copyright © 2014 alcatel-lucent. all rights reserved.€¦ · copyright © 2014 alcatel-lucent....

COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED. (Dora van Veen, [email protected])

September 21, 2014

Dora van Veen

WAVELENGTH OAM IN TWDM-PON USING PLOAM MESSAGES

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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.

• We will discuss activation of ONUs in a TWDM-PON by using the Physical

Layer Operations and Management (PLOAM) messaging channel

• Pros and cons

• Example implementation (ALU TWDM-PON 2013 demo)

• How to enable synchronized quiet windows

• Commercial RSSI details

• Conclusions

INTRODUCTION AND OVERVIEW

length field

2 ONU-ID

1 Message type

1 Sequence number

36 Message contents

8 MIC: message integrity check

A PLOAM message

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• PRO: Potential lowest cost, needed hardware already available (i.e. RSSI)

• PRO: Most of the needed signaling and concepts are already in place in existing

standards

• PRO: No optical power penalties to the main data-transmission

• CON: Synchronization of quiet windows is required (wavelength ONU is unknown

when it transmits for the first time so it can interfere with the other wavelength

channels)

• CON: Rate of quiet windows needs to be the same for each wavelength

PROS AND CONS

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ALCATEL-LUCENT TWDM-PON DEMO SYSTEM (2013)

7360 ISAM FX-8

ONUs with tunable Tx & tunable Rx

Cyclic AWG Bell Labs Integration and Subsystems

See: D. van Veen, W. Poehlmann et al.,"System demonstration of a time and

wavelength-set division multiplexing PON,“ ECOC 2013, paper We.3.F.2

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ALU-TWDM-PON DEMO SYSTEM SETUP

• The TWDM-PON demo system is integrated with an existing XG-PON1 system.

• We extended the standard physical layer processes with the new wavelength

control protocol to show automated activation and in service wavelength

tracking.

ONUx

tunable

TRx FPGA

MAC

µP

λ−control

opticalpowersplitter

WDM

cyclicup-streamAWG

OLT

MAC

FPGA XFP4

XFP3

XFP2

RSSI

XFP1

feeder

fiber

SO

A

WDM

down-stream4x1 coupler

4x10 Gbps

4x2.5Gbps

tunable

filter+WDMs

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AUTOMATED WAVELENGTH TUNING AND TRACKINGONU INITIATION PROCESS

• Before activation of ONU starts, the ONU

tunes it receiver until it has optimal

downstream data reception (no quiet

windows needed for this phase)

• We used the standard quiet windows in

XG-PON1 for activating an ONU.

• However these ranging windows need to

occur simultaneously on all wavelength

channels.

OLTmax.

distanceONU

time

distance

Synchronized arrival of upstream data traffic

Quiet window: No traffic on any upstreamTWDM channel

ArrivalSN response

Max. RTD

OLT sends SN request

SN response at un-known λ

…

Unsuccessful :New attempt withshift by δλ

Successful reading of SN:OLT starts next steps (fine tuning, putting ONUin operation)

Unsuccessful :New attempt withshift by δλ

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AUTOMATED WAVELENGTH TUNING AND TRACKINGONU INITIATION PROCESS

Port A Port APort B Port C Port D

-25

-20

-15

-10

-5

0

Inse

rtio

n Lo

ss (

dB)

Wavelength

A AB C D B

Step δλ=∆λ /4

∆λ∆λ∆λ∆λ

(i) (ii)

• Data transmission possible

in light blue areas.

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• After SN detection, RSSI (Received Signal Strength Indication) at the OLT Rx is used to fine tune through dithering the upstream wavelength to the maximum of the AWG filter before it becomes operational.

• We implemented a proprietary PLOAM message from OLT to ONU to instruct a wavelength change.

• During operation dithering stays active to track the wavelength when (slow) ambient temperature changes happen (without quiet windows).

AUTOMATED WAVELENGTH TUNING AND TRACKINGFINE TUNING AND TRACKING (DITHERING)

Port A Port APort B Port C Port D

-25

-20

-15

-10

-5

0

Inse

rtio

n Lo

ss (

dB)

Wavelength ditheringCombined with RSSI measurement at OLT

A AB C D B∆λ

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Two possible cases:

1. OLTs in same location (i.e. CO)

o Time-of-Day (ToD) interface comes standard on many telecom equipment, mature

technology (PLL-based) is available to interface with ToD.

2. OLTs in different locations

o GPS receiver at each location. Needs good visibility with the sky. Government

regulations need to be considered. Accuracy of GPS time signals is ±10 ns

o Precision time protocol (PTP)*. PTP is a protocol used to synchronize clocks

throughout a computer network. Sub-microsecond accuracy is possible.

Synchronization techniques are available and well known in the communication world

*IEEE 1588-2002 standard "Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control

Systems"

HOW TO ENABLE SYNCHRONIZED QUIET WINDOWSSYNCHRONIZING OLTS

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1. OLTs at same location

o In this case the quiet windows can sync using the time at the OLT as is, the inaccuracy

can be handled with very small safety margins.

2. OLTs at different locations

o In this case one needs to take a larger margin into account

o or alternatively one could measure the distance, or ‘range’ the OLTs as a more accurate

method

HOW TO ENABLE SYNCHRONIZED QUIET WINDOWSSYNCHRONIZING QUIET WINDOWS

OLT1

OLT2 quiet window

quiet window

quiet window with margin

Quiet window needs to be 400 µs to

accommodate 0-40 km PON reach

For example 10 km distance between OLTs

results in 100 µs margin

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• Rate of quiet windows needs to be the same on each wavelength.

- Considering the case of including 10 km margin for OLTs at different locations a 500 µs

quiet window is needed for a PON with reach of 0-40 km.

- Quiet window rate of 1 per second => 0.05 % overhead

- Quiet window rate of 10 per second => 0.5 % overhead

It does not seem a big deal to have a standard quiet window rate on all

wavelengths from an overhead perspective

HOW TO ENABLE SYNCHRONIZED QUIET WINDOWSEQUAL RATE OF QUIET WINDOWS PER WAVELENGTH

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• Commonly available in commercial OLT XFP modules

• RSSI circuit ‘mirrors’ the APD current after which it goes into an ADC and to an

output pin of an OLT XFP

• Typically -32dBm to -5dBm optical input range with ±0.5 dB accuracy is

supported

• Typical minimum sampling period is 300 ns

• Highest RSSI measurement rate in current OLT XFPs is limited by the serial

communication with the module, improvements possible

• In case of DML-based ONUs, the burst wavelength drift also causes an additional

inaccuracy of up to about ± 0.5 dB (less for short bursts).

• Averaging of RSSI measurements can result in a more accurate result (see also

for example Ning Cheng et al. paper PD4F4 at ECOC 2013).

MEASUREMENTS USING COMMERCIAL BURSTMODE RSSI

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• We described ONU activation in TWDM-PON using the

already available PLOAM channel.

• Pros and Cons have been listed.

• We showed an example implementation.

• We discussed ways to enable synchronized quiet windows.

• We discussed feasibility of using commercial RSSI function

for wavelength-OAM.

CONCLUSIONS

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• Ilija Hadzic for providing valuable insights into synchronization

• Peter Vetter, Thomas Pfeiffer and Ken Waters for fruitful discussions and

contributions.

ACKNOWLEDGEMENTS

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