Future Railway Mobile Communication System (FRMCS).

• Transport ($OB_{APP}$ & $TS_{APP}$)

  • The core architectural shift: Making railway applications completely agnostic to the underlying radio technology.

  • Practical usage of the $OB_{APP}$ and $TS_{APP}$ interfaces via standard APIs.

• Application Coupling Regimes

  • Engineering definitions and practical boundaries of Tight-Coupled, Loose-Coupled, and Super-Loose-Coupled (SLC) applications (e.g., how ETCS vs. Voice Apps interface with the network).

• 4G EPS vs. 5G Core Architecture Essentials

  • Mapping 4G MME/S-GW functionalities to 5G cloud-native Network Functions (AMF, SMF, UPF).

• Critical Network Interfaces and Reference Points

  • Setting up user and control planes: Technical implementation of $N1$, $N2$, $N3$, $N4$, and $N7$ interfaces.

• Network Topology and Exposure Functionality

  • Utilizing the Network Exposure Function (NEF) and Unified Data Management (UDM) to enforce user access profiles.

  • Deploying User Plane Functions (UPF) in series to enable low-latency edge edge-breakout of critical data.

• Architecting Bearer Flexibility

  • Enabling seamless operation across heterogeneous access networks (RMR spectrum, public MNOs, and Wi-Fi).

• Implementing FRMCS Multipath (Multi-UE Control)

  • Distributing a single application stream concurrently over multiple separate UEs for ultra-high reliability.

  • Practical protocols: Detailed deployment of MP-TCP and MP-QUIC layers.

• Multi-Access and Intra-RAT Handover

  • Configuring policy rule-sets to seamlessly switch or split traffic across RMR and Public Mobile Networks (PMNOs) without interrupting critical systems like ETCS.

• The QoS Mapping Architecture

  • Understanding the structural conversion from end-to-end (E2E) application KPIs down to transport-level resource flows.

• Allocation and Retention Priority (ARP) & Congestion Control

Configuring ARP values (1 to 8) to successfully execute pre-emption mechanisms when radio frequency bands are congested

• Transport Layer DSCP Mapping

  • Configuring gNodeB and UPF nodes to map wireless 5QIs to backhaul IP network DSCP values (e.g., mapping 5QI 65 to EF, 5QI 69 to CS5).

• Functional Addressing and Role-Based Identification

How FRMCS replaces rigid phone numbers with operational roles (Functional Aliases) using standard 3GPP MCX frameworks

• Anatomy of a Role-Based ID

  • Constructing alphanumeric identities matching standard formats: ***.IdentificationLabel.LocationLabel.FunctionLabel@OrganizationalCode

  • Practical engineering lookup: Mapping Train IDs, Vehicle IDs, and operational profiles (Drivers, Primary/Secondary Controllers, Shunting Teams).

• Network-Level Addressing Architecture

  • Configuring Host-to-Host (H2H) data routes for critical apps (ATP/ETCS, ATO).

  • Configuring Host-to-Network (H2N) data tunnels using public reachable domains for supportive infrastructure (DNS, PKI, KMS).

• Automatic Train Protection (ATP) & Responsibility Handover

  • Step-by-step transaction flow of an onboard ETCS system establishing an MCDATA IP connectivity session with trackside RBCs.

  • Managing boundary transitions: Nominal and non-nominal call flows when a train shifts its tracking data between different operational Service Domains.

• Engineering Railway Emergency Communications (REC)

  • Architecture of a combined REC alert and subsequent REC voice group call.

Geofencing integration: Dynamic participant determination based on real-time Initiating Area and Addressed Area polygons via automated GNSS/Cell ID tracking.

• Late Entry, Audits, and Dynamic Floor Control

  • How the server dynamically pushes a call connection to a train entering an active danger zone.

Enforcing pre-emptive floor control: Giving dispatchers overriding authorization to command the audio channel.