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

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

RTS/TSGS-0223468vf10

General Information

• Status: Published
• Publication Date: 30-Sep-2019
• Technical Committee: 3GPP SA 2 - Architecture
• Current Stage: 12 - Completion
• Completion Date: 01-Oct-2019

Standards Content (Sample)

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

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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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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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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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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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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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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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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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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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 signalling
from the UE. If the configured PLMN entry corresponding to the UE's IP address matches the HPLMN ID sent by the
UE, the GCS AS selects a PCRF from the UE's HPLMN (hPCRF) using the procedures defined in TS 23.203 [6].
Otherwise, the GCS AS may select a PCRF from either the HPLMN or the VPLMN using the procedures defined in
TS 23.203 [6]. The GCS AS makes this selection based on agreements with HPLMN/VPLMN operators.
4.2.4 Architecture model using a ProSe UE-to-Network Relay for Public
Safety
A Group Communication Service (GCS) is supported to the Remote UE using the ProSe UE-to-Network Relay through
the PC5 reference point specified in TS 23.303 [11]. In Figure 4.2.4-1, the architecture includes this scenario. This
architecture is only applied when using a Group Communication Service Application Server (GCS AS) for public
safety.
PC5
ProSe UE -to-
eNodeB + EPC
Remote UE GCS AS
Network Relay
GC1
Figure 4.2.4-1: Architecture model using a ProSe UE-to-Network Relay for Public Safety
4.3 Reference points
4.3.1 General
The reference points used to support group communications are listed in the following clauses.
4.3.2 List of Reference Points
4.3.2.1 GC1 reference point
The GC1 reference point exists between the GCS AS and the application client on the UE, and is not specified in this
release of this specification. However, this specification includes high level descriptions of interactions on the GC1
reference point, which are necessary in order to convey certain information (e.g. PLMN ID) and perform certain
functions (e.g. register or re-register with serving PLMN ID) in order for the EPS and MBMS bearer services to be
delivered accurately. Some of these aspects are specified in clauses 4.2.1, 4.4.1, 4.4.2, 4.5.1, 4.5.2, 5.3.2 and 5.3.3 of
this specification.
4.3.2.2 MB2 reference point
The MB2 reference point exists between the GCS AS and the BM-SC.
The MB2 reference point provides the ability for the application to:
- Request the allocation/deallocation of a set of TMGIs,
- Request to activate, deactivate, and modify an MBMS bearer:
- this may include request related to BM-SC applying FEC or RoHC or both to a set of media.
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The MB2 reference point provides the ability for the BM-SC to:
- Notify the application of the status of an MBMS bearer.
NOTE: The ability to indicate failure to deliver content is limited to current functionality.
4.3.2.3 SGmb/SGi-mb/M1/M3 reference points
The SGmb/SGi-mb/M1/M3 reference points are internal to the MBMS system and are defined in TS 23.246 [3].
4.3.2.4 Rx reference point
The Rx reference point is defined in TS 29.214 [4]. The GCS AS uses the Rx interface to manage unicast resources.
4.4 High level functions
4.4.1 Unicast Delivery
The UE and GCS AS use the EPS bearers defined in TS 23.401 [5] for Unicast Delivery. The EPS bearers are used for
the following:
- Exchanging GC1 signalling between UE and GCS AS.
- Transport of data on the uplink from UE to the GCS AS.
- Transport of data on the downlink from GCS AS to UE when MBMS Delivery is not desirable or possible.
The GCS AS uses the Rx interface to specify and modify the priority level of the EPS bearers used for the group
communication session (see clause 5.4).
4.4.2 MBMS Delivery
The GCS AS uses the MBMS bearers defined in TS 23.246 [3] for MBMS Delivery. The MBMS bearer is used to
transport data on the downlink from the GCS AS to the UE. The MBMS bearer(s) used for MBMS Delivery can be pre-
established before the group communication session is setup or can be dynamically established after the group
communication session is setup.
NOTE: Downlink data from the same or different group communication sessions may be multiplexed on the same
MBMS bearer as required by the GCS AS. The multiplexing of such data is transparent to the BM-SC.
4.4.3 Service continuity
The UE uses the service continuity procedures defined in clause 5.3 for switching between Unicast Delivery and
MBMS Delivery.
4.5 Network Elements
4.5.1 GCS AS
The GCS AS shall support the following functionality:
- Exchanging GC1 signalling (including GCS session and group management aspects) with the UE.
- Receiving uplink data from the UE over unicast
- Delivery of data to all the UEs belonging to a group using Unicast Delivery and/or MBMS Delivery.
- Transport of application level session information via Rx interface towards PCRF.
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- Support for service continuity procedures for a UE to switch between Unicast Delivery and MBMS Delivery as
specified in clause 5.3.
4.5.2 UE
The GCS capable UE shall support the following functionality:
- Exchanging GC1 signalling (including GCS session and group management aspects) with the GCS AS.
- Provision of a UE specific IDLE MODE DRX cycle length to the core network as specified in TS 23.401 [5]
clause 5.13.
- Receiving data from a GCS AS using either Unicast Delivery or MBMS Delivery, or both simultaneously.
- Sending data on the uplink to the GCS AS using unicast.
- Support for service continuity procedures to switch between Unicast Delivery and MBMS Delivery as specified
in clause 5.3.
- Simultaneous monitoring and reception of one or more MBMS bearer(s).
4.5.3 PCRF
The PCRF supports the functionality defined in TS 23.203 [6].
4.5.4 BM-SC
The BM-SC shall support the following functionality:
- MBMS Broadcast Mode procedures defined in TS 23.246 [3].
- MB2 procedures defined in clause 5.1 for activating, deactivating and modifying an MBMS bearer.
5 Functional Description and Information Flow
5.1 MB2: Interface between GCS AS and BM-SC
5.1.1 General
MB2 offers access to the MBMS bearer service from a GCS AS. MB2 carries control plane signalling (MB2-C) and
user plane (MB2-U) between GCS AS and BM-SC. MB2 has the following properties:
- MB2 is used by the GCS AS to interact with the BM-SC for MBMS bearer management.
- The GCS AS may use the MBMS service from multiple BM-SCs, each with a separate MB2 interface.
- The BM-SC shall provide service to multiple GCS ASs via a separate MB2 interface.
- Within one PLMN, an MBMS session is supported by exactly one BM-SC and provided for only one GCS AS.
- The data transferred via MBMS bearer(s) by the GCS AS is transparent to the BM-SC. A GCS AS may transfer
data from one or multiple GCS groups via a single MBMS bearer.
- MB2 is a standardized secured interface to an AS.
- The GCS AS needs to be configured with the IP addresses or a FQDN of the contact points of MB2-C. The
MB2-C contact points need to be configured per PLMN ID.
- The user plane transport information (e.g. IP address/UDP port) for delivering group communication data flow
from the GCS AS to the BM-SC over MB2-U shall be exchanged over MB2-C.
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3GPP TS 23.468 version 15.1.0 Release 15 15 ETSI TS 123 468 V15.1.0 (2019-10)
NOTE 1: The GCS AS is not associated to any specific PLMN from an ownership standpoint.
NOTE 2: It is up to stage 3 to define the protocol stack and security requirements for MB2-C/U, and any additional
parameters that may be needed by the MBMS procedure as defined in TS 23.246 [3].
5.1.2 MB2 Procedures
5.1.2.1 General
The MB2 interface provides the ability for the application to use the functionality of the MBMS system to deliver data
to group members over MBMS. The procedures supported include:
- allocation of a set of TMGIs (TS 23.246 [3]) by the BM-SC at the request of the GCS AS, (see clause 5.1.2.2.2),
- deallocation of a set of TMGIs by the BM-SC at the request of the GCS AS, (see clause 5.1.2.2.3),
- activating an MBMS bearer, (see clause 5.1.2.3.2):
- this may include request related to BM-SC applying FEC or RoHC or both to a set of media.
- deactivating an active MBMS bearer, (see clause 5.1.2.3.3),
- modifying characteristics of an active MBMS bearer, (see clause 5.1.2.4), and
- reporting of MBMS delivery status from the BM-SC to the GCS AS, (see clause 5.1.2.5).
The MB2 interface between the GCS AS and the BM-SC is established before any MB2 messages are sent between
these two entities, and carries all MB2 messages between the two entities for all MBMS bearers used by the GCS AS.
The TMGI/FlowID (see TS 23.246 [3]) is the unique identifier used by the GCS AS and BM-SC to refer to the MBMS
bearer.
5.1.2.2 TMGI Management
5.1.2.2.1 General
TMGIs are managed between the GCS AS and the BM-SC using the following explicit allocation and deallocation
procedures upon request from the GCS AS.
TMGIs may also be allocated automatically by the BM-SC at bearer activation as described in clause 5.1.2.3.2.
Each TMGI is allocated by the BM-SC for a given period of time determined by the BM-SC. If the GCS AS wants to
retain access to a TMGI for an extended period of time the GCS AS needs to request extension of the allocation period.
The GCS AS may request an extension of the allocation period at any time prior to expiry of the time period. The
actions consequent upon expiry of a TMGI allocation period are described in clause 5.1.2.2.4.
5.1.2.2.2 TMGI Allocation Procedure
The TMGI Allocation procedure is used by the GCS AS to request a set of TMGIs. This procedure may also be used to
renew the expiration time for already allocated TMGIs.
Figure 5.1.2.2.1-1 provides the procedure used between the GCS AS and the BM-SC to allocate a set of TMGIs to the
GCS AS.
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BM-SC GCS AS
1 . Allocate TMGI Request
(number of requested TMGIs,
list of TMGIs for allocation extension)
2. The BM -SC
determines that the
GCS AS is authorized
and allocates/extends
the desired TMGIs.
3. Allocate TMGI Response
(TMGI list, TMGI expiration)
Figure 5.1.2.2.1-1: TMGI Allocation Procedure
1. When the GCS AS wishes to have the BM-SC allocate one or more TMGIs to it, the GCS AS sends an Allocate
TMGI Request message to the BM-SC, including the number of requested TMGIs. The GCS AS may include a
list of TMGIs that are already allocated to the GCS AS, and for which the GCS AS wishes to obtain a later
expiration time. The number of TMGIs requested may be zero, if this procedure is used only to renew the
expiration time for already allocated TMGIs.
2. The BM-SC shall determine whether the GCS AS is authorized to receive the TMGIs and allocates a set of
TMGIs. The BM-SC determines an expiration time for the TMGIs. If a list of TMGIs has been received in the
Allocate TMGI Request message, the BM-SC also determines whether the TMGIs are allocated to the requesting
GCS AS and if yes, whether the expiration time for those TMGIs can be set to the new expiration time.
3. The BM-SC shall send an Allocate TMGI Response message to the GCS AS indicating the list of allocated
TMGIs, and an expiration time for those TMGIs.
5.1.2.2.3 TMGI Deallocation Procedure
The TMGI Deallocation procedure is used by the GCS AS to immediately release a set of TMGIs, irrespective of their
expiration times.
Figure 5.1.2.2.2-1 provides the procedure used between the GCS AS and the BM-SC to deallocate TMGIs.

BM-SC GCS AS
1. Deallocate TMGI Request
(list of TMGIs)
2. The BM-SC verifies that
all requested TMGIs are
eligible for deallocation by
the GCS AS. TMGIs with
allocated MBMS resources
are deactivated.
3. Deallocate TMGI Response
Figure 5.1.2.2.2-1: TMGI Deallocation Procedure
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1. When the GCS AS decides that it no longer needs one or more TMGIs that are allocated to it, the GCS AS shall
send a Deallocate TMGI Request message to the BM-SC with the list of TMGIs to be deallocated. Absence of
the list of TMGIs implies that all TMGIs currently allocated by the BM-SC to the GCS AS are to be deallocated.
2. The BM-SC shall determine that the GCS AS is authorized to deallocate the indicated TMGIs, and shall then
deallocate the TMGIs. If MBMS resources are in use for any of the deallocated TMGIs, those resources are
released using the Session Stop procedure defined in TS 23.246 [3] and the BM-SC shall release any
corresponding MB2 resources.
3. The BM-SC sends a Deallocate TMGI Response message to the GCS AS.
5.1.2.2.4 TMGI allocation period expiry
When the allocation period for a TMGI expires the TMGI and its associated Flow ID are no longer available for use by
the GCS AS.
If, at the time of expiry, the TMGI is associated with a previously activated MBMS bearer (clause 5.1.2.3.2) the BM-SC
shall autonomously take whatever actions are needed to stop broadcast of the MBMS bearer to the agreed MBMS
service area, and shall release the MBMS resources used for the MBMS bearer using the Session Stop procedure
defined in TS 23.246 [3]. The BM-SC shall send an MBMS Delivery Status Indication message to the GCS AS and
shall release any corresponding MB2 resources.
At any time prior to expiry, the allocation period for a TMGI(s) may be extended as described in clause 5.1.2.2.2. A
GCS AS wanting to ensure that it retains access to a TMGI should request extension of the allocation period at an
adequate time before expiry, e.g. halfway through the allocation period.
5.1.2.3 Activating and Deactivating an MBMS bearer
5.1.2.3.1 General
Activating and deactivating an MBMS bearer involves the allocation/deallocation of MBMS resources, based on the
MBMS bearer configuration provided by the GCS AS, using the following explicit activation and deactivation
procedures upon request from the GCS AS.
MBMS bearer resources may also be deallocated autonomously by the BM-SC, upon expiry of the allocation period of
the TMGI associated with the MBMS bearer, as described in clause 5.1.2.2.4.
5.1.2.3.2 Activate MBMS Bearer Procedure
The Activate MBMS Bearer procedure is used by the GCS AS to cause allocation of resources for an MBMS bearer. In
addition, the GCS AS acting in the role of the Mission Critical service server as specified in TS 23.280 [12] can request
the BM-SC to apply FEC and/or RoHC to a set of medias, transported by that MBMS bearer,
Figure 5.1.2.3.2-1 provides the procedure used between the GCS AS and the BM-SC to activate an MBMS bearer.
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BM-SC GCS AS
1. Activate MBMS Bearer Request
(TMGI, QoS, MBMS broadcast
area, start time)
2. The BM-SC
allocates resources in
the MBMS system to
support the data flow.
3. Activate MBMS Bearer Respo
...