Throughput Advice

Description

Throughput Advice is a mechanism introduced in 3GPP Release 20 to allow intermediate network elements, specifically the User Plane Function (UPF), to signal the maximum data rate that can be supported for a particular flow or session. This advice is conveyed using the IETF SCONE (Sending Congestion Notifications in the Network) protocol, which is designed to provide explicit congestion and throughput information to endpoints. The UPF, acting as an intermediate node, can indicate the maximum rate based on its current load, available resources, or policy constraints. This information is then used by the endpoints (e.g., UE, application server) to adapt their transmission rates, thereby improving overall network efficiency and user experience.

The Throughput Advice is part of the broader effort to enhance QoS management in 5G and beyond. Traditionally, QoS was enforced through static policies and bearer configurations. However, with the proliferation of diverse applications and dynamic traffic patterns, there is a need for more flexible and real-time rate control. The SCONE protocol enables the UPF to send feedback to the endpoints without requiring deep packet inspection or complex signaling. The advice is typically carried in packet headers or as separate control messages, depending on the protocol binding.

In the 3GPP architecture, the Throughput Advice is relevant to the Policy Control Function (PCF) and Session Management Function (SMF), which can use this information to adjust QoS rules. The UPF may generate the advice based on its internal metrics, such as queue occupancy, processing load, or backhaul capacity. The endpoints can then adjust their sending rate to match the advised maximum, avoiding congestion and packet loss. This is particularly useful for applications like video streaming, where adaptive bitrate algorithms can benefit from explicit network feedback.

The introduction of Throughput Advice in Rel-20 aligns with the ongoing work on 5G-Advanced and the evolution towards 6G, where network-programmable QoS and application-network interaction are key. It complements other mechanisms like ECN (Explicit Congestion Notification) and L4S (Low Latency, Low Loss, Scalable Throughput) by providing a more direct rate recommendation. The SCONE protocol is still in draft status within the IETF, and 3GPP has adopted it as a reference for this feature.

Key components include the UPF, which acts as the advice generator; the SMF/PCF, which may authorize and enforce the advice; and the endpoints, which consume the advice. The advice can be per-flow, per-session, or per-UE, depending on the granularity supported. Security and privacy considerations are addressed to prevent malicious manipulation of the advice. Overall, Throughput Advice represents a step towards a more collaborative and efficient network, where intermediate nodes actively participate in rate control.

Purpose & Motivation

Throughput Advice was created to address the limitations of traditional QoS enforcement in dynamic network environments. In earlier releases, QoS was primarily managed through static bearer parameters and policy rules, which could not adapt quickly to changing network conditions or application demands. This led to either over-provisioning (wasting resources) or under-provisioning (causing congestion and poor user experience). The need for real-time, fine-grained rate control became evident with the rise of interactive and bandwidth-intensive applications.

The SCONE protocol, developed in the IETF, provides a standardized way for intermediate nodes to signal maximum rates to endpoints. 3GPP adopted this concept to enable the UPF to act as an advisor, leveraging its vantage point in the user plane. This allows endpoints to adjust their transmission rates proactively, reducing the likelihood of congestion and improving overall network stability. It also enables better utilization of network resources by allowing the network to communicate its capacity constraints explicitly.

Historically, similar mechanisms like ECN and PCN (Pre-Congestion Notification) focused on congestion indication rather than rate advice. Throughput Advice goes further by suggesting a specific maximum rate, which is more actionable for applications. This is particularly beneficial for adaptive streaming, where the client can directly use the advice to select an appropriate bitrate. The feature also supports the vision of a programmable network where applications and network functions interact seamlessly.