1. ICTON 2016
paper Tu.B3.3
Impact of Fiber Type and Raman Pumping in NyWDM Flexible-grid Elastic Optical Networks
Arsalan Ahmad2, Andrea Bianco1, Hussein Chouman3,
Guido Marchetto4, Sarosh Tahir4,
Vittorio Curri1
1Dipartimento di Elettronica e Telecomunicazioni - Politecnico di Torino - Italy
2National University of Sciences and Technology, Islamabad, Pakistan
3 Télécom ParisTech , Université Paris-Sud, université paris saclay, Paris, France
4Dipartimento di Automatica e Informatica - Politecnico di Torino - Italy

2. Motivations
Tranceivers based on multilevel modulation formats with coherent receivers
No need for in-line compensation of chromatic dispersion
Transparent wavelength routing possible in nodes
Propagation impairment is a Gaussian disturbance enabling a simple closed-form for lightpath QoT
IP traffic will grow at the average rate of 23% per year ()
Physical layer solutions – as Raman amplification – enhancing transmission quality must be tested and analyzed for network effectiveness
() Cisco Visual Networking Index: Forecast and Methodology, 2015–2020

3. The GN-model and the OSNR as QoT of lightpaths
outline
The GN-model and the OSNR as QoT of lightpaths
The LOGO strategy
How to deal Hybrid Raman/EDFA amplification
A transparent optical network as a weighted graph
Network analysis heuristics
Analysis of a Pan-EU network topology with flex-grid transmission
Results presented as benefits of Raman amplification given as physical layer utilization

4. GN-model () : A simple and accurate equivalent model for fiber links with HFA…… Ls
D, adB, Aeff
EDFA
Raman pump
Transparency:
GEDFA +
GRA Lf
Degradation of the QoT of available lightpaths given by the generalized OSNR in Rs
NLI disturbance in Rs
ASE noise in Rs
() A. Carena et al. “Modeling of the impact of nonlinear propagation effects in uncompensated optical coherent transmission links,” JLT, vol. 30, no. 10, pp. 1524–1539, 2012

5. Hybrid Raman/EDFA fiber amplifiers (HFA)Ls z 1
No Raman
GRA
Raman
MPR()
Moderate Pumping Regime
The larger Ppump
The smaller PASE
The larger PNLI
The larger the saturation
() V. Curri, A. Carena, “Merit of Raman Pumping in Uniform and Uncompensated Links Supporting NyWDM Transmission, “ JLT, vol. 34, no. 2, pp , 2016

6. LOGO() startegy: local-optimized global-optimized
We globally optimize the transmission performance locally minimizing the OSNR degradation in each fiber span
Degradation of generalized OSNR in Rs
Optimal power per channel
() P. Poggiolini et al. “The LOGON Strategy for Low-Complexity Control Plane Implementation in New-Generation Flexible Networks”, OFC 2013

7. An all optical transparent network
With the knoweledge of the network physical details
We set the optimal power per channel and manage the network as a graph weighted by the inverse-OSNR (IOSNR) A E B D H C G I F
Example: QoT for lightpath travelling from node A to node G through nodes C and E:
where

8. Flex-grid and flex-format nyWDM
fch1
fch2
fch3
fch4
fch5 f
DSP
RSG=RS,slot· Ns
Modulation
Format
I/Q Modulator
Laser
Number of
Spectral Slots Ns
fch
Bch=RSG=RS,slot· Ns
RbG=RSG· BpS
Rb=RSG/(1+OH/100)
Data at
Bit-rate Rb
RS,slot =12.5 Gbaud
OH = 25%
Ns = 1  5
fch tunable on ½ RS,slot
Modulation formats
PM-BPSK : BpS = 2
PM-QPSK : BpS = 4
PM-16QAM: BpS = 8
PM-64QAM: BpS = 12
Btot = 4 THz  SLtot=320
Modulation
Format
Net Bit rate (Rb) Gbitps
Ns=1
Ns=2
Ns=3
Ns=4
Ns=5
PM-BPSK 20 40 60 80
100
PM-QPSK
120
140
280
PM-16QAM
160
240
320
400
PM-64QAM
360
480
600

9. Which modulation format?
PM-BPSK
PM-QPSK
PM-16QAM
PM-64QAM
Given the
in-service BER
BpS 2 4 8 12
Lightpath QoT OSNR in Rs [dB] 4 8 12 16 20 22
Given the origin node the destination node, and the route
QoT as route OSNR

10. Elastic flexible-grid networks design
We use a design procedure for elastic flexible-grid networks similar to the heuristic-based one used for fixed- grid
Transmission-aware Logical Topology Design (LTD):
Find the set of lightpaths but decide also which modulation format for each lightpath
Routing and Spectrum Assignment (RSA)
Route the lightpaths and assign portion of spectrum to each lightpath
Spectrum is divided in 12.5 GHz slots, up to five contiguous slots can be assigned to a lightpath
The RMLSA (Routing, Modulation Level and Spectrum Allocation) sub-problems are jointly solved
The choice of the modulation format depends on the route QoT and sets the capacity per spectral slot
Then the channel capacity can be enlarged occupying up to 5 slots, upon to spectral availability

11. Planning flexible-grid networks
Input: Network topology, traffic matrix, physical layer models
Proposed approach: describe Tx-Rx feasible configurations with (reach-rate-spectrum-guard band) tuples
Output: RMSA (Routes, modulation format and spectrum allocation)
Minimize utilized spectrum and/or number of transponders, and/or…
Satisfy physical layer constraints
Courtesy: E. Varvargios, OFC 2013

12. Network Design Heuristic
Simple heuristic chosen because the focus of the work is to discuss the influence of physical layer parameters on network performance metrics, with no major emphasis on resource allocation policies
Direct Lightpath Heuristic (DLH)()
Each traffic demand is fulfilled by establishing a new dedicated lightpath beginning from the largest one
Incorporation of detailed physical layer model ensures the a realistic adaptation of modulation format based on lightpath OSNR
After selecting the modulation format, required spectrum slots are calculated and their availability if verified on the physical path
In this work, we stop the analysis before reaching the traffic load that would imply request blocking
() A. Ahmad et al. “Traffic Grooming and Energy Efficiency in Flexible-grid Networks”, IEEE ICC 2014

13. PAN-European network topology
The analysis
Three fiber types
NZDSF
SSMF
PSCF
Ls = 80 km  120 km
HFA from 0% (EDFA) up to 60%
Network traffic level: 500 Gbps  3000 Gbps
Results presents as percentage of physical layer utilization, i.e., the spectral use :
PAN-European
network topology

14. SO vs. raman pumping Ls = 100 km - Traffic = 1000 or 1500 Gbitps RA0

15. SO vs. Span Length
Traffic = 1000 Gbitps

16. SO vs. traffic
Ls = 100 km

17. We showed that Raman pumping always helps network perfomances
conclusions
Transparent optical networks can be analyzed as a whole from the logical down to the physical layer thanks to a simple QoT parameter including ASE noise and propagation impairments
We showed that Raman pumping always helps network perfomances
Use of Raman pumping gives larger advantages in case of
Low dispersion fiber: NZDSF
Long span lengths
High traffic

18. Questions…

19. IGH with different traffic ordering policies
We explore the impact that serving demands in different orders has on network performance.
Six different orderings are defined using 2 parameters: The traffic capacity Ti,j and the physical length Di,j of the ligthpath:
Traffic Based Ordering
Ascending order of Ti,j (IT).
Descending order of Ti,j (DT).
Lightpath Physical Path Based Ordering
Ascending order of Di,j (IL).
Descending order of Di,j (DL).
Hybrid Ordering: Extension of IT. The ordering of the traffic demands that have Ti,j = Cmax, which is done in ascending order of their Ti,j (IT-IL).
Random Ordering (RAN)