ETSI TS 103 764 V1.1.0 (2025-11)

Final draft ETSI TS 103 764 V1.1.0 (2025-11)

TECHNICAL SPECIFICATION
Rail Telecommunications (RT);
Future Railway Mobile Communication System (FRMCS);
System Architecture
2 Final draft ETSI TS 103 764 V1.1.0 (2025-11)

Reference
DTS/RT-0082
Keywords
5G, architecture, FRMCS, mission critical
applications, railways
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from the
ETSI Search & Browse Standards application.
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format on ETSI deliver repository.
Users should be aware that the present document may be revised or have its status changed,
this information is available in the Milestones listing.
If you find errors in the present document, please send your comments to
the relevant service listed under Committee Support Staff.
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure (CVD) program.
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
and/or governmental rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2025.
All rights reserved.
ETSI
3 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Architecture principles and model . 8
4.1 Introduction . 8
4.2 General principles. 8
4.2.0 Overview . 8
4.2.1 Strata . 8
4.2.2 Modularity of deployment . 9
4.2.3 Modes of operation . 9
4.2.4 Applications enablement . 10
4.2.5 Cybersecurity . 10
4.2.6 GSM-R interworking . 10
4.2.7 FRMCS Multipath . 11
4.3 Architecture reference model . 11
4.3.1 General . 11
4.3.2 FRMCS System Architecture components . 11
4.3.3 Stand-alone reference architecture . 12
4.3.4 Interconnected reference architecture . 13
4.3.5 FRMCS Reference points at system level . 13
5 FRMCS System Architecture components . 14
5.1 FRMCS Domain . 14
5.1.0 Overview . 14
5.1.1 Transport Domain . 14
5.1.2 FRMCS Service Domain . 14
5.2 On-board FRMCS . 14
5.3 FRMCS-capable Handheld . 14
5.4 FRMCS-capable Object . 14
5.5 FRMCS Trackside Gateway . 14
5.6 On-Board FRMCS Multipath Function . 15
5.7 FRMCS Infrastructure Multipath Function . 15
5.8 EIRENE System (GSM-R based System) . 15
5.9 Non-EIRENE non-FRMCS System . 15
6 Non-application-specific procedures . 15
6.1 Introduction . 15
6.2 FRMCS Start of Operation . 15
6.2.0 Overview . 15
6.2.1 FRMCS Start of Operation served by the Home FRMCS Domain . 16
6.2.2 FRMCS Start of Operation served by a Foreign FRMCS Domain . 17
6.3 FRMCS Close of Operation . 17
6.4 Domain transitions . 18
6.4.1 Inter-FRMCS Domain transition . 18
6.4.1.0 General . 18
6.4.1.1 Inter-FRMCS Domain transition: Type I or Type III applications. 20
6.4.1.1.1 Inter-FRMCS Domain transition: Type I or Type III applications with no open session . 20
ETSI
4 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
6.4.1.1.2 Inter-FRMCS Domain transition: Type I or Type III applications with an open session . 20
6.4.1.2 Inter-FRMCS Domain transition: Type II applications . 20
6.4.1.2.1 Inter-FRMCS Domain transition: Type II applications entering the Domain of applicability . 20
6.4.1.2.2 Inter-FRMCS Domain transition: Type II applications entering an FRMCS Domain which is
not in the Domain of applicability . 21
6.4.1.3 Inter-FRMCS Domain transition: Type IV applications . 21
6.4.2 Transition between GSM-R and FRMCS Domain . 21
7 Deployment scenarios of FRMCS . 21
7.1 Introduction . 21
7.2 Stand-alone FRMCS Domain . 22
7.3 FRMCS Domain in interaction with other FRMCS Domains . 22
7.4 FRMCS Domain in interaction with a GSM-R system . 22
7.5 FRMCS Domain in interaction with a non-EIRENE non-FRMCS network . 22
8 IP addresses and routing . 22
8.0 Generalities. 22
8.1 IP address ranges - Loose-Coupled Applications, without FRMCS Multipath . 24
8.2 IP address ranges - Tight-Coupled Applications, without FRMCS Multipath . 25
History . 26

ETSI
5 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The declarations
pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
ETSI IPR online database.
Pursuant to the ETSI Directives including the ETSI IPR Policy, no investigation regarding the essentiality of IPRs,
including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not
referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become,
essential to the present document.
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ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
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DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its
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the oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
Foreword
This final draft Technical Specification (TS) has been produced by ETSI Technical Committee Railway
Telecommunications (RT), and is now submitted for the Vote phase of the ETSI Standardisation Request deliverable
Approval Procedure (SRdAP).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

ETSI
6 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
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.
2 References
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 are not found to be publicly available in the expected location might be found in the
ETSI docbox.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 103 765-1: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 1: Transport Stratum".
[2] ETSI TS 103 765-2: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 2: Service Stratum".
[3] ETSI TS 103 765-3: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 3: Train On-Board functions and
interfaces".
[4] ETSI TS 103 765-4: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 4: Trackside functions and interfaces".
[5] ETSI TS 103 792: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Interworking with GSM-R".
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 included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents may be useful in implementing an ETSI deliverable or add to the reader's
understanding, but are not required for conformance to the present document.
[i.1] UIC FRMCS FFFIS-7950: "FRMCS FFFIS Form Fit Functional Interface Specification".
[i.2] UIC FRMCS FIS-7970: "FRMCS FIS Functional Interface Specification".
[i.3] UIC FRMCS SRS: FRMCS System Requirements Specification".
[i.4] ETSI TR 103 791: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Terminology for FRMCS specifications".
ETSI
7 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
3 Definition of terms, symbols and abbreviations
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
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
th
5G 5 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 FRMCS Close of OPeration
FFFIS Form Fit Functional Interface Specification
FIS Functional Interface Specification
FRMCS Future Railway Mobile Communication System
FS FRMCS System
FSD FRMCS Service Domain
FSMPU FRMCS MultiPath User plane
FSOP FRMCS Start of OPeration
FTD FRMCS Transport Domain
GSM Global System for Mobile
GSM-R Global System for Mobile communications - Railway
H2N Host-To-Network
IM Infrastructure Manager
IP Internet Protocol
IWF InterWorking Function
LB Local Binding
MC Mission Critical
MCPTT Mission Critical Push To Talk
MCS Mission Critical Service
MCX Mission Critical Communications
MPM MultiPath Management
NAT Network Address Translation
NNI Network-to-Network Interface
NR New Radio
NTT Network Transition Trigger
OB On-Board
OM Operation and Maintenance
OMR OM Remote Interface
ONI Other Network-to-Network Interface
PDU Packet Data Unit
QoS Quality of Service
REC Railway Emergency Communication
ETSI
8 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
RM Radio Module
RMR Railway Mobile Radio
RU Railway Undertaking
SIP Session Initiation Protocol
SRS System Requirements Specification
SSE Server Sent Events
TCMS Train Control Management System
TLS Transport Layer Security
UE User Equipment
UIC Union Internationale des Chemins de Fer (International Union of Railways)
VAS Voice Application Subsystem
4 Architecture principles and model
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 enables communication
as services between two or multiple FRMCS Users for voice, video and data applications.
The following is described:
• overall architecture of FRMCS within one FRMCS Domain with principles and components;
• procedures applicable for an FRMCS Domain and interactions between FRMCS Domains.
FRMCS System Architecture is designed based on the high-level principles outlined in clause 4.2. In addition, the
architecture reference model is described.
4.2 General principles
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 independent evolution of the Transport Stratum
and/or of the Service Stratum without mandating an evolution of the Application Stratum.
• Supporting QoS and priority policies that allows differentiating the communications of different types of
railway applications.
• Supporting multiple Radio Access Technologies.
• Supporting Service Stratum security and Transport Stratum security.
• Supporting Operation and Maintenance for on-board FRMCS.
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
9 Final draft ETSI TS 103 764 V1.1.0 (2025-11)

Figure 4.2.1-1: Strata in FRMCS System Architecture
The Transport Stratum provides data connectivity and corresponding services (e.g. mobility, QoS, policy control,
authentication, etc.). The Service Stratum is centered around the 3GPP Mission Critical Communications (MCX)
Framework and decouples the application from the underlying transport networks.
The FRMCS Transport Stratum is described in more detail in ETSI TS 103 765-1 [1].
The FRMCS Service Stratum is described in more detail in ETSI TS 103 765-2 [2].
The Application Stratum is not considered to be part of the FRMCS architecture and therefore it will not be described in
the present document.
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.
• Deployment encompassing interworking with GSM-R, deployment of an FRMCS Domain with users
interacting with or moving to, or from a GSM-R system, under the control of the same operator or not.
• Deployment encompassing interconnection with non-EIRENE non-FRMCS networks.
The minimal deployment of the FRMCS System Architecture is that of a stand-alone FRMCS Domain.
For a description of the deployment scenarios of FRMCS, see clause 7 of the present document.
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 procedures defined in the
FRMCS Service Stratum apply. The specific modes of operation of an On-Board FRMCS need to be taken into account:
1) In some deployment scenarios, the On-Board FRMCS is equipped with more than one On-Board Radio
Module, potentially operating under the FRMCS Multipath Framework.
ETSI
10 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
2) The On-Board FRMCS has to facilitate the continuity of communication under mobility conditions for the
applications it enables through the OB reference point.
APP
For a description of high-level procedures applicable in FRMCS, see clause 6 of the present document.
4.2.4 Applications enablement
Within trains, FRMCS applications interact with the FRMCS System via the OB reference point exposed by the
APP
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 interactions are
then defined, either using the standard reference points of the 3GPP MCX Framework ("tight-coupled mode") or
through additional API features of the OB reference point ("loose-coupled mode").
APP
On the trackside, the FRMCS Trackside Gateway exposes the TS reference point with features similar to the OB
APP APP
reference point.
When operating in "loose-coupled mode", applications are represented in the 3GPP MCX Framework by one or more
MC Service User identities associated to one of the standardized mission critical services of the 3GPP MCX Framework
(i.e. MCPTT, MCData and MCVideo).
Four Application Types are identified in the UIC FRMCS SRS [i.3]:
• Type I: Interoperable IM applications (e.g. ATP, ATO, REC, driver-controller voice communication).
• Type II: Non-interoperable IM applications.
• Type III: Interoperable RU applications.
• Type IV: Non-Interoperable RU applications in the scope of FRMCS (e.g. TCMS).
For more details on the interrelation between the API end points and the FRMCS Service Domain procedures, see ETSI
TS 103 765-3 [3] for the OB reference point and to ETSI TS 103 765-4 [4] for the TS reference point.
APP APP
In addition to the above, the TS reference point (see UIC FRMCS SRS [i.3]) is exposed for the use of controller
CTRL
devices and applications.
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, additional cybersecurity measures are leveraged:
• Between On-Board applications and the On-Board FRMCS, the OB reference point specified in UIC
APP
FRMCS FFFIS-7950 [i.1] requires the usage of the Local Binding procedure which establishes a secured
TLS-backed mutually-authenticated control plane link complemented by lower layers' security measures in
train network deployments.
• Similarly, between trackside applications and the FRMCS Trackside Gateway, the TS reference point
APP
specified in UIC FRMCS FFFIS-7950 [i.1] requires the usage of the Local Binding procedure.
• For a deployment as part of an international network of FRMCS Domains, requirements related to
cybersecurity are identified in clause 7.3 of the present document.
• For a deployment in interaction with an EIRENE GSM-R system, requirements related to cybersecurity are
identified in clause 7.4 of the present document.
4.2.6 GSM-R interworking
Requirements induced by interworking with GSM-R are specified in ETSI TS 103 792 [5].
ETSI
11 Final draft ETSI TS 103 764 V1.1.0 (2025-11)
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 transition is documented in clause 6.4 of
the present document.
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 in ETSI
TS 103 765-1 [1]) for a given application, subject to FRMCS Multipath policies set in the FRMCS Domain and to
parameters within the FRMCS On-Board Application. The data paths are established over one or multiple of the
following Transport Domains:
1) FRMCS Transport Domain.
2) Non-FRMCS Transport Domains.
The FRMCS Multipath Function is specified in ETSI TS 103 765-1 [1], clause 5.3.
4.3 Architecture reference model
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.
4.3.2 FRMCS System Architecture components
The FRMCS system consists of:
1) FRMCS Domain (see clause 5.1):
-
...

SLOVENSKI STANDARD
oSIST-TS ETSI/prTS 103 764 V1.0.0:2025
01-september-2025
Železniške telekomunikacije (RT) - Prihodnji sistem radijskih komunikacij za
železnice (FRMCS) - Sistemska arhitektura
Rail Telecommunications (RT) - Future Railway Mobile Communication System
(FRMCS) - System Architecture
Ta slovenski standard je istoveten z: ETSI TS 103 764 V1.0.0 (2025-07)
ICS:
33.060.01 Radijske komunikacije na Radiocommunications in
splošno general
45.020 Železniška tehnika na Railway engineering in
splošno general
oSIST-TS ETSI/prTS 103 764 V1.0.0:2025 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST-TS ETSI/prTS 103 764 V1.0.0:2025

oSIST-TS ETSI/prTS 103 764 V1.0.0:2025
Draft ETSI TS 103 764 V1.0.0 (2025-07)

TECHNICAL SPECIFICATION
Rail Telecommunications (RT);
Future Railway Mobile Communication System (FRMCS);
System Architecture
oSIST-TS ETSI/prTS 103 764 V1.0.0:2025
2 Draft ETSI TS 103 764 V1.0.0 (2025-07)

Reference
DTS/RT-0082
Keywords
5G, architecture, FRMCS, mission critical
applications, railways
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16

Siret N° 348 623 562 00017 - APE 7112B
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° w061004871

Important notice
The present document can be downloaded from the
ETSI Search & Browse Standards application.
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format on ETSI deliver repository.
Users should be aware that the present document may be revised or have its status changed,
this information is available in the Milestones listing.
If you find errors in the present document, please send your comments to
the relevant service listed under Committee Support Staff.
If you find a security vulnerability in the present document, please report it through our
Coordinated Vulnerability Disclosure (CVD) program.
Notice of disclaimer & limitation of liability
The information provided in the present deliverable is directed solely to professionals who have the appropriate degree of
experience to understand and interpret its content in accordance with generally accepted engineering or
other professional standard and applicable regulations.
No recommendation as to products and services or vendors is made or should be implied.
No representation or warranty is made that this deliverable is technically accurate or sufficient or conforms to any law
and/or governmental rule and/or regulation and further, no representation or warranty is made of merchantability or fitness
for any particular purpose or against infringement of intellectual property rights.
In no event shall ETSI be held liable for loss of profits or any other incidental or consequential damages.

Any software contained in this deliverable is provided "AS IS" with no warranties, express or implied, including but not
limited to, the warranties of merchantability, fitness for a particular purpose and non-infringement of intellectual property
rights and ETSI shall not be held liable in any event for any damages whatsoever (including, without limitation, damages
for loss of profits, business interruption, loss of information, or any other pecuniary loss) arising out of or related to the use
of or inability to use the software.
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2025.
All rights reserved.
ETSI
oSIST-TS ETSI/prTS 103 764 V1.0.0:2025
3 Draft ETSI TS 103 764 V1.0.0 (2025-07)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Architecture principles and model . 8
4.1 Introduction . 8
4.2 General principles. 8
4.2.0 Overview . 8
4.2.1 Strata . 8
4.2.2 Modularity of deployment . 9
4.2.3 Modes of operation . 9
4.2.4 Applications enablement . 10
4.2.5 Cybersecurity . 10
4.2.6 GSM-R interworking . 10
4.2.7 FRMCS Multipath . 11
4.3 Architecture reference model . 11
4.3.1 General . 11
4.3.2 FRMCS System Architecture components . 11
4.3.3 Stand-alone reference architecture . 12
4.3.4 Interconnected reference architecture . 13
4.3.5 FRMCS Reference points at system level . 13
5 FRMCS System Architecture components . 14
5.1 FRMCS Domain . 14
5.1.0 Overview . 14
5.1.1 Transport Domain . 14
5.1.2 FRMCS Service Domain . 14
5.2 On-board FRMCS . 14
5.3 FRMCS-capable Handheld . 14
5.4 FRMCS-capable Object . 14
5.5 FRMCS Trackside Gateway . 14
5.6 On-Board FRMCS Multipath Function . 15
5.7 FRMCS Infrastructure Multipath Function . 15
5.8 EIRENE System (GSM-R based System) . 15
5.9 Non-EIRENE non-FRMCS System . 15
6 Non-application-specific procedures . 15
6.1 Introduction . 15
6.2 FRMCS Start of Operation . 15
6.2.0 Overview . 15
6.2.1 FRMCS Start of Operation served by the Home FRMCS Domain . 16
6.2.2 FRMCS Start of Operation served by a Foreign FRMCS Domain . 17
6.3 FRMCS Close of Operation . 17
6.4 Domain transitions . 18
6.4.1 Inter-FRMCS Domain transition . 18
6.4.1.0 General . 18
6.4.1.1 Inter-FRMCS Domain transition: Type I or Type III applications. 20
6.4.1.1.1 Inter-FRMCS Domain transition: Type I or Type III applications with no open session . 20
ETSI
oSIST-TS ETSI/prTS 103 764 V1.0.0:2025
4 Draft ETSI TS 103 764 V1.0.0 (2025-07)
6.4.1.1.2 Inter-FRMCS Domain transition: Type I or Type III applications with an open session . 20
6.4.1.2 Inter-FRMCS Domain transition: Type II applications . 20
6.4.1.2.1 Inter-FRMCS Domain transition: Type II applications entering the Domain of applicability . 20
6.4.1.2.2 Inter-FRMCS Domain transition: Type II applications entering an FRMCS Domain which is
not in the Domain of applicability . 21
6.4.1.3 Inter-FRMCS Domain transition: Type IV applications . 21
6.4.2 Transition between GSM-R and FRMCS Domain . 21
7 Deployment scenarios of FRMCS . 21
7.1 Introduction . 21
7.2 Stand-alone FRMCS Domain . 22
7.3 FRMCS Domain in interaction with other FRMCS Domains . 22
7.4 FRMCS Domain in interaction with a GSM-R system . 22
7.5 FRMCS Domain in interaction with a non-EIRENE non-FRMCS network . 22
8 IP addresses and routing . 22
8.0 Generalities. 22
8.1 IP address ranges - Loose-Coupled Applications, without FRMCS Multipath . 24
8.2 IP address ranges - Tight-Coupled Applications, without FRMCS Multipath . 25
History . 26

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Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Railway Telecommunications (RT)
and is now submitted for the combined Public Enquiry and Vote phase of the ETSI Standardisation Request deliverable
Approval Procedure (SRdAP).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
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provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

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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.
2 References
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 are not found to be publicly available in the expected location might be found in the
ETSI docbox.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 103 765-1: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 1: Transport Stratum".
[2] ETSI TS 103 765-2: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 2: Service Stratum".
[3] ETSI TS 103 765-3: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 3: Train On-Board functions and
interfaces".
[4] ETSI TS 103 765-4: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building Blocks and Functions; Part 4: Trackside functions and interfaces".
[5] ETSI TS 103 792: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Interworking with GSM-R".
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 included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents may be useful in implementing an ETSI deliverable or add to the reader's
understanding, but are not required for conformance to the present document.
[i.1] UIC FRMCS FFFIS-7950: "FRMCS FFFIS Form Fit Functional Interface Specification".
[i.2] UIC FRMCS FIS-7970: "FRMCS FIS Functional Interface Specification".
[i.3] UIC FRMCS SRS: FRMCS System Requirements Specification".
[i.4] ETSI TR 103 791: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Terminology for FRMCS specifications".
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3 Definition of terms, symbols and abbreviations
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
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
th
5G 5 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 FRMCS Close of OPeration
FFFIS Form Fit Functional Interface Specification
FIS Functional Interface Specification
FRMCS Future Railway Mobile Communication System
FS FRMCS System
FSD FRMCS Service Domain
FSMPU FRMCS MultiPath User plane
FSOP FRMCS Start of OPeration
FTD FRMCS Transport Domain
GSM Global System for Mobile
GSM-R Global System for Mobile communications - Railway
H2N Host-To-Network
IM Infrastructure Manager
IP Internet Protocol
IWF InterWorking Function
LB Local Binding
MC Mission Critical
MCPTT Mission Critical Push To Talk
MCS Mission Critical Service
MCX Mission Critical Communications
MPM MultiPath Management
NAT Network Address Translation
NNI Network-to-Network Interface
NR New Radio
NTT Network Transition Trigger
OB On-Board
OM Operation and Maintenance
OMR OM Remote Interface
ONI Other Network-to-Network Interface
PDU Packet Data Unit
QoS Quality of Service
REC Railway Emergency Communication
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RM Radio Module
RMR Railway Mobile Radio
RU Railway Undertaking
SIP Session Initiation Protocol
SRS System Requirements Specification
SSE Server Sent Events
TCMS Train Control Management System
TLS Transport Layer Security
UE User Equipment
UIC Union Internationale des Chemins de Fer (International Union of Railways)
VAS Voice Application Subsystem
4 Architecture principles and model
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 enables communication
as services between two or multiple FRMCS Users for voice, video and data applications.
The following is described:
• overall architecture of FRMCS within one FRMCS Domain with principles and components;
• procedures applicable for an FRMCS Domain and interactions between FRMCS Domains.
FRMCS System Architecture is designed based on the high-level principles outlined in clause 4.2. In addition, the
architecture reference model is described.
4.2 General principles
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 independent evolution of the Transport Stratum
and/or of the Service Stratum without mandating an evolution of the Application Stratum.
• Supporting QoS and priority policies that allows differentiating the communications of different types of
railway applications.
• Supporting multiple Radio Access Technologies.
• Supporting Service Stratum security and Transport Stratum security.
• Supporting Operation and Maintenance for on-board FRMCS.
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).
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Figure 4.2.1-1: Strata in FRMCS System Architecture
The Transport Stratum provides data connectivity and corresponding services (e.g. mobility, QoS, policy control,
authentication, etc.). The Service Stratum is centered around the 3GPP Mission Critical Communications (MCX)
Framework and decouples the application from the underlying transport networks.
The FRMCS Transport Stratum is described in more detail in ETSI TS 103 765-1 [1].
The FRMCS Service Stratum is described in more detail in ETSI TS 103 765-2 [2].
The Application Stratum is not considered to be part of the FRMCS architecture and therefore it will not be described in
the present document.
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.
• Deployment encompassing interworking with GSM-R, deployment of an FRMCS Domain with users
interacting with or moving to, or from a GSM-R system, under the control of the same operator or not.
• Deployment encompassing interconnection with non-EIRENE non-FRMCS networks.
The minimal deployment of the FRMCS System Architecture is that of a stand-alone FRMCS Domain.
For a description of the deployment scenarios of FRMCS, see clause 7 of the present document.
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 procedures defined in the
FRMCS Service Stratum apply. The specific modes of operation of an On-Board FRMCS need to be taken into account:
1) In some deployment scenarios, the On-Board FRMCS is equipped with more than one On-Board Radio
Module, potentially operating under the FRMCS Multipath Framework.
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2) The On-Board FRMCS has to facilitate the continuity of communication under mobility conditions for the
applications it enables through the OB reference point.
APP
For a description of high-level procedures applicable in FRMCS, see clause 6 of the present document.
4.2.4 Applications enablement
Within trains, FRMCS applications interact with the FRMCS System via the OB reference point exposed by the
APP
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 interactions are
then defined, either using the standard reference points of the 3GPP MCX Framework ("tight-coupled mode") or
through additional API features of the OB reference point ("loose-coupled mode").
APP
On the trackside, the FRMCS Trackside Gateway exposes the TS reference point with features similar to the OB
APP APP
reference point.
When operating in "loose-coupled mode", applications are represented in the 3GPP MCX Framework by one or more
MC Service User identities associated to one of the standardized mission critical services of the 3GPP MCX Framework
(i.e. MCPTT, MCData and MCVideo).
Four Application Types are identified in the UIC FRMCS SRS [i.3]:
• Type I: Interoperable IM applications (e.g. ATP, ATO, REC, driver-controller voice communication).
• Type II: Non-interoperable IM applications.
• Type III: Interoperable RU applications.
• Type IV: Non-Interoperable RU applications in the scope of FRMCS (e.g. TCMS).
For more details on the interrelation between the API end points and the FRMCS Service Domain procedures, see ETSI
TS 103 765-3 [3] for the OB reference point and to ETSI TS 103 765-4 [4] for the TS reference point.
APP APP
In addition to the above, the TS reference point (see UIC FRMCS SRS [i.3]) is exposed for the use of controller
CTRL
devices and applications.
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, additional cybersecurity measures are leveraged:
• Between On-Board applications and the On-Board FRMCS, the OB reference point specified in UIC
APP
FRMCS FFFIS-7950 [i.1] requires the usage of the Local Binding procedure which establishes a secured
TLS-backed mutually-authenticated control plane link complemented by lower layers' security measures in
train network deployments.
• Similarly, between trackside applications and the FRMCS Trackside Gateway, the TS reference point
APP
specified in UIC FRMCS FFFIS-7950 [i.1] requires the usage of the Local Binding procedure.
• For a deployment as part of an international network of FRMCS Domains, requirements related to
cybersecurity are identified in clause 7.3 of the present document.
• For a deployment in interaction with an EIRENE GSM-R system, requirements related to cybersecurity are
identified in clause 7.4 of the present document.
4.2.6 GSM-R interworking
Requirements induced by interworking with GSM-R are specified in ETSI TS 103 792 [5].
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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 transition is documented in clause 6.4 of
the present document.
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 in ETSI
TS 103 765-1 [1]) for a given application, subject to FRMCS Multipath policies set in the FRMCS Domain and to
parameters within the FRMCS On-Board Application. The data paths are established over one or multiple of the
following Transport Domains:
1) FRMCS Transport Domain.
2) Non-FRMCS Transport Domains.
The FRMCS Multip
...