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4.4.1 Introduction
The present document specifies a minimal set of 5G Core Session Management UE capabilities for an On-Board FRMCS Radio Module. NOTE: At the time of publication, ongoing industrial testing and validation programs are expected to help identifying any specific 5G Core Session Management UE capabilities to mandate from an ...
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4.4.2 5QI
An Onboard FRMCS Radio Module shall support at least the 5QI identified in ETSI TS 103 765-1 [4], Table 9.3-1. ETSI ETSI TS 103 765-5 V1.1.1 (2026-01) 8 Annex A (normative): Reference TDD frame from ECC Recommendation (23)01 Annex 5 of ECC Recommendation (23)01 [i.2] specifies the reference TDD parameters to be support...
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1 Scope
The present document specifies the FRMCS Transport Stratum for the Future Railway Mobile Communications System (FRMCS). In general, the FRMCS Transport Stratum provides data connectivity and the related services. The present document covers: • 3GPP terrestrial access. • Transport stratum interconnection scenarios in al...
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2 References
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2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which a...
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2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks i...
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3 Definition of terms, symbols and abbreviations
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3.1 Terms
For the purposes of the present document, the terms given in ETSI TR 103 791 [i.1] and the following apply: gNodeB: base station that provides NR radio access for 5G networks multipath dataflow: application flow of IP packets processed by the FRMCS Multipath Function, characterized by its application-related attributes...
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3.2 Symbols
Void.
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3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply: 5G NR 5G New Radio 5GC 5G Core Network 5G-EIR 5G-Equipment Identity Register 5GS 5G System 5QI 5G QoS Identifier AF Application Function AKA Authentication and Key Agreement AMF Access and Mobility Function API Application Programming Interfac...
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4 Principles and concept
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4.1 General
Clause 4 describes the system architecture of the FRMCS Transport Stratum to support packet switched data connectivity and service enabling deployments. The system architecture applicable for FRMCS is the 3GPP 5G System (5GS) and the related 5GS architecture defined in ETSI TS 123 501 [1].
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4.2 Architecture
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4.2.1 Common Architecture Principles
The Transport Stratum consists of the access domain and the 5G core network domain (see Figure 4.2.2-1). The transport stratum User Equipment (UE) is part of the transport stratum and requires appropriate credentials necessary to make use of the transport stratum. FRMCS Transport Stratum identities are described in cla...
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4.2.2 Architecture for a Standalone FRMCS Transport Domain
The Standalone FRMCS Architecture represents a FRMCS network without external connections, neither to foreign FRMCS Domain, nor to a GSM-R system or a Mobile Network Operator's 5G Core domain. FRMCS Access Domain FRMCS MC System Service Agents User Equipment 3GPP capable and non-3GPP via WAN MNO Access Domain NG-RAN Ra...
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4.2.3.0 General
A FRMCS Transport Domain in interaction with other FRMCS Domains shall implement a home routed interconnected domain architecture depicted in Figure 4.2.3.0-1, which enables the UE (from the own FRMCS Transport Domain or from another FRMCS Transport Domain) in a visited FRMCS network to communicate with the service str...
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4.2.3.1 FSNNI reference point (at FRMCS Transport Domain level)
The FSNNI reference point is the reference point between FRMCS Domains. At FRMCS Transport Domain level, it enables mobility of FRMCS Users between FRMCS Domains. The FSNNI reference point is composed of the 5GC reference points listed in Table 4.2.3.1-1 for Local Breakout (LBO), Home Routing (HR) or both. Table 4.2.3....
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4.2.4 FRMCS National Roaming Architecture (Home Routed)
National roaming allows the use of Mobile Network Operator spectrum in a National Roaming architecture. This architecture uses the FRMCS Access Domain radio module, which is equipped to handle Mobile Network Operator (MNO) spectrum as well, or a separate MNO radio module in the On-Board FRMCS, which is configured to ro...
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4.2.5 FRMCS Roaming Architecture (Local Breakout)
In roaming architecture with Local Breakout (Figure 4.2.5-1), FRMCS On-Board Service Clients use FRMCS On-Board UE that is attached to a foreign FRMCS (LBO roaming partner's) access domain. FRMCS bearers traverse only the foreign FRMCS 5G Core. The Home FRMCS 5G core is accessed for signaling only (e.g. for UE authenti...
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4.3 FRMCS Transport Stratum Capabilities
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4.3.1 General
For the use of the FRMCS Transport Stratum certain capabilities, e.g. UE mobility, are required encompassing one or various related functions for proper operation.
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4.3.2 Access Capabilities
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4.3.2.1 3GPP Radio Access
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4.3.2.1.1 General
FRMCS assumes the use of a dedicated spectrum n100 and n101 (as specified in ETSI TS 103 793 [35]) as a default approach to radio coverage. FRMCS allows the use of MNO spectrum in a MOCN configuration utilizing specific predefined shared MNO frequencies as described in clause 5.1.2.2. One of the FRMCS system principles...
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4.3.2.1.2 5G NR capabilities
For the provision of point-to-point, the corresponding 5G NR radio bearer type unicast shall be used. For the use of radio bearers, the FRMCS Transport Domain shall support the following functional areas (see Figure 4.3.2.1.2-1): • For the physical layer as specified in the standards ETSI TS 138 211 [11], ETSI TS 138 2...
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4.3.3 Core capabilities
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4.3.3.1 General
The FRMCS Transport Stratum Core, using the 5GC forms the connectivity layer for the FRMCS Service Stratum. 3GPP access can either be using the FRMCS Access Domain RMR spectrum or shared MNO spectrum. Wireline access is provided by interfacing with the core Data Network. The wireline FRMCS users (e.g. VAS controllers) ...
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4.3.3.2 3GPP NAS capabilities
5G Core capabilities are further detailed in clause 5 and shall apply for use by the FRMCS Transport Stratum.
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5 FRMCS Transport Stratum Constituents
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5.1 FRMCS Transport Stratum Access Domain Constituents
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5.1.1 General
The access domain for FRMCS shall support one or more of the following types of wireless access networks: • 3GPP terrestrial radio access using 5G NR radio access within FRMCS Access Domain spectrum portions controlled by a FRMCS 5GC. This type of wireless access network is specified in clause 5.1.2.1. • 3GPP terrestri...
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5.1.2 FRMCS Transport Wireless Access
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5.1.2.1 RMR Access
For RMR access, FRMCS Transport Domain shall comply to ETSI TS 103 793 [35], clauses 4 and 5. For RMR access in band n101, FRMCS Transport Domain shall comply to ETSI TS 103 765-5 [36], Annex A.
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5.1.2.2 MOCN Access
In MOCN access for a FRMCS operator A, a MOCN gNodeB (operated by MOCN operator B which can be an MNO operator or another FRMCS operator B) is shared between FRMCS operator A and MOCN operator B. The traffic belonging to FRMCS operator A will go to the FRMCS core network of the operator A, and the traffic belonging to ...
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5.2 FRMCS Transport - Core
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5.2.1 Core Architectural Element and Functions
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5.2.1.1 Access and Mobility Management Function (AMF)
The Access and Mobility Management Function (AMF) is specified in ETSI TS 123 501 [1], clause 6.2.1. The AMF is responsible for providing the following capabilities in FRMCS: a) Termination of interfacing with RAN Control Plane. b) Termination of NAS, NAS ciphering and integrity protection. c) Registration management. ...
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5.2.1.2 Session Management Function (SMF)
The Session Management Function (SMF) is specified in ETSI TS 123 501 [1], clause 6.2.2. The SMF is responsible for providing the following capabilities in FRMCS: a) Session Management. b) UE IP address allocation & management. c) Selection and control of User Plane Function. d) Configures traffic steering at UPF to ro...
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5.2.1.3 User Plane Function (UPF)
The User Plane Function (UPF) is specified in ETSI TS 123 501 [1], clause 6.2.3. The UPF is responsible for providing the following capabilities for FRMCS: a) Packet routing and forwarding. b) Packet inspection. c) QoS handling. d) Traffic usage reporting. e) Acts as external PDU session point of interconnect to Data N...
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5.2.1.4 Policy Control Function (PCF)
The Policy Control Function (PCF) is specified in ETSI TS 123 501 [1], clause 6.2.4. The PCF is responsible for providing the following capabilities in FRMCS: a) Unified policy framework. b) Policy rules to CP functions. ETSI ETSI TS 103 765-1 V1.1.1 (2026-01) 22 c) Access subscription information for policy decisions ...
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5.2.1.5 Authentication Server Function (AUSF)
The Authentication Server Function (AUSF), as defined in ETSI TS 123 501 [1], clause 6.2.8, shall be implemented in FRMCS. The AUSF is responsible for providing the following capabilities in FRMCS: a) Supports authentication for 3GPP access, as specified in ETSI TS 133 501 [20]. In a FRMCS Domain, the AUSF shall suppor...
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5.2.1.6 Unified Data Management (UDM)
The Unified Data Management (UDM) is specified in ETSI TS 123 501 [1], clause 6.2.7. The UDM is responsible for providing the following capabilities in FRMCS: a) Generation of Authentication and Key Agreement (AKA) credentials for UEs. b) UE User identification handling. c) UE Access authorization. d) UE Subscription m...
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5.2.1.7 Unified Data Repository (UDR)
The Unified Data Repository (UDR) is specified in ETSI TS 123 501 [1], clause 6.2.11. The following functions are supported in the UDR: a) Storage and retrieval of subscription data by the UDM. b) Storage and retrieval of policy data by the PCF. c) Storage and retrieval of application-related data (including of Packet ...
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5.2.2 Conditional Core Architectural Elements
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5.2.2.1 General
In addition to the minimal architectural components listed in clause 4.2.2, the FRMCS core architecture may require the following conditional architectural components. These components are not mandatory in the minimized FRMCS architecture. They may be required to fulfil national rules or to enhance the operation of FRM...
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5.2.2.2 5G-Equipment Identity Register (5G-EIR)
The 5G-Equipment Identity Register (5G-EIR) is used to check the status of equipment's identity (e.g. to check that it has not been listed as unauthorized or stolen). If the FRMCS Operator implements 5G-EIR, it shall be implemented according to ETSI TS 129 511 [26] and ETSI TS 123 502 [10]. This element is conditional ...
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5.2.2.3 Network Exposure Function (NEF)
The usage of Network Exposure Function (NEF) is conditional on the requirement to connect the FRMCS Transport Domain to additional Core Application Functions (AF) other than the MC Service Server. The NEF securely exposes network capabilities and events provided by 3GPP Network Functions to Application Functions. The N...
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5.2.2.4 Network Repository Function (NRF)
The Network Repository Function (NRF) is specified in ETSI TS 123 501 [1], clauses 6.2.6, 6.3.26 and 7.2.6. The NRF provides a centralized repository for all the 5G Network Functions (NFs) in the FRMCS Transport Domain. The NRF allows 5G NFs to register and discover each other via a standards-based API.
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5.2.2.5 Binding Support Function (BSF)
The Binding Support Function (BSF) is conditional on the need for a geo-redundant 5G core configuration. The Binding Support Function is used to bind sessions with the correct PCF instance(s). If FRMCS Operator implements BSF, it shall be implemented according to ETSI TS 123 501 [1], clause 7.2.15.
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5.2.2.6 Service Communication Proxy (SCP)
The Service Communication Proxy (SCP) is conditional on the need for a geo-redundant 5G core configuration or for other functions specified ETSI TS 123 501 [1], clause 6.2.19. It is used in geo-redundant 5G core configurations to provide functionalities such as message forwarding and routing, Delegated Discovery, Indir...
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5.2.2.7 Security Edge Protection Proxy (SEPP)
The Security Edge Protection Proxy (SEPP) is specified in ETSI TS 123 501 [1], clause 6.2.17.
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5.3 FRMCS Multipath Function
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5.3.1 General
The FRMCS Multipath Function distributes incoming Multipath Dataflows across one or multiple Multipath Datapaths according to available Multipath Datapaths and Multipath Policy. The FRMCS Multipath Function can make use of Multipath Datapaths over a FRMCS Transport Domain or over a Non-FRMCS Transport Domain. The FRMCS...
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5.3.2 FRMCS Multipath Function capability
The FRMCS Multipath Function supports the following features: • Multipath Datapath selection, i.e. determination of one or more eligible Multipath Datapaths based on evaluation of the Multipath Policy associated to a Multipath Dataflow. ETSI ETSI TS 103 765-1 V1.1.1 (2026-01) 25 • QoS control, i.e. conveyance of QoS re...
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5.3.3 Architecture
Figure 5.3.3-1 and Figure 5.3.3-2 illustrate the functional architecture of the FRMCS Multipath Function. It is constituted of two functions, the Multipath Client and the Multipath Gateway. The Multipath Client and the Multipath Gateway are connected via two reference points: • FSMPM which enables the FRMCS Multipath c...
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5.3.4 Multipath Gateway
The MPF-CTRL function of Multipath Gateway has the following responsibilities: • Control of multipath setup between a Multipath Client and the Multipath Gateway. • Instantiation of Multipath Dataflow Handlers. • Handling of IP Address management for each Multipath Dataflow Handler. • Allocation of each Multipath Datafl...
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5.3.5 Multipath Client
The MPF-CTRL function in the Multipath Client has the following responsibilities: • Control of multipath setup between the Multipath Client and a Multipath Gateway, based on control information received from the Multipath Gateway. • Instantiation of Multipath Dataflow Handlers, based on control information received fro...
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5.3.6 IP Address Assignment
IP Address assignment is required: a) for public service layer IP address for each Multipath Dataflow Handler; and b) for each transport domain Multipath Datapath for each Multipath Dataflow Handler. The 5G Core provides IPv6 prefix during the initial default data connection establishment to each UE. The procedure is I...
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5.3.7 FRMCS Multipath Function procedures
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5.3.7.1 FRMCS Multipath Function discovery procedure
The FRMCS Multipath Function discovery procedure allows a Multipath Client to discover the presence of a Multipath Gateway within a FRMCS Transport Domain. The following high-level steps are undertaken: 1) The MPF-CTRL of Multipath Client shall select a default connection mapped to a locally selected On-Board FRMCS Rad...
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5.3.7.3 FRMCS Multipath Function capability negotiation procedure
The FRMCS Multipath Function capability negotiation procedure is executed between a Multipath Client and a Multipath Gateway. The Multipath Gateway shall determine the parameters and Multipath Policy used. The following multipath capability negotiation shall apply on a per Multipath Dataflow Handler basis: 1) Multipath...
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5.3.7.4 FRMCS Multipath Function capability definition procedure
If the selected Multipath Protocol decided during Multipath capability negotiation as per clause 5.3.7.3 Point 1 is MP-TCP, the MP-TCP protocol shall be implemented according to IETF RFC 8684 [27]. If the selected Multipath protocol decided during Multipath capability negotiation as per clause 5.3.7.3 Point 1 is MP-QUI...
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5.3.7.5 FRMCS Multipath Function fallback procedure
The FRMCS Multipath Function fallback procedure shall be executed if the Multipath Client does not get a valid response on the DNS query. This is considered as an indication that there is no trackside MPF available or that it shall not be used. In this case, the IP assignment as per clause 5.3.6 shall be used.
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5.3.7.6 FRMCS Multipath Function cleanup procedure
The following steps are undertaken: 1) For each Multipath Dataflow of the Multipath Client, the procedure in clause 5.3.7.7 shall be performed. 2) The Multipath Gateway shall release the Multipath Dataflows Handler.
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5.3.7.7 Release of FRMCS Multipath Dataflow
The following steps are undertaken: 1) The Multipath Client shall request the release of the Multipath Dataflow. 2) The Multipath Gateway shall perform the release of Multipath Dataflow.
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6 Transport Stratum Procedures
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6.1 On-Board Radio Module Registration Procedure
Upon selection by the On-Board FRMCS of a FRMCS Transport Domain to register to, the On-Board FRMCS Radio Module shall execute the network selection, ETSI TS 123 501 [1], clause 5.2.2. PLMN selection procedure in "manual network selection" mode as specified in ETSI TS 123 122 [38], clause 4.2 towards the designated FRM...
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6.3 On-Board Radio Module deregistration procedure
The On-Board FRMCS Radio Module shall execute the "UE-initiated Deregistration" procedure as specified in ETSI TS 123 502 [10], clause 4.2.2.3.2.
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6.4 Roaming Home-Routed Transport Path Establishment
In the Home-Routed case, the On-Board FRMCS Radio Module shall execute the "UE Requested PDU Session Establishment" procedure as specified in ETSI TS 123 502 [10], clause 4.2.3.2.2. This procedure is typically used in FRMCS to: • Enable roaming of a UE onto an MNO network with home routing to the Home FRMCS Domain (Nat...
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6.5 Release of transport path
If the transport path is a Multipath Dataflow, the procedure in clause 5.3.7.7 shall be performed. If the transport path is not a Multipath Dataflow, the UE-requested PDU session release as specified in ETSI TS 123 502 [10], clause 4.3.4 shall be performed.
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7 Interaction of Service Stratum and Transport Stratum
The ETSI reference point to be used for interaction between the transport stratum and service stratum including FRMCS SIP core as defined in ETSI TS 103 765-2 [6] and in ETSI TS 123 501 [1], clause 6.2.10. The following functions are supported between the transport stratum and service stratum: a) Interacting with the 5...
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8.1 FRMCS Quality of Service Principles
The FRMCS Transport Stratum QoS framework is based on the following principles: a) QoS is applied via PDU sessions (up to 15 per UE) and QoS flows (up to 63 per PDU session). b) QoS is enforced at UE, gNodeB and UPF based on rules propagated from the UDM/PCF or pre-configured. c) QoS policy is controlled from the FRMCS...
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8.2 FRMCS Unified Access Control (UAC)
In FRMCS, UAC enables the prioritization of access for FRMCS users and helps the gNodeB load control functions to effectively handle the high-load scenarios. Access prioritization is carried out by barring the mobile-originated access and service requests at the UE side. The UE will decide if it is allowed to submit a ...
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8.3 5QI and ARP Application per FRMCS Service
The FRMCS Transport Domain shall support at least the 5QI identified in Table 8.3-1. Table 8.3-1: List of 5QI in FRMCS 5QI 4 5 8 65 69 As an example, two of the Communication Session Categories listed (informative) in ETSI TS 103 765-2 [6], Annex A, can be mapped as defined in Table 8.3-2. Table 8.3-2: An example of ma...
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8.4 5QI to DSCP Mapping
The QoS of FRMCS Transport Stratum traffic is classified using 5QI. Since the traffic flow to some endpoints (Trackside Gateway, VAS controller, etc.) traverses an IP/MPLS backbone the 5QI shall be mapped to a Traffic Class. For each QoS Flow characterized by its 5QI, the mapping of 5QI to DSCP values are done on diffe...
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9 Transport Stratum Synchronization
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9.1 Radio Network Synchronization
NR SA TDD radio networks require frequency and phase synchronization. When the Baseband Radio Node is time and phase synchronized, it is also frequency synchronized. FRMCS TDD cells operating at the same frequency in overlapping coverage areas would benefit from time domain isolation to minimize base station-to-base st...
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9.2 Time-of-Day Synchronization
Network Time Protocol (NTP) (see IETF RFC 5905 [i.2]) or Network Time Security, IETF RFC 8915 [i.3] can be used to synchronize the time of day. The main objective of NTP is long-term event synchronization across core and radio access nodes. The core network elements and elements in the baseband nodes can then send NTP ...
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10 Transport Stratum Identities
FRMCS uses the following identities in the transport stratum: • GPSI as external identifier. • SUPI/SUCI using IMSI identifier. • NAI using IMSI with MCC and MNC. ETSI ETSI TS 103 765-1 V1.1.1 (2026-01) 39 Annex A (informative): Generalities on synchronization This annex is intended as informative on possible approache...
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1 Scope
The present document describes the high-level System Architecture for the Future Railway Mobile Communications System (FRMCS). The interaction between FRMCS domains, high-level procedures, deployment scenarios and IP addressing/routing are also outlined.
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2 References
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2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which a...
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2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks i...
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3 Definition of terms, symbols and abbreviations
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3.1 Terms
For the purposes of the present document, the terms given in ETSI TR 103 791 [i.4] and the following apply: open session: session which has not been terminated via MCData procedures session: tunnel established between two MCData clients on behalf of an application
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3.2 Symbols
Void.
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3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply: 5G 5th Generation 5GC 5G Core API Application Programming Interface APP APPlication ATO Automatic Train Operation ATP Automatic Train Protection EIRENE European Integrated Railway radio Enhanced NEtwork ETCS European Train Control System FCOP ...
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4 Architecture principles and model
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4.1 Introduction
The present document defines the architecture for the Future Railway Mobile Communications System (FRMCS) in on-network mode. FRMCS architecture is described and specified based on a transport stratum and a service stratum. FRMCS transport stratum provides connectivity for data transport and FRMCS service stratum enabl...
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4.2 General principles
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4.2.0 Overview
The FRMCS System Architecture is defined to support communications between various types of FRMCS Users such as train and trackside end-users/applications, and railway personnel. The FRMCS System Architecture satisfies the following key principles: • Maximizing the decoupling between the strata to facilitate an indepen...
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4.2.1 Strata
The FRMCS System Architecture is structured in two strata called Service Stratum and Transport Stratum as illustrated in Figure 4.2.1-1. External to the FRMCS System, railway applications using the FRMCS System are grouped in a third stratum named Railway Application Stratum (see Figure 4.2.1-1). ETSI ETSI TS 103 764 V...
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4.2.2 Modularity of deployment
The FRMCS System Architecture is intended to be deployed in different ways: • Stand-alone deployment, i.e. deployment of an FRMCS Domain with no external connection to other FRMCS Domains. • Deployment as part of an international network of networks, i.e. deployment of an FRMCS Domain connected to other FRMCS Domains. ...
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4.2.3 Modes of operation
The FRMCS System Architecture enables: • The communication of an FRMCS User served by its Home FRMCS Domain or served by a foreign FRMCS Domain. • The mobility of an FRMCS User within an FRMCS Domain as well as across FRMCS Domains. In general, mobility procedures defined at the FRMCS Transport Stratum and migration pr...
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4.2.4 Applications enablement
Within trains, FRMCS applications interact with the FRMCS System via the OBAPP reference point exposed by the On-Board FRMCS. All applications directly interfacing with the On-Board FRMCS are expected to call a Local Binding procedure to authenticate themselves with the On-Board FRMCS. Subsequently, two modes of intera...
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4.2.5 Cybersecurity
For an FRMCS Domain, the approach to cybersecurity in FRMCS is multi-layered by leveraging cybersecurity measures at the FRMCS Transport Stratum and FRMCS Service Stratum levels. Applications can also implement their own additional security measures at the Application Stratum level. At the periphery of an FRMCS Domain,...
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4.2.6 GSM-R interworking
Requirements induced by interworking with GSM-R are specified in ETSI TS 103 792 [5]. ETSI ETSI TS 103 764 V1.1.1 (2026-01) 11 In particular, interworking scenarios for various services (group calls, point-to-point calls, text messaging) are specified. An overview of the mobility procedure applied in GSM-R/FRMCS Domain...
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4.2.7 FRMCS Multipath
FRMCS Multipath introduces a capability to establish communication between the On-Board FRMCS Multipath Function (called Multipath Client in ETSI TS 103 765-1 [1]) and an FRMCS Infrastructure Multipath Function (called Multipath Gateway in ETSI TS 103 765-1 [1]) over one or more data paths (called Multipath Datapaths i...
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4.3 Architecture reference model
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4.3.1 General
The interaction between functional blocks is represented with point-to-point reference points, showing how various network functions interact with each other.