Cisco DWDM Chromatic Dispertion Calculation in CTP\XLS

Kayukov Valeriy
Optical System Engineer Step Logic
April 15, 2016
Cisco Optical Networking – Chromatic Dispersion
calculation.
Cisco Support Community
Expert Series Webcast

Question1
Have you ever had deal with DWDM
Cisco ONS devices?
1. Yes
2. No
3. Cisco have such platforms?

• Chromatic Dispersion
• Measurement of CD in real Fiber
• Sample of calculation in CTP
• Polarization Mode Dispersion
Content of presentation

•Chromatic Dispersion (CD) – is based on effect of
impulse broadening during passing through optical fiber.
•Polarization Mode Dispersion - a temporary difference
between the polarization components of the same signal.
Optical Dispersion types:

• Optical pulse time-expanded by passing through the
optical fiber. This process triggers limitation of bandwidth
throughput or maximum transition distance with constant
bandwidth.
• Chromatic Dispersion is fiber characteristic with is
measured in ps/km*nm and depends on wavelength.
• To compensate dispersion used pre-compensation and
post-compensation techniques. Dispersion compensators is
based on negative dispersion fiber.
Chromatic Dispersion (CD)

Different cables have different CD depending on internal
construction
Typical CD values of different fibers
Fiber type Normal dispersion at 1550 nm
measured in ps/km-nm
Single Mode Fiber (SMF) 17
E-Large Effective area fiber
(ELEAF)
4
TrueWave RS (TW-RS) 4.2
Dispersion shifted fiber (DSF) -0.33

• Cisco DCU compensators uses
fiber loops with negative
dispersion fiber.
• Attenuation of DCU varieties
from 2.1db to 8.8 db.
•Compensation Level (ps/nm)
varieties from 100ps/nm to 1950
ps/nm
Cisco ONS 15216 DCU modules
DCU chassis PN:
15216-DCU-SA=
DCU module PN:
15216-DCU-XXXX=

Optical spool produced and measured in Thailand,
completed in in hard case in Denmark.
For Sample this DCU has 1950 psnm nominal, but in real
how we see in report it has 1957,33 ps/nm. Insertion loss
6.97db vs 8.8db in data sheet.
What is inside DCU module?

•Disadvantage of use DCU in network is that DC add
significant attenuationloss. This is due to difference of
coupling transition and fiber and fiber used in DCU.
• Advantage of use compensators is that DCU limit
nonlinear effects. Different dispersion profile result in a
phase mismatch, witch prevent from FWM happening.
Pluses and minuses of use DCU

Values of CD Tolerance XFP:
• Fixed Wavelength XFP
-500 to +1100 ps/nm
• Tunable Wavelenght XFP
-400 to +1300 ps/nm
CD Tolerance of different XFP 10G modules

Values of CD Tolerance SFP+:
• Fixed Wavelength XFP
-500 to +1100 ps/nm
• Tunable Wavelenght XFP
-400 to +1300 ps/nm
CD Tolerance of different SFP+ 10G modules

• Use of fixed wavelength SFP+XFP has disadvantages in
case failure. Fixed wavelength could be replaced by tunable
module or the SAME wavelength module.
• GLP Price Discount could be higher for tunable modules
that for fixed. Contact to your Cisco CAM.
• In future line DWDM network could be upgraded to
colorless or directionless.
Comparison of SFP+ vs XFP modules

Single-Shelf DCU Application
East-to-West and West-to-East
Samples of use DCU modules
Cascaded DCU Shelf per
Direction
DCU Placed Between
Wavelength Selective Switch
(WSS) and Amplifier

CD Tolerance of different SFP+ 10G modules

DWDM network based on 10G services called coherent
networks and networks based on 100G and higher services
called non-coherent networks.
Design coherent networks depends on compensation
systems. Non-coherent networks in most (but not in all)
cases doesn’t depends on compensation systems because
tolerance of recoveries around 94 000 ps/nm for 200G. For
example 94 000ps/nm is equivalent to 5200 km with
18ps/nm-km.
CD Tolerance of 10G, 200G, 400G modules

Measurement
of CD of real
fiber

What parameters are measured:
• dispersion coefficient values measured at specified
wavelength
• dispersion maximum over specified range of wavelengths
• zero dispersion wavelength and dispersion slope at this
wavelength
CD measurement, Introduction

Both methods measure propagation delay (or group delay) at selected
wavelength and, from the measured delay versus wavelength data, interpolate
the delay for other wavelength not directly measured by using numerical fitting
algorithms.
• Phase Shift – method of comparison of test signal and reference signal used to
modulate the input signal. The phase difference is performed versus wavelength
over the entire wavelength range of source.
• Pulse Delay -
Measurement methods (Phase Shift vs Pulse
Delay )

Phase Shift advantages:
 high accuracy measurement
 high dynamic range (40 db+) (>15 db
higher than the Pulse Delay method)
 high measurement reliability
 compatible with non-biderectional
components (such EDFA amplifiers)
Phase Shift Method
Phase Shift disentangles:
 measurement time can depend on
number of data ponts
 requires two units
 dispersion versus length info not
provided
Fiber length must be known to calculate
the average CD coefficient

Group Delay advantages:
 require access to only one end of link
 detects regions of different dispersion
within a link? As it can analyze reflections
at intermediate points (only if reflectance
are present mid-span)
Combines an OTDR allowing a
simultaneous distance and loss
measurement
Group Delay Method
Group Delay disentangles:
 distance range is limited by the end
reflection: higher reflectance? The longer
distance. Not suitable for APC
connections installed.
 Not suitable for long-haul or high-loss
fiber link (>30db)
 not compatible with non-biderectional
components (EDFA amplifiers)

100G/100G/400G Cards now
have advanced measurement
method build in.
100G/100G/400G Cards CD measurement

Sample of
calculation in
CTP, XLS

Need to design network with
requirements:
• 5 sites
• 4 channel 10GE
• fiber used is SMF G652
In this example we will not
consider design of multiplexing,
adddrop and amplification
systems.
Real Sample of Calculation. Planning of DCU
Scheme of compensation in DWDM network

In this step we will make:
• Start – “Project Creation Wizard”
• Start – “Run the Network Wizard Now”
• Create circuit – “Create Net Point-to-Point Demand”
• Start – “Network Analyze”
• Go to – “Summary” –> “Optical Reports”
Lets start to work in CTP. Step 1 – Preparation.

In this section we will not
cover types of transponders
and so on, just create circuit.
Create Circuits

DWDM trunk type we are changing to Tunable SFP+. It is not matter
what type of coding (FECEFECNO-FEC), it doesn’t add any price for
total BOM. Coding (FECEFECNO-FEC) in 10G networks no licensable
by Cisco. After this choice we exactly know CD tolerance of trunk ports.
Edit trunk SFP manually to SFP+ Tunable C
band

 Report shows per channel CD calculation at the end of
circuit in BOTH directions. Chromatic Dispersion
compensation systems is separate per each direction.
 Cisco Transport Planner (CTP) use value 1100ps/nm for
Tunable SFP+, but in data sheet 1300ps/nm. Advantage of
use CTP is that it has fundmargin in reports.
 CTP doesn’t use any fiber characteristicfunction of DC
depending on wavelength.
 If Residual CD cross CD Robustness (CD tolerance) value
than CTP triggers Single-Channel NLE Status RED. Later will
discus situation with Single-Channel NLE Status RED.
 CTP maximum optimally calculates DCU unites. In case of
alarms power EOL , EOS you can manually change DCU to
lower values, in most cases it helps to improve power SOL
value.
Analyze “Optical Report”

• Click on Site 1-5,
choose “Layout”
• Click on Site 1-5,
choose
“Functional view”
Lets do that for
every Site and
draw big topology
per each direction
Lets understand what CTP calculated

 In attach XLS based calculation of DC of Channel
between Site-1 and Site-5
XLS based DC Calculation
Site ID DCU-XXXX CD value Site ID DCU-XXXX CD value Site ID DCU-XXXXCD value Site ID DCU-XXXXCD value
Site-1 none 0 Site-5-B none 0 Site-1 none 0 Site-5-B none 0
Fiber length 85 Fiber length 50 Fiber length 85 Fiber length 50
Fiber CD total 1402,5 Fiber CD total 825 Fiber CD total 1402,5 Fiber CD total 825
CD after fiber 1402,5 CD after fiber 825 CD after fiber 1402,5 CD after fiber 825
Site-2-B 1350 Site-4-A 450 Site-2-B 1350 Site-4-A 450
52,5 375 52,5 375
Fiber length 90 Fiber length 120 Calculation CD in CTP----------> Fiber length 90 Fiber length 120
Fiber CD total 1485 Fiber CD total 1980 Fiber CD total 1485 Fiber CD total 1980
CD after fiber 1537,5 CD after fiber 2355 CD after fiber 1537,5 CD after fiber 2355
Site-3-B 1350 Site-3-A 1350 Site-3-B 1350 Site-3-A 1350
187,5 550 187,5 550
Fiber length 120 455 5 This value calculates CTP Fiber length 120 450 5
Fiber CD total 1980 Fiber length 90 But have to be 455, CTP makes errorFiber CD total 1980 Fiber length 90
CD after fiber 2167,5 Fiber CD total 1485 It add aditional DCU-450 CD after fiber 2167,5 Fiber CD total 1485
Site-4-B 1350 CD after fiber 1940 Site-4-B 1350 CD after fiber 1490
450 Site-2-A 1350 450 Site-2-A 1150
550 590 340 This value calculates CTP 550 340
-182,5 Fiber length 85 But have to be 590, CTP makes error -182,5 Fiber length 85
Fiber length 50 Fiber CD total 1402,5 It add aditional DCU-450 Fiber length 50 Fiber CD total 1402,5
Fiber CD total 825 CD after fiber 1992,5 Fiber CD total 825 CD after fiber 1742,5
CD after fiber 642,5 Site-1-A 1350 CD after fiber 642,5 Site-1-A 1350
Site-5-B 550 642,5 392 This value calculates CTP Site-5-B 550 392,5
92,5 But have to be 642, CTP makes error 92,5
It add aditional DCU-450

As result we can see some errors and make some conclutions:
 CTP show in layout or doesn’t show correct DCU values on which based DC results in
“Optical Results” report
 Be care with CTP, use manual calculation to check, also use Forcing Manager to unlock
and clear CD cache calculation.
 Use “Forcing Manager” when you add new circuits in design
 Do not make “Over-Compensation” and “Under-Compensation”, try to have CD of signal
all the time in tolerance window. For example tolerance window for SFP+ Tunable from -
100 to 1100 ps/nm
XLS based DC Calculation

Polarization Mode Dispersion - a temporary difference between the polarization
components of the same signal.
Example A - optic cable has ideal dimensions of the X-axis and Y -> the same velocity of
propagation.
Example B - optic cable has different dimensions to the X-axis and Y -> propagation
speed is different.
Polarization Mode Dispersion (PMD)

Causes of PMD:
• The asymmetry of the core or the internal stress caused by the core during production
• Internal stress caused by the core during the installation of optical cable
Polarization Mode Dispersion (PMD)

Cisco DWDM Chromatic Dispertion Calculation in CTP\XLS

Cisco DWDM Chromatic Dispertion Calculation in CTP\XLS

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