Energy consumption of network communication

The energy intensity of the Internet (EI) has been addressed in several studies, such as (Schien et al. 2013; Coroama et al. 2013). For fixed access networks, the current academic state-of-the-art indicates an average energy intensity of 0.007 kWh/GB for 2020 (Aslan et al. 2018). For the energy consumption of networks as a whole, on the other hand, there is some divergence in the academic literature, ranging from 325 TWh yearly (Malmodin and Lundén 2018) to 723 TWh (Andrae and Edler 2015).

Figure 3 High-level topology of the Internet, distinguishing between data centres (DCs), end devices, and three distinct types of the  network: the wide-area network (WAN), fixed access network (FAN), and radio access network (RAN).

As stated in the Introduction, the study by (Aslan et al. 2018) is the current state of the art of the academic understanding on the energy intensity of the WAN. Extrapolating exponential past trends (up to 2017) via least squares fit yields a value of around EI2019 (WAN) = 0.01 kWh/GB and EI2020 (WAN) = 0.007 kWh/GB. The study does not address the energy intensities of either FAN or RAN.

(Pihkola et al. 2018) also extrapolate their 2010-2017 results into the future, devising an energy intensity of just below EI2020 (RAN) = 0.1 kWh/GB.

Table 1 Summary of existing estimates for EI (WAN), EI (FAN), and EI (RAN) for the last decade (2010 – 2019) and for today (2021).

These estimates, whose exact values are presented in row 10 of Table 3 and in Section 5.2, can be rounded as follows:

• EI2020 (WAN) = 0.02 kWh/GB,
• EI2020 (FAN) = 0.07 kWh/GB,
• EI2020 (RAN) = 0.2 kWh/GB,
• E2020 (WAN) = 110 TWh,
• E2020 (FAN) = 130 TWh,
• E2020 (RAN) = 100 TWh

These numbers probably also represent a reasonable basis for extrapolation for a couple of years into the future. The yearly efficiency gains (corresponding to the yearly decreases of the energy intensity) need to be taken into account according to the rather trivial equation:

(14)
EIᵧ₊₁(X) = eirfᵧ(X) × EIᵧ(X)

for all X ∈ {WAN, FAN, RAN}, and where eirfᵧ(X) represents the yearly energy intensity reduction factor for the year y.

There are approximations of the intensity reduction factors in the literature; their caveat, however, is that – as shown above – they typically resulted in too optimistic results in the past. Until updated factors validated against top-down studies emerge, we suggest using slightly more pessimistic values than those of the literature, as follows:

1. eirf₂₀₂₀(WAN) = 0.7 (Aslan et al. 2018) + 0.1 = 0.8
2. eirf₂₀₂₀(FAN) = 0.75 (Wu 2021) + 0.1 = 0.85
3. eirf₂₀₂₀(RAN) = 0.7 (Pihkola et al. 2018) − 0.8 (Elisa 2020)
   Choose the more pessimistic and directly measured value: 0.8.

Of course, Equation (14) can be used for several years if assuming a constant reduction factor:

(15)
EIᵧ₊ₙ(X) = (eirfᵧ(X))ⁿ × EIᵧ(X)

This is a reasonable assumption for a couple of years; equation (15) should not be used for a longer time horizon anyway, given the uncertainties of the current data (see also next section) and the need for mutual validation between energy and energy intensity values in the new studies to come, which will thus hopefully decrease current uncertainties.

Transmission network = IP core network (e.g. core/metro/edge switches and routers) + access network (e.g. DSLAM)

Not included: undersea cables, data centers, home/on-site network equipment, user devices

Estimates for average transmission network electricity intensity that meet these criteria show a halving of intensity every 2 years.

Aslan’s rule
Analysis of estimates for the average electricity intensity of fixed-line internet transmission networks for data transfers from 2000 to 2015 concluded that electricity intensity (in kWh/GB) decreased by half approximately every two years over that time period (Aslan et al., 2018).

Fixed network energy intensity (2020) = 0.0065 kWh/GB
Mobile network energy intensity (2020) = 0.1 kWh/GB
Home router energy intensity (2019) = 0.025 kWh/GB

we estimate that the yearly carbon footprint of data-use by advertising and tracking services in smartphone apps in Europe is between 5 and 14 Mt CO2-eq.