1. HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS
Chapter 22:
Green Optical Core networks
Mohammad Ali Mohseni and Dr. Akbar Ghaffarpour Rahbar
Sahand University of Technology, Tabriz, IRAN
Sahand University of Technology, IRAN

2. Outlines Introduction Energy consumption in optical core networks
Network layers overview
Power consumption models
Energy efficiency metrics
Energy consumption of network equipment: Switches, Amplifiers, Transmitter, Receivers
Energy efficient optical network design
Modular structure of switch
Static and dynamic node structures
Single line and multi-line rate network
Optimum repeater spacing
Energy-aware optical core networks
Power-aware routing and wavelength assignment
Power-aware grooming
Selectively switching sleep network elements
Power-aware survivable networks
conclusion
Sahand University of Technology, IRAN

3. Introduction
Green attribute refers to component, system, or network which consume energy efficiently
Why greening the networks?
Growing the number of users and services leads to increase power consumption of ICT
Decreasing cost
Lack of energy resources
Environmental effects: decreasing emission of green house gas in the air
Sahand University of Technology, IRAN

4. Introduction Green research approaches Energy efficient approach:
A network is energy efficient if its power consumption is minimized without degrading its performance. Energy efficiency should be considered when designing a network
Energy awareness approach:
Networks are usually designed for peak traffic load; however network traffic varies during time and in wide margin time is less than peak.
A network is energy aware if its power consumption change according to changing offered traffic load
Sahand University of Technology, IRAN

5. Energy consumption in optical core networks
Network layers
Sahand University of Technology, IRAN

6. Power consumption metrics
There are few metrics for evaluating energy efficiency of network equipments. Most simple and common metric is ratio of total power consumption to capacity of system
Higher value means the system is more energy-hungry
If system is a switch then the system capacity is summation of bit rates of line cards, this ratio estimates a lower bound for energy consuming per bit for a typical switch
In practice, a system does not work at high capacity because traffic changes during time. So it is more acceptable to replace equipment capacity with equipment throughput
Sahand University of Technology, IRAN

7. Power consumption models
Power consumption models express power consumption of equipment versus offered traffic load:
Linear power consumption model
Theoretical power consumption model
Combined power consumption model
Statistical power consumption model
Sahand University of Technology, IRAN

8. Energy consumption of switches
Switches are classified in two distinct classes:
Linear analog switch
Digital switch
Input and output interfaces can involve optical demultiplexers/multiplexers, transponders, O/E or E/O converters, wavelength converters components
control unit configures switch fabric for an input wavelength adjust to appropriate output if switch fabric is active ones
Pswitch=Pinput+Pswitch_fabric+Poutput+Pcontrol_unit
Sahand University of Technology, IRAN

9. Energy consumption of optical amplifier
Optical amplifiers
Power of optical signal is attenuated while passing through  optical fibers.
Attenuation increases exponentially by length of fibers
Attenuation should be compensated by optical amplifiers or repeaters
Amplifiers perform re-amplifying, re-timing and reshaping signal in all optical domain so optical signals remain in optical domain during passing through links
Sahand University of Technology, IRAN

10. Energy consumption of optical transmitter and receiver
Optical receiver

11. Energy efficient network design
A network is energy efficient if its power consumption is minimized without degradation of its performance. Energy efficiency should be considered when a network is designed
Modular switches
Static and dynamics network
Single rate and multi rate network
Optimum repeater spacing
Sahand University of Technology, IRAN

12. Modular structure of switches
A modular switch has several chassis and each chassis has some line cards
Each line card has several ports for establishing connections with other nodes
Modular structure provides possibility of load-less components to go to sleep mode for power efficiency purposes
power consumption of cisco catalyst 6500 components
component
Power consumption(Watt)
powerfixed 60
powerswitch_fabric
315
power­first_line_card
powersubsequence_line_card 49
poweractive_port 3
Poweridle_port
0.1
                 
Sahand University of Technology, IRAN

13. Energy efficient network design
Static and dynamic network
In static network, allocation of wavelengths is performed statically and do not change during time
In dynamic network, allocation may change during time based on traffic volume and network topology
Dynamic operation needs lower number of wavelengths than static due to wavelength conversion possibility
Static classic optical node(SCON)
Static low consumption optical node(SLON)
Dynamic optical node(DON)
Sahand University of Technology, IRAN

14. Static and dynamic network
Two parameters determine which structure is more energy efficient
ratio of energy consumption of LR (Long Reach transponder) and SR (Short Reach) transponders
ratio of power consumption of a device in sleep state and active state
Sahand University of Technology, IRAN

15. Single rate and multi line rate network
Current optical backbone networks supports 10/40 Gbps data rates and 100 Gbps data rate is in way
In SLR (Single Line Rate) network equipments operate at the same bit rate
In MLR (Multi Line Rate) network wavelength channels have variety of capacities (10/40/100)
Optical impairments limit the usage of high data rates (40 and 100 Gbps) to short distances
normalized energy consumption of 10/40/100 transponders, EDFA, and electronic processing
Device
Energy consumption(normalized)
10 Gbps transponder 1
40 Gbps transponder 5
100 Gbps transponder 14
EDFA amplifier
0.25
Electronic processing
0.5(per Gbps)
Sahand University of Technology, IRAN

16. Single rate and multi line rate network
There are some facts which determine power consumption of network which should be considered:
More number of wavelengths needs more number of transponders
Long distance requires more amplifiers
BER threshold limits the distance on which a lightpath with data rate r on wavelength λ can reach
Low data rates need more fibers to support high capacity requests
Sahand University of Technology, IRAN

17. Optimum repeater spacing
Optical signals are attenuated while passed through fiber
Amplifiers are applied to compensate attenuation
Amplified spontaneous emission(ASE) noise
when an optical signal is amplified by an EDFA, ASE noise is added to original signals
For long fiber, it is required to use electronic repeaters
Sahand University of Technology, IRAN

18. Optimum repeater spacing
lopt is optimum distance between repeaters which minimizes power consumption of link L
Sahand University of Technology, IRAN

19. Power aware optical core network
Networks are usually designed for peak traffic load
However, network traffic varies during time and is less than peak in wide margin time.
A network is energy aware if power consumption of network changes according to changing offered traffic load
Power aware routing and wavelength assignment
End to end versus link by link traffic grooming
Selectively switching sleep network elements
Power aware survivable WDM network
Sahand University of Technology, IRAN

20. Power aware routing and wavelength assignment(PA-RWA)
RWA establishes a minimum cost route between source and destination nodes and assigns an appropriate wavelength to the established path
The objectives of conventional RWAs are to minimize routing cost and blocking probability
Route cost : path length, hop count, and etc.
PA-RWA aims to adjust network power consumption with offered traffic load
PA-RWA is modeled as an ILP formulation.
Since there are usually many constraints for an ILP problem, these problems are classified in NP-hard problems
Heuristics
Least Cost Path (LCP)
Most Used Path (MUP)
Ordered-Lightpath Most Used Path (OLMUP)
Sahand University of Technology, IRAN

21. Weighted power aware routing and wavelength assignment (WPA-RWA)
PA-RWAs decrease the power consumption of network but also decrease network performance
PA-RWAs set cost of links as link power consumption so routing algorithm may select minimum power consumption path which is not shortest path.
Selecting long paths decreases some QoS parameters such as BER and delay
Weighted PA-RWA (WPA-RWA) shows the impact of energy minimization on path length and blocking probability
Sahand University of Technology, IRAN

22. Traffic grooming
Traffic grooming is a traffic engineering approach, i.e., process of aggregating small traffic in bigger units
Traffic grooming is performed by three strategies:
End to end traffic strategy
Link by link traffic strategy
Hybrid strategy
In hybrid strategy, a lightpath partially can be aggregated with previously established lightpaths or partially established new routes. Intermediate nodes of a new route operate in bypassing strategy.
Sahand University of Technology, IRAN

23. Traffic grooming End to end strategy
Pend_to_end=PDS+PEO+POS+PTX+Pamp+PRX+ POS+ PTX +Pamp+ PRX+ POS +POE + PDS
Sahand University of Technology, IRAN

24. Traffic grooming Link by link grooming
Plink_by_link=PDS+PEO+POS+PTX+Pamp+PRX+ POS+ POE + PDS +PEO+POS+PTX+Pamp+ PRX+POS+ POE + PDS
Sahand University of Technology, IRAN

25. Traffic grooming Traffic grooming
Evaluation of the power consumption over 5 years for both the link-by-link and end to end grooming scenario, following a traffic increase of 50% per year
Sahand University of Technology, IRAN

26. Traffic grooming Traffic grooming is modeled as an ILP problem.
Like other hard problems, it is solved by heuristics:
Path based heuristic
Link based heuristic
Request size based
Link utilization based
Sahand University of Technology, IRAN

27. Traffic grooming Differentiate power saving traffic grooming
Grooming degrades some QoS parameters such as delay and BER because it may route some light-paths in longer routes than minimum available routes.
Some users not eager to use unproven technologies:
Solution: divide demands by two classes:
Red class: Red class demands are served as traditional routing algorithm such as shortest path objective function
Green class: Green class demands are routed with energy saving objectives
Differentiate power saving
Red demand base heuristic
Total demand base heuristic
Sahand University of Technology, IRAN

28. Selectively switching sleep network elements
Network consumption is more than required because:
Over provisioning
Traffic is time varying
Protection resources are always active
Solution:
Switching off or sleep additional network equipments
Selecting the elements that should go to sleep mode
Rerouting
Reactivation
Sahand University of Technology, IRAN

29. Selectively switching sleep network elements
Switching off network elements
Which network elements go to sleep mode?
Load-less
Load-less than threshold
Most power
Least flow
Random
Least link (node degree is least)
ILP
Rerouting:
Reactive rerouting
Proactive rerouting
Reactivation
Sahand University of Technology, IRAN

30. Survivability
Survivability is an essential necessity to protect links and nodes against failures. Protection can be provisioned at different levels: node, link, and path
Path protection schemes:
1:1 protection
1+1 protection
1:N protection
M:N protection
Protection resources of networks, always are active due to rapidly recovering of failures. These resources consume energy, whereas unused for a long time.
Solution is switching exclusively protection resources to sleep mode.
Sahand University of Technology, IRAN

31. Energy aware shared path protection
In conventional networks, load balancing improves performance parameters because it distributes traffic over network resources and utilizes them as equal as possible.
Load balancing reduces congestion in links and nodes, and also it decreases requirement protection resources
Traffic aggregating increases requirement protection resources
Sahand University of Technology, IRAN

32. Energy aware path protection
Aggregating primary and secondary resources separately can lead to more energy conservation
Sahand University of Technology, IRAN

33. Energy aware dedicated path protection
Separating working and secondary paths increases power saving and also blocking probability since resources are divided for different purposes, working and protection.
Energy aware dedicated path protection with differentiation of primary and secondary path(EA-DPP-Dif)
Initially, cost of link is set based on required power for activating amplifiers
After establishing the first lightpath over a link, other lightpaths can be established with lower cost because links are turned on now. Path cost degradation is performed for aggregating lightpaths on turned on links.
EA-DPP-Dif considers two different penalties: one for differencing between primary and secondary paths and another for aggregating primary and secondary paths separately
Primary path provisioning phase
Protection path provisioning phase
Sahand University of Technology, IRAN

34. Energy aware dedicated path protection
Energy aware dedicated path protection with mixing secondary path with primary path(EA-DPP-MixS)
Initially, cost of link is set based on required power for activating amplifiers.
After establishing the first lightpath over a link, other lightpaths can be established with lower cost because links are turned on now. Path cost degradation is performed for aggregating lightpaths on turned on links.
EA-DPP-MixS permits mixing primary and secondary paths, especially when routing the secondary path
Primary path provisioning phase
Protection path provisioning phase
Sahand University of Technology, IRAN

35. Conclusion Energy conserving in ICT is inevitable due to Solutions
Current networks are not energy efficient
Rapid growth of networks infrastructures
High cost: economical, environmental, …
Lack of energy resources
Guaranty of current increasing growth of these networks
Solutions
Develop networks energy efficiently
Modular structure of switch, static and dynamic node structures, single line and multi-line rate network, optimum repeater spacing
Networks adjust their energy consumption by traffic loads (energy aware networks)
PA-RWA, Power-aware grooming, selectively switching network elements to sleep mode, power-aware survivable networks
Sahand university of technology, IRAN