GREEN A. Rodriguez-Natal Internet-Draft Cisco Intended status: Informational L. M. Contreras Expires: 4 May 2027 Telefonica M. Palmero Independent Consultant J. Lindblad All For Eco A. Gallego Sanchez T-SYSTEMS 31 October 2026 Path Energy Traffic Ratio API (PETRA) draft-petra-green-api-05 Abstract This document describes an API to query a network regarding its Energy Traffic Ratio for a given path. 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 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 4 May 2027. 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. Code Components Rodriguez-Natal, et al. Expires 4 May 2027 [Page 1] Internet-Draft Energy-API October 2026 extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology and Requirements Notation . . . . . . . . . . . . 3 3. Path Energy Traffic Ratio API (PETRA) . . . . . . . . . . . . 3 3.1. Energy Information . . . . . . . . . . . . . . . . . . . 3 3.2. Recursive Usage . . . . . . . . . . . . . . . . . . . . . 3 4. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Module Structure . . . . . . . . . . . . . . . . . . . . 5 4.2. Module Definition . . . . . . . . . . . . . . . . . . . . 6 5. Operational Considerations . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . 16 Appendix A. Use Cases . . . . . . . . . . . . . . . . . . . . . 17 A.1. SD-WAN . . . . . . . . . . . . . . . . . . . . . . . . . 17 A.2. Multilayer Energy Management . . . . . . . . . . . . . . 18 A.3. SLA Negotiation for Energy-Efficient Services . . . . . . 18 Appendix B. Requirements for Energy Efficiency Management . . . 18 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 1. Introduction Energy management is becoming one of the major societal goals for the next decade, and networks are one of the major consumers of energy nowadays. Energy management 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 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 metrics towards network consumers so that can be uniformly reported, particularly in heterogeneous network scenarios. This document introduces an API to query networks about Energy Traffic Ratio. Rodriguez-Natal, et al. Expires 4 May 2027 [Page 2] Internet-Draft Energy-API October 2026 2. Terminology and Requirements Notation 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. 3. Path Energy Traffic Ratio API (PETRA) This documents describes an API to query a network about the Energy Traffic Ratio for a given path. It takes as input the source and destination of a path along with the traffic throughput between and returns energy 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 underlaying 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. In the current version of this document, source and destination endpoints can be IP addresses, IP prefixes, or MAC addresses. 3.1. Energy Information This API allows to return a number of energy attributes associated with the path and the traffic. Currently the parameters that could be returned as energy information as part of the query are: * Watts per Gigabit: How many Watts are consumed per Gigabit of traffic traversing the path. 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 PETRA and such energy consumption could be aggregated and reported for the overall path also using PETRA. 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 (below), PETRA 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). Rodriguez-Natal, et al. Expires 4 May 2027 [Page 3] Internet-Draft Energy-API October 2026 Customer ------------------ Service ---------- | | Model | | PETRA as | Service |<-------->| Customer | Customer Service | Orchestrator | (a) | | related API | | ---------- ------------------ . . ########################## . . (b) ----------- . (b) . ......|Application| . . : | BSS/OSS | PETRA as . . : ----------- Service related API . Service Delivery . : . Model . : ------------------ ------------------ | | | | ############# | Network | | Network | | Orchestrator | | Orchestrator | | | | | .------------------ ------------------. PETRA as . : : . Network API . : Network Configuration : . . : Model : . ------------ ------------ ------------ ------------ | | | | | | | | ### | Controller | | Controller | | Controller | | Controller | | | | | | | | | ------------ ------------ ------------ ------------ : . . : : : . . Device : : : . . Configuration : : : . . Model : : --------- --------- --------- --------- --------- | Network | | Network | | Network | | Network | | Network | | Element | | Element | | Element | | Element | | Element | --------- --------- --------- --------- --------- 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 PETRA in a recursive manner need to take appropriate measures to ensure no double-counting occurs across recursive calls to the API. Rodriguez-Natal, et al. Expires 4 May 2027 [Page 4] Internet-Draft Energy-API October 2026 4. YANG Module This is a posible definition of PETRA as a module following the YANG specification [RFC7950]. The module uses the common YANG data types defined in [RFC9911], and imports the network slice model from [I-D.ietf-teas-ietf-network-slice-nbi-yang] and the power and energy model from [I-D.bcmj-green-power-and-energy-yang]. 4.1. Module Structure This section uses the graphical representation of data models defined in [RFC8340]. Rodriguez-Natal, et al. Expires 4 May 2027 [Page 5] Internet-Draft Energy-API October 2026 module: ietf-petra +--rw energy +---x query +---w input | +---w source | | +---w (identifier) | | +--:(ip-address) | | | +---w ip-address ietf-inet-types:ip-address | | +--:(ip-prefix) | | | +---w ip-prefix ietf-inet-types:ip-prefix | | +--:(mac-address) | | | +---w mac-address ietf-yang-types:mac-address | | +--:(sdp-id) | | +---w sdp-id -> /ietf-nss:network-slice-services/slice-service/sdps/sdp/id | +---w destination | | +---w (identifier) | | +--:(ip-address) | | | +---w ip-address ietf-inet-types:ip-address | | +--:(ip-prefix) | | | +---w ip-prefix ietf-inet-types:ip-prefix | | +--:(mac-address) | | | +---w mac-address ietf-yang-types:mac-address | | +--:(sdp-id) | | +---w sdp-id -> /ietf-nss:network-slice-services/slice-service/sdps/sdp/id | +---w (traffic-characterization)? | +--:(throughput) | | +---w throughput? decimal64 | +--:(time-window-and-data-transmitted) | +---w time-window | | +---w start-time ietf-yang-types:date-and-time | | +---w end-time ietf-yang-types:date-and-time | +---w data-transmitted decimal64 +--ro output +--ro (result)? +--:(success) | +--ro success | +--ro watts-per-gigabit? decimal64 | +--ro data-source-accuracy? identityref +--:(invalid-endpoint) +--ro invalid-endpoint! 4.2. Module Definition Rodriguez-Natal, et al. Expires 4 May 2027 [Page 6] Internet-Draft Energy-API October 2026 file "ietf-petra@2026-07-06.yang" module ietf-petra { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-petra"; prefix petra; import ietf-inet-types { prefix ietf-inet-types; reference "RFC 9911: Common YANG Data Types"; } import ietf-yang-types { prefix ietf-yang-types; reference "RFC 9911: Common YANG Data Types"; } import ietf-network-slice-service { prefix ietf-nss; revision-date 2026-05-27; reference "draft-ietf-teas-ietf-network-slice-nbi-yang-26: A YANG Data Model for the RFC 9543 Network Slice Service."; } import ietf-power-and-energy { prefix eo; reference "draft-bcmj-green-power-and-energy-yang: Power and Energy YANG Module."; } organization "IETF GREEN Working Group"; contact "WG Web: WG List: "; description "Initial YANG rendition of the PETRA Energy API, v1.0.1 Copyright (c) 2025 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). Rodriguez-Natal, et al. Expires 4 May 2027 [Page 7] Internet-Draft Energy-API October 2026 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-petra: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' } }' 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' } } } */ revision 2026-07-06 { description "Initial YANG rendition of the PETRA Energy API, v1.0.1"; reference Rodriguez-Natal, et al. Expires 4 May 2027 [Page 8] Internet-Draft Energy-API October 2026 "RFC XXXX: ..."; } grouping endpoint { description "Identifies one endpoint of an energy-measurement path."; choice identifier { mandatory true; description "Endpoint represented as an IP address, IP prefix, MAC address, or Service Demarcation Point (SDP) identifier."; case ip-address { leaf ip-address { type ietf-inet-types:ip-address; mandatory true; description "IPv4 or IPv6 address."; } } case ip-prefix { leaf ip-prefix { type ietf-inet-types:ip-prefix; mandatory true; description "IPv4 or IPv6 network prefix."; } } case mac-address { leaf mac-address { type ietf-yang-types:mac-address; mandatory true; description "IEEE 802 MAC address."; } } case sdp-id { leaf sdp-id { type leafref { path "/ietf-nss:network-slice-services" + "/ietf-nss:slice-service" + "/ietf-nss:sdps" + "/ietf-nss:sdp" + "/ietf-nss:id"; require-instance true; } mandatory true; description "Reference to a Service Demarcation Point (SDP) within the Rodriguez-Natal, et al. Expires 4 May 2027 [Page 9] Internet-Draft Energy-API October 2026 scope of a Network Slice Controller (NSC)."; } } } } grouping energy-metrics { description "Grouping for query result metrics."; leaf watts-per-gigabit { type decimal64 { fraction-digits 3; } units W/Gb; description "Watts consumed per Gigabit transmitted"; } leaf data-source-accuracy { type identityref { base eo:data-source-accuracy; } description "Accuracy classification of the watts-per-gigabit value, using the GREEN data-source-accuracy hierarchy. Implementations SHOULD populate this leaf to enable consumers to assess reliability. For path-aggregated values derived from multiple components, the RECOMMENDED value is the LEAST accurate accuracy class among all contributing energy objects."; } } container energy { description "PETRA API top level container."; action query { description "Query the network for energy consumption"; input { must "throughput or (time-window/start-time and time-window/end-time and data-transmitted)" { error-message "Provide either throughput or a time window with start and end times together with data-transmitted."; } container source { description "Source endpoint."; uses endpoint; } Rodriguez-Natal, et al. Expires 4 May 2027 [Page 10] Internet-Draft Energy-API October 2026 container destination { description "Destination endpoint."; uses endpoint; } choice traffic-characterization { default throughput; description "Characterizes the traffic either by its throughput or by the amount of data transmitted during a time window."; case throughput { leaf throughput { type decimal64 { fraction-digits 3; } units Gb/s; description "Throughput between source and destination (in gigabits per second)."; } } case time-window-and-data-transmitted { container time-window { description "Interval during which the data was transmitted."; leaf start-time { type ietf-yang-types:date-and-time; mandatory true; description "Start date and time of the interval."; } leaf end-time { type ietf-yang-types:date-and-time; mandatory true; description "End date and time of the interval."; } } leaf data-transmitted { type decimal64 { fraction-digits 3; } units Gb; mandatory true; description "Amount of data transmitted between source and destination during the time window (in gigabits)."; } Rodriguez-Natal, et al. Expires 4 May 2027 [Page 11] Internet-Draft Energy-API October 2026 } } } output { choice result { description "Choice of which kind of result the query gave."; container success { description "Successful operation"; uses energy-metrics; } container invalid-endpoint { presence "Indicates that an invalid endpoint was supplied."; description "Invalid source or destination endpoint supplied."; } } } } } } 5. Operational Considerations This section highlights deployment and operations considerations for PETRA, following the guidance in [I-D.ietf-opsawg-rfc5706bis]. * Measurement method impact: PETRA results can differ depending on whether values are directly measured, estimated, or model-derived. Operators SHOULD document the methodology used for each exposed metric. * Provenance: PETRA does not require provenance support. Deployments that require provenance assurance for the Energy Object telemetry used to derive a PETRA result can use the per- Energy-Object verification state defined in [I-D.madpr-green-provenance]. * Consumer intent differences: customer-facing use cases (for example, SD-WAN visibility and SLA reporting) prioritize repeatability and explainability, while operator optimization use cases may prioritize freshness and control-loop responsiveness. Rodriguez-Natal, et al. Expires 4 May 2027 [Page 12] Internet-Draft Energy-API October 2026 * Recursive aggregation and double counting: recursive or multi- domain use of PETRA can count the same contribution more than once. Implementations SHOULD define aggregation boundaries and controls that avoid double counting across segments and administrative domains. 6. Security Considerations The YANG module defined in this document is specified and reviewed following the guidance in [RFC9907]. PETRA query exchanges can reveal operationally sensitive information related to endpoints, traffic, and energy behavior, and therefore require careful deployment controls. When this API is exposed over NETCONF [RFC6241] or RESTCONF [RFC8040], implementations inherit those protocols' security properties and deployment requirements. The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available protocol operations and content. The module defines no particularly sensitive readable or writable datastore nodes. The "energy" container serves only as the parent of the "energy/query" action. Implementations and deployments SHOULD consider at least the following: * Secure transport: mutual authentication, confidentiality, and integrity protection for PETRA exchanges MUST be provided by the underlying management protocol and transport. * Authentication and authorization: servers MUST authenticate clients and MUST enforce authorization before processing requests. In particular, invocation of the "energy/query" action MUST be limited to authorized users. * Input validation: implementations SHOULD validate endpoint identifiers and traffic characterization values to prevent invalid requests and abusive workloads. * Information disclosure control: an "energy/query" request contains source and destination identifiers plus throughput or time-and- volume traffic information. A response can expose energy metrics, their accuracy, or whether the supplied endpoints are valid. Unauthorized invocation or observation can therefore disclose Rodriguez-Natal, et al. Expires 4 May 2027 [Page 13] Internet-Draft Energy-API October 2026 customer traffic and operational energy information or enable endpoint enumeration. Queries SHOULD be filtered according to policy and client privileges. * Denial-of-service resilience: repeated or computationally expensive invocations of "energy/query" can consume controller or orchestrator resources. Implementations SHOULD apply rate limiting, quotas, and/or bounded processing. * Privacy: where measurements can be correlated to customer behavior, operators SHOULD minimize retention and protect logs and telemetry generated by queries. 7. Acknowledgments Kudos to Elis Lulja for his help with the OpenAPI specification in early versions of this draft. Thanks to Fernando Sanz Garcia and Lori Jakab for their help and support on this work. The contribution of Telefonica to this document has been 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). 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). 8. IANA Considerations IANA is requested to register the following URI in the "ns" registry within the "IETF XML Registry" group [RFC3688]: URI: urn:ietf:params:xml:ns:yang:ietf-petra Registrant Contact: The IESG XML: N/A; the requested URI is an XML namespace. IANA is requested to register the following YANG module in the "YANG Module Names" registry [RFC7950] within the "YANG Parameters" registry group: Name: ietf-petra Maintained by IANA? N Rodriguez-Natal, et al. Expires 4 May 2027 [Page 14] Internet-Draft Energy-API October 2026 Namespace: urn:ietf:params:xml:ns:yang:ietf-petra Prefix: petra Reference: RFC XXXX 9. References 9.1. Normative 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.belmq-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-belmq-green-framework-10, 8 February 2026, . [I-D.ietf-teas-ietf-network-slice-nbi-yang] Wu, B., Dhody, D., Rokui, R., Saad, T., and J. Mullooly, "A YANG Data Model for the RFC 9543 Network Slice Service", Work in Progress, Internet-Draft, draft-ietf- teas-ietf-network-slice-nbi-yang-26, 26 May 2026, . [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, . Rodriguez-Natal, et al. Expires 4 May 2027 [Page 15] Internet-Draft Energy-API October 2026 [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, . [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, . [RFC9911] Schönwälder, J., Ed., "Common YANG Data Types", RFC 9911, DOI 10.17487/RFC9911, December 2025, . 9.2. Informative References [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-09, 6 October 2026, . Rodriguez-Natal, et al. Expires 4 May 2027 [Page 16] Internet-Draft Energy-API October 2026 [I-D.madpr-green-provenance] Palmero, M. P., Lopez, D., Pérez, A. M., Andersson, P., and R. Osterberg, "Provenance Traceability Augmentation for the GREEN Power and Energy YANG Module", Work in Progress, Internet-Draft, draft-madpr-green-provenance-00, 5 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, . Appendix A. Use Cases This section describes some use-cases where this specification might be useful. 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 energy 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 PETRA specification presented in this document enables the operator of the SD-WAN network to coordinate with the underlay operator to capture energy 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 energy-efficient operation of the network. In addition to energy considerations in SD-WAN deployments, PETRA 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, Rodriguez-Natal, et al. Expires 4 May 2027 [Page 17] Internet-Draft Energy-API October 2026 or multi-domain service orchestrators, can use PETRA metrics not only to balance latency, throughput, or load, but also to optimize path selection according to energy-efficiency objectives. For example, paths with the lowest energy-consumption could be preferred, enabling service differentiation where energy-efficient paths are explicitly prioritized. This extends the SD-WAN use case into a more general paradigm where routing decisions are jointly driven by network performance and energy impact. 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 PETRA API for multilayer L3-L1 collection use case enhances energy management by providing comprehensive visibility, enabling optimization, and supporting proactive management. This makes PETRA a useful tool for more accurate, efficient and effective energy management in modern networks. A.3. SLA Negotiation for Energy-Efficient Services Another use case for PETRA could the negotiation of Service Level Agreements (SLAs) between operators and enterprise customers. By exposing PETRA-derived metrics such as watts-per-gigabit, providers can offer differentiated SLAs that explicitly include environmental targets. This enables customers to select network services not only based on performance guarantees (e.g. latency), but also on their environmental footprint (or a combination of both). Such SLAs empower customers to align their digital services with corporate energy-efficient and sustainability goals and reporting requirements, while operators can use PETRA to provide the energy metrics used for such services. Appendix B. Requirements for Energy Efficiency Management The document Framework for Energy Efficiency Management [I-D.belmq-green-framework] describes a reference model for energy management. The model includes an 'API Service Interface', labeled as interface (g) in the document, which "enables access for service consumption, enabling data retrieval, control, and integration through API". Rodriguez-Natal, et al. Expires 4 May 2027 [Page 18] Internet-Draft Energy-API October 2026 In that context, PETRA is one example of such 'API Service Interface'. In the particular case of PETRA, the API might be used to consume from the Network controller, the Domain controller, or both. Appendix A describes a few use-cases that could make use of PETRA as an 'API Service Interface' within the Framework for Energy Efficiency Management [I-D.belmq-green-framework]. Contributors Fernando Munoz Cisco Madrid Spain Email: fmunozma@cisco.com Alejandro Muniz Madrid Spain Roland Schott Deutsche Telekom Deutsche-Telekom-Allee 9 64295 Darmstadt Germany Email: Roland.Schott@telekom.de Authors' Addresses Alberto Rodriguez-Natal Cisco Barcelona Spain Email: natal@cisco.com Luis M. Contreras Telefonica Madrid Spain Email: luismiguel.contrerasmurillo@telefonica.com Marisol Palmero Independent Consultant Spain Rodriguez-Natal, et al. Expires 4 May 2027 [Page 19] Internet-Draft Energy-API October 2026 Email: marisol.ietf@gmail.com Jan Lindblad All For Eco Email: jan.lindblad+ietf@for.eco Adrian Gallego Sanchez T-SYSTEMS Madrid Spain Email: ADRIAN.GALLEGO-SANCHEZ@t-systems.com Rodriguez-Natal, et al. Expires 4 May 2027 [Page 20]