SPRING                                                           Y. Liu
Internet Draft                                             China Mobile
Intended status: Standards Track                                 C. Lin
Expires: April 12, 2026                            New H3C Technologies
                                                                R. Chen
                                                        ZTE Corporation
                                                                  J. Li
                                                           China Mobile
                                                       October 11, 2025


       Computing Energy Consumption Path in Segment Routing Networks
              draft-liu-spring-sr-policy-energy-efficiency-02


Abstract

   This document describes a method for computing energy consumption
   paths in Segment Routing (SR) networks, aiming to optimize network
   traffic routing for energy efficiency, including procedures for
   energy consumption data collection, path calculation, and issuance,
   as well as considerations for data plane implementation in both MPLS
   SR and SRv6 networks.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on April 12, 2026.






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Copyright Notice

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Table of Contents


   1. Introduction...................................................2
      1.1. Requirements Language.....................................3
   2. Terminology....................................................3
   3. Background.....................................................3
   4. Energy consumption.............................................4
   5. Mechanism......................................................5
      5.1. Energy Consumption Collection.............................6
      5.2. Path Calculation Based on Energy Consumption..............6
      5.3. Issuance of Path..........................................6
   6. Procedures.....................................................7
      6.1. Energy Consumption Collection.............................7
      6.2. Path calculation based on Energy Consumption..............7
      6.3. Path seletion based on Energy Consumption.................7
      6.4. Data Planes...............................................8
   7. Use Case.......................................................8
      7.1. Path Calculation Based on Maximum Energy Consumption......8
      7.2. Path Calculation Based on Average Energy Consumption......9
   8. IANA Considerations...........................................10
   9. Security Considerations.......................................10
   10. References...................................................10
      10.1. Normative References....................................10
      10.2. Informational References................................11
   Authors' Addresses...............................................11

1. Introduction

   The importance of energy consumption in modern networks is
   increasingly evident. In addition to reducing the power consumption
   of devices, network technologies can be leveraged to redirect


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   traffic towards energy-efficient devices and paths, effectively
   lowering the energy consumption of network communications.

   [draft-cx-green-green-metrics] outlines a variety of metrics that
   can be utilized to assess energy consumption. However, the intricate
   details of these metrics extend beyond the scope of this document.

   [RFC9252] defines the fundamental architecture and operational
   principles of Segment Routing (SR) and describes the SR network
   programming model, which enables flexible network path control
   through the definition of Segment Identifiers (SIDs). This document
   focuses on path computation based on energy consumption information
   and utilizes SR to implement energy-aware path control.



1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2. Terminology

   TBD.

3. Background

   In the modern digital era, network energy consumption has become a
   critical focus, driven by the growing demand for sustainable
   practices and the need to reduce operational costs. Networks consume
   substantial energy, leading to carbon emissions and environmental
   degradation. Optimizing energy usage helps reduce their carbon
   footprint and supports global efforts to combat climate change.
   Energy is a major operational expense for network operators, and
   improving efficiency directly lowers electricity costs, especially
   in large-scale networks, resulting in significant financial savings.
   As network traffic grows exponentially, energy-efficient designs
   ensure sustainable scalability without proportional increases in
   energy consumption, which is essential for supporting future
   technologies such as 5G, IoT, and cloud computing.

   The source routing characteristics of SR make it a flexible,
   scalable, and efficient networking technology. By simplifying
   network control, enabling explicit path definition, and ensuring
   compatibility with existing technologies, SR meets the demands of

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   modern networks for traffic engineering, fault recovery, and
   scalability while reducing complexity and overhead. Additionally, SR
   networks support network slicing, allowing the creation of
   independent paths for different service types.

   SR networks can be utilized for energy-efficient path optimization
   in large-scale networks and seamlessly integrate with existing
   IPv4/IPv6 infrastructures. By collecting energy consumption data
   from each node and link, SR enables the planning of energy-efficient
   paths based on routing policies, thereby achieving the goal of
   reducing overall network energy consumption.

   The motivations for addressing energy consumption in SR networks
   include, but are not limited to:

       Reducing energy consumption in network communications by
       selecting energy-efficient paths and leveraging energy-related
       information associated with SR paths and policies.

       Allowing the source node or controller/PCE to use energy
       consumption metrics as constraints and optimization criteria for
       path computation, thereby optimizing the routing of network
       communications.

4. Energy consumption

   Based on the scope of energy consumption measurement, it includes
   overall device energy consumption, board-level energy consumption,
   and interface-level energy consumption. Since routing protocols
   typically use node-level or interface-level energy consumption
   information for path selection, energy consumption measurements can
   be conducted at the overall device or board level. However, when
   advertising the information, board-level energy consumption can be
   converted into corresponding interface-level information for
   dissemination.

   Energy consumption metrics, measured in watts per gigabyte (W/GB),
   indicate the energy consumed for every gigabyte of data transmitted.
   Based on the measurement objectives, these metrics can be classified
   into the following types: maximum energy consumption, real-time
   energy consumption.

      1) Maximum Energy Consumption: The energy consumed per unit of
         traffic when the device operates at maximum load.

      2) Real-Time Energy Consumption: The energy consumed per unit of
         traffic under current operating conditions.


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   The first metric is a static parameter of the device, while the
   second one is a dynamic parameter that requires real-time
   measurement and dissemination.

   When the device is not currently forwarding traffic, the real-time
   energy consumption is meaningless. In such cases, maximum energy
   consumption can be used to calculate the path.

   Differentiating by the scope of energy consumption testing, it
   includes overall energy consumption and interface energy
   consumption.

      1) overall energy consumption: Measuring energy consumption of the
         device as a whole.

      2) Energy consumption by interface: Measuring energy consumption
         at the granularity of interfaces. Generally, measuring energy
         consumption by interface is challenging to implement on
         devices, so a rough measurement can be conducted on the entire
         board and then averaged for each interface.

5. Mechanism

   The framework of computing energy consumption path in SR networks:
   The controller centrally collects energy consumption information
   from all nodes within the SR network domain, computes the most
   energy-efficient path uniformly, and distributes the optimized path
   as SR-policy to head end.

                             +------------------+
                    +--------|Network Controller| Energy Consumption
                    |        +--------/|\-------+
                    |                  |
                SR-Policy    Energy Consumption Collection
                    |                  |
                 +-\|/-+   +-----------|-----------+   +-----+
       Handling  |Head |---|    Segment Routing    |---|End  |
       behaviors |Point|   |    Network Domain     |   |Point|
                 |     |   |  PE ----- P ------ PE |   |     |
                 +-----+   +-----------------------+   +-----+

     Figure 1. Framework of Computing Energy Consumption path in SR
   network






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5.1. Energy Consumption Collection

   Energy consumption information is disseminated and collected within
   a SR network domain through IGP protocol extensions. In inter-domain
   scenarios, it can be propagated and collected using BGP protocol
   extensions by BGP-LS extensions.

   Energy consumption information is collected between the SR network
   domain and the Network Controller using methods such as YANG,
   NETCONF, and SNMP.

   The specific information classification of Energy consumption is
   detailed in section 4.

5.2. Path Calculation Based on Energy Consumption

   The network controller selects network paths based on the collected
   energy consumption information and calculates the paths according to
   the specified policy. During the calculation, both node energy
   consumption and link energy consumption are considered. If the
   device advertises link energy consumption, it is prioritized;
   otherwise, node energy consumption is used.

   These consumption metrics may include maximum energy consumption,
   real-time energy consumption. When selecting energy consumption
   parameters, if the device is currently forwarding traffic, the real-
   time energy consumption is used as the energy consumption parameter
   for path selection. When the device is not forwarding traffic, the
   maximum energy consumption is used.

   During the calculation process, nodes and links that do not meet the
   energy consumption criteria are excluded, and the path with the
   lowest energy consumption is prioritized for selection.

5.3. Issuance of Path

   The network controller distributes path to the head end. This
   distribution can be performed using YANG, BGP or PCEP. The head end
   then conducts network forwarding based on the distributed SR-Policy.
   When using YANG, BGP and PCEP, necessary expansions for the energy
   consumption metric should be made.







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6. Procedures

6.1. Energy Consumption Collection

   Energy consumption information can be integrated into network
   topology as attributes of nodes and links, serving as criteria for
   routing calculations.

   Energy consumption information can be directly reported to the
   controller by each node through the NETCONF reporting mechanism.

   Alternatively, energy consumption information can be propagated
   within the domain through IGP flooding and then reported to the
   controller via BGP-LS at a designated point. To prevent frequent
   changes in energy consumption information from causing excessive
   updates to IGP LSPs, a refresh interval must be established, during
   which the energy consumption information in the LSP remains
   unchanged. If the refresh interval is too long, the energy
   consumption information may become outdated; if it is too short, it
   could lead to frequent LSP flooding.

6.2. Path calculation based on Energy Consumption

   When performing routing calculations, the controller can adopt
   various strategies based on energy consumption metrics. It may
   exclude nodes and links with excessively high maximum energy
   consumption, filter out those with high traffic-related energy
   consumption, or eliminate nodes and links with significant energy
   consumption fluctuation rates. The specific strategy can rely on a
   single energy consumption parameter or a combination of multiple
   parameters for decision-making.

   When planning paths, the network can be divided into different
   topologies using Flex-Algo and Multi-Topo technologies to
   accommodate varying energy consumption requirements.

   To prevent traffic oscillation, the controller must set a threshold
   when calculating paths based on energy consumption information.
   Traffic will only be switched to a new path if the calculated energy
   consumption change exceeds this threshold.

6.3. Path seletion based on Energy Consumption

   Calculate N optimal paths using traditional metrics such as
   bandwidth, delay, and packet loss rate. Then compute energy
   consumption values for these paths, such as maximum energy
   consumption along the path and additional energy consumption.
   Finally, select the energy-optimal path from these N paths based on

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   an energy-aware routing strategy. The difference from section 6.2 is
   that path planning still relies on traditional metrics to compute
   multiple candidate paths, and then selects the best path based on
   energy consumption.

6.4. Data Planes

   After the controller performs routing calculations and generates the
   path, it can deliver the path to the headend via PCEP or NETCONF.
   Depending on the data plane, the generated path can be implemented
   as an SR-Policy or SRv6-Policy.

   For an MPLS SR network, during route calculation, energy consumption
   information is combined with node label and adjacent label
   information. By specifying node labels and adjacent labels, nodes
   and links can be selected while excluding those with high energy
   consumption.

   For SRv6 networks, during route calculation, energy consumption
   information is combined with node SIDs and adjacent End.X SIDs. By
   specifying node SIDs and adjacent End.X SIDs, nodes and links can be
   selected while excluding those with high energy consumption.

7. Use Case

7.1. Path Calculation Based on Maximum Energy Consumption

                             +------------------+
                    +--------|Network Controller|
                    |        +------------------+
                    |
                    |
                    |                 Max:10
                 +-\|/-+     +---------P1-------+    +-----+
                 |     |   10|                  |10  |     |
                 |Head |--- PE1                PE2---|End  |
                 |Point|     |      Max:15      |    |Point|
                 +-----+     +---------P2-------+    +-----+



        When calculating the energy consumption path based on maximum
        energy consumption, the path computation is performed using the
        node energy consumption, interface energy consumption, or board
        energy consumption information published by each node.

        The maximum energy consumption is a fixed value and does not
        require dynamic measurement or updates.

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        During the energy consumption path calculation, both primary
        and backup paths are supported.

        In the diagram, the maximum energy consumption of P1 is 10,
        while that of P2 is 15. Therefore, the computed primary path is
        PE1 -> P1 -> PE2, and the backup path is PE1 -> P2 -> PE2.

        In the event of a failure on the primary path, such as a fault
        in P1, traffic is quickly switched to the backup path PE1 -> P2
        -> PE2 for forwarding.



7.2. Path Calculation Based on Average Energy Consumption

                             +------------------+
                    +--------|Network Controller|
                    |        +------------------+
                    |
                    |                Real:10
                    |                Real:20
                    |                Real:30
                 +-\|/-+     +---------P1-------+    +-----+
                 |     | 10  |                  |10  |     |
                 |Head |--- PE1                PE2---|End  |
                 |Point|     |      Real:15     |    |Point|
                 +-----+     +---------P2-------+    +-----+


   When calculating the energy consumption path based on the real-time
   energy consumption, the path computation is performed using the node
   energy consumption, interface energy consumption, or board energy
   consumption information published by each node.

   During the energy consumption path calculation, both primary and
   backup paths are supported. In the event of a failure on the primary
   path, traffic can be quickly switched to the backup path.

   In the diagram, the real-time energy consumption of P2 is 15, while
   that of other devices is 10. The primary path is calculated as PE1
   -> P1 -> PE2, with a path energy consumption of 30, and the backup
   path is PE1 -> P2 -> PE2, with a path energy consumption of 35.

   If the primary path fails, such as a fault in P1, traffic is quickly
   switched to the backup path PE1 -> P2 -> PE2 for forwarding.

   When the path energy consumption changes, the path energy
   consumption must be recalculated. To avoid traffic oscillation,

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   switching to a new path is only triggered when the energy
   consumption of the new path falls below a threshold relative to the
   original path.

   For example, we set the threshold to 80%, meaning the new path is
   only adopted if its energy consumption is less than 80% of the
   original path.

   For instance, when the energy consumption of P1 increases to 20, the
   energy consumption of PE1 -> P1 -> PE2 becomes 40, while that of PE1
   -> P2 -> PE2 remains 35. At this point, the backup path energy
   consumption is 87.5% of the original path, which does not meet the
   80% threshold, so no path switch occurs.

   However, when the energy consumption of P1 further increases to 30,
   the original path energy consumption becomes 50, and the backup path
   energy consumption is now 70% of the original path. This triggers a
   path switch, and the controller updates the primary path to PE1 ->
   P2 -> PE2 and the backup path to PE1 -> P1 -> PE2.

8. IANA Considerations

   This document does not have any IANA requests.

9. Security Considerations

   TBD.



10. References

10.1. Normative References

   [draft-cx-green-green-metrics] A. Clemm, Ed., Santa Clara
             University, C. Pignataro, Ed., NC State University, E.
             Schooler, University of Oxford, L. Ciavaglia, A. Rezaki,
             Nokia, G. Mirsky, Ericsson, J. Tantsura, Nvidia, "Green
             Networking Metrics for Environmentally Sustainable
             Networking", draft-cx-green-green-metrics, DOI
             10.17487/draft-cx-green-green-metrics, October 2024,
             <https://www.rfc-editor.org/info/draft-cx-green-green-
             metrics>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
             Decraene, B., Litkowski, S., and R. Shakir, "Segment
             Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
             July 2018, <https://www.rfc-editor.org/info/rfc8402>.

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   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
             A., and P. Mattes, "Segment Routing Policy Architecture",
             RFC 9256, DOI 10.17487/RFC9256, July 2022,
             <https://www.rfc-editor.org/info/rfc9256>.

10.2. Informational References

   TBD

Authors' Addresses

   Yisong Liu
   China Mobile
   China
   Email: liuyisong@chinamobile.com

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com


   Ran Chen
   ZTE Corporation
   Email: chen.ran@zte.com.cn

   Jinming Li
   China Mobile
   32 Xuanwumen West Street
   Beijing
   Xicheng District, 100053
   China
   Email: lijinming@chinamobile.com















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