Energy Metrics For Data Networks

3.1. Power Consumption per Data Rate (PCDR)

Power Consumption per Data Rate (PCDR) measures the amount of power consumed to transmit data at a specific rate. It is expressed in watts per gigabit per second (W/(Gbps)). Using watts as the unit provides a clear understanding of how much power is required to sustain a certain data transmission rate, which is crucial for evaluating the efficiency of network devices and links.¶

The PCDR metric applies explicitly to a single link (connection between two neighboring nodes at the same layer in the network) or group of links or to the whole network as a system.¶

PCDR is calculated based on current, actual performance, not potential or theoretical capacity. It uses the actual power consumed and the actual data transmission rate during a defined measurement period, reflecting real-world operating conditions for a fair basis of comparison.¶

Environmental factors such as ambient temperature, altitude, and humidity significantly affect power consumption and, consequently, the PCDR. The testing should follow the ISO 13443 or NIST/EPA Standard. If setting those environmental variables is not possible, the environmental conditions during testing must must be measured and documented to ensure transparency:¶

Ambient Temperature: C (Centigrade)
Pressure: atm (atmoshere)
relative humidity: percentage

Formula:
          Power Consumption (W)
PCDR = -----------------------------
         Transmission Rate (Gbps)

Where:
Power Consumption (W): The average power in watts consumed by the
specified link, group of links or the network during the measurement
period.

Data Transmission Rate (Gbps): The average data rate in bits per second
transmitted over the link, group of links or the network during the
same period.

3.2. Power Usage Effectiveness (PUE)

Power Usage Effectiveness (PUE), originally used in data centers, and can be reused in the networking space. PUE is calculated as the ratio of the energy consumed by the actual networking equipment (switches, routers, etc.) to total energy consumed by the network supporting infrastructure (building, cooling, etc. This metric helps understand the efficiency of the network and supporting infrastructure.¶

Formula:
         Energy Consumed by Networking Equipment (kWh)
PUE = -----------------------------------------------------
      Total Energy Consumed by Network Infrastructure (kWh)

A good PUE is typically considered to be around 1.5 or lower.¶

1.0 to 1.2: This range is considered excellent. It means that almost all the energy consumed by the network is used for data transmission (network equipment), with very little energy wasted on cooling, lighting, and other non-IT systems. Achieving this level typically requires efficient energy management practices.¶

1.2 to 1.5: This is still very good and indicates a highly efficient network.¶

Above 1.5 suggests that the network has room for improvement in its energy efficiency. A higher PUE means inefficient network equipment (older generation) and there is lot of room for improvement.¶

The goal is to get as close to 1.0 as possible, indicating that nearly all the energy is being used directly for network operations. However, achieving extremely low PUE values can be challenging and may involve substantial investments in energy-efficient infrastructure.¶

3.3. Network Equipment Energy Efficiency (NEEE)

Network Equipment Energy Efficiency (NEEE) measures the energy efficiency of network devices such as switches, routers, etc. It is calculated as the ratio of data throughput (bits per second) to the power consumption (watts), expressed in bits per second per watt (bps/W). This metric provides insight into how efficiently a network device can forward data relative to the power it consumes.¶

Data Throughput (Gbps): The actual, measured data rate at which the network device is forwarding data during the measurement period. It's essential to specify the exact bandwidth involved because NEEE can vary significantly with different throughput levels. For meaningful and comparable results, measurements should be taken at defined bandwidth levels that reflect typical operational scenarios, such as:¶

Idle State (0 bps): When the device is powered on but not forwarding any data.¶

Low Utilization: A percentage (15%) of the device's maximum forwarding capacity.¶

Medium Utilization: 50% of maximum capacity.¶

High Utilization: Near the device's maximum forwarding capacity (90%).¶

Idle Power Consumption: Even when not actively forwarding data, network devices consume a baseline amount of power (idle power) to stay operational. This idle power consumption contributes to the overall energy usage and should be considered when evaluating energy efficiency.¶

Importance of Measuring at Specific Bandwidth Levels:¶

Load-Dependent Efficiency: NEEE can vary depending on the network device's load. Devices may be more efficient at certain throughput levels due to factors like hardware design and power scaling features.¶

For fair comparisons, NEEE should be measured under standardized conditions, as described in Standard Testing Conditions (STC), including specified bandwidth levels.¶

Formula:

        Data Throughput (Gbps)
NEEE = -----------------------
        Power Consumption (W)

3.4. Energy Proportionality Coefficient (EPC)

Energy proportionality coefficient is significant in energy efficiency metrics because network devices rarely operate at maximum capacity continuously, so metrics must account for varying levels of utilization to provide a realistic assessment. By incorporating energy proportionality into metrics like the Network Equipment Energy Efficiency (NEEE), evaluations can reflect a device's performance across different operational states, from idle to peak throughput. Since devices consume a baseline amount of power even when not actively processing data, energy proportionality aims to minimize this idle consumption. Designing devices that consume significantly less power at low loads improves overall energy efficiency, which is especially beneficial in networks with fluctuating traffic patterns.¶

Energy proportionality offers significant benefits, including reduced energy consumption and improved device efficiency. By lowering power consumption during periods of low network activity, organizations achieve operational savings through lower energy bills and contribute to environmental sustainability by decreasing their carbon footprint and aligning with sustainability goals. Additionally, devices designed with energy proportionality in mind operate efficiently across all workloads, ensuring optimal performance. Reduced thermal stress from lower power usage can also lead to an extended hardware lifespan, enhancing the longevity and reliability of the equipment.¶

Definition: A metric that quantifies how closely a device's power consumption scales with its workload.¶

Calculation:

        Power Consumption at Given Load − Idle Power Consumption
EPC = ------------------------------------------------------------
        Maximum Power Consumption − Idle Power Consumption

Interpretation: An EPC value closer to 1 indicates better energy proportionality at that specific load level.¶

Standardized Testing Conditions: Ensure consistent environmental factors per STC during testing.¶

Workload Profiles: Use realistic traffic patterns to simulate different network conditions using consistent device physical (number of physical links inserted) and logical configuration.¶

Data Collection: Record power consumption and throughput at each workload level to compute NEEE and EPC.¶