T-5GS: A Full-Scale Multi-Operator 5G Roaming Testbed Beyond Core-Level Simulations

Providing seamless service beyond geographical boundaries has long been a core objective of mobile networks, with roaming playing a pivotal role [1]. However, experimental support for 5G Standalone (5G SA) roaming remains limited---lagging behind both architectural progress and research needs. To address this, we present T-5GS, a full-scale, reproducible and open-source testbed. Unlike partially implemented stacks in existing platforms that cover only 38% of the roaming protocol stack, T-5GS improves protocol coverage to nearly 100%. By enabling realistic end-to-end testing through VM-based isolation---avoiding the kernel-sharing issues common in container-based setups---T-5GS offers a forward-looking foundation for advancing 5G roaming design, interoperability, and security research. The complete implementation is publicly available at https://github.com/T-5GS/T-5GS.