an upstream frame according to a GPON in an embodiment of the present invention. In the upstream frame of the GPON, bit  0  in the real time state indication (Ind) field in the Physical Layer Overhead upstream (PLOu) field is idle, and may serve as a back-transmission indication of the RDIu alarm. Table 4 shows functions of the bits in the Ind field in the PLOu field of the GPON upstream frame. 
     
       
         
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Bit 
                 Function 
               
               
                   
               
             
             
               
                 7 (MSB) 
                 PLOAMu emergent message waiting indication in the 
               
               
                   
                 upstream direction (1 = emergent message waiting; 
               
               
                   
                 0 = no emergent message waiting) 
               
               
                 6 
                 FEC state (1 = FEC; 0 = no FEC) 
               
               
                 5 
                 RDI state (1 = defective; 0 = normal) 
               
               
                 4 
                 Traffic waiting in type 2 T-CONTs 
               
               
                 3 
                 Traffic waiting in type 3 T-CONTs 
               
               
                 2 
                 Traffic waiting in type 4 T-CONTs 
               
               
                 1 
                 Traffic waiting in type 5 T-CONTs 
               
               
                 0 (LSB)  
                 Reserved bit. This bit may indicate the RDIu state in the 
               
               
                   
                 LR-PON (1 = defective; 0 = normal) 
               
               
                   
               
             
          
         
       
     
     Upstream Direction: 
     After detecting the LOS alarm, the E-R regenerator inserts the set first-type upstream AIS to the OLT. The first-type upstream AIS is an AISu alarm. 
     As shown in Table 1, after receiving the AISu alarm, the OLT determines that a failure leading to LOS occurs on the upstream path from the ONU to the E-R regenerator. As shown in Table 2, the OLT suppresses the LOSi, LOFI, and AISi alarms. 
     Further, after detecting the LOSi and LOFi alarms, the E-R regenerator inserts the set second-type upstream AIS to the OLT. The second-type upstream AIS is an AISi alarm. 
     As shown in Table 1, after receiving the AISi alarm, the OLT determines that a failure leading to LOS or LOF in the upstream data of the ONU occurs on the upstream path from ONU i  to the E-R regenerator. As shown in Table 2, the OLT suppresses the LOFi alarm. 
     In the foregoing step, the inserted AISu and AISi alarms are “alarm frames”. Their frame header is similar to the pattern format of the upstream frame delimiter “a byte” and “b byte” of the GPON. A simple mode is to fill the upstream data with “a byte” and “b byte” to make a new alarm signal without frame boundary, which facilitates the OLT to detect, distinguish and suppress the LOS, LOSi, and LOFi alarms. 
     Third Embodiment 
       FIG. 7  shows alarm links according to the third embodiment of the present invention. The features that make this embodiment different from the second embodiment are as follows: One more alarm back-transmission function is added to the E-R regenerator, and the ONU can detect and process two additional types of alarms. 
     Downstream Direction: 
     After detecting the LOS and LOF alarms, the E-R regenerator does not switch off the transmitting laser in the downstream direction, but inserts the first-type downstream AIS to the ONU. The first-type downstream AIS is an AISd alarm. 
     After receiving the AISd alarm, the ONU determines that a failure leading to LOS or LOF occurs on the downstream path from the OLT to the E-R regenerator. As shown in Table 3, the ONU suppresses the LOF alarm. 
     In the foregoing step, the inserted AISd alarm is an “alarm frame”. Its frame header is similar to the pattern format of the downstream frame delimiter “PSync” of the GPON. A simple mode is to fill the downstream data with “PSync” characters to make a new alarm signal without frame boundary, which facilitates the downstream ONU to detect, distinguish and suppress the LOS and LOF alarms. 
     Upstream Direction: 
     Unlike the practice in the second embodiment, after detecting the LOS alarm of the whole upstream data stream, the E-R regenerator sends the set third-type upstream AIS back to all ONUs, where the third-type upstream AIS is an RDId alarm. After detecting the LOSi and LOFi alarms of the upstream data of the ONU, the E-R regenerator sends the set third-type upstream AIS back to the corresponding ONU. The third-type upstream AIS is an RDIdi alarm. 
     After receiving the RDId alarm, the ONU determines that a failure occurs on the upstream path from the ONU to the E-R regenerator and this failure leads to LOS of the whole data stream or leads to LOS or LOF in the upstream data sent by the corresponding ONU. 
     In the foregoing step, the E-R regenerator may send back the RDId through idle bits in the PON downstream frame.  FIG. 8  shows an US BW Map structure in a PCBd overhead field in a GPON in an embodiment of the present invention. In the downstream frame of the GPON, the US BW Map in the PCBd overhead field is composed of 8-byte vector groups. Each vector group has a flag field, and the functions of the bits in the flag field are described in Table 5. In the existing GPON, bits  0 - 6  are idle. One of the bits may be selected to indicate whether to allow the ONU to process new alarms, and another bit is selected as an RDId back-transmitted alarm. 
     
       
         
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Bit 
                 Function 
               
               
                   
               
             
             
               
                 11 (MSB) 
                 An indication of sending a PLSu (1 = allow ONU to send 
               
               
                   
                 PLSu; 0 = not allow ONU to send PLSu) 
               
               
                 10  
                 An indication of sending a PLOAMu (1 = allow ONU to send 
               
               
                   
                 PLOAMu; 0 = not allow ONU to send PLOAMu) 
               
               
                 9 
                 An indication of using an FEC (1 = allow ONU to insert FEC; 
               
               
                   
                 0 = not allow ONU to send FEC) 
               
               
                 8, 7 
                 Mode of sending DBRu (00 = not send DBRu; 01 = allow 
               
               
                   
                 ONU to send mode-0 DBRu; 10 = allow ONU to send 
               
               
                   
                 mode-1 DBRu; 11 = allow ONU to send mode-2 DBRu) 
               
               
                 6 
                 Reserved bit. In the LR-PON, this bit may indicate whether to 
               
               
                   
                 allow the ONU to process new alarms (1 = allow; 
               
               
                   
                 0 = not process) 
               
               
                 5 
                 Reserved bit. This bit may indicate the RDId alarm in the 
               
               
                   
                 LR-PON (1 = defective; 0 = normal) 
               
               
                 4-0 
                 Reserved 
               
               
                   
               
             
          
         
       
     
     Fourth Embodiment 
       FIG. 9  shows alarm links in the fourth embodiment of the present invention. The features that make this embodiment different from the third embodiment are: The E-R regenerator, the OLT and the ONU are modified, and performance monitoring of data transmission quality and the method for processing the corresponding detected alarms are added. 
     Downstream Direction: 
     Unlike the practice in the third embodiment, if the E-R regenerator does not detect any LOS or LOF alarm, the E-R regenerator performs data check for the determined downstream data frame, measures the Bit Error Rate (BER) according to the data check result, and judges whether the BER is higher than the preset BER threshold. If the BER is higher than the preset threshold, the E-R regenerator sends the set third-type downstream AIS to the OLT. The third-type downstream AIS is an RDIu alarm. 
     Unlike the practice in the third embodiment, after receiving the AISd alarm, the ONU sends the AISd alarm back to the OLT. 
     According to the received AISd alarm, the OLT determines that a failure leading to LOS or LOF occurs on the downstream path from the OLT to the E-R regenerator. 
     Upstream Direction: 
     Unlike the practice in the third embodiment, if the E-R regenerator does not detect any LOS, LOSi or LOFi alarm, the E-R regenerator performs data check for the determined upstream data frame, measures the BER according to the data check result, and judges whether the BER is higher than the preset BER threshold. If the BER is higher than the preset threshold, the E-R regenerator sends the third-type upstream AIS to the ONU. The third-type upstream AIS is an RDId alarm. 
     According to the received RDId alarm, the ONU determines that a failure leading to increase of the BER of the data frame occurs on the upstream path from the ONU to the E-R regenerator, and attempts to recover the upstream interface processing unit of the ONU. 
     The ONU sends the received RDId alarm back to the OLT. After receiving the RDId alarm, the OLT determines that a failure leading to increase of the BER of the data frame occurs on the upstream path from the ONU to the E-R regenerator. 
     In the foregoing process, the ONU may send the AISd alarm and the RDId alarm back to the OLT through a PLOAM message in two modes: 
     The first mode is to define a new PLOAM message. Table 6 shows a newly defined message for sending back the AISd alarm and the RDId alarm. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Remote Alarm and Defect Indication Message 
               
             
          
           
               
                 Byte 
                 Content 
                 Description 
               
               
                   
               
               
                 1 
                 ONU-ID 
                 This byte specifies an ONU. 
               
               
                 2 
                 00001010 
                 This byte indicates a message type, and is defined as a 
               
               
                   
                   
                 “remote alarm and defect indication message”. The 
               
               
                   
                   
                 existing GPON has specified nine types of upstream 
               
               
                   
                   
                 PLAOM messages. The value of this byte needs to be 
               
               
                   
                   
                 greater than 9, for example, “00001010”. 
               
               
                 3 
                 xxxxxxab 
                 If a = 1, an AISd alarm frame is received; if a = 0, 
               
               
                   
                   
                 no AISd alarm frame is received; 
               
               
                   
                   
                 If b = RDId and b = 1, a defect exists (if b = 1, 
               
               
                   
                   
                 preferably this message needs to be sent for three 
               
               
                   
                   
                 consecutive times); if b = 0, no defect exists; 
               
               
                   
                   
                 x: undefined 
               
               
                 4-12 
                 Undefined 
               
               
                   
               
             
          
         
       
     
     The second mode is to use the existing PLOAM message such as an REI message, and use the idle byte in the message to define the AISd alarm and the RDId alarm. Table 7 shows the newly defined AISd alarm and RDId alarm in an REI message. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Remote Alarm and Defect Indication Message 
               
             
          
           
               
                 Byte 
                 Content 
                 Description 
               
               
                   
               
               
                 1 
                 ONU-ID 
                 This byte specifies an ONU. 
               
               
                 2 
                 00001000 
                 This byte indicates a message type. In the existing 
               
               
                   
                   
                 GPON, this type is defined as a “remote error 
               
               
                   
                   
                 indication message”. In the LR-PON application, 
               
               
                   
                   
                 this byte is defined as a “remote alarm and defect 
               
               
                   
                   
                 indication message”. 
               
               
                 3 
                 Error block 
                 Highest 8 bits of the 32-bit REI counter. 
               
               
                   
                 count 1 
               
               
                 4 
                 Error block 
               
               
                   
                 count 2 
               
               
                 5 
                 Error block 
               
               
                   
                 count 3 
               
               
                 6 
                 Error block 
                 Lowest 8 bits of the 32-bit REI counter. 
               
               
                   
                 count 4 
               
               
                 7 
                 0000ssss 
                 Serial number: The value of ssss increases by 1 once 
               
               
                   
                   
                 a REI message is sent. 
               
               
                 8 
                 xxxxxxab 
                 In the existing GPON, this byte is undefined. In the 
               
               
                   
                   
                 LR-PON application, this byte serves as a back- 
               
               
                   
                   
                 transmission indication signal of the AISd and 
               
               
                   
                   
                 RDId alarms: 
               
               
                   
                   
                 If a = 1, an AISd alarm frame is received; if a = 0, 
               
               
                   
                   
                 no AISd alarm frame is received; 
               
               
                   
                   
                 If b = RDId and b = 1, a defect exists (if b = 1, 
               
               
                   
                   
                 preferably this message needs to be sent for three 
               
               
                   
                   
                 consecutive times); if b = 0, no defect exists; 
               
               
                   
                   
                 x: undefined 
               
               
                 9-12 
                 Undefined 
               
               
                   
               
             
          
         
       
     
     Specially, when the ONU detects an RDId, it indicates that the transmission performance of the upstream data is degraded. Therefore, even if the data is transmitted through a PLOAM message which provides CRC-8 check, the PLOAM message is preferably sent repeatedly (for example, for three consecutive times) to resist errors and to improve reliability. 
     The foregoing four embodiments meet different cost requirements and application scenarios, and exert different impacts on the existing functions of the ONU and the OLT. The first embodiment is the simplest and the most cost-efficient. It exerts no impact on the existing functions of the ONU or the OLT in the prior art, involves no modification to the existing ONU or OLT, and is compatible with the existing devices. The second embodiment involves a little modification to the existing OLT, and supports a few new types of alarms. It analyzes, judges and locates the main failures on the path between both sides of the E-R in the LR-PON, and on the path between the ONU and the OLT; and at the same time, it is compatible with the existing ONU. The third and the fourth embodiments involve a little modification to the existing ONU and OLT. The third embodiment considers only the failure detection for the PON signals in the E-R, and does not consider data transmission performance monitoring. The fourth embodiment is the most comprehensive. It adds only three types of alarm signals to the OLT and adds only two types of alarm signals to the ONU, but ensures that the OLT can analyze various alarm signals, locate failures, and implement alarm management and maintenance for the E-R. 
     A system for managing alarms in an LR-PON system is provided in an embodiment of the present invention. The system includes: 
     a first PON apparatus, adapted to send a PON signal to the E-R regenerator; 
     an E-R regenerator, adapted to: obtain the PON signal from the first PON apparatus, check whether the obtained PON signal fails, and notify a second PON apparatus if the PON signal fails; and 
     the second PON apparatus, adapted to: judge and locate the failure according to the received notification and take a corresponding action. 
     An E-R regenerator is provided in an embodiment of the present invention. The E-R regenerator includes: 
     a detecting module, adapted to: check whether a PON signal from a first PON apparatus fails, and notify the alarm module to send an alarm to a second PON apparatus if the PON signal fails; and 
     the alarm module, adapted to send an alarm to the second PON apparatus according to the received notification. 
     The E-R regenerator for managing alarms in an LR-PON system under the present invention is detailed below with reference to exemplary embodiments. 
     First Apparatus Embodiment 
       FIG. 10  shows a structure of an E-R regenerator according to the first embodiment of the present invention. 
     Downstream Direction: 
     The detecting module includes: 
     an LOS detecting submodule, adapted to: detect whether LOS occurs in a PON signal obtained from an OLT, and send an LOS notification to the alarm module if LOS occurs. 
     The alarm module includes: 
     a laser switching submodule, adapted to switch off the transmitting laser in the downstream direction according to the received LOS notification. 
     The detecting module may further include: 
     an LOF detecting submodule, adapted to: perform frame alignment for the electrical signal which is obtained through O/E conversion of the PON signal from the OLT, judge whether LOF occurs, and send an LOF notification to the alarm module if LOF occurs. 
     The laser switching submodule is further adapted to switch off the transmitting laser in the downstream direction according to the received LOF notification. 
     Upstream Direction: 
     The detecting module includes: 
     an LOS detecting submodule, adapted to: detect whether LOS occurs in the PON signal obtained from the ONU, and send an LOS notification to the alarm module if LOS occurs. 
     The alarm module includes: 
     a laser switching submodule, adapted to switch off the transmitting laser in the upstream direction according to the received LOS notification. 
     The detecting module may further include: 
     an LOS or LOF detecting submodule, adapted to: perform detection and frame alignment for the electrical signal which is obtained through O/E conversion of the PON signal from the corresponding ONU, judge whether LOS or LOF occurs in the upstream data sent by the corresponding ONU, and send an LOS or LOF notification of the corresponding ONU to the alarm module if LOS or LOF occurs. 
     The alarm module may further include: 
     a transparent transmission submodule, adapted to transparently transmit an alarm signal to the OLT according to the received LOS or LOF notification of the corresponding ONU, where the alarm signal indicates that the LOS of the corresponding ONU occurs on the upstream path from the E-R regenerator to the OLT. 
     The E-R regenerator in this embodiment implements alarm management in the LR-PON system without making any modification to the existing ONU or OLT. 
     Second Apparatus Embodiment 
       FIG. 11  shows a structure of an E-R regenerator in the second embodiment of the present invention. 
     Downstream Direction: 
     Compared with the alarm module in the first apparatus embodiment, the alarm module in this embodiment may further include: 
     a third-type downstream AIS sending submodule, adapted to send a set third-type downstream AIS back to the OLT according to the received LOS or LOF notification. 
     Upstream Direction: 
     As against the alarm module in the first apparatus embodiment, the alarm module in this embodiment may include: 
     a first-type upstream AIS sending submodule, adapted to send a set first-type upstream AIS to the OLT according to the received LOS notification; and 
     a second-type upstream AIS sending submodule, adapted to send a set second-type upstream AIS to the OLT according to the received LOS or LOF notification. 
     The E-R regenerator disclosed in this embodiment adds three types of AIS and involves certain modification to the existing OLT, so that the OLT can judge, identify and process the received AIS. 
     Third Apparatus Embodiment 
       FIG. 12  shows a structure of an E-R regenerator according to the third embodiment of the present invention. 
     Downstream Direction: 
     The detecting module may include: 
     an LOS detecting submodule, adapted to: detect whether LOS occurs in the PON signal obtained from the OLT, and send an LOS notification to the alarm module if LOS occurs; and 
     an LOF detecting submodule, adapted to: perform frame alignment for the electrical signal which is obtained through O/E conversion of the PON signal from the OLT, judge whether LOF occurs, and send an LOF notification to the alarm module if LOF occurs. 
     The alarm module may include: 
     a first-type downstream AIS sending submodule, adapted to send a set first-type downstream AIS to the ONU according to the received LOS or LOF notification; and 
     a third-type downstream AIS sending submodule, adapted to send a set third-type downstream AIS back to the OLT according to the received LOS or LOF notification. 
     Upstream Direction: 
     Compared with the alarm module in the second apparatus embodiment, the alarm module in this embodiment may further include: 
     a third-type upstream AIS sending submodule, adapted to send a set third-type upstream AIS to the corresponding ONU according to the received LOS notification or the received LOS or LOF notification of the corresponding ONU. 
     The E-R regenerator disclosed in this embodiment adds five types of AIS and involves certain modification to the existing OLT and ONU, so that the OLT and ONU can judge, identify and process the received AIS. 
     Fourth Apparatus Embodiment 
       FIG. 13  shows a structure of an E-R regenerator in the fourth embodiment of the present invention. 
     Downstream Direction: 
     Compared with the detecting module in the third apparatus embodiment, the detecting module in this embodiment may further include: 
     a BER detecting submodule, adapted to: perform data check for the determined downstream data frame, measure the BER according to the result of the data check, judge whether the BER is higher than a preset BER threshold, and send a BER excess notification to the alarm module if the BER is higher than the preset threshold; and 
     a third-type downstream AIS sending submodule, adapted to send a set third-type downstream AIS to the OLT according to the received BER excess notification. 
     Upstream Direction: 
     Compared with the detecting module in the third apparatus embodiment, the detecting module in this embodiment may further include: 
     a BER detecting submodule, adapted to: perform data check for the determined downstream data frame, measure the BER according to the result of the data check, judge whether the BER is higher than a preset BER threshold, and send a BER excess notification to the alarm module if the BER is higher than the preset threshold; and 
     a third-type upstream AIS sending submodule, adapted to send a set third-type upstream AIS to the ONU according to the received BER excess notification. 
     The E-R regenerator disclosed in this embodiment adds five types of AIS, performs failure detection and performance monitoring, and involves certain modification to the existing OLT and ONU, so that the OLT and ONU can judge, identify and process the received AIS. 
     Evidently, the method, system and apparatus for managing alarms in an LR-PON system under the present invention provide a whole set of alarm management links, and implement main alarm detection and management functions with little modification to the existing ONU and OLT, thus facilitating detection, locating and processing of failures, and saving costs of operation and maintenance. Moreover, different alarm link solutions are disclosed herein to meet different requirements and application scenarios. Further, the alarm links disclosed herein involve little technical difficulty and are easily practicable and cost-efficient, and can satisfy the requirements of the service provider shortly. 
     Although the invention has been described through several 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 claims or their equivalents.