oSIST-TS ETSI/prTS 103 765-4 V1.0.0:2025
(Main)Rail Telecommunications (RT) - Future Railway Mobile Communication System (FRMCS) - Building Blocks and Functions - Part 4: Trackside functions and interfaces
Rail Telecommunications (RT) - Future Railway Mobile Communication System (FRMCS) - Building Blocks and Functions - Part 4: Trackside functions and interfaces
DTS/RT-0086
Železniške telekomunikacije (RT) - Prihodnji sistem radijskih komunikacij za železnice (FRMCS) - Gradniki in funkcionalnosti - 4. del: Funkcionalnosti in vmesniki ob progi
General Information
Standards Content (Sample)
Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
TECHNICAL SPECIFICATION
Rail Telecommunications (RT);
Future Railway Mobile Communication System (FRMCS);
Building Blocks and Functions;
Part 4: Trackside functions and interfaces
2 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
Reference
DTS/RT-0086
Keywords
FRMCS, interface, protocol, 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
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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 Draft ETSI TS 103 765-4 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 . 7
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Trackside network architecture . 8
5 FRMCS Trackside Gateway . 9
5.1 General . 9
5.2 FRMCS Trackside Gateway architecture . 9
5.3 FRMCS Trackside Gateway functionalities . 9
5.4 FRMCS Trackside Gateway Functions . 10
5.4.1 Trackside Application Network NAT Function . 10
5.4.2 Trackside Service NAT Function . 11
5.5 FRMCS Trackside Gateway interfaces . 11
5.5.0 Introduction. 11
5.5.1 TS . 11
APP
5.5.2 TAP TS . 11
6 FRMCS Trackside Gateway procedures . 12
6.1 General procedures . 12
6.1.1 General provisioning. 12
6.1.2 Host-to-Network provisioning . 12
6.2 Procedures not associated to a reference point . 12
6.2.1 MC Service Client IP assignment procedure . 12
6.2.2 MC Service Client readiness procedure . 13
6.2.3 MC Service Client teardown procedure . 13
6.2.4 TS Application Context clearance procedure . 14
APP
6.2.5 Ongoing communication release . 14
6.2.6 Logging . 14
6.3 Procedures associated with TS endpoints . 14
APP
6.3.0 Introduction. 14
6.3.1 /registrations endpoint procedures . 15
6.3.1.1 Application registration procedure . 15
6.3.1.2 Application-initiated deregistration procedure . 15
6.3.1.3 FRMCS-Trackside-Gateway-initiated deregistration procedure . 15
6.3.2 /sessions endpoint procedures . 16
6.3.2.1 FRMCS-Trackside-Gateway-initiated session initiation procedure . 16
6.3.2.2 FRMCS-Trackside-Gateway-initiated session termination procedure . 17
6.3.2.3 FRMCS-Trackside-Gateway-terminated incoming session invite procedure . 18
6.3.2.4 FRMCS-Trackside-Gateway-terminated incoming session response procedure . 18
6.3.2.5 FRMCS-Trackside-Gateway-terminated session termination procedure . 19
6.3.2.6 Information query on ongoing sessions for an application. 19
6.3.2.7 Information query on a specific ongoing session for an application . 19
6.3.3 /notifications endpoint procedures . 19
6.3.3.1 Procedure for opening the notification event stream . 19
6.3.3.2 Procedure of notification to an application over a channel . 20
6.3.4 /versions endpoint procedures. 20
6.3.5 /keepalive endpoint procedures . 20
ETSI
4 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
7 VAS-Controller Equipment connection . 21
7.1 Functions . 21
7.2 Interfaces . 21
History . 22
ETSI
5 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
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.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its
Members. 3GPP™, LTE™ and 5G™ logo are trademarks of ETSI registered for the benefit of its Members and of the
3GPP Organizational Partners. oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and of ®
the oneM2M Partners. GSM and the GSM logo are trademarks registered and owned by the GSM Association.
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).
The present document is part 4 of a multi-part deliverable covering Building Blocks and Functions for the Future
Railway Mobile Communication System (FRMCS), as identified below:
Part 1: "Transport Stratum";
Part 2: "Service Stratum";
Part 3: "Train On-Board functions and interfaces";
Part 4: "Trackside functions and interfaces";
Part 5: "User Equipment (UE) capabilities".
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 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
1 Scope
The present document specifies non-3GPP network functions and interfaces applicable to the FRMCS Trackside
Infrastructure.
The present document describes the trackside network architecture and proceeds with specifying the non-3GPP
trackside network functional entities (such as the FRMCS Trackside Gateway), including functions, interfaces and
procedures they need to comply to.
The present document does not consider message sequences within and between 3GPP and non-3GPP building blocks.
These message sequences will be defined by related 3GPP specifications, ETSI FRMCS transport stratum definition
and FRMCS service stratum definition documents or UIC FRMCS FIS [i.3] and UIC FRMCS FFFIS [1].
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] UIC FFFIS-7950 (V2.1.0): "FRMCS FFFIS Form Fit Functional Interface Specification".
[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 103 765-1: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building blocks and functions; Part 1: Transport Stratum".
[4] ETSI TS 123 280 (V18.12.0): "LTE; Common functional architecture to support mission critical
services; Stage 2 (3GPP TS 23.280 version 18.12.0 Release 18)".
[5] ETSI TS 133 180 (V18.1.0): "LTE; Security of the Mission Critical (MC) service (3GPP
TS 33.180 version 18.1.0 Release 18)".
[6] ETSI TS 103 792: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Interworking with GSM-R".
[7] ETSI TS 123 379 (V18.12.0): "LTE; Functional architecture and information flows to support
Mission Critical Push To Talk (MCPTT); Stage 2 (3GPP TS 23.379 version 18.12.0 Release 18)".
[8] ETSI TS 123 282 (V18.10.0): "LTE; Functional architecture and information flows to support
Mission Critical Data (MCData); Stage 2 (3GPP TS 23.282 version 18.10.0 Release 18)".
[9] ISO 8601 (2019): "Date and time — Representations for information interchange".
ETSI
7 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
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] ETSI TR 103 791: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Terminology for FRMCS specifications".
[i.2] UIC FW-AT 7800 (V2.1.0): "Future Railway Mobile Communication System - System
Requirements Specification".
[i.3] UIC FIS-7970 (V2.1.0): "Future Railway Mobile Communication System - Functional Interface
Specification".
[i.4] ETSI TS 124 229 (V18.7.0): "Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS); LTE; 5G; IP multimedia call control
protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP);
Stage 3 (3GPP TS 24.229 version 18.7.0 Release 18)".
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.1] and the following apply:
Hosting Clients: MC Service Client located in FRMCS Trackside Gateway
NOTE: Hosting Client connects Loose-Coupled FRMCS applications to FRMCS system.
Reference point TAP TS: reference point represents the connection from FRMCS Trackside Gateway to transport core
network(s) and to the FRMCS Service Server
TS Application Context: context maintained by the FRMCS Trackside Gateway for an application instance
APP
(identified by the TS application tuple), in between registration and de-registration
APP
TS application tuple (RegisterData): tuple of (appCategory, staticId, couplingMode) as specified in UIC FRMCS
APP
FFFIS-7950 [1], clause 10.8.1 and Annex B, clause A.3
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
DNS Domain Name Server
FRMCS Future Railway Mobile Communication System
H2H Host-to-Host
H2N Host-to-Network
HTTP Hyper Text Transfer Protocol
IP Internet Protocol
ETSI
8 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
IWF Interworking Function
JSON JavaScript Object Notation
MC Mission Critical
MCPTT Mission Critical Push-To-Talk
MCX Mission Critical Communications
NAT Network Address Translation
SIP Session Initiation Protocol
SSE Server Sent Events
TAP TS TAP Trackside
TAP Transport Access Point
TS Trackside Application Reference Point
APP
TS Reference point between VAS Controller Equipment and FRMCS System
CTRL
VAS Voice Application Subsystem
4 Trackside network architecture
FRMCS trackside architecture consists of at least one FRMCS Transport Domain (as described in ETSI
TS 103 765-1 [3], clause 4.2) and zero or more non-FRMCS Transport Domains. The FRMCS Service Domain (as
described in ETSI TS 103 765-2 [2], clause 5.1) enables communication as services between two or multiple FRMCS
Users for voice and data applications. The Service Stratum is specified over the 3GPP Mission Critical Communications
(MCX) Framework and decouples the application from the underlying transport networks.
The focus of clause 5 is the FRMCS Trackside Gateway, which provides access to communication and complementary
services supported by the FRMCS System to and from trackside applications.
The IWF provides centralized support for interworking between an MCPTT or MCData system and a GSM-R system
specified in ETSI TS 103 792 [6], clause 5.
Figure 4-1 shows the FRMCS trackside architecture.
The TS reference point in Figure 4-1 is described in UIC FRMCS FFFIS-7950 [1] (Form Fit Functional Interface
APP
Specification).
The TS reference point supports the coupling modes for FRMCS (outlined in UIC FRMCS SRS (FW-AT 7800)
APP
[i.2]) defined in ETSI TR 103 791 [i.1].
The TS reference point is described in clause 7 of the present document.
CTRL
VAS-
Trackside
Controller
Application
Equipment
IWF
MCx Server
Data Network
Data Network
Data Network
FRMCS
Multipath
5G Core
Trackside
Gateway
Gateway
NOTE: Multipath Gateway can be combined with the FRMCS Trackside Gateway. The selected deployment
option is the choice of the FRMCS operator.
Figure 4-1: FRMCS trackside architecture
ETSI
9 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
5 FRMCS Trackside Gateway
5.1 General
The FRMCS Trackside Gateway is a logical component which is used to host specific functions.
The FRMCS Trackside Gateway is the logical symmetrical component to the On-Board FRMCS. It is the link between
the Transport Network and the Application at the infrastructure side (see UIC FRMCS SRS (FW-AT 7800) [i.2],
Figure 6-4).
NOTE: Implementors have the choice of combining the FRMCS Trackside Gateway functionalities with the
functionalities of the Multipath Gateway as specified in ETSI TS 103 765-1 [3], clause 5.3. In this case,
the combined entity inherits the Reference points from both the FRMCS Trackside Gateway (TS and
APP
TAP TS) and from the Multipath Gateway (TAP Service Agents and FSMPM).
5.2 FRMCS Trackside Gateway architecture
The functional architecture of FRMCS Trackside Gateway is illustrated in Figure 5.2-1. The FRMCS Trackside
Gateway links the trackside application.
FRMCS Service
Serverl
FRMCS Trackside Gateway
Multipath Gateway
TAP TS
TAP Service
TSAPP
Agents
Figure 5.2-1: Functional architecture of FRMCS Trackside Gateway
The generic reference points of the FRMCS Trackside Gateway are shown in Figure 5.2-1:
• TS .
APP
• TAP TS (TAP Trackside).
Reference point TSAPP: This reference point represents the connection from the FRMCS Trackside Gateway to the
Application(s). The TS reference point is specified in UIC FRMCS FFFIS [1]. The behaviour expected from the
APP
FRMCS Trackside in relation with TS is specified in clause 6.3.
APP
Reference point TAP TS: This reference point represents the connection from FRMCS Trackside Gateway to transport
core network(s) and to the FRMCS Service Server. It consists of a control plane and a user plane and is defined as per
FRMCS Service Stratum based on MCX control plane (FRMCS Service Control Plane) and MCX user plane (FRMCS
Service User Plane) client interfaces and information flows.
5.3 FRMCS Trackside Gateway functionalities
The FRMCS Trackside Gateway hosts the FRMCS Service Stratum functions when the FRMCS Trackside Gateway is
configured to serve a Loose-Coupled Application (including H2H and H2N models). The detailed functional
architecture of the FRMCS Trackside Gateway is depicted in Figure 5.3-1 (note that the figure does not resume a
specific internal implementation variant of the different functions).
ETSI
10 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
FRMCS Service Server
CP/N5 or N33
FRMCS Service
CP and UP
r
e
v
r
e
S
P
Hosting Client 1
P
A
(MC Service Client 1) handling
S
T
) Loose-Coupled Applications
…
,
UP/N6 T
LC Application
A
N
UserPlane handling (ApplNAT, …)
e
c
i
v
y r
e
a
S
w
e
e
d
t i
s
a )
k
Hosting Client 2
c
G
G
a
r (MC Service Client 2) handling
P
h T
.
t M
l Loose-Coupled Applications
a ( TAP Service c
n
p i
i
TAP TS (
t
l F
Agents
/
u I
UserPlane handling
S
M
T
P
A
T
Hosting Client n
TSAPP
Trackside Gateway
(TS-GW)
Figure 5.3-1: Functions of FRMCS Trackside Gateway
The following functions are provided by the FRMCS Trackside Gateway:
• Hosting Clients: For Loose-Coupled Applications the FRMCS Trackside Gateway provides MC service clients
for integration into the MC service system.
• TS Server: Server for handling communication via TS reference point towards applications.
APP APP
The FRMCS Trackside Gateway shall implement the functionalities associated with the Trackside Application Network
NAT Function as specified in clause 5.4.1.
The FRMCS Trackside Gateway shall implement the functionalities associated with the Trackside Service NAT
Function as specified in clause 5.4.2.
The FRMCS Trackside Gateway shall support the functionalities required for Host-to-Network provisioning as
specified in clause 6.1.2.
5.4 FRMCS Trackside Gateway Functions
5.4.1 Trackside Application Network NAT Function
The FRMCS Trackside Gateway requires the implementation of NAT functionality when enabling communication with
an On-Board FRMCS.
The Trackside Application Network NAT Function is responsible for NAT for the Application Plane communication
between an on-Board Loose-Coupled application and a Trackside application.
ETSI
11 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
When a MCData IPcon session of type Host-to-Host or Host-to-Network is established between an On-Board Loose-
Coupled Application using IP address OBA1 on the Application Plane and a Trackside Loose-Coupled Application
using IP address TSA1 on the Application Plane, the Trackside Application Network NAT Function shall maintain a
mapping for the duration of the session between the tuple of IP addresses (OBA1, ViOB TSAx) and the tuple of IP
addresses (ViTS OBA1, TSAx) where:
• ViOB TSAx is a virtual IP selected by the On-Board FRMCS to represent for this session TSAx within the
On-Board FRMCS.
• ViTS OBA1 is a virtual IP selected by the FRMCS Trackside Gateway to represent for this session OBA1
within the FRMCS Trackside Gateway.
When a Host-to-Host or Host-to-Network session is terminated, the Trackside Application Network NAT Function shall
delete the mapping between the two tuple of IP addresses it created at session establishment.
5.4.2 Trackside Service NAT Function
The FRMCS Trackside Gateway requires the implementation of NAT functionality when enabling communication with
an On-Board FRMCS.
The Trackside Service NAT Function is responsible for NAT or the following particular aspects listed in the bullet
point s below:
• For the FRMCS Service Control Plane communication between a MC Service Client within the FRMCS
Trackside Gateway towards the FRMCS Service Domain.
• For the FRMCS Service User Plane communication between a MC Service Client within the FRMCS
Trackside Gateway and, for example, a MC Service Client within the On-Board FRMCS.
5.5 FRMCS Trackside Gateway interfaces
5.5.0 Introduction
As defined in clause 5.2, the FRMCS Trackside Gateway supports two interfaces:
• TS .
APP
• TAP TS.
5.5.1 TS
APP
The TS interface is the interface between trackside applications and the FRMCS Trackside Gateway.
APP
The FRMCS Trackside Gateway shall implement the procedures associated to the TS interface specified in
APP
clause 6.3.
5.5.2 TAP TS
The TAP TS reference point connects
...
SLOVENSKI STANDARD
01-september-2025
Železniške telekomunikacije (RT) - Prihodnji sistem radijskih komunikacij za
železnice (FRMCS) - Gradniki in funkcionalnosti - 4. del: Funkcionalnosti in
vmesniki ob progi
Rail Telecommunications (RT) - Future Railway Mobile Communication System
(FRMCS) - Building Blocks and Functions - Part 4: Trackside functions and interfaces
Ta slovenski standard je istoveten z: ETSI TS 103 765-4 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 103 765-4 en
V1.0.0:2025
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
TECHNICAL SPECIFICATION
Rail Telecommunications (RT);
Future Railway Mobile Communication System (FRMCS);
Building Blocks and Functions;
Part 4: Trackside functions and interfaces
2 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
Reference
DTS/RT-0086
Keywords
FRMCS, interface, protocol, 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 Draft ETSI TS 103 765-4 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 . 7
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Trackside network architecture . 8
5 FRMCS Trackside Gateway . 9
5.1 General . 9
5.2 FRMCS Trackside Gateway architecture . 9
5.3 FRMCS Trackside Gateway functionalities . 9
5.4 FRMCS Trackside Gateway Functions . 10
5.4.1 Trackside Application Network NAT Function . 10
5.4.2 Trackside Service NAT Function . 11
5.5 FRMCS Trackside Gateway interfaces . 11
5.5.0 Introduction. 11
5.5.1 TS . 11
APP
5.5.2 TAP TS . 11
6 FRMCS Trackside Gateway procedures . 12
6.1 General procedures . 12
6.1.1 General provisioning. 12
6.1.2 Host-to-Network provisioning . 12
6.2 Procedures not associated to a reference point . 12
6.2.1 MC Service Client IP assignment procedure . 12
6.2.2 MC Service Client readiness procedure . 13
6.2.3 MC Service Client teardown procedure . 13
6.2.4 TS Application Context clearance procedure . 14
APP
6.2.5 Ongoing communication release . 14
6.2.6 Logging . 14
6.3 Procedures associated with TS endpoints . 14
APP
6.3.0 Introduction. 14
6.3.1 /registrations endpoint procedures . 15
6.3.1.1 Application registration procedure . 15
6.3.1.2 Application-initiated deregistration procedure . 15
6.3.1.3 FRMCS-Trackside-Gateway-initiated deregistration procedure . 15
6.3.2 /sessions endpoint procedures . 16
6.3.2.1 FRMCS-Trackside-Gateway-initiated session initiation procedure . 16
6.3.2.2 FRMCS-Trackside-Gateway-initiated session termination procedure . 17
6.3.2.3 FRMCS-Trackside-Gateway-terminated incoming session invite procedure . 18
6.3.2.4 FRMCS-Trackside-Gateway-terminated incoming session response procedure . 18
6.3.2.5 FRMCS-Trackside-Gateway-terminated session termination procedure . 19
6.3.2.6 Information query on ongoing sessions for an application. 19
6.3.2.7 Information query on a specific ongoing session for an application . 19
6.3.3 /notifications endpoint procedures . 19
6.3.3.1 Procedure for opening the notification event stream . 19
6.3.3.2 Procedure of notification to an application over a channel . 20
6.3.4 /versions endpoint procedures. 20
6.3.5 /keepalive endpoint procedures . 20
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4 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
7 VAS-Controller Equipment connection . 21
7.1 Functions . 21
7.2 Interfaces . 21
History . 22
ETSI
5 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
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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).
The present document is part 4 of a multi-part deliverable covering Building Blocks and Functions for the Future
Railway Mobile Communication System (FRMCS), as identified below:
Part 1: "Transport Stratum";
Part 2: "Service Stratum";
Part 3: "Train On-Board functions and interfaces";
Part 4: "Trackside functions and interfaces";
Part 5: "User Equipment (UE) capabilities".
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 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
1 Scope
The present document specifies non-3GPP network functions and interfaces applicable to the FRMCS Trackside
Infrastructure.
The present document describes the trackside network architecture and proceeds with specifying the non-3GPP
trackside network functional entities (such as the FRMCS Trackside Gateway), including functions, interfaces and
procedures they need to comply to.
The present document does not consider message sequences within and between 3GPP and non-3GPP building blocks.
These message sequences will be defined by related 3GPP specifications, ETSI FRMCS transport stratum definition
and FRMCS service stratum definition documents or UIC FRMCS FIS [i.3] and UIC FRMCS FFFIS [1].
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] UIC FFFIS-7950 (V2.1.0): "FRMCS FFFIS Form Fit Functional Interface Specification".
[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 103 765-1: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Building blocks and functions; Part 1: Transport Stratum".
[4] ETSI TS 123 280 (V18.12.0): "LTE; Common functional architecture to support mission critical
services; Stage 2 (3GPP TS 23.280 version 18.12.0 Release 18)".
[5] ETSI TS 133 180 (V18.1.0): "LTE; Security of the Mission Critical (MC) service (3GPP
TS 33.180 version 18.1.0 Release 18)".
[6] ETSI TS 103 792: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Interworking with GSM-R".
[7] ETSI TS 123 379 (V18.12.0): "LTE; Functional architecture and information flows to support
Mission Critical Push To Talk (MCPTT); Stage 2 (3GPP TS 23.379 version 18.12.0 Release 18)".
[8] ETSI TS 123 282 (V18.10.0): "LTE; Functional architecture and information flows to support
Mission Critical Data (MCData); Stage 2 (3GPP TS 23.282 version 18.10.0 Release 18)".
[9] ISO 8601 (2019): "Date and time — Representations for information interchange".
ETSI
7 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
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] ETSI TR 103 791: "Rail Telecommunications (RT); Future Railway Mobile Communication
System (FRMCS); Terminology for FRMCS specifications".
[i.2] UIC FW-AT 7800 (V2.1.0): "Future Railway Mobile Communication System - System
Requirements Specification".
[i.3] UIC FIS-7970 (V2.1.0): "Future Railway Mobile Communication System - Functional Interface
Specification".
[i.4] ETSI TS 124 229 (V18.7.0): "Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS); LTE; 5G; IP multimedia call control
protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP);
Stage 3 (3GPP TS 24.229 version 18.7.0 Release 18)".
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.1] and the following apply:
Hosting Clients: MC Service Client located in FRMCS Trackside Gateway
NOTE: Hosting Client connects Loose-Coupled FRMCS applications to FRMCS system.
Reference point TAP TS: reference point represents the connection from FRMCS Trackside Gateway to transport core
network(s) and to the FRMCS Service Server
TS Application Context: context maintained by the FRMCS Trackside Gateway for an application instance
APP
(identified by the TS application tuple), in between registration and de-registration
APP
TS application tuple (RegisterData): tuple of (appCategory, staticId, couplingMode) as specified in UIC FRMCS
APP
FFFIS-7950 [1], clause 10.8.1 and Annex B, clause A.3
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
DNS Domain Name Server
FRMCS Future Railway Mobile Communication System
H2H Host-to-Host
H2N Host-to-Network
HTTP Hyper Text Transfer Protocol
IP Internet Protocol
ETSI
8 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
IWF Interworking Function
JSON JavaScript Object Notation
MC Mission Critical
MCPTT Mission Critical Push-To-Talk
MCX Mission Critical Communications
NAT Network Address Translation
SIP Session Initiation Protocol
SSE Server Sent Events
TAP TS TAP Trackside
TAP Transport Access Point
TS Trackside Application Reference Point
APP
TS Reference point between VAS Controller Equipment and FRMCS System
CTRL
VAS Voice Application Subsystem
4 Trackside network architecture
FRMCS trackside architecture consists of at least one FRMCS Transport Domain (as described in ETSI
TS 103 765-1 [3], clause 4.2) and zero or more non-FRMCS Transport Domains. The FRMCS Service Domain (as
described in ETSI TS 103 765-2 [2], clause 5.1) enables communication as services between two or multiple FRMCS
Users for voice and data applications. The Service Stratum is specified over the 3GPP Mission Critical Communications
(MCX) Framework and decouples the application from the underlying transport networks.
The focus of clause 5 is the FRMCS Trackside Gateway, which provides access to communication and complementary
services supported by the FRMCS System to and from trackside applications.
The IWF provides centralized support for interworking between an MCPTT or MCData system and a GSM-R system
specified in ETSI TS 103 792 [6], clause 5.
Figure 4-1 shows the FRMCS trackside architecture.
The TS reference point in Figure 4-1 is described in UIC FRMCS FFFIS-7950 [1] (Form Fit Functional Interface
APP
Specification).
The TS reference point supports the coupling modes for FRMCS (outlined in UIC FRMCS SRS (FW-AT 7800)
APP
[i.2]) defined in ETSI TR 103 791 [i.1].
The TS reference point is described in clause 7 of the present document.
CTRL
VAS-
Trackside
Controller
Application
Equipment
IWF
MCx Server
Data Network
Data Network
Data Network
FRMCS
Multipath
5G Core
Trackside
Gateway
Gateway
NOTE: Multipath Gateway can be combined with the FRMCS Trackside Gateway. The selected deployment
option is the choice of the FRMCS operator.
Figure 4-1: FRMCS trackside architecture
ETSI
9 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
5 FRMCS Trackside Gateway
5.1 General
The FRMCS Trackside Gateway is a logical component which is used to host specific functions.
The FRMCS Trackside Gateway is the logical symmetrical component to the On-Board FRMCS. It is the link between
the Transport Network and the Application at the infrastructure side (see UIC FRMCS SRS (FW-AT 7800) [i.2],
Figure 6-4).
NOTE: Implementors have the choice of combining the FRMCS Trackside Gateway functionalities with the
functionalities of the Multipath Gateway as specified in ETSI TS 103 765-1 [3], clause 5.3. In this case,
the combined entity inherits the Reference points from both the FRMCS Trackside Gateway (TS and
APP
TAP TS) and from the Multipath Gateway (TAP Service Agents and FSMPM).
5.2 FRMCS Trackside Gateway architecture
The functional architecture of FRMCS Trackside Gateway is illustrated in Figure 5.2-1. The FRMCS Trackside
Gateway links the trackside application.
FRMCS Service
Serverl
FRMCS Trackside Gateway
Multipath Gateway
TAP TS
TAP Service
TSAPP
Agents
Figure 5.2-1: Functional architecture of FRMCS Trackside Gateway
The generic reference points of the FRMCS Trackside Gateway are shown in Figure 5.2-1:
• TS .
APP
• TAP TS (TAP Trackside).
Reference point TSAPP: This reference point represents the connection from the FRMCS Trackside Gateway to the
Application(s). The TS reference point is specified in UIC FRMCS FFFIS [1]. The behaviour expected from the
APP
FRMCS Trackside in relation with TS is specified in clause 6.3.
APP
Reference point TAP TS: This reference point represents the connection from FRMCS Trackside Gateway to transport
core network(s) and to the FRMCS Service Server. It consists of a control plane and a user plane and is defined as per
FRMCS Service Stratum based on MCX control plane (FRMCS Service Control Plane) and MCX user plane (FRMCS
Service User Plane) client interfaces and information flows.
5.3 FRMCS Trackside Gateway functionalities
The FRMCS Trackside Gateway hosts the FRMCS Service Stratum functions when the FRMCS Trackside Gateway is
configured to serve a Loose-Coupled Application (including H2H and H2N models). The detailed functional
architecture of the FRMCS Trackside Gateway is depicted in Figure 5.3-1 (note that the figure does not resume a
specific internal implementation variant of the different functions).
ETSI
10 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
FRMCS Service Server
CP/N5 or N33
FRMCS Service
CP and UP
r
e
v
r
e
S
P
Hosting Client 1
P
A
(MC Service Client 1) handling
S
T
) Loose-Coupled Applications
…
,
UP/N6 T
LC Application
A
N
UserPlane handling (ApplNAT, …)
e
c
i
v
y r
e
a
S
w
e
e
d
t i
s
a )
k
Hosting Client 2
c
G
G
a
r (MC Service Client 2) handling
P
h T
.
t M
l Loose-Coupled Applications
a ( TAP Service c
n
p i
i
TAP TS (
t
l F
Agents
/
u I
UserPlane handling
S
M
T
P
A
T
Hosting Client n
TSAPP
Trackside Gateway
(TS-GW)
Figure 5.3-1: Functions of FRMCS Trackside Gateway
The following functions are provided by the FRMCS Trackside Gateway:
• Hosting Clients: For Loose-Coupled Applications the FRMCS Trackside Gateway provides MC service clients
for integration into the MC service system.
• TS Server: Server for handling communication via TS reference point towards applications.
APP APP
The FRMCS Trackside Gateway shall implement the functionalities associated with the Trackside Application Network
NAT Function as specified in clause 5.4.1.
The FRMCS Trackside Gateway shall implement the functionalities associated with the Trackside Service NAT
Function as specified in clause 5.4.2.
The FRMCS Trackside Gateway shall support the functionalities required for Host-to-Network provisioning as
specified in clause 6.1.2.
5.4 FRMCS Trackside Gateway Functions
5.4.1 Trackside Application Network NAT Function
The FRMCS Trackside Gateway requires the implementation of NAT functionality when enabling communication with
an On-Board FRMCS.
The Trackside Application Network NAT Function is responsible for NAT for the Application Plane communication
between an on-Board Loose-Coupled application and a Trackside application.
ETSI
11 Draft ETSI TS 103 765-4 V1.0.0 (2025-07)
When a MCData IPcon session of type Host-to-Host or Host-to-Network is established between an On-Board Loose-
Coupled Application using IP address OBA1 on the Application Plane and a Trackside Loose-Coupled Application
using IP address TSA1 on the Application Plane, the Trackside Application Network NAT Function shall maintain a
mapping for the duration of the session between the tuple of IP addresses (OBA1, ViOB TSAx) and the tuple of IP
addresses (ViTS OBA1, TSAx) where:
• ViOB TSAx is a virtual IP selected by the On-Board FRMCS to represent for this session TSAx within the
On-Board FRMCS.
• ViTS OBA1 is a virtual IP selected by the FRMCS Trackside Gateway to represent for this session OBA1
within the FRMCS Trackside Gateway.
When a Host-to-Host or Host-to-Network session is terminated, the Trackside Application Network NAT Function shall
delete the mapping between the two tuple of IP addresses it created at session establishment.
5.4.2 Trackside Service NAT Function
The FRMCS Trackside Gateway requires the implementation of NAT functionality when enabling communication with
an On-Board FRMCS.
The Trackside Service NAT Function is responsible for NAT or the following particular aspects listed in the bullet
point s below:
• For the FRMCS Service Control Plane communication between a MC Service Client within the FRMCS
Trackside Gateway towards the FRMCS Service Domain.
• For the FRMCS Service User Plane communication between a MC Service Client within the FRMCS
Trackside Gateway and, for example, a MC Service Client within
...
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