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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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
• 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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
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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COPYRIGHT © 2013 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
• 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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
• 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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COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
• Ilija Hadzic for providing valuable insights into synchronization
• Peter Vetter, Thomas Pfeiffer and Ken Waters for fruitful discussions and
contributions.
ACKNOWLEDGEMENTS