Non-Aggregated RUCI Report Answer

Description

The Non-Aggregated RUCI Report Answer (NRA) is a protocol message defined within the 3GPP's RAN and User Plane Congestion Information (RUCI) reporting mechanism, specified in the Policy and Charging Control (PCC) architecture. It is transmitted from the Radio Access Network (RAN) node, such as an eNB or gNB, to a core network function, typically the Traffic Detection Function (TDF) or a Policy and Charging Rules Function (PCRF) via the Policy and Charging Enforcement Function (PCEF). The message is a direct response to a request for congestion information and contains detailed, per-event or per-flow data, as opposed to aggregated statistics.

How it works is part of a larger congestion awareness loop. When the RAN experiences user plane congestion (e.g., high latency, packet loss on a specific bearer or QoS Flow), it can be configured to report this. The core network, via the TDF/PCRF, may send a RUCI Report Request asking for specific information. The RAN node then generates an NRA message. This message includes detailed fields such as the User Equipment (UE) identifier (e.g., IMSI or GPSI), the affected bearer/QoS Flow identifier, the congestion level (e.g., severity), timestamps, and potentially location information of the UE. This data is formatted according to the Diameter-based Rx or Gx reference points (specified in 29.213, 29.217) or other management interfaces.

Key components involved are the RAN node (the reporter), the PCEF (often in the PGW/UPF which enforces policies), the PCRF (which makes policy decisions), and the TDF (which performs application detection). The NRA message's role is to provide the finest granularity of congestion data. This allows the core network to understand precisely which user's specific data flow is causing or experiencing congestion. With this information, the PCRF can make intelligent, targeted policy decisions. For example, it might dynamically adjust the QoS parameters for that specific flow, initiate traffic steering to a different access network, or trigger application-specific charging actions. This enables highly granular and reactive traffic management within the 3GPP network.

Purpose & Motivation

NRA exists to solve the problem of coarse and reactive congestion management in mobile networks. Traditional methods often relied on aggregate cell-level metrics, which made it difficult to identify the specific users or applications causing congestion. This led to blanket throttling policies that degraded all user experience rather than targeting the problematic traffic. The RUCI framework, and NRA specifically, was created to provide the core network with deep, actionable visibility into RAN-level user plane congestion on a per-flow basis.

The historical context stems from the increasing complexity of traffic with the rise of diverse Internet applications and the need for smarter Policy and Charging Control (PCC). Earlier PCC mechanisms could enforce rules but were often blind to real-time RAN conditions. The motivation for NRA was to close this loop, enabling the PCRF to apply policies based on actual radio network performance, not just subscription data or generic network load. This allows for more efficient use of scarce radio resources and a better quality of experience for all users.

Furthermore, NRA addresses the need for application-aware networking and traffic optimization. By reporting non-aggregated data, operators can correlate congestion events with specific applications (detected by the TDF). This enables advanced use cases like sponsored data, where an application provider can pay to ensure a certain QoS level even during congestion, or parental controls that limit bandwidth for specific services. In essence, NRA provides the critical data feed that transforms the mobile network from a static pipe into a dynamically optimized and monetizable service platform.