TASSTA at the 5th ETSI FRMCS Plugtests in Paris: What We Tested and Why It Matters

In October 2025, TASSTA participated in the 5th ETSI FRMCS Plugtests hosted by UIC in Paris. This event is part of the ETSI MCX Plugtests Programme and is designed to validate real interoperability between mission-critical (MCX) solutions and multi-vendor 5G/IMS core networks.

FRMa Railway Mobile Communication System) is the railway industry’s next-generation communication system, intended to replace GSM-R with broadband, secure and interoperable services.

The Plugtests series is ETSI’s way to ensure that different vendors’ implementations actually work together in practice — not just on paper.

– confirm interoperability between vendors
– validate understanding of 3GPP/ETSI standards
– help implementers find and resolve issues early

The 5th edition brought together a large multi-vendor lab with more than 170 participants, simulating an environment close to real railway deployments.

We brought:
– TASSTA T.Quasar MCX Application Server
– our MCX client(s)

This allowed us to integrate and test against multiple 5G cores from different vendors in a shared interoperability lab.

This is important because in live railway networks, MCX services must operate reliably across whichever 5G core an operator chooses. Demonstrating multi-vendor compatibility is therefore a key milestone for market readiness.

All test cases were taken from ETSI’s MCX Plugtests scenario specification ETSI TS 103 564.

What we tested
– Creating an ad-hoc MCPTT group call on demand, without security
[CONNMCPTT/ONN/GROUP/ADHOC/ONDEM/NOSEC/NFC/02] – Releasing that ad-hoc group call
[CONNMCPTT/ONN/GROUP/ADHOC/ONDEM/NOSEC/NFC/03]

In simple terms
We verified that a user can start a spontaneous push-to-talk group — for example, “all staff in this station right now” — and later end it cleanly. The group is created dynamically by the MCX system and correctly transported through the 5G core.

MCPTT is not like a normal voice call — only one person (or a controlled set of people) speaks at a time. The mechanism that manages this is Floor Control (FC).

Basic FC
– Effect of priorities [FC/BASIC/02]

Advanced FC
– Revoking the floor when a timer expires (T2) [FC/ADV/01]
– Queueing requests after release [FC/ADV/02]
– Queueing requests after revoke [FC/ADV/03]

Awareness and special cases
– Functional Alias (FA) display during FC [FC/FA/BASIC/01]
FA allows users to speak under a role (e.g., “Train Driver 17”) instead of a personal name.
– Multi-talker basic operation [FC/MT/BASIC/01]
– Location sharing during FC [FC/LOC/BASIC/01]
– Location sharing during multi-talker FC [FC/MT/LOC/BASIC/01]

In simple terms
We validated that:
– the system correctly assigns the “right to speak”
– priority users override lower-priority requests
– the floor is revoked automatically if held too long
– queued talkers get their turn in order
– operators can immediately see who is speaking (via alias/role) and, when relevant, where they are — even in multi-talker situations

These are essential railway features, enabling dispatchers and field teams to maintain clear, disciplined voice communication in high-stress situations.

Mission-critical voice requires guaranteed quality (latency, priority, stability). In 5G, this is achieved via dedicated QoS flows.

We tested:
– Creating a unicast 5GS QoS flow via Rx [PCC/5GSQOSFLOWSETUP/Rx/02]
– Creating a unicast 5GS QoS flow via N5 [PCC/5GSQOSFLOWSETUP/N5/02]
– Updating a unicast 5GS QoS flow via Rx [PCC/5GSQOSFLOWUPDATE/Rx/02]

In simple terms

We checked that the TASSTA MCX server can request mission-critical treatment from the 5G core — using standard 3GPP policy control interfaces — for specific users’ media streams.
This allows the network to prioritize MCPTT traffic over normal data traffic, which is a core requirement for FRMCS deployment.

Even without sharing confidential results, the value is clear:
– Multi-vendor realism — testing our stack against diverse 5G cores and MCX implementations in one environment
– Standards confirmation — verifying our implementation aligns with ETSI/3GPP intent
– Early issue discovery — solving interoperability problems in the lab, before they appear in real railway networks

FRMCS will only succeed if:
1. vendors interoperate,
2. mission-critical QoS is correctly enforced in 5G cores,
3. railway-specific MCX behavior (roles, priorities, multi-talker logic, location) operates reliably.

This Plugtests edition showed the ecosystem moving from “specification compliance” to field-ready interoperability.

Big thanks to ETSI Plugtests, UIC, and all participating vendors and operators for a highly collaborative environment.
TASSTA is proud to contribute to the maturity of FRMCS and MCX interoperability, and we will continue this work in upcoming ETSI/3GPP programmes.