SPRING Y. Liu
Internet Draft China Mobile
Intended status: Standards Track C. Lin
Expires: September 03, 2025 New H3C Technologies
March 03, 2025
Computing Energy Consumption Path in Segment Routing Networks
draft-liu-spring-sr-policy-energy-efficiency-00
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.
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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.............................5
5.2. Path Calculation Based on Energy Consumption..............6
5.3. Issuance of Path..........................................6
6. Procedures.....................................................6
6.1. Energy Consumption Collection.............................6
6.2. Path calculation based on Energy Consumption..............7
6.3. Data Planes...............................................7
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................................10
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
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.
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[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
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
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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.
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.
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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
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.
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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.
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
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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. 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.
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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.
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.
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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,
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.
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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>.
[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
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Authors' Addresses
Yisong Liu
China Mobile
China
Email: liuyisong@chinamobile.com
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
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