| Internet-Draft | SCONE Applicability & Manageability | November 2025 |
| Mishra, et al. | Expires 10 May 2026 | [Page] |
This document describes the Applicability and Manageability considerations for providing throughput guidance to application endpoints. This guidance is specifically addressed within the context of telecommunications service provider networks utilizing the Standard Communication with Network Elements (SCONE) protocol.¶
This note is to be removed before publishing as an RFC.¶
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The SCONE protocol [I-D.ietf-scone-protocol] provides a signaling mechanism that enables on-path SCONE-capable Network Elements to communicate the advisory maximum allowable bit rate to application endpoints, which is particularly relevant for adaptive bit-rate applications. This document addresses the Applicability and Manageability considerations for deploying the SCONE protocol within telecommunications service provider networks.¶
SCONE operates based on a UDP 4-tuple. Network Elements capable of rate limiting at this granularity can send notifications of the advisory maximum allowable bit rate in each direction of the observed traffic. Such Network Elements may also drop or delay packets within the corresponding UDP 4-tuple flows. This implies that on-path SCONE-capable Network Elements (referred to as SCONE Network Elements in the rest of this document) are assumed to have the following capabilities: detect and maintain UDP 4-tuple flows, be aware of or configurable with rate-limiting policies, and identify flows that carry SCONE packets in order to insert throughput advice into those packets.¶
In this document, on-path SCONE Network Elements are generally considered within the access portion of the Telecommunications provider's network. However, multiple SCONE Network Elements may exist along a path between the communicating peers. Depending on their configuration and roles they are likely to generate different throughput advices for the SCONE enabled application traffic flows, especially when different access technologies are in use. For example, the SCONE protocol in a wireless access network element may operate differently from one in a fixed broadband network. Wi-Fi networks provide another example, where enforcement is often per user or per Service Set Identifier (SSID), but visibility into individual UDP 4-tuples may be limited. Among access networks, mobile networks offer the most fine-grained visibility into traffic flows and can act on individual flows. For example, in mobile networks, the User Plane Function (UPF) in 5G [_5G-Arch] and the Packet Data Network Gateway (P-GW) in 4G [_4G-Arch] can generate throughput advice to guide adaptive bit-rates applications on a per-flow basis. In contrast, wireline broadband networks typically apply rate limiting at a centralized Broadband Network Gateway (BNG) or at aggregation points serving multiple Customer Premises Equipment (CPE) devices.¶
Accordingly, Applicability and Manageability considerations must encompass a wide range of access-network scenarios, each of which handles per-flow rate limiting differently. However, the scope of this document is limited to discussing the core Applicability and Manageability considerations for the SCONE protocol.¶
This document uses terms and definitions described in [I-D.ietf-scone-protocol].¶
SCONE signaling operates only over established sessions. SCONE Network Elements ought to be able to unambiguously associate throughput advice with application flows. Each session is bound to an IP address and port, ensuring SCONE packets are routed precisely without affecting unrelated traffic.¶
Throughput advice is applied on a UDP 4-tuple basis. SCONE Network Elements ought to maintain flow-specific context to ensure signaling correctness. This enables applications to receive targeted throughput advice while preventing unintended impact on unrelated flows.¶
Quality of Service (QoS) may be enforced by networks through a variety of mechanisms. In certain deployments, network operators may choose to apply distinct QoS policies to SCONE-enabled flows. The SCONE Network Element responsible for inserting SCONE advice is not required to interpret or enforce QoS policies; its role is limited to the signaling of the advisory throughput information. It is expected that network operators shall be able to identify SCONE-enabled flows and, where appropriate, provide throughput advice in accordance to their policy objectives.¶
SCONE-aware applications ought to provide hints to the SCONE Network Elements, enabling it to generate appropriate throughput advice for a given UDP 4-tuple. Such hints prevent unnecessary default rate-limiting, allow the network to signal the maximum allowable bit rate, and reduce CPU overhead by eliminating additional classification steps.¶
Packet loss or non-delivery of SCONE advice reduces its effectiveness. Both SCONE Network Elements and application endpoints should support retransmission or periodic re-sending of SCONE packets to ensure reliable delivery. Conformance depends on the behavior of both network and application endpoint.¶
The rate at which SCONE updates are issued depends on flow characteristics and available computational resources. Excessively frequent updates may increase CPU load, while infrequent updates may reduce advisory effectiveness. Network Operators can define adjustable update intervals based on application requirements, network capacity, and operational constraints.¶
Dynamic rate limits updates can be enforced by the network during active application sessions due to:¶
Changes in access network type (requiring updated throughput advice)¶
Changes in Subscriber policy (e.g., exceeding usage thresholds)¶
In such cases, the SCONE Network Elements need to be able to initiate SCONE packets to provide updated advice, or applications should generate SCONE packets frequently enough to trigger network responses.¶
SCONE signaling can be integrated into existing operational and management frameworks to enable monitoring, troubleshooting, and fault isolation. Metrics of interest include:¶
Networks providing SCONE throughput advice ought to implement mechanisms to measure compliance, either per application flow or in aggregate. This allows operators to validate advisory effectiveness and adjust policies. Due to flow awareness, such mechanisms are typically implemented in a SCONE Network Element but may also be implemented elsewhere in the network.¶
SCONE signaling is expected to traverse the existing data path associated with the UDP 4-tuple flow for which the Network Element intends to send the advisory bit-rate.¶
SCONE operates independently of transport-layer mechanisms such as Explicit Congestion Notification (ECN) or Low Latency, Low Loss, and Scalable throughput (L4S). Operators would benefit from harmonizing multiple congestion signaling methods by policy or scope deployments to manage conflicting feedback.¶
Security considerations are included separately in the SCONE protocol documents.¶
This document has no IANA actions.¶
The authors thank Wesley Eddy, Renjie Tang, Kevin Smith, Tina Tsou, Tianji Jiang, Lucas Pardue, and Martin Thomson for their helpful comments and contributions to this document. The authors also thank members of the SCONE Working Group for their review and support throughout the development of this document.¶