ETSI TS 123 468 V15.1.0 (2019-10)

ETSI TS 123 468 V15.1.0 (2019-10)






TECHNICAL SPECIFICATION
LTE;
Group Communication System Enablers for LTE (GCSE_LTE);
Stage 2
(3GPP TS 23.468 version 15.1.0 Release 15)

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3GPP TS 23.468 version 15.1.0 Release 15 1 ETSI TS 123 468 V15.1.0 (2019-10)



Reference
RTS/TSGS-0223468vf10
Keywords
LTE
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3GPP TS 23.468 version 15.1.0 Release 15 2 ETSI TS 123 468 V15.1.0 (2019-10)
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Legal Notice
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ETSI

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3GPP TS 23.468 version 15.1.0 Release 15 3 ETSI TS 123 468 V15.1.0 (2019-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 Architecture Model and Concepts . 7
4.1 General Concept . 7
4.2 Architectural Reference Model . 9
4.2.1 General . 9
4.2.2 Non-roaming architecture . 10
4.2.3 Roaming architecture . 10
4.2.4 Architecture model using a ProSe UE-to-Network Relay for Public Safety. 12
4.3 Reference points . 12
4.3.1 General . 12
4.3.2 List of Reference Points . 12
4.3.2.1 GC1 reference point . 12
4.3.2.2 MB2 reference point . 12
4.3.2.3 SGmb/SGi-mb/M1/M3 reference points . 13
4.3.2.4 Rx reference point . 13
4.4 High level functions . 13
4.4.1 Unicast Delivery . 13
4.4.2 MBMS Delivery . 13
4.4.3 Service continuity . 13
4.5 Network Elements . 13
4.5.1 GCS AS . 13
4.5.2 UE . 14
4.5.3 PCRF . 14
4.5.4 BM-SC . 14
5 Functional Description and Information Flow . 14
5.1 MB2: Interface between GCS AS and BM-SC . 14
5.1.1 General . 14
5.1.2 MB2 Procedures . 15
5.1.2.1 General . 15
5.1.2.2 TMGI Management . 15
5.1.2.2.1 General . 15
5.1.2.2.2 TMGI Allocation Procedure . 15
5.1.2.2.3 TMGI Deallocation Procedure . 16
5.1.2.2.4 TMGI allocation period expiry . 17
5.1.2.3 Activating and Deactivating an MBMS bearer . 17
5.1.2.3.1 General . 17
5.1.2.3.2 Activate MBMS Bearer Procedure . 17
5.1.2.3.3 Deactivate MBMS Bearer Procedure . 19
5.1.2.4 Modify MBMS Bearer Procedure . 20
5.1.2.5 MBMS Delivery Status Indication Procedure . 21
5.2 Specific Usage of EPS Bearers for GCS . 21
5.3 Service Continuity . 22
5.3.1 General . 22
5.3.2 Switching from Unicast Delivery to MBMS Delivery. 22
5.3.3 Switching from MBMS Delivery to Unicast Delivery . 23
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3GPP TS 23.468 version 15.1.0 Release 15 4 ETSI TS 123 468 V15.1.0 (2019-10)
5.3.3.1 General . 23
5.3.3.2 MBMS Delivery to Unicast Delivery (make-before-break) . 23
5.3.3.3 MBMS Delivery to Unicast Delivery (break-before-make) . 25
5.4 Priority and Pre-emption for Group Communication . 25
5.5 Charging . 28
5.6 Security . 28
Annex A (Informative): Utilisation of the Group Communication Service . 29
A.1 General . 29
A.2 Downlink Media path setup for MBMS Delivery . 29
A.2.1 General . 29
A.2.2 Use of Pre-established MBMS bearers . 29
A.2.3 Use of Dynamic MBMS bearer establishment . 30
Annex B (Informative): Change history . 31
History . 32

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3GPP TS 23.468 version 15.1.0 Release 15 5 ETSI TS 123 468 V15.1.0 (2019-10)
Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
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3GPP TS 23.468 version 15.1.0 Release 15 6 ETSI TS 123 468 V15.1.0 (2019-10)
1 Scope
The present document provides the stage 2 description for the 3GPP system provided enablers to support group
communication services using EUTRAN access. The corresponding stage 1 requirements are defined in TS 22.468 [2].
The group communication system is represented by an Application Server (GCS AS) using the 3GPP system provided
enablers for transferring its application signalling and for delivering application data, e.g. media data, to a group of UEs
either (i) over MBMS Bearer Services using the Broadcast Mode of MBMS (TS 23.246 [3]); or (ii) over EPS Bearers;
or (iii) over both MBMS and EPS bearer services.
The specification covers both roaming and non-roaming scenarios and also includes support for service continuity, i.e.
support for continuous reception of application data when a UE changes between reception of application data via EPS
and MBMS Bearer Services.
Application level interactions between the UE and the GCS Application Server are out of scope of this specification.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.468: "Group Communication System Enablers for LTE (GCSE_LTE)".
[3] 3GPP TS 23.246: "Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional
description".
[4] 3GPP TS 29.214: "Policy and charging control over Rx reference point".
[5] 3GPP TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access".
[6] 3GPP TS 23.203: "Policy and charging control architecture".
[7] 3GPP TS 26.346: " Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs".
[8] 3GPP TS 33.246: "3G Security; Security of Multimedia Broadcast/Multicast Service (MBMS)".
[9] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2".
[10] 3GPP TS 36.321: "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access
Control (MAC) protocol specification".
[11] 3GPP TS 23.303: "Proximity-based services (ProSe); Stage 2".
[12] 3GPP TS 23.280: "Common functional architecture to support mission critical services; Stage 2".
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3GPP TS 23.468 version 15.1.0 Release 15 7 ETSI TS 123 468 V15.1.0 (2019-10)
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A
term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
MBMS Delivery: A mechanism by which application data and signaling are delivered using MBMS bearer service
over EUTRAN as defined in TS 23.246 [3].
Unicast Delivery: A mechanism by which application data and signaling are delivered using EPS bearer service over
EUTRAN as defined in TS 23.401 [5].
ProSe UE-to-Network Relay: see TS 23.303 [11].
Remote UE: see TS 23.303 [11].
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
AS Application Server
ARP Allocation and Retention Priority
BM-SC Broadcast Multicast - Service Centre
DL Down Link
DRX Discontinuous Reception
FEC Forward Error Correction
FQDN Fully Qualified Domain Name
GCS Group Communication Service
GCS AS Group Communication Service Application Server
GCSE_LTE Group Communication System Enabler for LTE
MBMS Multimedia Broadcast/Multicast Service
MBSFN Multimedia Broadcast multicast service Single Frequency Network
MCH Multicast Channel
MCCH Multicast Control Channel
MTCH Multicast Traffic Channel
PCC Policy and Charging Control
PCEF Policy and Charging Enforcement Function
ProSe Proximity-based Services
QCI QoS Class Identifier
RoHC Robust Header Compression
TMGI Temporary Mobile Group Identity
UDP User Datagram Protocol
vPCRF visited Policy and Charging Rules Function

4 Architecture Model and Concepts
4.1 General Concept
This specification describes how a GCS Application Server (GCS AS) may use the enablers offered by the 3GPP
system for providing a Group Communication Service (GCS). These enablers are denoted as Group Communication
System Enablers (GCSE).
The GCS AS uses EPS bearer services and may use in addition MBMS bearer services for transferring application
signalling and data between the GCS AS and the UEs. In uplink direction, the UE uses an EPS bearer service to
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exchange application signalling with the GCS AS or when it wants to send data to the GCS AS. In downlink direction
the GCS AS may transfer application signalling and data via the UE individual EPS bearer services and/or via MBMS
bearer service. The GCS UEs register with their GCS AS using application signalling for participating in one or
multiple GCS groups.
NOTE 1: GCS application signalling (e.g. for group admission and floor control) and GCS group management
aspects (such as group creation, deletion, modification, group membership control, etc) are out of scope
of this specification.
When an MBMS bearer service is used, its broadcast service area may be pre-configured for use by the GCS AS.
Alternatively, the GCS AS may dynamically decide to use an MBMS bearer service when it determines that the number
of UE for a GCS group is sufficiently large within an area (e.g. within a cell or a collection of cells).
When MBMS bearer service is used, GCS AS may transfer data from different GCS groups over a single MBMS
broadcast bearer. The application signalling and data transferred via MBMS bearer(s) are transparent to BM-SC and the
MBMS bearer service. The GCS AS provides the UEs via GCS application signalling with all configuration information
that the UE needs to receive application data via MBMS bearer services and to handle that data appropriately.
When a GCS UE moves between areas where its MBMS broadcast bearers are available or not, the UE informs the
GCS AS via application signalling that it changes from MBMS broadcast bearer reception to non-reception, or vice
versa, the GCS AS activates or deactivates the downlink application signalling and data transfer via the UE individual
EPS bearer(s) as appropriate. To accomplish service continuity, a UE may temporarily receive the same GCS
application signalling and data in parallel via EPS bearer(s) and MBMS service(s). The GCS UE application discards
any received application signalling or data duplicates.
The following diagram shows an example of a scenario where a combination of Unicast and MBMS Delivery is used
for a particular media, belonging to a single group, by the GCS AS on the DL to different UEs. Here, UE-1 and UE-2
receive DL traffic over unicast whereas UEs 3-6 receive DL traffic over MBMS.
NOTE 2: Even though UE-2, UE-3 and UE-4 are connected to the same eNB (eNB-2), the UEs may be using
different delivery modes. For example, UE-2 is using unicast since it may be in an area where the MBMS
signal strength is weak.
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3GPP TS 23.468 version 15.1.0 Release 15 9 ETSI TS 123 468 V15.1.0 (2019-10)

GCS AS
Unicast

MBMS
IP Network
PDN GW
BM-SC/MBMS-GW
eNB-1 eNB-2 eNB-3
UE-1 UE-2
UE-3 UE-4 UE-5 UE-6

Figure 4.1-1: Media traffic with unicast and MBMS on DL
NOTE 3: During service continuity procedures a UE may simultaneously receive traffic from both unicast and
MBMS.
4.2 Architectural Reference Model
4.2.1 General
This model assumes that the GCS AS is not associated with any PLMN (regardless of the subscription of the UEs that
use it). The GCS AS is merely perceived as a third party application server by each serving PLMN. In addition:
- When the group communication service is provided using Unicast Delivery, there are no additional requirements
in order to provide GCS in roaming other than enabling normal EPS roaming and the ability of the GCS AS to
access QoS control capabilities via Rx interface in the HPLMN (for the non-roaming case and the roaming
Home routed case). For the Local breakout scenario, QoS control may be established via hPCRF and the S9
interface towards the vPCRF directly to the vPCRF as specified in TS 23.203 [6]. The GCS AS shall provide
information to enable session binding as defined in clause 6.1.1.2 of TS 23.203 [6].
- When MBMS Delivery to particular regions of the serving PLMN is required, the GCS AS needs to have access
to an MB2 interface offered by the serving PLMN.
Since the GCS AS is a third party application server, the GCS AS can access the required network resources to deliver
the group communication service, whether the serving PLMN is the Home PLMN or a different VPLMN, based on
operator agreement.
The PLMN selection process is according to the existing 3GPP procedures. When a PLMN is selected, the UE should,
in order to enable group communication services, register or re-register with the GCS AS and report to it the PLMN ID
of the current serving network as well as its HPLMN ID. The GCS AS may then, based on this information, determine
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3GPP TS 23.468 version 15.1.0 Release 15 10 ETSI TS 123 468 V15.1.0 (2019-10)
if it has an MB2 connection agreement for the serving PLMN, and if so report to the UE the MBMS related service data
required to use the service via MBMS Delivery in that PLMN.
Both the Home and serving PLMN ID(s) are needed to identify the contact point for the Rx interface, in addition to
existing parameters as defined in TS 23.203 [6] in order to accurately identify the UE and the session. The GCS AS
finds the entry point at the HPLMN using the home PLMN ID, the GCS AS finds the entry point at the VPLMN using
the serving PLMN ID. Within the PLMN, the information listed in TS 23.203 [6] is used to find the PCRF.
If no MB2 connection agreement with the GCS AS is available in the serving PLMN, then the GCS AS may deliver the
group communication data using Unicast Delivery.
NOTE: In the architecture figures shown in clauses 4.2.2, 4.2.3 and 4.2.4, "GCS AS" is being shown as one entity
for simplicity. It may be comprised of different functional entities to handle user and control plane. A
BM-SC may be connected to multiple GCS AS, and a UE may be served simultaneously by multiple GCS
AS (via separate GC1 connections).
The GCS AS provides the Service Information to the PCRF and the BM-SC. The Service Information is mapped by the
PCRF and the BM-SC to the QoS parameters under the consideration of the respective EPS network.
4.2.2 Non-roaming architecture
Figure 4.2.2-1 shows a high level view of the architecture for the non-roaming scenario.

Application
H-PLMN
HSS
domain
PCRF Rx
S6a
Gx
MME
S-11
GCS AS
S1- MM E
S/P- GW
SGi
Sm
M3
MB2-U
S1-u
MB2-C
M1
SGimb
UE E-UTRAN MBMS-GW BM-SC
Uu
SGmb
GC1

Figure 4.2.2-1: Non-roaming architecture model for GCSE_LTE
4.2.3 Roaming architecture
Figure 4.2.3-1 shows a high level view of the architecture applicable for the Home routed roaming model for Unicast
Delivery. For MBMS Delivery, BM-SC in the V-PLMN has a direct MB2 connection with the GCS AS.
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Application
PCRF
domain
Rx
HSS GCS AS
Gx
H-PLMN
SGi
P-GW
V-PLMN
S6a
S8
MME S-11
S1-MMe
S-GW
Sm
M3
MB2- U
S1- u
MB2-C
M1
SGimb
UE E-UTRAN MBMS-GW BM-SC
Uu
SGmb
GC1

Figure 4.2.3-1: Home routed roaming model
Figure 4.2.3-2 shows a high level view of the architecture applicable for the Local Breakout roaming model for Unicast
Delivery. For MBMS Delivery, BM-SC in the V-PLMN has a direct MB2 connection with the GCS AS.

Application
domain
Rx
H- PCRF
HSS GCS AS
H-PLMN
S9
Rx
V-PCRF
V-PLMN
S6a
S- Gi
Gx
MME S-11
S1-MMe
S-GW/PGW
MB2-U
Sm
M3
MB2-C
S1-u
M1
UE E-UTRAN MBMS- GW BM-SC
SGimb
Uu
SGmb
GC1

Figure 4.2.3-2: Local Break Out model
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3GPP TS 23.468 version 15.1.0 Release 15 12 ETSI TS 123 468 V15.1.0 (2019-10)
The GCS AS is configured with mapping information which contains an IP address range and the corresponding PLMN
which is responsible for this IP address range {(IPx.IPy) -> PLMN ID}.
In roaming scenarios, the GCS AS receives the UE IP address, the HPLMN ID and the VPLMN ID via GC1 signal
...