Description
ATSSS is a comprehensive framework standardized in 3GPP Release 16 and beyond that enables a User Equipment (UE) to establish and utilize a single Protocol Data Unit (PDU) Session across multiple access networks simultaneously. These access networks can include 3GPP access types (like 5G NR or LTE) and non-3GPP access types (like Wi-Fi or fixed networks). The core architectural principle involves the ATSSS Function, which resides in the User Plane Function (UPF) and the UE, working in coordination with the Session Management Function (SMF) in the control plane.
The system operates through three fundamental traffic handling mechanisms: Steering, Switching, and Splitting. Steering involves selecting the most appropriate access network for a new traffic flow based on policies (e.g., send latency-sensitive traffic to 5G, bulk download to Wi-Fi). Switching involves dynamically moving an ongoing flow from one access to another, typically for service continuity if the quality of the current access degrades. Splitting involves distributing the packets of a single IP flow across multiple access networks, which can be done at the packet level (MPTCP-based) or the IP layer (ATSSS-LL-based), to aggregate bandwidth and enhance reliability.
Key components include the ATSSS Control Function (part of the SMF), which manages ATSSS policies and rules, and the ATSSS User Plane Function (within the UPF and UE), which executes the actual traffic distribution. The framework relies on the N4 interface for the SMF to provision these rules to the UPF. Policies are derived from the Policy Control Function (PCF) and can consider real-time access network conditions, user subscription, and application requirements. The UE's ATSSS capability is negotiated during PDU Session Establishment.
ATSSS plays a pivotal role in the 5G architecture by realizing true multi-access convergence. It moves beyond simple access selection (like ANDSF/MPTCP) to provide seamless, policy-driven, and granular control over how user traffic utilizes heterogeneous access resources. This enables operators to deliver enhanced Quality of Experience (QoE) by always using the best available network path(s) for a given service, improving overall network efficiency and resource utilization.
Purpose & Motivation
ATSSS was created to solve the fundamental challenge of efficiently and intelligently utilizing multiple available access networks (cellular and non-cellular) that a modern UE can connect to. Prior to ATSSS, solutions like Access Network Discovery and Selection Function (ANDSF) provided policy-based access selection but lacked the ability to use multiple accesses simultaneously for a single session or to dynamically switch/split traffic within a flow. Multi-Path TCP (MPTCP) offered application-layer splitting but required application support and was not tightly integrated with the core network's policy framework.
The primary motivation was to enhance user experience through improved performance, reliability, and seamless mobility. By allowing traffic steering, switching, and splitting, ATSSS ensures that critical applications always use the best available path, can survive the failure of one access type without service interruption, and can aggregate bandwidth from multiple accesses. This is especially important for 5G's vision of supporting diverse services (eMBB, URLLC, mMTC) where requirements for latency, bandwidth, and reliability vary dramatically.
Furthermore, ATSSS provides operators with a standardized, network-controlled mechanism for traffic management across heterogeneous accesses. It enables new business models, such as fixed-mobile convergence, by treating Wi-Fi and 5G as complementary resources under unified policy control. It addresses the limitations of previous fragmented approaches by integrating deeply into the 5G Core's service-based architecture, providing a scalable and flexible framework essential for the future of converged networks.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (289 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the ATSSS (Access Traffic Steering, Switching, and Splitting) function was newly introduced, defining the core procedures for multi-access management. It specifically established Access Traffic Steering for initial access selection, Access Traffic Switching for moving an ongoing flow between accesses, and Access Traffic Splitting for distributing a flow across both 3GPP and non-3GPP access networks. The foundational architecture was extended to support these capabilities, including mechanisms for Application Function (AF) influence on traffic routing and traffic detection.
- Support for Traffic Segregation TS 24.501CR0476
- Update on Traffic Detection Information TS 23.501CR0026
- Correction to AF influence on traffic routing TS 23.501CR0037
- Clarifications to AF influence on traffic routing TS 23.501CR0038
- Traffic mapping information that disallows UL packets TS 23.501CR0053
- Updates to AF influence on traffic routing TS 23.501CR0150
+ 26 more changes
In Release 16, the ATSSS function was introduced, defining the new core procedures of Access Traffic Steering, Switching, and Splitting for multi-access PDU sessions. This release specified the system architecture extensions and the necessary support from network functions like the SMF and UPF, including the Uplink Classifier for traffic distribution. It also added PCC integration and enabled interworking with EPS for these new traffic management capabilities.
- Introduction of ATSSS Support TS 23.501CR0735
- Support of Steering Functions for ATSSS TS 23.501CR0740
- ATSSS-SMF and UPF selection TS 23.501CR0761
- Updating 5.8.2.11 for N4 Rules to support ATSSS TS 23.501CR0785
- Control of traffic forwarding in 5G-LAN TS 23.501CR0909
- Transfer of N4 information for local traffic switching from SMF to I-SMF TS 23.501CR1050
+ 116 more changes
In Release 17, the ATSSS function was enhanced with new capabilities including the application of thresholds to its Load-Balancing steering mode and enabling traffic steering control for 5G-LAN type services. The release also introduced mechanisms for a partial ATSSS rule update using an ATSSS Rule ID and expanded Policy and Charging Control (PCC) rule definitions for ATSSS. Furthermore, it enabled the provisioning and modification of ATSSS parameters through EPS procedures and introduced traffic usage reporting for Redundant Transmission at the transport layer.
- Applying thresholds to Load-Balancing steering mode in ATSSS TS 23.501CR2590
- Partial ATSSS rule update by using ATSSS rule ID TS 23.501CR2886
- Updates to AF requests to influence traffic routing TS 23.501CR2913
- ATSSS parameters provisioned and modified through EPS procedure - 24301 Part TS 24.301CR3660
- Enabling and disabling the adjustment of DL traffic steering rules TS 29.244CR0579
- Traffic steering control for 5G-LAN type of services TS 29.512CR0549
+ 30 more changes
In Release 18, key ATSSS enhancements included support for MP-QUIC for traffic steering, the introduction of procedures for PIN traffic routing, and the ability for an Application Function to influence traffic for common Edge Application Server and DNAI selection. Furthermore, the release added support for delivering traffic influence information in Home Routed-Session Breakout scenarios and defined the suspend and resume procedures for performance measurement traffic duplication.
- KI#4 23.501 AF traffic influence for common EAS, DNAI selection TS 23.501CR3788
- KI#4 AF traffic influence for common EAS, DNAI selection TS 23.501CR3987
- KI#3: provisioning of traffic characteristics and monitoring of performance characteristics TS 23.501CR4087
- Delivery of Traffic Influence information for Home Routed-Session Breakout (HR-SBO) support TS 23.501CR4160
- Support of extra traffic characteristics for alternative QoS profile TS 23.501CR4183
- Determining the ATSSS capabilities of a MA PDU Session when the UE supports MPQUIC TS 23.501CR4457
+ 54 more changes
In Release 19, ATSSS enhancements introduced support for MPQUIC-based proxy functionalities and MPQUIC-UDP steering, expanded traffic routing analytics, and improved support for QoS differentiation for traffic from non-3GPP devices behind a UE or 5G-RG. The release also added mechanisms for better handling of encrypted traffic, including PDU Set information identification for end-to-end encrypted traffic using connect-UDP. Furthermore, it included updates to ATSSS capability handling and clarifications on UPF selection for the ATSSS feature.
- Support PDU Set information identification based on MoQ for encrypted XRM traffic TS 23.501CR5632
- PDU Set Information Identification for end-to-end encrypted traffic using connect-UDP - architecture part TS 23.501CR5728
- KI#3: Enhancement for AF influence on traffic routing with Energy related information TS 23.501CR5713
- HSBO_roaming traffic offloading via session breakout in HPLMN TS 23.501CR5748
- Support of QoS differentiation of traffic for N3GPP device behind UE or 5G-RG TS 24.501CR6618
- Inclusion of ATSSS status in related session management messages TS 24.501CR6880
+ 32 more changes
In Release 20, the ATSSS function was enhanced with new mitigation actions based on analytics for abnormal user plane traffic. This introduces a capability for the system to detect and react to anomalous traffic patterns within the ATSSS framework. The specific procedures for steering, switching, or splitting traffic across 3GPP and non-3GPP accesses can now be informed by this new analytical input.
- Mitigation actions based on New Abnormal user plane traffic Analytics TS 23.501CR6507
Explore further
Broader topics and technologies where ATSSS plays a role.
Defining Specifications
3GPP specifications that define or reference ATSSS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.793 vg00 | 5G ATSSS Study | Rel-16 |
| TS 24.193 vj50 | ATSSS Procedures Specification | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 28.104 vj30 | Management Data Analytics (MDA) | Rel-19 |
| TS 29.214 vj20 | Policy and Charging Control over Rx | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.519 vj40 | UDR Usage for Policy & Exposure Data | Rel-19 |
| TS 29.523 vj20 | 5G Policy Control Event Exposure Service | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.291 vj40 | Charging Management: Service-Based Interface Protocol | Rel-19 |
| TS 32.298 vj30 | Charging Data Record (CDR) Parameter Specification | Rel-19 |