The Core-Network Energy-Efficiency Challenge

 

By Dr. Klaus Grobe, Director Global Sustainability, ADVA Optical Networking SE, Germany
Winter 2016


INTRODUCTION
Bit rates in the Internet are growing exponentially. So is the negative environmental impact of the global ICT sector, albeit somewhat slower. This is primarily driven by the Internet energy consumption and the associated greenhouse gases (GHG). It holds as long as electricity is not fully based on renewable energy.

ICT energy consumption splits into core and access networks, data centers, and end-user equipment. There is a significant difference between core-networks and data centers on the one hand, and end-user equipment on the other. In the recent years, the energy consumption of end-user equipment decreased globally, which was primarily driven by improvements in flat-panel displays and (laptop) computers. On the other hand, core-network and data-center energy consumption is commonly predicted to grow significantly. Broadband access networks are also predicted to grow, but growth rate depends on technology. With Passive Optical Networks, growth can be kept to a minimum.

Relevant core-network components are IP/MPLS core routers and highcapacity transport. The latter is based on Wavelength-Division Multiplexing (WDM). In WDM, multiple wavelengths are used in optical fibers, each carrying digital information.

This started approximately 20 years ago with per-wavelength bit rates of 2.5 Gb/s, the latest generation is carrying up to 200 Gb/s per wavelength. Although the WDM contribution to global ICT electricity consumption is comparatively low, WDM is one of the areas where growth is predicted. This is shown in Figure 1, where WDM contributes to Networks.

Figure 1. Internet energy consumption in Germany [Hintemann et al., EGG 2016+, Berlin, September 2016

 

ICT AND THE CORE-NETWORK CONTRIBUTION
The main environmental impact from core-network equipment results from its use-phase energy consumption. This is confirmed in so-called Life-Cycle Analysis (LCA), where various impact aspects like GHG production, Ozone depletion and others are calculated over the entire equipment life, from extracting raw materials via production, transport, use-phase up to end-of-life (recycling, landfill). A simplified WDM LCA example is given in Figure 2, which shows the dominance of the use-phase.

Figure 2. Simple WDM LCA example

 

The energy efficiency of core-network equipment, in particular core routers and WDM, has been substantially increased in the last two decades. Unfortunately, the bit-rate increase – throughput in core routers and WDM transport capacity – has grown even faster. For both equipment categories, one can approximately derive duplicated energy consumption for 10-fold bit-rate increase. This is shown in Figure 3 for typical routers and WDM gear. It is relevant to note that the latest numbers in both equipment categories are only achieved by combining the most energy-efficient measures in all equipment aspects. This includes latest chip sets, optimized voltage supply, deactivation of unused parts, etc. In other words – even if the best technologies are combined today, the resulting efficiency increase is slightly lower than the bit-rate increase. This behavior is different as compared to other equipment, e.g., computers, TV sets etc.

Figure 3. Energy efficiency of core-network equipment
Source: [Vereecken et al., IEEE COMMAG, Vol. 49, No. 6, 2011].

 

ENERGY-EFFICIENCY INCREASE IN THE CORE – THE CHALLENGE
The fast Internet bit-rate increase puts an additional challenge on the respective equipment vendors. On the one hand, they must seek for new technologies for further efficiency increase, even though many areas have already been optimized. As in example, with latest power-supply units, there is little space left for further improvements. On the other hand, they may even be penalized for not decreasing the energy consumption of their equipment. The latter meanwhile happens in an increasing number of environmental-performance assessments. Here, the goal often is to demonstrate year-over-year decrease of relevant impact factors, namely, energy consumption and/or GHG production. Most assessments today use metrics (for energy consumption or efficiency) which do not consider the exponential bit-rate increase with whom today's core-network equipment efficiency cannot keep up. This also disregards the fact that proper use of the Internet is one of very few known ways to decrease global energy consumption elsewhere, an effect known as Greenby-ICT that can substantially overcompensate energy consumption growth in parts of the Internet. This aspect must be considered in particular for core-networks since all Internet traffic has to pass this part of the network. The non-consideration of the strong Internet bit-rate growth with regard to core-network equipment energy consumption is common practice in assessments today.

One possible solution to this problem consists of applying an analogue to using intensity energy-consumption or GHG-production metrics when assessing companies with regard to these impact factors. Here, the respective numbers are normalized to, e.g., company growth or number of goods sold, in order not to penalize growth. This is done, for example, in assessments done by the Carbon Disclose Project (CDP).

The analogue to intensity metrics can be some sort of Internet-growth metrics. Here, the approximate average efficiency increase as per Figure 3, duplication in energy consumption per 10-fold bit-rate increase, can be considered.

Falling behind this trend may then be penalized, whereas staying ahead can be rewarded. Such a metric can – and should – be applied until disruptive new technologies appear which may drastically increase energy efficiency.

It is relevant to note that this proposal does not intend to reduce the respective vendors' efforts to developing better equipment energy efficiency. The intention is to achieve somewhat better assessment fairness for a certain group of equipment.

We will discuss this approach in relevant sustainability fora, including CDP and the QuEST Forum Sustainability Initiative.

CONCLUSION
Core-network equipment in the Internet is getting more energy-efficient quickly, but this trend today cannot compensate even faster bit-rate growth. We therefore propose to apply Internet growth metrics in energy-efficiency or GHG-production assessments. This approach will be discussed in relevant sustainability fora.


Contact details:
Dr. Klaus Grobe
ADVA Optical Networking SE
Fraunhoferstr. 9a
82152 Martinsried, Germany
KGrobe@ADVAoptical.com