OTDR trace analysis in PON systems

Patent metadata

Field	Value
Publication number	US-9281892-B2
Application number	US-201114128740-A
Country	US
Kind code	B2
Filing date	Jun 30, 2011
Priority date	Jun 30, 2011
Publication date	Mar 8, 2016
Grant date	Mar 8, 2016

Abstract

Fault analysis of a Passive Optical Network comprising Optical Network Terminal(s) uses Optical Time Domain Reflectometry (OTDR). An OTDR measurement signal is supplied to a multistage splitter having a ratio 2:N root . At least one drop link which is connected to the multistage splitter comprises one or more sub-splitters which having a ratio 1:N branch . A new event location is determined based on the OTDR measurement signal by analyzing OTDR measurement data relating to the sub-splitter based on distance from the multistage splitter and to the sub-splitter. A fault magnitude is calculated for a given location by subtracting an event magnitude obtained from the new OTDR measurement from a reference OTDR measurement and taking into account the number of drop links connected to the last splitter stage and to the sub-splitter in the reference measurement and the new measurement, thereby enabling determination of position and severity of the fault locations.

First claim

The invention claimed is:

1. A method of performing fault analysis, performed by an arrangement in a Passive Optical Network (PON), comprising at least one Optical Network Terminal (ONT), by using Optical Time Domain Reflectometry (OTDR), said method 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 said last splitter stage is of ratio 2:Nroot, so that the last splitter stage is connected to a plurality of drop links, and wherein at least one of the plurality of drop links being connected to said multistage splitter comprises at least one sub-splitter, wherein said at least one sub-splitter is of a ratio 1:N branch so that the at least one sub-splitter has one or more branches and one input port connected to the multistage splitter;
determining at least one new event location based on the OTDR measurement signal by analyzing OTDR measurement data, in a predefined sequence, relating to said at least one sub-splitter connected to said last splitter stage starting based on the drop links for which an upstream optical signal needs to travel through the largest number of sub-splitters in order to reach the last splitter stage; 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 the number of drop links connected to the last splitter stage and to the at least one sub-splitter in the reference measurement and the new measurement, thereby enabling determination of position and severity of said fault locations.

2. A method according to claim 1 , wherein said OTDR measurement data relates to a fibre link connecting a first sub-splitter to one of: an ONT or a second sub-splitter.

3. A method according to claim 2 , wherein said predefined sequence is based on the number of serially connected sub-splitters between an ONT and said last splitters stage.

4. A method according to claim 3 , wherein said predefined sequence is determined to start by analyzing OTDR measurement data relating to a sub-splitter having drop links being connected to ONTs only.

5. A method according to claim 1 , wherein the new OTDR measurement is triggered by the reception of a fault alarm or an Optical Transceiver Monitoring (OTM), measurement report from at least one ONT connected to said PON.

6. A method according to claim 1 , further comprising querying the ONTs being connected to said PON about their received optical power periodically.

7. A method according to claim 1 , further comprising querying the ONTs being connected to said PON about their received optical power on-demand.

8. A method according to claim 1 , wherein a total loss (TLref), in said reference OTDR measurement for a sub-splitter is represented by:

TLref
=

5
*

log
(

N
2

∑

n
=
1

N

⁢

∏

j
=
1

J

⁢

α
⁢

⁢

REF

n
,
j

2

-

M
REF

)

,

wherein N is the number of drop links of the last splitter stage of said multistage splitter (N root ), or where N is the number of drop links of a sub-splitter (N branch ), J is the number of events and M is either the number of non-connected drop links of said last splitter stage of said multistage splitter, or the number of non-connected drop links of said sub-splitter.

9. A method according to claim 8 , wherein the difference, ΔTL, between said total loss in said reference OTDR measurement and said total loss in said new OTDR measurement is represented by

Δ
⁢

⁢
TL

=



5
*

log
⁡

(

∑

n
=
1

N

⁢

∏

j
=
1

J

⁢

α
⁢

⁢

NEW

n
,
j

2

-

M
NEW

Assignees

• Urban Patryk
• Ericsson Telefon Ab L M

Inventors

• Urban Patryk

Classifications

• G01M11/3145 Primary

  Details of the optoelectronics or data analysis · CPC title

• G01M11/3136

  for testing of multiple fibers · CPC title

• H04B10/0771

  Fault location on the transmission path · CPC title

• H04B10/071 Primary

  using a reflected signal, e.g. using optical time domain reflectometers [OTDR] · CPC title

• H04B10/27

  Arrangements for networking · CPC title