nascTime: A Full-Stack 5G-TSN Bridge Simulation Framework with SDAP-Based QoS Mapping and IEEE 802.1AS Transparent Clock

Abstract: 3GPP Release~16 specifies how a 5G system can operate as a transparent IEEE~802.1 TSN bridge, yet no existing simulation framework implements the complete bridge architecture with end-to-end QoS mapping through the SDAP layer, per-flow Data Radio Bearer selection, and IEEE~802.1AS transparent clock behaviour with measured residence time. Existing tools model either QoS mapping without time synchronisation, or time synchronisation without a data plane. This paper presents nascTime, a simulation framework built on OMNeT++~6.3, INET~4.6, and Simu5G that implements the full 3GPP 5G-TSN bridge model. The NW-TT and DS-TT are realised as modular compound modules that integrate with INET's \texttt{LayeredEthernetInterface} and streaming PHY. QoS mapping traverses the complete PCP\,$\rightarrow$\,DSCP\,$\rightarrow$\,QFI\,$\rightarrow$\,SDAP/DRB pipeline, and gPTP frames are transported through the simulated 5G radio path via L2-in-GTP-U encapsulation with per-message residence-time correction. We validate the framework with a three-endpoint factory topology under both ideal and fading channel conditions. In the ideal scenario, high-priority traffic achieves 99.9\% delivery with a mean end-to-end delay of 2.58\,ms, while the measured 5GS residence time exhibits a variance below 0.2\,$μ$s. Under a fading channel, residence-time variance increases to 48\,$μ$s, confirming that the framework captures radio-induced timing effects absent from abstract-delay simulators. nascTime is publicly available and constitutes the first full-stack 5G-TSN bridge simulation with SDAP-based QoS differentiation and measured IEEE~802.1AS transparent clock behaviour.

• The paper introduces nascTime, a framework integrating 5G-TSN bridging with SDAP-based per-flow QoS mapping and IEEE 802.1AS transparent clocks.
• It rigorously models radio channel effects, achieving near-lossless high-priority traffic delivery (99.9%) and an average latency of 2.58 ms.
• Its modular architecture enables scalable multi-endpoint testing and detailed analysis of QoS mapping and time synchronization under varying conditions.

nascTime: A Comprehensive Simulation Framework for 5G-TSN Bridge with Full-Stack SDAP-Based QoS and Transparent Clock

Introduction

The integration of IEEE 802.1 Time-Sensitive Networking (TSN) and 5G New Radio (NR) remains a critical enabler for deterministic, reliable, and time-synchronized wireless industrial networking. While 3GPP Release 16 explicitly defines the operation of a 5G system as a logical TSN bridge, prior simulation tools fail to provide a complete realization that encompasses SDAP-based per-flow QoS mapping, end-to-end Data Radio Bearer (DRB) selection, and transparent clock operation according to IEEE 802.1AS with measured residence time. The nascTime framework, built atop OMNeT++ 6.3, INET 4.6, and Simu5G, achieves a technically complete representation of the 3GPP 5G-TSN bridge, including robust multi-endpoint validation under both ideal and fading radio conditions (2604.04616).

Architecture and Methodology

nascTime realizes the 3GPP bridge model by implementing the Network-side TSN Translator (NW-TT) and Device-side TSN Translator (DS-TT) as composable OMNeT++ modules. The TSN Application Function (TSN AF) exposes bridge properties to a Centralized Network Controller, supporting network management and time-aware scheduling integration. The architecture enables per-flow QoS mapping, faithful gPTP propagation, and detailed modeling of residence time.

The QoS pipeline rigorously maps TSN Priority Code Points (PCP) through IPv4 DSCP, into 5G QFIs, and finally to SDAP-selected DRBs, maintaining traffic class fidelity across the entire stack. Notably, the SDAP layer—contributed to Simu5G by the authors—enables per-flow DRB instantiation, which is critical for supporting differentiated scheduling at the gNB MAC level. This is depicted in the end-to-end mapping pipeline, in which high-priority TSN flows are ultimately scheduled on dedicated DRBs with tight MAC resource allocation, while lower-priority or best-effort flows converge on default DRBs.

The gPTP (generalized Precision Time Protocol) frames are encapsulated at Layer 2 in GTP-U, including custom residence time headers. The bridge accurately timestamps ingress and egress events, updating the correction field as specified by IEEE 802.1AS, thereby supporting transparent clock operation essential for industrial automation.

Implementation Considerations

Achieving full-stack integration between OMNeT++/INET and Simu5G required several critical architectural solutions:

• The translation modules orchestrate the passage and modification of both data and synchronization frames, maintaining separation of data paths and explicit protocol registrations.
• Per-UE DRB mapping and SDAP layer configuration are JSON-driven, supporting extension to arbitrary endpoint counts and QoS chains.
• Multi-session operation across PDCP and RLC submodules is enabled for multi-UE support, addressing original Simu5G limitations.

The asymmetric PHY configuration on the DS-TT (streaming for TSN, non-streaming for UE) ensures compatibility with both deterministic Ethernet and 5G NR devices, while the TSN AF and Static BMCA modules provide live bridge delay monitoring and clock hierarchy management.

Results: Data Delivery, Latency, and Synchronization

In a three-endpoint configuration, nascTime achieves near-lossless high-priority traffic delivery (99.9%), with mean one-way latency of 2.58 ms and $<$0.2 μs residence time variance under ideal channel conditions. Best-effort traffic demonstrates higher delay spread, in correspondence with its scheduling discipline, capturing the impact of DRB separation on real-time and monitoring traffic. Notably, bidirectional traffic and gPTP frame forwarding are validated, with observed results confirming correct operation of the L2-in-GTP-U encapsulation and per-endpoint replication.

Upon introduction of Rayleigh fading, residence time variance increases to 48 μs, and high-priority traffic delivery minimally degrades to 99.7%. This confirms that nascTime rigorously exposes radio-induced timing stochasticity and retransmission effects, which are fundamentally absent from abstract or statistical delay-based simulators.

Scaling to three endpoints introduces negligible impact ($<$70 μs mean delay increase) to high-priority flows, demonstrating the robustness of the simulation framework for multi-endpoint industrial topologies. gPTP field updates for all endpoints remain correct, with the TSN AF providing real-time delay statistics suitable for CNC-driven control logic.

Comparative Analysis

Relative to 5GTQ, 6GDetCom, P5G-TSN, and other frameworks, nascTime is distinctive in simultaneously supporting:

• End-to-end per-flow SDAP/DRB-based QoS mapping
• Faithful radio stack modeling with full MAC scheduling and channel effects
• Transparent IEEE 802.1AS residence time measurement via actual 5G traversal
• Scalable, bidirectional, multi-endpoint evaluation
• Integration with INET and Simu5G for composability and extensibility

By contrast, alternatives either omit SDAP/DRB modeling, neglect gPTP propagation, or treat the radio segment as undifferentiated delay, precluding the nuanced analysis of real-time industrial use cases.

Limitations and Future Directions

Current limitations include: restriction to three endpoints and a single gNB; lack of dynamic BMCA or TAS gate scheduling feedback; and partial gPTP message set support (static exclusion of PdelayReq responses). These present salient opportunities for extension, especially scaling validation to higher device counts, integrating finer-grained scheduler coordination, and supporting mobile and handover scenarios.

Conclusion

nascTime defines the state of the art in simulation-based 5G-TSN bridge emulation, enabling detailed technical exploration of QoS mapping, time synchronization accuracy, and radio-induced delay effects in industrial networks. The framework’s numerical results validate both architectural fidelity and traffic performance in accordance with 3GPP and IEEE standards. The public release of nascTime promises to accelerate both academic research and applied development of integrated wireless industrial automation solutions.