CHAPTER 7. SUMMARY AND CONCLUSIONS
7.2. Future research challenges
The work presented in this thesis attempted to address the rising energy consumption problem in optical transport networks by proposing and evaluating different approaches. Nevertheless, there is still significant work to complete in this area with the ultimate objective of achieving an energy-efficient network in the future. In fact, the work carried out during this thesis opened some new directions for research that could be interesting to explore:
• EON paradigm: As discussed in Chapter 4, the EON paradigm offers enormous potentials to improve the energy efficiency of the network and to make the resource allocation more flexible. However, there is still significant research to be done at different levels. At the node level, BVTs with adaptive transmission capabilities both at the line and client sides need to be developed considering the energy efficiency implications as well (e.g. enabling partial deactivation of some subcarriers and “on-the-fly” modulation format changes to reduce PC). At the network level, almost “hitless” defragmentation techniques would be necessary when assuming dynamic operation in order to simplify the spectrum management and reduce blocking (and thus the number of employed fibers). The development of an intelligent control plane would also be required to fully exploit the potentials of EON, taking the energy consumption issues into account. In this regard, it would also be interesting to monitor how much power will be consumed by the control plane tasks. Furthermore, new physical layer modeling techniques that are different from the ones considered for fixed-grid networks might be needed as well, especially for dynamically operated networks.
• Resilience schemes: Improved multi-layer interaction would be desired to make the optical layer aware of the reliability and availability requirements of the services and applications running on top of it. An intelligent control plane that is aware of these requirements would facilitate the application of the Diff QoP concept to reduce energy consumption. Some other interesting directions for future work can exploit the combination of restoration and protection schemes, so that the amount of redundant dedicated resources (and thus the power consumed for protection purposes) can be reduced. Moreover, the potential advantages brought by the adaptive modulation format
and elastic bandwidth transmission of EON architectures could be exploited in different manners by novel protection schemes to improve the overall energy consumption. • Amplification strategies: The evaluation of amplification scenarios carried out in this
dissertation assumed an existing network where in-line OAs were already deployed at given locations. However, it would be interesting to design a network from scratch or completely re-design the network to select the most efficient locations to place OAs (both EDFA and HRE) with the ultimate objective of improving the overall energy and spectral efficiency. Moreover, the different amplification strategies were evaluated in this thesis for WDM MLR architectures with DP 1+1. It would be interesting to evaluate the overall energy benefits of such amplification solutions with more energy-efficient network architectures such as EON, and adopting novel energy-efficient protection schemes like DP TAPA or Diff QoP.
• Implementability in real networks: The potential advantages of the different approaches evaluated in this thesis have been assessed by simulations. However, it would be required to test the potential advantages in real deployment scenarios by considering the implementability issues that may arise as well. Moreover, cost implications also have to be carefully evaluated. Reducing energy consumption will certainly reduce part of the OpEx, but some energy-aware approaches may rely on novel equipment which could be initially expensive and have a considerable impact in terms of CapEx. Accordingly, it is necessary for operators to investigate the overall cost advantages to assess the successful applicability of the energy-aware techniques.
• Carbon footprint reduction: Although the reduction of GHG emissions is implicitly taken into account by the proposed energy-aware approaches, more specific work can be done to face this challenge. For instance, considering the utilization of renewable energy sources at some equipment locations (nodes and links).
149
LIST OF PUBLICATIONS
The work presented in this thesis has been partly published in the proceedings of International conferences and journals. The following list gives an overview of the related publications in chronological order:
1. J. López, Y. Ye, V. López, F. Jiménez, R. Duque, P. Krummrich, “On the Energy Efficiency of Survivable Optical Transport Networks with Flexible-grid,” European Conference and Exhibition on Optical Communications
(ECOC), Sep. 2012.
2. J. López, Y. Ye, V. López, F. Jiménez, R. Duque, P. Krummrich, F. Musumeci, M. Tornatore, and A. Pattavina, “Traffic and Power-Aware Protection Scheme in Elastic Optical Networks,” XVth International
Telecommunications Network Strategy and Planning Symposium (NETWORKS), vol., no., pp.1,6, 15-18 Oct.
2012.
3. J. López Vizcaíno, Y. Ye, V. López, F. Jiménez, R. Duque, P. Krummrich, “Cost Evaluation for Flexible-Grid Optical Networks,” IEEE Global Telecommunications Conference (GLOBECOM) Workshops, vol., no., pp.358,363, Dec. 2012.
4. J. López Vizcaíno, Y. Ye, F. Jimenez, R. Duque, F. Musumeci, M. Tornatore, P.M. Krummrich, A. Pattavina, "Quality of protection schemes with extended flexibility for improved energy efficiency in transport networks," 9th International Conference on the Design of Reliable Communication Networks (DRCN), vol., no., pp.28,35, Mar. 2013.
5. J. López Vizcaíno, Y. Ye, V. Lopez, F. Jimenez, R. Duque, F. Musumeci, A. Pattavina, and P. Krummrich, "Differentiated Quality of Protection to Improve Energy Efficiency of Survivable Optical Transport Networks,"
Optical Fiber Communication Conference/National Fiber Optic Engineers Conference (OFC/NFOEC), pp.
OM3A.1. Mar. 2013.
6. J. López Vizcaíno, P. Soto, Y. Ye, F. Jimenez, P. Krummrich, “Energy-efficient and Low Blocking Probability Differentiated Quality of Protection Scheme for Dynamic Elastic Optical Networks,” 21st International
Conference on Software, Telecommunications and Computer Networks (SoftCOM), vol., no., pp.1,5, Sep. 2013.
7. J. López Vizcaíno, Y. Ye, F. Jiménez, P. Krummrich, “Energy- and Cost-Efficient Protection in Core Networks by a Differentiated Quality of Protection Scheme,” European Conference on Optical Communications (ECOC), Sep. 2013.
8. J. López Vizcaíno, Y. Ye, V. López, F. Jiménez, R. Duque, I. Tafur Monroy, Peter M. Krummrich, “Green Networking and Communications: ICT for Sustainability,” Chapter 17-Energy Efficiency Improvement with the
Innovative Flexible-grid Optical Transport Network, Auerbach Publications- CRC Press, Taylor & Francis Group,
ISBN: 978-1-4665-6874-7, Nov. 2013.
9. J. López Vizcaíno, Y. Ye, V. López, F. Jiménez, F. Musumeci, M. Tornatore, A. Pattavina, P. M. Krummrich. "Protection in optical transport networks with fixed and flexible grid: Cost and energy efficiency evaluation," Optical Switching and Networking, vol. 11, pp 55-71, Jan. 2014.
10. J. López Vizcaíno, Y. Ye, F. Jiménez, A. Macho, P. Krummrich, "Optimized Amplifier Placements for Improved Energy and Spectral Efficiency in Protected Mixed-Line-Rate Networks," Optical Fiber Communication
Conference (OFC), pp. Th1E-5, Mar. 2014.
11. J. López Vizcaíno, Y. Ye, F. Jiménez, P. M. Krummrich. "Amplifier placements optimization for enhanced energy efficiency in optical transport networks," IEEE International Conference on Communications (ICC), 2014, pp. 3700-3706, Jun. 2014.
12. J. López Vizcaíno, Y. Ye, F. Jiménez, A. Macho, P. Krummrich, "Increased energy efficiency and capacity for mixed-line-rate WDM networks with hybrid Raman-EDFA amplification," European Conference on Optical
Communication (ECOC), pp. 1-3, Sep. 2014.
13. J. López Vizcaíno, P. Soto, Y. Ye, P. M. Krummrich, "Differentiated quality of protection: An energy-and spectral- efficient resilience scheme for survivable static and dynamic optical transport networks with fixed-and flexible- grid,“ Optical Switching and Networking, vol. 19, Part 2, pp 78-96, 2016.
14. J. López Vizcaíno, Y. Ye, V. López, P. Krummrich, “Cost Evaluation of Amplification Strategies for WDM Mixed- Line-Rate Networks,” International Conference on Transparent Optical Networks (ICTON), July 2015.
151
LIST OF ACRONYMS
ADSL Advanced Digital Subscriber Line NF Noise Figure
AMC Adaptive Modulation and Coding NZDSF Non-Zero Dispersion Shifted Fiber
APS Automated Protection Switching OA Optical Amplifier
ASE Amplified Spontaneous Emission OBS Optical Burst Switching
BER Bit Error Ratio OCS Optical Circuit Switching
BoD Bandwidth on Demand ODF Optical Distribution Frame
BPSK Binary Phase Shift Keying ODU Optical Data Unit
BV-OXC Bandwidth-Variable OXC OEO Optical-Electrical-Optical
BVT Bandwidth-Variable Transponder OFDM Orthogonal Frequency Division Multiplexing
CAPEX Capital Expenditures OOK On-Off Keying
CDC Colorless, Directionless and Contentionless
OPEX Operational Expenditures
CMOS Complementary Metal–Oxide–
Semiconductor
OPS Optical Packet Switching
CO-OFDM Coherent Optical OFDM OSI Open Systems Interconnection
CW Continuous Wave OSNR Optical Signal-to-Noise Ratio
CWDM Coarse WDM OTN Optical Transport Network
DAC Digital to Analog Converter O-VPN Optical Virtual Private Networks
DEE Dynamic Energy Efficiency OXC Optical Cross Connect
DEEI Dynamic Energy Efficiency Improvement PC Power Consumption
DEMUX De-multiplexer PCE Path Computation Element
Diff-QoP Differentiated Quality of Protection PD Propagation Delay
DiR Differentiated Reliability PDL Polarization-Dependent Loss
DLP Dedicated Link Protection PDM Polarization Division Multiplexing
DP Dedicated Protection PIC Photonic Integrated Circuit
DP 1:1 Dedicated Protection 1:1 PMD Polarization-Mode Dispersion
DP 1+1 Dedicated Protection 1+1 PON Passive Optical Network
DPP Dedicated Path Protection PP Protection Path
DP-16QAM Dual-Polarization 16QAM PSK Phase Shift Keying
DP-QPSK Dual-Polarization QPSK PUE Power Usage Effectiveness
DP TAPA Dedicated Protection Traffic-Aware
Power-Aware
QAM Quadrature Amplitude Modulation
DQPSK Differential Quadrature Phase Shift
Keying
QoP Quality of Protection
DRA Distributed Raman Amplification QoS Quality of Service
DSBR Dynamic Service Blocking Ratio QoT Quality of Transmission
DSF Dispersion Shifted Fiber QPSK Quadrature Phase Shift Keying
DSP Digital Signal Processing REG Regenerator
DT Deutsche Telekom RMLSA Routing, Modulation Level and Spectrum Allocation
DWDM Dense WDM ROADM Reconfigurable Optical Add/Drop
EA-RMLSA Energy-Aware-Routing, Modulation Level, and Spectrum Allocation
ROSNR Required OSNR
EA-RWA Energy-Aware-Routing and Wavelength
Assignment
RP Regenerator Placement
EASPP Energy-Aware Shared Path Protection RSA Routing and Spectrum Allocation
EDF Erbium-doped Fiber RT Recovery Time
EDFA Erbium-doped Fiber Amplifier RWA Routing and Wavelength Assignment
EE Energy Efficiency RX Receiver
EEI Energy Efficiency Improvement SBR Service Blocking Ratio
EEPG Energy Efficiency per GHz SDH Synchronous Digital Hierarchy
EON Elastic Optical Networks SDM Space Division Multiplexing
FD Failure Detection time SDN Software-Defined Network
FEC Forward Error Correction SEI Spectral Efficiency Improvement
FF First-fit SiP Silicon Photonics
FS Frequency Slot SLA Service Level Agreement
FTTH Fiber to The Home SLP Shared Link Protection
FWM Four Wave Mixing SLR Single Line Rate
GB Guard Band SMF Single Mode Fiber
GbE Gigabit Ethernet SO Spectral Occupancy
GeSI Global e-Sustainable Initiative SP Shared Protection
GHG Greenhouse gas SPM Self-phase Modulation
GMPLS Generalized Multi-Protocol Label
Switching
SPP Shared Path Protection
HRE Hybrid Raman-EDFA SRG Shared Risk Group
ICT Information and Communication Technology
SRS Stimulated Raman Scattering
IP Internet Protocol TAPA Traffic-aware and Power-aware
ISP Internet Service Provider TID Telefónica I+D
ITU International Telecommunications Union TO Time setup cross connection at OXC
ITU-T International Telecommunications Union-
Telecommunication
TR Transmission Rate
KSP K-Shortest Paths TS Traffic Scenarios
LP Lightpath TSPs Transponders
LR Line Rate TX Transmitter
LTE Long-Term Evolution UMTS Universal Mobile Telecommunications System
LWPF Low Water Peak Fiber VLAN Virtual Local Area Network
MCS Multicast Switch WA Wavelength Assignment
MF Modulation Format WDM Wavelength Division Multiplexing
MILP Mixed Integer Linear Programming WP Working Path
MLR Mixed Line Rate WSON Wavelength Switched Optical Networks
MMF Multi-Mode Fiber WSS Wavelength Selective Switch
MP Message Processing time XPM Cross-Phase Modulation
155
LIST OF SYMBOLS
Notation Description Units
10Gs Number of 10 Gbps WDM TSPs in WDM MLR architectures N/A
40Gs Number of 40 Gbps WDM TSPs in WDM MLR architectures N/A
100Gs Number of 100 Gbps WDM TSPs in WDM MLR architectures N/A
a Add/Drop degree N/A
α Fiber attenuation factor dB/km
Aggregated PRX Total aggregated power obtained at the RX dBm
ASpE Average spectral efficiency in the links of the network bits/Hz
AvgSO Average spectral occupancy in the links of the network GHz
BlockedTraffic Summation of the TR of all the blocked demands in the network Gbps
Br Resolution bandwidth for OSNR measure Hz
BWCBand Entire useful bandwidth in the ITU-T C band, i.e. 4 THz THz
ChannelSpacing Chosen ITU-T grid in WDM architectures GHz
currentTrafficDemand Traffic demand value at a specific time (considering traffic variations) Gbps
D Diameter of the network topology km
DataFlow Data transmitted in the duration of the flow bits
DEE Energy efficiency in the dynamic scenario considering the data transmitted and the energy consumed
bits/Joule
DEEI Energy efficiency improvements of Diff QoP with respect to DP 1+1 in a dynamic scenario
percent
DemandIndex Index used to select the traffic demand in ListOfDemands N/A
DSBR Service blocking ratio measures to indicate the percentage of data that could not be allocated in the network with respect to the total data in the dynamic scenario
percent
ECFlow Energy consumed during the transmission of a particular flow Joules
ECOA Energy consumed by an OA in the simulated time Joules
ECOXC Energy consumed by an OXC in the simulated time Joules
EE Overall Energy Efficiency in the network considering the total carried traffic demands and the PC of all the network elements
bits/Joule
EEI Energy efficiency improvements of Diff QoP with respect to DP 1+1 percent
EEPath Energy efficiency of a LP bits/Joule
EEPG Overall Energy Efficiency per GHz in the network considering the total carried traffic, the PC of all the network elements and the average spectral occupancy in the links of the network
bits/Joule/GHz
EEPGMetric Energy efficiency per GHz metric used to determine the most energy- and spectral-efficient transmission for a LP
bits/Joule/GHz
f Frequency Hz
Fcap Flow request value bps
FD Time to detect a failure s
FDur Time duration of a flow s
FS Frequency slot size in flexible-grid architectures GHz
FStTime Starting time of a flow in the dynamic scenario s
FTC QoP traffic class of a flow N/A
G Optical amplifier gain dB
GB Guard band N/A
HighestEEPGMetric Variable to store the highest EEPG metric obtained for a LP transmission bits/Joule/GHz
HighestEEPGMetricPP Variable to store the highest EEPG metric obtained for a LP transmission in the PP
HighestEEPGMetricWP Variable to store the highest EEPG metric obtained for a LP transmission in the WP
bits/Joule/GHz Arrival rate in dynamic scenario Num. of new
requests/time unit
L Span length km
Li Number of bidirectional links N/A
LinkExists Variable that determines whether there are LPs not using the optimum
LRComb in LinkList
N/A
LinkList List which contains the links that are traversed by LPs not using the optimum LRComb in terms of EEPG
N/A
ListOfDemands List which contains the information of the traffic demands, i.e. source node, destination node, and demand value
N/A
ListOfPaths List which contains the information regarding the KSP from source to destination nodes, i.e. link and node sequences, total length
N/A
ListOfProtectPaths List which contains the information about possible PPs for each WP in DP, i.e., node sequence, link sequence, and path length
N/A
ListOfWorkingPaths List which contains the information about possible WPs in DP, i.e., node sequence, link sequence, and path length
N/A
ListUnprotected List which contains all the LPs that cannot be protected with SP N/A
LpCandIndex Index used to select the LP to perform grooming among the possible candidates in ListOfPaths
N/A
LPGroomingList List of LPs candidate for grooming of a demand, i.e. sharing the same source and destination nodes
LPTC QoP traffic class of the LP N/A
LRComb Line rate combination, i.e. combination of TSPs used to serve a traffic demand in WDM MLR architectures
N/A
LRCombList List which contains the possible LRComb to serve a particular traffic demand
N/A
LRCombListIndex Index used to select the LRComb in LRCombList for WDM MLR architectures
N/A
LRCombListIndexPP Index used to select the LRComb in LRCombList in the PP for WDM MLR architectures
N/A
LRCombListIndexWP Index used to select the LRComb in LRCombList in the WP for WDM MLR architectures
N/A
m Number of spans in the WP N/A
MardB Margin to account for extra power penalties due to non-linear effects,
aging, operational tasks, etc.
dB
MF Modulation format used in EON transmission N/A
MostEfficientAllocation Stores the information about the solution providing the highest EEPG metric, i.e. link sequence, spectral resource IDs, and line rates/MFs
N/A
MostEfficientAllocationPP Stores the information about the solution for PP in DP schemes providing the highest EEPG metric, i.e. link sequence, spectral resource Ids, and line rates/modulation formats
N/A
MostEfficientAllocationWP Stores the information about the solution for WP in DP schemes providing the highest EEPG metric, i.e. link sequence, spectral resource Ids, and line rates/modulation formats
N/A
MP Message processing time at the node s
n Number of spans in the PP N/A
N Node degree N/A
NAmp Number of OAs that can be added or upgraded per link N/A
NAmpLinks Number of OAs in the link N/A
ND Average node degree of the network topology N/A
NFi Noise figure of the OA dB
No Number of nodes N/A
NoDataSubc Number of data subcarriers needed for the transmission of a LP N/A
Nos Number of wavelengths used to allocate a traffic demand in the network with WDM architectures
N/A
LIST OF SYMBOLS 157
NSimLinksToOptimize Number of simultaneous links that can be evaluated for optimization (adding new OAs or upgrading existing EDFAs to HREs)
N/A
OSNRidB Linear OSNR value at the output of the OA dB
OSNRRX OSNR value at the receiver dB
OSNRS OSNR at the transmission source dB
PC Power consumption Watts
PCLINKS Approximated power consumption contribution in the links of a LP
considering OAs and OXCs
Watts
PCOA Power consumption of the OA Watts
PCOAsLP Contribution to power consumption of the OAs traversed by a LP Watts
PCOFDM Power consumption of an OFDM subcarrier Watts
PCOXCPP Power consumption of the OXCs used in the PPs in protection schemes Watts
PCOXC Power consumption of the OXC Watts
PCOXCsLP Contribution to power consumption of the OXCs traversed by a LP Watts
PCoxcWP Power consumption of the OXCs used in the WPs in protection schemes Watts
PCPath Power consumption metric of a LP Watts
PCT100G Power consumption of a 100 Gbps WDM TSP Watts
PCT10G Power consumption of a 10 Gbps WDM TSP Watts
PCT40G Power consumption of a 40 Gbps WDM TSP Watts
PCTRANS Power consumption of the TSPs required to serve a traffic demand Watts
PCTSP Power consumption of the TSPs Watts
PCTSPWP Power consumption of the TSPs used in the WPs in protection schemes Watts
PCWDMTSP Power consumption of the chosen WDM TSP Watts
PD Propagation delay s
peakTrafficDemand Traffic demand value in the traffic matrix Gbps
Pin Launched power at the TSPs dBm
PP Protection path N/A
PRX Power value at the receiver dBm
PSAT Saturation power at the receiver dBm
ROSNR Required OSNR at the receiver dB
RT Recovery time s
RXsensitivity Power sensitivity at the receiver dBm
SBR Service blocking ratio measures to indicate the percentage of traffic that could not be allocated in the network with respect to the total traffic
percent
SEI Spectral efficiency improvements of Diff QoP with respect to DP 1+1 percent
SOPath Spectral occupancy of a LP, i.e. bandwidth required to serve a traffic demand
GHz
SRGList List with all the LPs affected by a particular link failure (Shared Risk Group)
N/A
TMC QoP traffic class of the demands contained in the traffic matrix N/A
TO Time to configure and setup a cross-connection in the optical switch s
TotalCarriedTraffic Summation of all the traffic demands carried in the network Gbps
TotalDataTR summation of all the data transmitted in the dynamic scenario bits
TotalEC Total energy consumed during the operation of the network in the dynamic scenario
Joules
TotalHighestEEPGmetric Variable to store the highest EEPG metric obtained for a LP transmission