UE Aggregate Maximum Bit Rate

Description

The UE Aggregate Maximum Bit Rate (UE-AMBR) is a Quality of Service (QoS) parameter defined in the EPS and 5GS architectures to control the aggregate bandwidth consumption of a User Equipment (UE). Specifically, it applies to the sum of the data rates of all Non-Guaranteed Bit Rate (Non-GBR) bearers or QoS Flows associated with that UE. Non-GBR bearers are used for best-effort traffic like web browsing or video streaming, where the network does not guarantee a minimum bit rate. The UE-AMBR acts as a ceiling for this aggregate traffic, ensuring fair sharing of radio resources among multiple UEs in a cell.

The UE-AMBR is subscribed in the user's profile in the Home Subscriber Server (HSS) or Unified Data Management (UDM) and is downloaded to the Mobility Management Entity (MME) or Access and Mobility Management Function (AMF) during UE attachment. The MME/AMF then signals the subscribed UE-AMBR value to the base station—the eNodeB (eNB) in LTE or the gNodeB (gNB) in 5G NR. The enforcement of the UE-AMBR is performed solely by the base station in both the uplink and downlink directions. The base station uses scheduling algorithms to ensure that the aggregate data rate for a UE's Non-GBR bearers does not exceed the UE-AMBR limit, while still attempting to meet the QoS requirements of individual bearers.

It is crucial to distinguish UE-AMBR from per-bearer QoS parameters like the Aggregate Maximum Bit Rate (APN-AMBR) and the Guaranteed Bit Rate (GBR). The APN-AMBR limits traffic per Access Point Name (APN) and is enforced by the Packet Gateway (PGW/UPF), while the GBR is a committed rate for dedicated bearers. The UE-AMBR, in contrast, is a radio-level enforcement point. It does not apply to GBR bearers, which have their own dedicated resource reservations. This hierarchical QoS control allows operators to manage network capacity efficiently: APN-AMBR controls core network resource usage per PDN connection, and UE-AMBR controls the radio interface usage per subscriber device.

Purpose & Motivation

UE-AMBR was introduced in 3GPP Release 8 with the Evolved Packet System (EPS) to address the need for subscriber-level radio resource policing in all-IP networks. Prior QoS mechanisms in 2G/3G often focused on per-bearer or per-PDP context guarantees but lacked an efficient way to cap the total radio resource consumption of a single device, especially with the rise of flat-rate data plans and bandwidth-hungry applications. Without UE-AMBR, a single UE with multiple active best-effort sessions (e.g., simultaneous downloads and video streams) could potentially consume a disproportionate share of a cell's capacity, degrading service for other users.

The primary problem UE-AMBR solves is ensuring radio resource fairness and preventing congestion at the air interface. It allows mobile operators to offer tiered data plans by associating different UE-AMBR values with different subscription tiers (e.g., premium vs. basic). It also provides a tool for traffic management, ensuring that the shared nature of the radio medium is respected. Its enforcement at the base station is critical because the radio scheduler has the most accurate and real-time view of resource availability and UE channel conditions, enabling dynamic and efficient application of the limit.

Key Features

• Limits aggregate bit rate for all of a UE's Non-GBR bearers/QoS Flows
• Enforced by the RAN node (eNB/gNB) in both uplink and downlink directions
• Subscribed in HSS/UDM and provisioned to the MME/AMF and subsequently to the RAN
• Does not apply to GBR bearers, which have dedicated resource guarantees
• Operates independently of APN-AMBR, which is enforced at the core network gateway
• Key parameter for implementing tiered subscriber data plans and radio fairness policies

Evolution Across Releases

Defining Specifications