Proposed Sustainability and the Internet Proposed Research GroupA. Gallego Sanchez Internet-Draft Deutsche Telekom Intended status: Informational A. Rodriguez-Natal Expires: 1 September 2026 Cisco L. M. Contreras Telefonica M. Palmero J. Lindblad All For Eco February 2026 Sustainability holistic API for Path Energy Evaluation (SHAPE) draft-amalj-sustain-shape-03 Abstract This document describes an API to query a network regarding its Energy Traffic Ratio and other sustainability-related metrics for a given network path. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://galledohm.github.io/draft-amalj-sustain-shape/draft-amalj- sustain-shape.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-amalj-sustain-shape/. Discussion of this document takes place on the Proposed Sustainability and the Internet Proposed Research Group Research Group mailing list (mailto:sustain@irtf.org), which is archived at https://mailarchive.ietf.org/arch/browse/sustain/. Subscribe at https://www.ietf.org/mailman/listinfo/sustain/. Source for this draft and an issue tracker can be found at https://github.com/galledohm/draft-amalj-sustain-shape. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Gallego Sanchez, et al. Expires 1 September 2026 [Page 1] Internet-Draft Sustainability Network-API February 2026 Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 5 August 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Sustainability holistic API for Path Energy Evaluation (SHAPE) . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Energy Information . . . . . . . . . . . . . . . . . . . 5 3.2. Recursive Usage . . . . . . . . . . . . . . . . . . . . . 7 4. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. Module Structure . . . . . . . . . . . . . . . . . . . . 9 4.2. Module Definition . . . . . . . . . . . . . . . . . . . . 9 5. Operational Considerations . . . . . . . . . . . . . . . . . 16 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 8.1. Normative References . . . . . . . . . . . . . . . . . . 19 8.2. Informative References . . . . . . . . . . . . . . . . . 20 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 21 Appendix A. Use Cases . . . . . . . . . . . . . . . . . . . . . 21 A.1. SD-WAN . . . . . . . . . . . . . . . . . . . . . . . . . 22 A.2. Multilayer Energy Management . . . . . . . . . . . . . . 23 A.3. SLA Negotiation for Green Services . . . . . . . . . . . 23 A.4. Energy-Aware UPF and Edge Selection in 5G . . . . . . . . 24 A.5. Sustainability Reporting Across Leased Backhaul and Network Sharing . . . . . . . . . . . . . . . . . . . . . . . . . 24 Gallego Sanchez, et al. Expires 1 September 2026 [Page 2] Internet-Draft Sustainability Network-API February 2026 Appendix B. Requirements for Energy Efficiency Management . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction Sustainability is becoming one of the major societal goals for the next decade, and networks are one of the major consumers of energy nowadays. Sustainability of network services is thus one of the forefronts of innovation and action from network service stakeholders, involving manufacturers, operators and customers. In this line, there is a shared goal of achieving better energy and carbon awareness. As with any other network metric, the energy traffic ratio could be collected from the underlying network infrastructure. However, there is not a common or single definition of energy and sustainability metrics towards network consumers so that they can be uniformly reported, particularly in heterogeneous network scenarios. This document introduces an API to query networks about the Energy Traffic Ratio. Beyond simple efficiency indicators such as Watts per Gigabit, network stakeholders are increasingly interested in richer sustainability information, such as carbon intensity, energy mix, idle energy draw, transmission losses, and cooling overheads (e.g., Cooling Energy Ratio). In addition, operational and temporal aspects matter: the ability of a path to spend time in low-power states (Sleep-mode Availability), the variability of carbon intensity over time (Temporal Carbon Variability), and the stability of reported sustainability behavior (e.g., Sustainability Stability Index). Finally, sustainability data is increasingly used for automated decision-making and assurance (e.g., in green SLAs), which introduces a need for indicators of data quality and robustness. Metrics such as variance of energy consumption (VEC), anomaly detection signals (e.g., Anomaly Factor), and a trustworthiness score of data sources (TDS) help distinguish persistent characteristics from transient conditions and support more reliable sustainability reporting and policy enforcement. 2. Conventions and Definitions 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. Gallego Sanchez, et al. Expires 1 September 2026 [Page 3] Internet-Draft Sustainability Network-API February 2026 3. Sustainability holistic API for Path Energy Evaluation (SHAPE) This document describes an API to query a network about several sustainability-related metrics for a given path. SHAPE extends PETRA as defined in [I-D.petra-green-api] with additional sustainability metrics. It reuses PETRA endpoint identifiers for source and destination (e.g., IP address, IP prefix, MAC address, or slice SDP identifier) and PETRA traffic characterization (i.e., throughput, or time-window plus transmitted data volume), and returns sustainability information related to the traffic on the path. This is energy computed by the infrastructure that is dynamically part of the traffic path. The API is agnostic to the actual hops and underlying infrastructure that enables a path, which might change transparently to the API. This document only describes the API; the computation of the energy information to return is out of the scope of this document. The API can return a variety of energy-related parameters to provide a complete view of path sustainability. These include PETRA baseline efficiency indicators (e.g., Watts per Gigabit) and SHAPE-specific sustainability extensions (e.g., carbon intensity, energy mix, transmission losses, idle energy draw, cooling overheads, and the availability of low-power states such as sleep modes). For authoritative sustainability comparison and optimization, carbon- intensity and temporal variability indicators are the primary actionable metrics. In addition to point-in-time values, the API can expose temporal and assurance-oriented information, such as the variability of carbon intensity over a defined observation window, stability indices for sustainability behavior (e.g., Sustainability Stability Index), statistical measures of energy variability, anomaly signals, and indicators of confidence in the underlying data sources. Such metrics can help consumers distinguish persistent characteristics from transient fluctuations. Furthermore, the SHAPE's energy parameters complement ongoing work on green service intents [I-D.irtf-nmrg-ibn-usecases], enabling customers to express sustainability objectives such as energy consumption thresholds, renewable energy usage, and carbon intensity limits. SHAPE provides the underlying energy measurement interface necessary for providers to fulfill, assure, and report on these green intents. Moreover, by exposing detailed energy and carbon-related parameters, SHAPE can allow intent translation components to map green service objectives into network resource allocation and path selection decisions. Gallego Sanchez, et al. Expires 1 September 2026 [Page 4] Internet-Draft Sustainability Network-API February 2026 3.1. Energy Information This API allows to return a number of energy attributes associated with the path and the traffic. PETRA defines the base query and baseline energy metric (Watts per Gigabit); SHAPE augments PETRA with additional sustainability metrics emphasizing carbon impact and operational variability. Currently the parameters that could be returned as energy information as part of the query are: * *Watts per Gigabit:* (Inherited from PETRA) How many Watts are consumed per Gigabit of traffic traversing the path. * *Carbon Intensity:* How much carbon emissions (e.g., gCO2e/kWh) are generated as a consequence of the energy consumed. This is the primary actionable metric for sustainability-aware routing and policy enforcement. * *Energy Mix (%):* Percentage of energy used in the path that comes from different energy sources (e.g., solar, wind, biomass, nuclear, fossil fuel). Comparability of renewable percentages across paths may be limited by measurement scope, time window, and accounting/certification boundaries. * *Greenness Degree (%):* The aggregated percentage of energy consumed on the path that comes from renewable sources. This metric can support policy-driven reporting, but by itself does not fully characterize carbon impact across operators or countries. * *Sustainability Score (0–1):* (Informative) Composite metric combining greenness degree and energy efficiency. This can be used as an implementation-specific ranking aid, but carbon- intensity and temporal variability metrics are recommended for authoritative sustainability assessment. * *Transmission Loss (%):* The percentage of energy lost along the path due to transmission inefficiencies. * *Idle Energy Draw (Watts):* The amount of energy consumed by the path infrastructure when idle or under negligible load. * *Temporal Carbon Variability (TCV) (gCO2/kWh over period):* Quantifies how much the carbon intensity of the electricity powering the network path fluctuates over a defined time window (e.g., 15 minutes, 1 hour, 24 hours). It reflects the stability or volatility of the renewable/fossil mix affecting the path during that period. A low TCV indicates predictable carbon characteristics; a high TCV suggests inconsistent or rapidly changing energy sources. Gallego Sanchez, et al. Expires 1 September 2026 [Page 5] Internet-Draft Sustainability Network-API February 2026 * *Sleep-mode Availability (%):* Measures the percentage of time during which network devices or segments along a path support and can enter low-power or idle energy-saving modes. It can also reflect real usage of these modes depending on the operator’s instrumentation (when supported or/and instrumented). * *Sustainability Stability Index (SSI) (0–1):* Quantifies the stability over time of a sustainability metric (i.e., carbon intensity or greenness degree), it is particularly relevant for gSLAs, where predictable sustainability performance matters as much as absolute values. Values close to 1 indicate highly stable behavior. * *Trustworthiness Score of Data Sources (TDS) (0–1):* characterizes how reliable the API’s sustainability-related data is, based on provenance, measurement quality, freshness, and cross-source consistency. Higher values indicate stronger confidence in the reported data. * *Variance of Energy Consumption (VEC) (W^2):* VEC measures how much the energy use of the path fluctuates during an observation window. It helps detect energy instability, noisy equipment, or poorly tuned power-management algorithms. High VEC indicates unstable or erratic energy usage; low VEC indicates consistent energy behavior. * *Anomaly Factor (AF) (z-factor):* Identifies whether the energy usage of a path at a given moment deviates significantly from its historical baseline or expected statistical behavior, normalized by standard deviation. AF < 1 indicates normal behavior, AF around 2 indicates elevated deviation, and AF > 3 indicates an anomaly (classic 3-sigma rule). * *Cooling Energy Ratio (CER) (%):* Quantifies the share of total energy consumed by a path or segment that is attributable to cooling rather than networking/IT workload. It is a path- or segment-level metric rather than a facility-wide efficiency metric. Higher values indicate higher cooling overhead relative to useful forwarding energy. These metrics are OPTIONAL, and an implementation MAY support a subset depending on available measurement capabilities. Gallego Sanchez, et al. Expires 1 September 2026 [Page 6] Internet-Draft Sustainability Network-API February 2026 3.2. Recursive Usage The API is envisioned in such a way that could be used recursively. That means, subpaths could report their energy consumption using SHAPE and such energy consumption could be aggregated and reported for the overall path also using SHAPE. Similarly, this API could be (recursively) used to provide energy information according to the definition of Service Models in an SDN context as described in [RFC8309]. In that case, using Figure 3 in [RFC8309] as reference, SHAPE could be used between the Controller(s) and the Network Orchestrator(s), between the Network Orchestrator(s) and the Service Orchestrator, and between the Service Orchestrator and the Customer(s). While considering recursive usage, the aspect of double-counting shall also be taken into consideration. Double counting refers to the fact of counting more than once the same energy consumed. Organizations using SHAPE in a recursive manner need to take appropriate measures to ensure no double-counting occurs across recursive calls to the API. Gallego Sanchez, et al. Expires 1 September 2026 [Page 7] Internet-Draft Sustainability Network-API February 2026 Customer ------------------ Service ---------- | | Model | | SHAPE as | Service |<-------->| Customer | Customer Service | Orchestrator | (a) | | related API | | ---------- ------------------ . . ########################## . . (b) ----------- . (b) . ......|Application| . . : | BSS/OSS | SHAPE as . . : ----------- Service related API . Service Delivery . : . Model . : ------------------ ------------------ | | | | ############# | Network | | Network | | Orchestrator | | Orchestrator | | | | | .------------------ ------------------. SHAPE as . : : . Network API . : Network Configuration : . . : Model : . ------------ ------------ ------------ ------------ | | | | | | | | ### | Controller | | Controller | | Controller | | Controller | | | | | | | | | ------------ ------------ ------------ ------------ : . . : : : . . Device : : : . . Configuration : : : . . Model : : --------- --------- --------- --------- --------- | Network | | Network | | Network | | Network | | Network | | Element | | Element | | Element | | Element | | Element | --------- --------- --------- --------- --------- 4. YANG Module SHAPE is specified as an augmentation to the PETRA YANG module defined in [I-D.petra-green-api]. This section provides an example YANG module, as per the YANG specification [RFC7950], that imports PETRA and augments it with additional inputs and metrics. Gallego Sanchez, et al. Expires 1 September 2026 [Page 8] Internet-Draft Sustainability Network-API February 2026 SHAPE reuses PETRA input and output structures. In particular, source and destination are modeled using PETRA endpoint identifier choices, traffic is characterized using PETRA traffic alternatives, and SHAPE adds optional sustainability metrics on top of PETRA successful query output. 4.1. Module Structure module: ietf-shape +--imports ietf-petra augment /petra:energy/petra:query/petra:input: +---w measurement-interval? uint32 +---w recursive? boolean augment /petra:energy/petra:query/petra:output/petra:result/petra:success: +--ro shape-metrics +--ro carbon-intensity? uint32 +--ro energy-mix* -> list of sources and percentages +--ro greenness-degree? decimal64 +--ro sustainability-score? decimal64 +--ro transmission-loss? decimal64 +--ro idle-watts? decimal64 +--ro temporal-carbon-variability? decimal64 +--ro sleep-mode-availability? decimal64 +--ro sustainability-stability-index? decimal64 +--ro trustworthiness-score? decimal64 +--ro variance-energy-consumption? decimal64 +--ro anomaly-factor? decimal64 +--ro cooling-energy-ratio? decimal64 4.2. Module Definition module ietf-shape { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-shape"; prefix shape; import ietf-petra { prefix petra; } organization "IRTF SUSTAIN Research Group"; contact "RG Web: RG List: "; description Gallego Sanchez, et al. Expires 1 September 2026 [Page 9] Internet-Draft Sustainability Network-API February 2026 "Initial YANG module for SHAPE API, v1.0.0 SHAPE extends the PETRA YANG module ('draft-petra-green-api') with additional optional sustainability-related metrics and, where needed, additional input parameters to qualify observation windows. Copyright (c) 2026 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here. "; /* If you have an implementation of this YANG module, you could access it like something this over RESTCONF: $ curl --location --request POST \ 'https://localhost:8008/restconf/operations/ietf-shape:energy/query' \ --header 'Content-Type: application/yang-data+json' \ --user 'admin:admin' \ --data-raw '{ "input" : { "source": { "ip-prefix": "10.10.10.0/24" }, "destination": { "ip-prefix": "10.20.20.0/24" }, "throughput": 40, "measurement-interval": 900, "recursive": false Gallego Sanchez, et al. Expires 1 September 2026 [Page 10] Internet-Draft Sustainability Network-API February 2026 } }' And if all goes well, you might receive (besides all the HTTP headers) a reply body with something like this: { "output": { "success": { "watts-per-gigabit": 191.855, "shape-metrics": { "carbon-intensity": 108, "energy-mix": [ { "source": "solar", "percentage": 35.00 }, { "source": "wind", "percentage": 25.00 }, { "source": "gas", "percentage": 40.00 } ], "greenness-degree": 60.00, "sustainability-score": 0.312, "transmission-loss": 3.50, "idle-watts": 12.500, "temporal-carbon-variability": 14.250, "sleep-mode-availability": 20.00, "sustainability-stability-index": 0.880, "trustworthiness-score": 0.950, "variance-energy-consumption": 1.750, "anomaly-factor": 0.420, "cooling-energy-ratio": 15.00 } } } } */ revision 2026-02-26 { description "Initial SHAPE augmentation of PETRA, adding additional sustainability metrics (including temporal/stability and trustworthiness indicators)."; reference "RFC XXXX: ..."; } // ===== Groupings ===== grouping shape-metrics { description "Additional sustainability metrics defined by SHAPE that extend Gallego Sanchez, et al. Expires 1 September 2026 [Page 11] Internet-Draft Sustainability Network-API February 2026 the base PETRA query output."; leaf carbon-intensity { type uint32 { range "0..max"; } units "gCO2e/kWh"; description "Carbon intensity of the electricity powering the path."; } list energy-mix { key "source"; description "Percentage contribution of each energy source to the total energy used on the path."; leaf source { type enumeration { enum solar { description "Energy sourced from solar generation."; } enum wind { description "Energy sourced from wind generation."; } enum hydro { description "Energy sourced from hydroelectric generation."; } enum nuclear { description "Energy sourced from nuclear generation."; } enum coal { description "Energy sourced from coal-based generation."; } enum gas { description "Energy sourced from gas-based generation."; } enum biomass { description "Energy sourced from biomass generation."; } enum other { description "Energy sourced from other or unspecified generation."; Gallego Sanchez, et al. Expires 1 September 2026 [Page 12] Internet-Draft Sustainability Network-API February 2026 } } description "Type of energy source."; } leaf percentage { type decimal64 { fraction-digits 2; range "0..100"; } units "%"; description "Percentage of path energy from this source."; } } leaf greenness-degree { type decimal64 { fraction-digits 2; range "0..100"; } units "%"; description "Aggregated percentage of energy from renewable sources. This metric is not always directly comparable across domains and accounting boundaries; carbon-intensity is the primary cross-domain sustainability metric."; } leaf sustainability-score { type decimal64 { fraction-digits 3; range "0..1"; } description "Informative composite metric combining greenness degree and energy efficiency for implementation-specific ranking. Carbon-intensity and temporal variability metrics are RECOMMENDED for authoritative sustainability assessment."; } leaf transmission-loss { type decimal64 { fraction-digits 2; range "0..100"; } units "%"; description Gallego Sanchez, et al. Expires 1 September 2026 [Page 13] Internet-Draft Sustainability Network-API February 2026 "Energy lost in transmission as percentage of total energy input."; } leaf idle-watts { type decimal64 { fraction-digits 3; range "0..max"; } units "W"; description "Energy consumed by the path infrastructure when idle."; } leaf temporal-carbon-variability { type decimal64 { fraction-digits 3; range "0..max"; } units "gCO2e/kWh"; description "Quantifies how much the carbon intensity powering the path fluctuates over an observation window (e.g., 15 minutes, 1 hour, 24 hours)."; } leaf sleep-mode-availability { type decimal64 { fraction-digits 2; range "0..100"; } units "%"; description "Percentage of time during which devices or segments on the path can enter low-power or idle energy-saving modes (when supported and instrumented)."; } leaf sustainability-stability-index { type decimal64 { fraction-digits 3; range "0..1"; } description "Index (0..1) capturing the stability over time of a sustainability metric (e.g., carbon intensity or greenness degree)."; } leaf trustworthiness-score { type decimal64 { fraction-digits 3; Gallego Sanchez, et al. Expires 1 September 2026 [Page 14] Internet-Draft Sustainability Network-API February 2026 range "0..1"; } description "Composite score (0..1) reflecting reliability of reported sustainability data, e.g., based on provenance, quality, freshness, and cross-source consistency."; } leaf variance-energy-consumption { type decimal64 { fraction-digits 3; range "0..max"; } units "W^2"; description "Variance of energy consumption over an observation window."; } leaf anomaly-factor { type decimal64 { fraction-digits 3; } units "z-score"; description "Deviation of current energy consumption from a historical mean, normalized by standard deviation (z-factor)."; } leaf cooling-energy-ratio { type decimal64 { fraction-digits 2; range "0..100"; } units "%"; description "Ratio between cooling energy and IT/network energy for a path or segment."; } } // ===== Augmentations ===== augment "/petra:energy/petra:query/petra:input" { description "Additional optional input parameters for SHAPE that qualify the observation window and, when supported, recursive collection."; leaf measurement-interval { type uint32 { range "1..max"; } units "seconds"; Gallego Sanchez, et al. Expires 1 September 2026 [Page 15] Internet-Draft Sustainability Network-API February 2026 description "Observation window used to compute time-dependent metrics (e.g., variability, stability, variance, and anomaly indicators)."; } leaf recursive { type boolean; default "false"; description "Whether the query should be expanded recursively across multiple administrative domains (if supported)."; } } augment "/petra:energy/petra:query/petra:output/petra:result/petra:success" { description "Add SHAPE sustainability metrics to the successful PETRA query result."; container shape-metrics { description "Collection of additional sustainability metrics defined by SHAPE."; uses shape-metrics; } } } 5. Operational Considerations This section highlights deployment and operation aspects for SHAPE, following the operational guidance commonly applied to network management specifications and the guidance in [I-D.ietf-opsawg-rfc5706bis]. * *Measurement method impacts:* SHAPE results can vary depending on how measurements are obtained (e.g., direct telemetry, estimates, model-based aggregation, or historical averaging). Operators SHOULD document which methods are used for each metric and SHOULD expose measurement confidence where possible. * *Traffic characterization impacts:* Query results can differ when traffic is characterized by throughput versus time-window plus transmitted volume. Implementations SHOULD document supported PETRA traffic-characterization modes and SHOULD avoid mixing incomparable measurement bases in trend analysis. * *Comparability caveat for renewable percentages:* Renewable- percentage indicators (e.g., greenness-degree) can be influenced by measurement boundaries, time windows, and accounting Gallego Sanchez, et al. Expires 1 September 2026 [Page 16] Internet-Draft Sustainability Network-API February 2026 instruments. Implementations SHOULD avoid using a single aggregated renewable percentage as the sole basis for cross-domain optimization. * *Consumer intent differences:* Operational use cases may have different requirements. Customer-facing use cases (e.g., SD-WAN sustainability visibility) generally require stability, repeatability, and clear policy constraints, while operator optimization use cases may prioritize freshness and responsiveness over strict comparability. * *Recursive aggregation and double counting:* Recursive operation across domains introduces a risk of counting the same energy contribution multiple times. Implementations SHOULD define clear aggregation boundaries (e.g., segment ownership, handoff points, or unique contribution identifiers) and SHOULD provide auditability for aggregation logic. * *Subset support and policy controls:* SHAPE metrics are optional and may be supported only partially. Implementations SHOULD make unsupported metrics explicit in operational documentation and SHOULD align metric exposure with authorization and disclosure policies. 6. Security Considerations The YANG module defined in this document augments PETRA query input and output nodes under /petra:energy/petra:query. SHAPE queries and responses can reveal operational and business-sensitive information (e.g., energy efficiency, carbon footprint, facility overheads, and potentially location- or time-correlated behavior). SHAPE API MAY be exposed via management protocols such as NETCONF [RFC6241] and RESTCONF [RFC8040] and, therefore, it inherits their security properties and deployment practices. The SHAPE input leaves measurement-interval and recursive are configuration inputs to an action invocation. Unauthorized manipulation of these inputs can increase computation cost and disclosure scope. The SHAPE output container shape-metrics exposes additional sustainability data and can reveal sensitive operational characteristics. Implementations MUST consider the following aspects: * *Secure transport:* Implementations MUST ensure confidentiality and integrity protection for SHAPE exchanges (i.e., by using secure transports mandated by the underlying management protocol). Where RESTCONF is used, HTTPS is REQUIRED by [RFC8040]. Gallego Sanchez, et al. Expires 1 September 2026 [Page 17] Internet-Draft Sustainability Network-API February 2026 * *Authentication and authorization:* SHAPE servers MUST authenticate clients and MUST enforce authorization on a per- request basis. Authorization SHOULD be granular (e.g., via access-control mechanisms such as NACM [RFC8341]) and cover: (i) which path endpoints can be queried, (ii) which PETRA and SHAPE metrics can be returned, and (iii) which precision/granularity is permitted. * *Information disclosure controls:* Returned sustainability data (i.e., energy mix, cooling-energy ratio, or temporal variability) can be used to infer facility characteristics, topology, utilization patterns, or operational policies. Servers SHOULD support policy controls that reduce disclosure risk (e.g., aggregation, reduced precision, or suppressing specific metrics) for less-privileged clients. * *Input validation and bounds:* Servers MUST validate all inputs (i.e., including PETRA endpoint identifiers, PETRA traffic characterization inputs such as throughput or time-window with transmitted volume, measurement-interval, and the recursive flag) and enforce reasonable bounds to prevent expensive computations and state growth. In particular, servers SHOULD enforce upper limits on observation-window durations, recursion depth/scope, and the amount of per-request data returned. * *Denial-of-service resilience:* SHAPE computations may involve multi-device sampling, aggregation, and historical lookups. Servers SHOULD implement DoS mitigations such as rate limiting, per-client quotas, request prioritization, and caching of commonly requested results. If requests are rejected due to overload or policy, servers SHOULD return explicit errors rather than silently ignoring requests. * *Multi-domain and recursive operation:* When the query is expanded recursively across administrative domains, each domain MUST enforce its own local policy and MUST NOT assume that upstream requests are safe. Implementations SHOULD ensure that recursive expansion does not leak credentials, does not bypass local authorization, and does not create amplification (e.g., fan-out storms). Responses obtained from external domains SHOULD be treated as untrusted inputs. * *Integrity of measurement chain:* SHAPE metrics can be used for automated decisions (e.g., policy enforcement or gSLAs). Implementations SHOULD protect the integrity of the measurement pipeline (collection, aggregation, and publication) and SHOULD provide operational mechanisms such as audit logs and provenance tracking to help detect tampering or misconfiguration. Gallego Sanchez, et al. Expires 1 September 2026 [Page 18] Internet-Draft Sustainability Network-API February 2026 * *Privacy:* Sustainability metrics may correlate with customer traffic patterns or reveal information about customer locations and activity. Implementations SHOULD minimize retention of per- customer/per-flow data and SHOULD protect logs and telemetry derived from SHAPE requests. 7. IANA Considerations IANA is requested to register the following YANG module in the "YANG Module Names" registry [RFC3688]. Name: ietf-shape Namespace: urn:ietf:params:xml:ns:yang:ietf-shape Prefix: shape Reference: RFC XXXX Maintained by IANA? N 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . Gallego Sanchez, et al. Expires 1 September 2026 [Page 19] Internet-Draft Sustainability Network-API February 2026 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8309] Wu, Q., Liu, W., and A. Farrel, "Service Models Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [RFC9315] Clemm, A., Ciavaglia, L., Granville, L. Z., and J. Tantsura, "Intent-Based Networking - Concepts and Definitions", RFC 9315, DOI 10.17487/RFC9315, October 2022, . [RFC9911] Schönwälder, J., Ed., "Common YANG Data Types", RFC 9911, DOI 10.17487/RFC9911, December 2025, . 8.2. Informative References [I-D.bcmj-green-power-and-energy-yang] Claise, B., Chen, G., Palmero, M. P., and J. Lindblad, "Power and Energy YANG Module", Work in Progress, Internet-Draft, draft-bcmj-green-power-and-energy-yang-07, 26 May 2026, . [I-D.ietf-green-framework] Claise, B., Contreras, L. M., Lindblad, J., Palmero, M. P., Stephan, E., and Q. Wu, "Framework for Energy Efficiency Management", Work in Progress, Internet-Draft, draft-ietf-green-framework-02, 5 July 2026, . Gallego Sanchez, et al. Expires 1 September 2026 [Page 20] Internet-Draft Sustainability Network-API February 2026 [I-D.ietf-opsawg-rfc5706bis] Claise, B., Clarke, J., Farrel, A., Barguil, S., Pignataro, C., and R. Chen, "Guidelines for Considering Operations and Management in IETF Specifications", Work in Progress, Internet-Draft, draft-ietf-opsawg-rfc5706bis-05, 26 June 2026, . [I-D.irtf-nmrg-ibn-usecases] Yao, K., Chen, D., Jeong, J. P., Wu, Q., Yang, C., Contreras, L. M., and G. Fioccola, "Use Cases and Practices for Intent-Based Networking", Work in Progress, Internet-Draft, draft-irtf-nmrg-ibn-usecases-03, 15 March 2026, . [I-D.petra-green-api] Rodriguez-Natal, A., Contreras, L. M., Palmero, M. P., Lindblad, J., and A. G. Sánchez, "Path Energy Traffic Ratio API (PETRA)", Work in Progress, Internet-Draft, draft-petra-green-api-04, 6 July 2026, . [RFC9907] Bierman, A., Boucadair, M., Ed., and Q. Wu, "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 9907, DOI 10.17487/RFC9907, March 2026, . Acknowledgments The contribution of A. Gallego Sánchez to this document has been partially supported by the Smart Networks and Services Joint Undertaking (SNS JU) under the European Union's Horizon Europe research and innovation project Sustain6G (Grant Agreement no. 101191936). The contribution of L.M. Contreras to this document has been partially supported by the Smart Networks and Services Joint Undertaking (SNS JU) under the European Union's Horizon Europe research and innovation projects 6Green (Grant Agreement no. 101096925) and Exigence (Grant Agreement no. 101139120). Appendix A. Use Cases This section describes some use-cases where this specification might be useful. Gallego Sanchez, et al. Expires 1 September 2026 [Page 21] Internet-Draft Sustainability Network-API February 2026 A.1. SD-WAN Software-Defined Wide-Area Networks (SD-WAN) have become a common way for enterprises to provide cost-effective connectivity across their different geographically distributed sites. Typically, SD-WAN deployments operate as an overlay network that is established on top of an existing underlay connectivity network. One aspect to consider is that in many SD-WAN production deployments the operator of the overlay network and the operator of the underlay network are different organizations. This poses an additional challenge when trying to derive sustainability metrics. Even if the underlay network is instrumented to collect energy data, this data is opaque to the operator of the overlay network which has no access to underlay information. While operators of underlay networks offer certain general network metrics to overlay operators, no interface has been defined to allow the overlay operator to query the underlay network for energy information. In this context, the SHAPE specification presented in this document enables the operator of the SD-WAN network to coordinate with the underlay operator to capture sustainability data. This in turns opens further use-cases, from observability and reporting to potentially overlay policies based on underlay energy data, further enabling an overall more sustainable operation of the network. In addition to energy considerations in SD-WAN deployments, SHAPE can also be leveraged for broader energy-aware service routing. In this context, network controllers and service orchestrators—such as SD-WAN controllers, transport SDN controllers, 5G slice orchestrators, or multi-domain service orchestrators—can use SHAPE metrics not only to balance latency, throughput, or load, but also to optimize path selection according to sustainability objectives. Carbon-intensity and temporal-carbon-variability metrics are the primary optimization levers for low-emission routing. Energy mix and renewable percentages can complement decisions where policy requires specific sourcing criteria, but should not be used as standalone sustainability indicators. This brings a paradigm where routing decisions are jointly driven by network performance and carbon impact. Gallego Sanchez, et al. Expires 1 September 2026 [Page 22] Internet-Draft Sustainability Network-API February 2026 A.2. Multilayer Energy Management The concept of multilayer L3-L1 collection involves integrating data from different network layers to provide a comprehensive view of network operations. The use case of multilayer involves collecting and correlating data from Layer 3 (network layer) down to Layer 1 (physical layer). This multilayer approach allows for better network performance, optimization, and troubleshooting by providing end-to- end visibility. Leveraging SHAPE API for multilayer L3-L1 collection use case enhances energy management by providing comprehensive visibility, enabling optimization, and supporting proactive management. This makes SHAPE a useful tool for more accurate, efficient and effective energy management in modern networks. A.3. SLA Negotiation for Green Services Another use case for SHAPE could be the negotiation of green Service Level Agreements (gSLAs) between operators and enterprise customers. By exposing SHAPE-derived metrics such as carbon intensity, energy efficiency, and temporal variability, providers can offer differentiated SLAs that explicitly include environmental targets. This enables customers to select network services not only based on performance guarantees, but also on their actual carbon impact. Renewable-percentage and energy-mix metrics MAY support policy-driven sourcing requirements, but carbon-intensity remains the primary metric for carbon accounting and SLA compliance. Such gSLAs empower customers to align their digital services with verifiable sustainability goals, while operators can use SHAPE as the trusted source of energy and carbon data. gSLAs can be negotiated using customer-expressed green intents that specify objectives such as maximum energy consumption, minimum energy efficiency, carbon emission limits, and renewable-energy constraints [I-D.irtf-nmrg-ibn-usecases]. SHAPE's metrics, including Watts per Gigabit, carbon intensity, temporal carbon variability, and energy mix, provide essential measurements to translate these intents into network configurations and to monitor compliance during service operation. The lifecycle of green intents, encompassing fulfillment and assurance phases [RFC9315], can be supported by SHAPE through its capability to deliver real-time energy metrics for translation into network policies and subsequent monitoring and validation. Gallego Sanchez, et al. Expires 1 September 2026 [Page 23] Internet-Draft Sustainability Network-API February 2026 A.4. Energy-Aware UPF and Edge Selection in 5G Mobile Network Operators (MNOs) often have choices regarding the placement of user-plane functions (UPFs), traffic break-out points, and Multi-access Edge Computing (MEC) sites. These choices influence not only latency and capacity, but also the energy and carbon footprint of the end-to-end user-plane path (e.g., from a radio site or aggregation point towards a selected UPF/MEC and onwards to a data network). In this context, SHAPE can be used by the 5G slice orchestrator, policy controller, or transport controller to query candidate paths associated with alternative UPF/MEC selections and compare sustainability metrics (e.g., watts-per-gigabit, carbon intensity, energy mix, and temporal carbon variability over a defined observation window). This enables energy-aware traffic steering, selection of greener break-out points when service constraints allow it, and assurance of sustainability objectives for enterprise slices. A.5. Sustainability Reporting Across Leased Backhaul and Network Sharing MNOs frequently rely on third-party transport (e.g., leased lines or wholesale backhaul) and may participate in network sharing arrangements where different administrative domains contribute to the effective end-to-end service path. This makes it difficult to obtain consistent and comparable sustainability metrics for internal carbon accounting, regulatory reporting, or customer-facing sustainability statements. SHAPE's recursive usage model can support these scenarios by allowing an MNO to obtain per-segment sustainability metrics from each contributing domain (subject to authorization and policy) and then aggregate them for an overall view of the service path. When combined with appropriate safeguards against double counting (Section "Recursive Usage"), this enables a more robust, auditable decomposition of energy and carbon contributions across shared or outsourced infrastructure. Appendix B. Requirements for Energy Efficiency Management The document Framework for Energy Efficiency Management [I-D.ietf-green-framework] describes a framework where an Energy Management System (EnMS) coordinates inventory, monitoring, and control functions through a controller element. In that context, SHAPE can be exposed via the API Service Interface (interface 'g') to provide path-related energy and sustainability information to external consumers. Gallego Sanchez, et al. Expires 1 September 2026 [Page 24] Internet-Draft Sustainability Network-API February 2026 +------------------------------------------------------------------+ | | | (3) Energy Management System (EnMS) | | | +------------------------------------------------------------------+ ^ ^ | | (a) | (b) +- (c) | | Inventory of | Monitor | DataSheets/DataBase | | identity and | Energy | and/or via API, v API Service | Capability | Efficiency | Metadata and other (g) Interface | | | device, component and | | | network related ^ | | | information | | | | | | | | | | | | | | | v | +------------------------------------------------------------------+ | | | (2) Controller (collection, compute and aggregate?) | | | +------------------------------------------------------------------+ ^ ^ ^ | | (d) | (e) | | (f) | Inventory | Monitor power | | Control | Capability | Proportion | | (Energy saving | | Energy efficiency | | Functionality | | ratio, power | | Localized mgmt/ | | consumption, | | network wide mgmt) | | etc) | | | | | v +--------------------------------------------------------------------+ | | | (1) Device/Component | | | | +---------+ +-----------+ +----------------+ +----------------+ | | | (I) | | (II) | | (III) | | (IV) | | | | | | | | Legacy | | 'Attached'(PoE | | | | Device | | Component | | Device | | end Point) | | | | | | | | | | | | | +---------+ +-----------+ +----------------+ +----------------+ | +--------------------------------------------------------------------+ Authors' Addresses Gallego Sanchez, et al. Expires 1 September 2026 [Page 25] Internet-Draft Sustainability Network-API February 2026 Adrian Gallego Sanchez Deutsche Telekom Guadalajara Spain Email: ADRIAN.GALLEGO-SANCHEZ@t-systems.com Alberto Rodriguez-Natal Cisco Madrid Spain Email: natal@cisco.com Luis M. Contreras Telefonica Madrid Spain Email: luismiguel.contrerasmurillo@telefonica.com Marisol Palmero Toledo Spain Email: marisol.ietf@gmail.com Jan Lindblad All For Eco Email: jan.lindblad+ietf@for.eco Gallego Sanchez, et al. Expires 1 September 2026 [Page 26]