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PON monitoring Joint work between Multitel and FPMs/TCTS. e1+ VD-A workshop Barcelona – 26th February 2007. Multitel main interests in VD-A. Optical amplification in PON Remote amplification Remote pumping Remote powering Bi-directional amplification Monitoring of PON (passive layer)

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pon monitoring joint work between multitel and fpms tcts

PON monitoringJoint work between Multitel and FPMs/TCTS

e1+ VD-A workshop

Barcelona – 26th February 2007

multitel main interests in vd a
Multitel main interests in VD-A
  • Optical amplification in PON
    • Remote amplification
      • Remote pumping
      • Remote powering
    • Bi-directional amplification
  • Monitoring of PON (passive layer)
    • P2MP (Point-to-Multipoints) architectures

=> collaboration with FPMs/TCTS labs

e1+_VD.A_workshop_Barcelona_Feb07

multitel main interests in vd a1
Multitel main interests in VD-A
  • Optical amplification in PON
    • Remote amplification
      • Remote pumping
      • Remote powering
    • Bi-directional amplification
  • Monitoring of PON (passive layer)
    • P2MP (Point-to-Multipoints) architectures

=> collaboration with FPMs/TCTS labs

e1+_VD.A_workshop_Barcelona_Feb07

pon monitoring
PON monitoring

Main problem to be solved:

In-service FTTx networks optical layer monitoring.

[To be integrated in the Network Management System]

State of the art: two monitoring layers to consider

- Active components monitoring :

. Each active component uses autodiagnostic functions which are centralized and analysed through the NMS

=> Alarms below specified threshold levels

- Passive components monitoring (Fiber, splitters, connectors, splices) :

For the moment, a failure identification and resolution takes a long time. After determining that a fiber break has occured, a qualified technician must be dispatched with an OTDR to the closest access point with visibility to the fault to determine the optical distance to the fault.

e1+_VD.A_workshop_Barcelona_Feb07

pon monitoring1
PON monitoring

Main problem to be solved:

In-service FTTx networks optical layer monitoring.

[To be integrated in the Network Management System]

State of the art: two monitoring layers to consider

- Active components monitoring :

. Each active component uses autodiagnostic functions which are centralized and analysed through the NMS (Network Management System)

=> Alarms below specified threshold levels

- Passive components monitoring (Fiber, splitters, connectors, splices) :

For the moment, a failure identification and resolution takes a long time. After determining that a fiber break has occured, a qualified technician must be dispatched with an OTDR to the closest access point with visibility to the fault to determine the optical distance to the fault.

e1+_VD.A_workshop_Barcelona_Feb07

fttx networks monitoring
FTTx Networks Monitoring

Passive components : Two monitoring methods

- Preventive one :

Analysis of passive components progressive aging. Makes it possible to anticipate and organize network maintenance, thus reducing OPEX.

- Curative one :

Automatic diagnostic and location of critical faults. Workflow efficiency enhancement.

Main failures reasons :

Public works, digging, human mistakes during maintenance operations, local reasons (rodents, …)

Failure statistics from installed PONs :

No clear data available

e1+_VD.A_workshop_Barcelona_Feb07

specifications
Specifications

Main requirements:

- Intelligence centralized at the CO

- should not impact the PON architecture (e.g. branches of same length)

- should maintain colorless ONUs

The OTDR system must be fully-automated, enabling the following functions :

- PON’s branches monitoring (split ratio and configuration to be determined)

- Optical faults and breaks localisation

- Faults database updates

e1+_VD.A_workshop_Barcelona_Feb07

slide8

ONU

1550nm

1550nm

Mux

DeMux

Central Office

1310nm

1310nm

1*N Splitter

1625nm

OTDR

1625nm

SRE

Components- OTDR in the Central Office (@ 1625nm to be used in-service)- SRE (element switchable between two reflective states : R=0 and R=100%)

Monitoring method

e1+_VD.A_workshop_Barcelona_Feb07

slide9

Monitoring method :

Problem to be solved :

The OTDR trace shows whether a fault is located on one of the PON’s branches or not.

- The useful information is the distance from the CO to the fault.

- BUT it is not possible to know which branch contains the fault - ANDthe measured fault is only an apparent one, much weaker than the real one

Solution :

- Only one SRE in reflective position. Monitoring of each branch in turn

- The SRE generates an intense OTDR reflective peak. Its amplitude decreases in case of a fault on the monitored branch

- The real fault value is calculated from the apparent loss one, using previous networks’ detected faults database

e1+_VD.A_workshop_Barcelona_Feb07

slide10

1st year achievements

  • SRE :
      • Determination of the best SRE optical design
      • SRE electronic design
  • Realistic PON setup construction (split ratio = 16, 32, or even 64)
  • Statistical study of the OTDR trace for a random break in a PON
  • Theoritical determination of minimum OTDR performances to detect a given fault in a PON (considering FTTx norms)

e1+_VD.A_workshop_Barcelona_Feb07

sre optical design

SRE

1* 2

Coupler

PON

Optical

Switch

Photodiode

+ TIA

Electronics

µP

SRE Optical Design

Constraints to be considered :

- Technical ones :

The SRE must switch when it receives a message from the CO

When off, the SRE must be only a few reflective (not to interfer with the signal from other branches)

- Economical ones :

Monitoring system cost reduction

In parallel, study of installation cost per user

- Best design :

Optical configuration that minimizes the number of components

Compatible with Planar Lightwave Circuit Technology that enables cost saving by wafer scale process.

SOA

Coupler

SOA

e1+_VD.A_workshop_Barcelona_Feb07

sre electronic design
SRE Electronic Design
  • For a fully-automated monitoring system, the SRE must have the following functions :
  • Photodiode output signal amplification

(signal sent from the C.O. @ 1625nm, TTL format)

- Signal treatment (Micro-controller) :

- Address reading

- Comparison with SRE address

- Delaying reading

  • Switch commutation during the delaying read.

- Switch commutation at the end of the delaying period.

e1+_VD.A_workshop_Barcelona_Feb07

realistic pon construction

1625nm

Laser Driver

SRE

1 * 2

Optical

Coupler

RS232 +

Electronics

Distribution Cable (10km)

Feeder Cable (10km)

Optical

Switch

1 * N

PLC

Splitter

Photodiode

+ Ampli

PC

Driver

Software

DAQ

Optical Switch

µP

Electronics

(N=16, 32 and 64 available)

GPIB

Only 4 SREs on this Setup

(low take rate)

1625 nm

Monomode

OTDR

Realistic PON construction

Driver Functionalities:

Communication between Central Office and SRE

OTDR measurements

OTDR trace import & treatment

Faults database update.

e1+_VD.A_workshop_Barcelona_Feb07

statistical study of random fiber breaks
Statistical study of random fiber breaks
  • Fiber breaks detection is linked to curative monitoring :
  • - A fiber break is either reflective & non reflective.

- The reflective behaviour is random (depends on the shape of the break, the environnement)

The study of numerous fiber breaks makes it possible to trace a statistical profile :

This statistic will later be used to evaluate the number of detectable breaks in a given PON, with given OTDR performances – Thus, it will be possible to evaluate the monitoring method limits.

.

e1+_VD.A_workshop_Barcelona_Feb07

theoritical study of otdr performances
Theoritical study of OTDR performances

Experimental validation of the OTDR waveform noise (NW) theoritical equation :

Measured OTDR Trace

Measured Waveform Noise

Calculated Waveform Noise

e1+_VD.A_workshop_Barcelona_Feb07

theoritical study of otdr performances1
Theoritical study of OTDR performances

Experimental validation of the apparent fault theoritical equation :

ATT : Real loss value

Hmarche: Apparent loss value

e1+_VD.A_workshop_Barcelona_Feb07

theoritical study of otdr performances2
Theoritical study of OTDR performances

Thanks to the two previous results, it is now possible to calculate the apparent fault and the theoritical minimum DR necessary in each of the following cases :

Monitored branch loss bound by PON Norms (MIN and MAX values)

Other branches loss also bound by PON Norms (MIN and MAX values)

4 extrem combinations considered : MIN/MIN, MIN/MAX, MAX/MIN, MAX/MAX

Given Split ratio

Given Real fault value (1dB to be consistent with the monitoring system definition)

k depends on the OTDR trace analysis method (k=2 here)

e1+_VD.A_workshop_Barcelona_Feb07

theoritical study of otdr performances3
Theoritical study of OTDR performances

Results:

For N=32 or 64, and for a given real loss value of 1dB,

- The apparent fault is, in most cases, lower than the OTDR resolution limit. This is true for all the considered norms.

- Even if the apparent fault value is high enough to be visible on the OTDR trace, the necessary DR can vary from 30 to 45 dB. These high values lead to the use of long OTDR pulses, thus highly reducing the OTDR spatial resolution.

e1+_VD.A_workshop_Barcelona_Feb07

cases of reflective faults fibre breaks
Cases of reflective faults (fibre breaks)

In case of reflective faults, the equation giving the minimum DR is :

Conclusions:

In the same conditions than previous calculation (for non reflective faults), the necessary DR to see a -50dB reflective fault can vary from 20 to 35dB.

Other values : -40dB, DR= 12 to 30 dB

-30dB, DR= 10 to 25 dB

e1+_VD.A_workshop_Barcelona_Feb07

in service monitoring
In-service monitoring
  • - If all the branches are the same length, it is possible to use this property to virtually extend the monitored branch. Thus, the backscattered signal from a fault that belongs to this branch is no more in competition with the others branches backscattered signals. It is so the REAL LOSS value that is measured on the OTDR trace.
  • - Moreover, this technique makes it possible see all the faults affecting the branch at the same time (major advantage in comparison with the SRE technique
  • - BUT, this technique needs strong OTDR pulses and, thus, a poor spatial resolution
  • => next steps : can we possibly amplify this secondary trace ?

e1+_VD.A_workshop_Barcelona_Feb07

potential options

PON

Potential options
  • Semiconductor Optical Amplifier :
  • Could potentially be compatible with RSOA based ONUs
  • Issue: how to remove the CW component ?
  • Raman amplification

Need of a Raman laser source @ 1455nm to amplifiy OTDR pulses @ 1550nm (much more expensive than an SOA, but shared between N users)

e1+_VD.A_workshop_Barcelona_Feb07