Optical time domain reflectometry (OTDR) trace analysis in PON systems

• US 8,724,102 B2
• Filed: 12/22/2010
• Issued: 05/13/2014
• Est. Priority Date: 12/22/2010
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Urban, Patryk
• Primary Examiner(s): Stock, Jr., Gordon J
• Application Number:
  US12/976,954
• Publication Number:
  US 20120163800A1
• Time in Patent Office: 1,238 Days
• Field of Search: None
• US Class Current: 356/73.1
• CPC Class Codes: G01M 11/3136 for testing of multiple fibers
• CPC Class Codes: H04B 10/071 using a reflected signal, e.g. using optical time domain reflectometers [OTDR]

Abstract

A client unit and a method are provided performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR. The method comprises triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of the PON. The method further comprises inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of the multistage splitter, and wherein the last splitter stage is of ratio 2:N; and obtaining at least one new event location based on the OTDR measurement signal. Further, the method comprises calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from the reference OTDR measurement and taking into account the number of drop links connected to the last splitter stage in the reference measurement and the new measurement. Thereby, determination of position and severity of the fault locations is enabled.

Claims

1. A method of performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N;

obtaining at least one new event location based on the OTDR measurement signal; and

calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein a total loss, TLref, in said reference OTDR measurement is represented by

2. A method according to claim 1, wherein the new OTDR measurement is triggered by a fault alarm or an Optical Transceiver Monitoring, OTM, measurement report received from at least one Optical Network Terminal, ONT, connected to said PON.

3. A method according to claim 1, further comprising querying one or more ONTs connected to said PON about their received optical power periodically.

4. A method according to claim 1, further comprising querying one or more ONTs connected to said PON about their received optical power on-demand.

5. A method according to claim 1, wherein a total loss, TLnew, in said new OTDR measurement is represented by

6. A computer program comprising computer readable instructions embodied in a non-transitory storage medium, which when run in one or more processing units, is operable to perform the method according to claim 1.

7. A computer program product, comprising the computer program according to claim 6.

8. A method according to claim 5, wherein a difference, Δ

TL, between said total loss in said reference OTDR measurement and said total loss in said new OTDR measurement is represented by

9. A method of performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N;

obtaining at least one new event location based on the OTDR measurement signal; and

calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein an alarm is received from one ONT, the at least one new event location is one new event location, and no events were detected in the reference measurement, wherein all of a plurality of branches were connected to said multistage splitter in said OTDR reference measurement and are connected in the new OTDR measurement, further comprising calculating the magnitude of the fault, α

, using

10. A method of performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N;

obtaining at least one new event location based on the OTDR measurement signal; and

calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein an alarm is received from one ONT and the at least one new event location is j new event locations, j>

1, and no events were detected in the reference measurement, further comprising calculating the magnitude of the fault in a first ONT, α

, using,

α

_j [dB]=5*log(1−

N+N*10<sup>−

|Δ

TL</sup>_j^|).

11. A method of performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N;

obtaining at least one new event location based on the OTDR measurement signal; and

calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein an alarm is received from n number of ONTs, n>

1, and the at least one new event location is one new event location and no events were detected in the reference measurement, further comprising calculating the magnitude of the fault in a first ONT, α

, using

12. A client unit in a fibre plant manager adapted to perform fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

an interface unit; and

a processing unit, wherein the processing unit is configured to;

trigger a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

insert an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N, via said interface unit;

obtain at least one new event location based on the OTDR measurement signal, via said interface unit; and

calculate a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein the client unit, the interface unit, and the processing unit are embodied in at least one non-transitory storage medium, hardware, and/or circuitry, and

wherein said processing unit is adapted to represent a total loss, TLref, in said reference OTDR measurement by

13. A client unit according to claim 12, wherein said interface unit is further adapted to receive a fault alarm or an Optical Transceiver Monitoring, OTM, measurement report from at least one Optical Network Terminal, ONT, connected to said PON, wherein said processing unit is triggered to insert said OTDR measurement signal into said multistage splitter before said last splitter stage of said multistage splitter.

14. A client unit according to claim 12, wherein said processing unit is further adapted to periodically query one or more ONTs connected to said PON about their received optical power.

15. A client unit according to claim 12, wherein said processing unit is further adapted to query one or more ONTs connected to said PON about their received optical power on-demand.

16. A client unit according to claim 12, wherein said processing unit is adapted to represent a total loss, TLnew, in said new OTDR measurement by

17. A client unit according to claim 16, wherein said processing unit is adapted to represent a difference, Δ

TL, between said total loss in said reference OTDR measurement and said total loss in said new OTDR measurement, Δ

TL, by

18. A client unit in a fibre plant manager adapted to perform fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

an interface unit; and

a processing unit, wherein the processing unit is configured to;

trigger a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

insert an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N, via said interface unit;

obtain at least one new event location based on the OTDR measurement signal, via said interface unit; and

calculate a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein the client unit, the interface unit, and the processing unit are embodied in at least one non-transitory storage medium, hardware, and/or circuitry, and

wherein an alarm is received from one ONT, the at least one new event location is one new event location, and no events were detected in the reference measurement, wherein all of a plurality of branches were connected to said multistage splitter in said OTDR reference measurement and are connected in the new OTDR measurement, wherein said processing unit is adapted to calculate the magnitude of the fault, α

, using

19. A client unit in a fibre plant manager adapted to perform fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

an interface unit; and

a processing unit, wherein the processing unit is configured to;

trigger a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

insert an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N, via said interface unit;

obtain at least one new event location based on the OTDR measurement signal, via said interface unit; and

calculate a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein the client unit, the interface unit, and the processing unit are embodied in at least one non-transitory storage medium, hardware, and/or circuitry, and

wherein an alarm is received from one ONT and the at least one new event location is j new event locations, j>

1, and no events were detected in the reference measurement, wherein said processing unit is adapted to calculate the magnitude of the fault in a first ONT, α

, using

α

_j [dB]=5*log(1−

N+N*10<sup>−

|Δ

TL</sup>_j^|).

20. A client unit in a fibre plant manager adapted to perform fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR, comprising:

an interface unit; and

a processing unit, wherein the processing unit is configured to;

trigger a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of said PON;

insert an OTDR measurement signal into a multistage splitter before a last splitter stage of said multistage splitter, and wherein the last splitter stage is of ratio 2;

N, via said interface unit;

obtain at least one new event location based on the OTDR measurement signal, via said interface unit; and

calculate a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from said reference OTDR measurement and taking into account a number of drop links connected to the last splitter stage in the reference measurement and the new measurement,

thereby enabling determination of position and severity of fault locations,

wherein the client unit, the interface unit, and the processing unit are embodied in at least one non-transitory storage medium, hardware, and/or circuitry, and

wherein an alarm is received from n number of ONTs, n>

1, and the at least one new event location is one new event location and no events were detected in the reference measurement, wherein said processing unit is adapted to calculate the magnitude of the fault in a first ONT, α

, using