Description
User Plane Congestion management (UPCON) is a comprehensive set of features and procedures standardized by 3GPP to address congestion occurring in the data path (user plane) of cellular networks. Unlike control plane congestion, which affects signaling, UPCON deals with the scarcity of resources for actual user data traffic, such as radio bandwidth, transport network capacity, or processing power in user plane nodes. The framework is detailed in specifications like 3GPP TS 23.705 (proximity-based services) and TS 26.938 (multimedia broadcast/multicast service). It encompasses detection mechanisms, mitigation policies, and control actions that can be applied at various points in the network, including the Radio Access Network (RAN) and the core network.
Architecturally, UPCON involves several network functions. Key components include the Policy and Charging Rules Function (PCRF), the Access Network Discovery and Selection Function (ANDSF) for traffic steering, the RAN Congestion Awareness Function (RCAF), and the User Plane Function (UPF) in 5G. Congestion detection can be based on monitoring key performance indicators (KPIs) like radio resource utilization, packet delay, packet loss rate, or buffer occupancy in network nodes. Once congestion is identified, mitigation actions are triggered. These actions are diverse and can be applied per user, per application, or per traffic aggregate.
How it works involves a closed-loop control process. The network element experiencing congestion (e.g., an eNodeB in LTE or a gNB in NR) can report its status to control plane functions like the RCAF or directly to the core network. Based on predefined policies, the network can then enact measures such as dynamically adjusting Quality of Service (QoS) parameters (e.g., downgrading QoS Class Identifier (QCI) for certain bearers), implementing application-aware traffic shaping and throttling, offloading traffic to alternative access networks (e.g., Wi-Fi), or even selectively rejecting new service requests for low-priority traffic. In the context of Proximity Services (ProSe) and Multimedia Broadcast Multicast Service (MBMS), UPCON mechanisms are crucial for managing congestion caused by many devices simultaneously requesting or participating in group communications, often by employing intelligent broadcast/multicast scheduling and resource allocation.
Purpose & Motivation
UPCON was introduced to solve the growing problem of user plane congestion in increasingly dense and traffic-heavy mobile networks, particularly with the rise of video streaming and always-connected applications. Traditional network planning and static capacity allocation were insufficient to handle unpredictable traffic surges, leading to severe degradation of user experience for all subscribers during peak times. The creation of a standardized management framework was motivated by the need for dynamic, automated, and policy-driven responses to congestion.
It addresses the limitations of earlier, more rudimentary approaches like simple packet dropping or blanket bandwidth throttling, which are inefficient and unfair. UPCON enables smarter congestion management by considering factors like user subscription tiers, application type, and current network policies. This is especially critical for enabling new services like Mission Critical Push-To-Talk (MCPTT) and public safety communications over LTE/5G, where guaranteed access and priority during congestion are non-negotiable requirements. The framework allows operators to maintain service quality for premium users and critical applications even under heavy load, optimizing the overall utilization of scarce network resources.
Key Features
- Network-based detection of user plane congestion using KPIs (e.g., resource utilization, latency)
- Policy-driven mitigation actions (e.g., QoS modification, traffic throttling, offload)
- Support for application-aware congestion control (e.g., differentiating video from background sync)
- Mechanisms for congestion-aware traffic steering between 3GPP and non-3GPP access
- Enhanced control for group communications and broadcast/multicast services (MBMS)
- Standardized interfaces for congestion reporting and control between RAN and core network
Evolution Across Releases
Introduced the foundational framework for User Plane Congestion management. Initial work focused on defining use cases, requirements, and architectural enhancements for Proximity-based Services (ProSe) and Group Communication System Enablers (GCSE) to manage congestion in scenarios involving many devices in close proximity. Specifications 23.705 and 26.938 began detailing the procedures.
Enhanced UPCON mechanisms for Mission Critical services over LTE, introducing more granular control for priority and pre-emption during congestion. Defined the RAN Congestion Awareness Function (RCAF) to improve interaction between RAN and core for congestion reporting and mitigation.
Defining Specifications
| Specification | Title |
|---|---|
| TS 23.705 | 3GPP TS 23.705 |
| TS 26.938 | 3GPP TS 26.938 |