((((Compute Infrastructure + Network Storage + Intra-Region Data Transfer + Intra-Region Non-compute Networking) * PUE) + (Inter-Region Data Transfer + External Data Transfer + Inter-Region Non-compute Networking + External Non-compute Networking)) * Carbon Intensity * Power Transmission Losses)
Networking is the transfer of data between devices. As detailed in Network Interface Cards, each virtual machine is associated with one or more physical NICs that facilitate networking between devices. As explained in the NIC section, these cards require power to keep them active and ready to receive or transmit data. In addition, the act of networking itself also requires power consumption, which generates further emissions. Tailpipe calculates the emissions associated with a customer’s networking by first categorizing their transfers:
- Intra-Region: data transfer within the same region of a cloud service provider.
- Inter-Region: data transfer between two regions of a cloud service provider.
- External: data transfer between the data center and customers or other cloud service providers (and vice versa), via the internet.
Tailpipe identifies which of these categories each data transfer that a customer completes falls into from the customer’s usage and billing reports. These reports identify where a data transfer begins and ends, informing Tailpipe of whether the transfer was inter- or intra-region, or external. Tailpipe only accounts for customer traffic in its calculation; monitoring and control traffic by the provider is excluded.
Intra-region Networking
As with any networked computing equipment, cloud service provider servers are connected to Ethernet switches to provide layer 2 connectivity. These switches are also connected to routers to enable layer 3 routing of packets to internal and external networks. The routers are further connected to firewalls that protect the internal network and services from malicious actors. There may also be other network equipment such as load balancers that are used in delivering intra-region networking. Transfers within and between cloud service provider regions occur on a specialized backbone network, rather than the public internet. This means that intra-region networking must be calculated differently to the external data transfers that occur via the internet.
In addition, all these elements of network equipment are shared among all customers and any operational and administrative processes run by the cloud service provider. It is therefore necessary to apportion the appropriate resource and time share of the shared networking equipment.
Intra-region transfers are measured based on a calculation of the average energy intensity of a data transfer across a network. This calculation estimates how many kilowatt-hours of power are needed to transfer 1 GB of data. Tailpipe calculated a figure of 0.0045 kWh/GB, based on a 2021 study by Ficher et al. into the CO2e generated from transfers across a backbone network. This study found an energy intensity of 0.007 kWh/GB and 0.002 kWh/GB respectively for transfers on off-peak and peak days. As there is no way of measuring actual network traffic on a cloud provider backbone, Tailpipe takes the average of these two values: 0.0045 kWh/GB.
Tailpipe then scales the 0.0045 kWh/GB figure by an energy proportionality of 13.7%. Networking equipment is not energy proportional. This means that at 100% load, the equipment is only using 10-20% more energy than at 0% load. This is because networking equipment must constantly be powered and ready to receive and send data. Tailpipe assumes an average energy proportionality of 13.7% for data center networking equipment, averaged from a meta-analysis of five studies into the energy proportionality of networking equipment conducted between 2008 and 2016 (see Appendix E). Tailpipe therefore multiplies the 0.0045 kWh/GB figure for energy consumption by the 13.7% energy proportionality, to obtain a constant energy factor of 0.0006 kWh/GB:
0.0045 * 0.137 = 0.0006 kWh/GB
This value is then multiplied by the number of GB transferred in intra-region transfers as identified in the customer’s usage and billing report, and converted to Watts:
Intra-region Networking Energy Consumption (Wh) = (0.0006 kWh * Intra-region GB of Data Transferred) / 1000
Inter-region Networking
Inter-region transfers are measured based on the same formula as intra-region transfers. This is because inter-region transfers also occur on a backbone network, and not via the internet.
Inter-region networking is therefore calculated as:
Inter-region Networking Energy Consumption (Wh) = (0.0006 kWh * Inter-region GB of Data Transferred) / 1000
External Networking
Tailpipe calculates the power consumption of external data center networking using a lower energy intensity than inter-region networking. This is because Ficher et al.’s study was based on a single backbone network, similar to the single backbone network a cloud provider uses to transfer data between data centers. External data transfers take place in a different context: across the internet core network.
Therefore, to calculate external data transfer power, Tailpipe uses an average energy consumption per GB of data transfer across the internet’s core network. This average figure is leveraged from Tailpipe’s meta-analysis of seven studies into the networking power consumption of the internet’s core network, conducted between 2014 and 2021 (see Appendix F).
This assumed figure is 0.0424 kWh/GB.
Tailpipe then scales the 0.0424 kWh/GB figure by the energy proportionality of 13.7%:
0.0424 * 0.137 = 0.0058 kWh/GB.
To calculate the customer’s power consumption from networking, Tailpipe multiplies this 0.0058 kWh/GB figure by the GB of data externally transferred by the customer, and converts to Watts:
External Networking Energy Consumption (Wh) = (0.0058 kWh * External GB of Data Transferred) / 1000
Non-compute Networking
Non-compute Networking = Regional Networking Power Consumption * GB of Regional Non-compute Networking Data Transfer
Non-compute networking refers to the data transfers that facilitate a customer’s use of a cloud service provider, that do not interact with the operational compute virtual machines. These are additional services that the customer pays their cloud service provider for. For example, uploading data into storage buckets, using monitoring software, and running threat detection. These services require power in the same way that networking between virtual machines does.
Tailpipe accounts for non-compute networking using the same regional power factors as inter-region and external networking:
Intra-region Non-compute Networking (Wh) = ((0.0006 kWh * GB of Inter-region Non-compute Data Transferred)/1000
Inter-region Non-compute Networking (Wh) = ((0.0006 kWh * GB of Inter-region Non-compute Data Transferred)/1000
External Non-compute Networking (Wh) = ((0.0058 kWh * GB of External Non-compute Data Transferred)/1000
Tailpipe uses the inter-region networking figure of 0.0006 kWh/GB for intra-region non-compute networking because the intra-region networking figure depends upon the physical hardware used by the virtual machine. Because non-compute networking does not interact with the same switches, routers, and firewalls that virtual machine networking does, Tailpipe does not include this specific calculation. Instead, the inter-regional networking figure of 0.0006 kWh/GB represents the average power consumption of transfers over a backbone network, which cloud providers use to provide non-compute networking.
