1. Mattia Cantono, Vittorio CurrI
ICTON 2017
paper Th.B4.5
Flex- vs. fix-grid merit in progressive loading of networks already carrying legacy traffic
Mattia Cantono, Vittorio CurrI
Optcom group
Dipartimento di Elettronica e Telecomunicazioni
Politecnico di Torino
Italy

2. Supposed to be defragmented
motivation
Total available bandwidth
Allocated bandwidth
Supposed to be defragmented
Bandwidth available
for dynamic
spectral allocation
Bstat
Bdyn
Btot
Most networks are running out of spectrum
New – and supposedly dynamic – traffic has to be allocated on the residual bandwidth
What is the advantage of flex- vs. fix-grid given the residual bandwidth?

3. outline
The generalized OSNR as l QoT and the LOGO control plane and the statistical network assessment process (SNAP)
Residual bandwidth percentage
Traffic model
Fix- and fle-grid transceivers
The Italian network topology
Results as BP vs. Total allocated traffic
Comments and conclusions

4. 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 an inverse-OSNR (IOSNR) weighted graph 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

5. Statistical network assessment process
Start
Network
evolution
storage
J-th Traffic request
Traffic model
RWA
algorithm
description
saturation
i-th Monte Carlo run
I > NMC
i=i+1
j=j+1 NO
snap-shot
@ i,j
YES
SNAP
Metrics’ evolution vs. j
Static
Metrics
M. Cantono et al. “Potentialities and Criticalities of Flexible-Rate Transponders in DWDM networks: a Statistical Approach ,” JOCN, 2016
V. Curri et. al., “Elastic All-Optical Networks: a New Paradigm Enabled by the Physical Layer. How to Optimize Network Performances?,” JLT, 2017

6. Residual bandwidth percentage (RBP)
Btot: C-band
Allocated bandwidth
Supposed to be defragmented
Bandwidth available
for dynamic
spectral allocation
Bstat
Bdyn
Total available bandwidth: C-band of 4000 GHz
RBP=Bdyn/Btot x 100 [%]
We consider three different scenarios
Lightly loaded network: RPB = 25%
Moderately loaded network: RBP = 50%
Heavily loaded network: RBP = 75%

7. Traffic model Any-to-any traffic Flat probability in traffic requests
Traffic requests «groomed» at
RG = 20 Gbps
RG = 40 Gbps
RG = 100 Gbps
5000 Monte-Carlo progressive network loading up to blocking probability BP of 30%
RSWA algorithm: shortest path up to kmax=50

8. Fix and flex grid transceivers
Fix-grid
fLPi+1
fLPi+2
fLPi+3
fLPi+4
Flex-grid
fLPi
fLPi+1
fLPi+2
fLPi+3
fLPi+4 f
WDM grid: Df =37.5 GHz
RS =31.25 Gbaud
Coding overhead = 25%
Guard-band: = 6.25 GHz
Grid: Df=RS,slot =12.5 Gbaud, up to 5 slots
Coding overhead = 25%
fch tunable on 6.25 GHz
Guard-band = 6.25 GHz
Modulation
Format
Net Bit rate (Rb) Gbps
PM-BPSK 50
PM-QPSK
100
PM-16QAM
200
PM-64QAM
300
Modulation
Format
Net Bit rate (Rb) Gbps
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. The italian network topology

10. Results
Metrics
Normalized Network Traffic (T) is the total traffic loading the network normalized with respect the available bandwidth: it is indeed a specrat eexploitation efficiency
Blocking probability (BP): it is the probability that a new traffic request is rejected
Results are shown as BP vs. T for the different scenarios
Comparisons at BP = 1% are shown as well

11. Blocking Probability [%]
BP vs. T: fix-grid 5 10 15 20 25 30 35
0.1% 1%
10%
30%
Normalized Network Traffic [Tbps/THz]
Blocking Probability [%]
… RBP= 25%
_._RBP= 50%
_ _RBP= 75%
__ RG= 20G
__ RG= 40G
__ RG=100G

12. BP vs. T: flex-grid 5 10 15 20 25 30 35
0.1% 1%
10%
30%
Blocking Probability [%]
Normalized Network Traffic [Tbps/THz]
… RBP= 25%
_._RBP= 50%
_ _RBP= 75%
__ RG= 20G
__ RG= 40G
__ RG=100G

13. Flex vs. Fix @ bp=1% RBP=25% RBP=25% RBP=25% RBP=50% RBP=50% RBP=50%
Normalized Network Traffic [Tbps/THz]
Residual Bandwidth [%]
RG = 20 Gbps
Normalized Network Traffic [Tbps/THz]
Residual Bandwidth [%]
RG = 40 Gbps
Residual Bandwidth [%]
Normalized Network Traffic [Tbps/THz]
RG = 100 Gbps
RBP=25%
Flex2Fix  2.5
RBP=50%
RBP=75%
Flex2Fix  3.3
RBP=25%
Flex2Fix  2.5
RBP=50%
RBP=75%
RBP=25%
Flex2Fix  1.3
RBP=50%
RBP=75%

14. conclusions
We showed that flex-grid is always advantageous with respect to fix-grid
The relative advantage that is around 2.5 times for grooming sizes of 20 and 40 Gbps, decreases to 1.3 times for RG= 100 Gbps because of saturation effects
Spread of spectral efficiency for different scenarios of RBP and RG is much smaller for flex-grid, while using fix-grid the larger RG, the better

15. This work was supported by CISCO Systems within a SRA contract