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Content for  TS 23.379  Word version:  19.0.0

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1  Scopep. 13

This document specifies the functional architecture, procedures and information flows needed to support the mission critical push to talk (MCPTT) service. The MCPTT service utilizes the common functional architecture to support MC services over LTE including the common services core defined in TS 23.280.Support for both MCPTT group calls and MCPTT private calls operating in on-network and off-network modes of operation is specified.
The corresponding service requirements are defined in TS 22.179 and TS 22.280.
The present document is applicable primarily to MCPTT voice service using E-UTRAN access based on the EPC architecture defined in TS 23.401. Certain application functions of the MCPTT service such as dispatch and administrative functions could also be supported via non-3GPP access networks but no additional functionality is specified to support non-3GPP access.
The MCPTT service requires preferential handling compared to normal telecommunication services e.g. in support of police or fire brigade including the handling of prioritised MCPTT calls for emergency and imminent threats.
The MCPTT service can be used for public safety applications and also for general commercial applications e.g. utility companies and railways.
In the present document, MCPTT calls between MCPTT users on different MCPTT systems are considered.
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2  Referencesp. 13

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]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
TS 22.179: "Mission Critical Push to Talk (MCPTT)"; Stage 1.
[3]
TS 23.002: "Network Architecture".
[4]
TS 23.203: "Policy and charging control architecture".
[5]
TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
[6]
TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity; Stage 2".
[7]
TS 23.303: "Proximity-based services (ProSe); Stage 2".
[8]
TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access".
[9]
TS 23.468: "Group Communication System Enablers for LTE (GCSE_LTE); Stage 2".
[10]
TS 29.468: "Group Communication System Enablers for LTE (GCSE_LTE); MB2 Reference Point; Stage 3".
[11]  Void
[12]
TS 36.331: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification".
[13]
RFC 5245  (April 2010): "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols".
[14]  Void
[15]  Void
[16]
TS 23.280: "Common functional architecture to support mission critical services".
[17]
TS 22.280: "Mission Critical Common Requirements (MCCoRe); Stage 1".
[18]
TS 29.283: "Diameter data management applications".
[19]
TS 33.180: "Security of the mission critical service".
[20]
TS 23.283: "Mission Critical Communication Interworking with Land Mobile Radio Systems; Stage 2".
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3  Definitions, symbols and abbreviationsp. 14

3.1  Definitionsp. 14

For the purposes of the present document, the terms and definitions given in TR 21.905 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.
Automatic commencement mode:
A mode in which the initiation of the private call does not require any action on the part of the receiving MCPTT user.
First-to-answer call:
A call that is started when the first MCPTT user among multiple potential target recipients' answers. This call requires the answering MCPTT user to answer manually; automatic answer is not allowed
Group call:
A mechanism by which an MCPTT user can make a one-to-many MCPTT transmission to other users that are members of MCPTT group(s).
Group home MCPTT system:
The MCPTT system where the MCPTT group is defined.
Group host MCPTT server:
The MCPTT server within an MCPTT system that provides centralised support for MCPTT services of an MCPTT group defined in a group home MCPTT system.
Manual commencement mode:
A mode in which the initiation of the private call requires the receiving MCPTT user to perform some action to accept or reject the call setup.
MCPTT client:
An instance of an MC service client that provides the client application function for the MCPTT service.
MCPTT group:
An MC service group configured for MCPTT service.
MCPTT group affiliation:
An MC service group affiliation for MCPTT.
MCPTT group de-affiliation:
An MC service group de-affiliation for MCPTT.
MCPTT ID:
An instance of an MC service ID within the MCPTT service.
MCPTT server:
An instance of an MC service server that provides the server application function for the MCPTT service.
On-network MCPTT service:
The collection of functions and capabilities required to provide MCPTT via EPS bearers using E-UTRAN to provide the last hop radio bearers.
Preconfigured MCPTT group:
an MCPTT group used only for regrouping that has been configured in advance of a group or user regrouping operation to serve as the source of regroup group configuration.
Pre-selected MCPTT user profile:
An instance of the pre-selected MC service user profile for MCPTT.
UE-to-network relay MCPTT service:
The collection of functions and capabilities required to provide MCPTT via a ProSe UE-to-network relay using ProSe direct communication paths to provide the last hop radio bearer(s).
For the purposes of the present document, the following terms and definitions given in TS 22.179 apply:
Dispatcher
Floor control
Group-broadcast group
MCPTT administrator
MCPTT service
MCPTT system
MCPTT UE
MCPTT user
MCPTT User Profile
Mission Critical Organization
Mission Critical Push To Talk
Off-network MCPTT service
Partner MCPTT system
Primary MCPTT system
Private call
Multi-talker control
User-broadcast group
For the purposes of the present document, the following terms and definitions given in RFC 5245 apply:
Candidate
Candidate pair
For the purposes of the present document, the following terms and definitions given in TS 23.280 apply:
Ad hoc Group Communication
Active MC service user profile
Chat group
MC service client
MC service group
MC service group affiliation
MC service group de-affiliation
MC service ID
MC service server
Pre-arranged group
Pre-selected MC service user profile
For the purposes of the present document, the following terms and definitions given in TS 22.280 apply:
Functional alias
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3.2  Symbolsp. 15

For the purposes of the present document, the following symbols given in TS 22.179 apply:
B1
B2
N2
N3
N4
N5
N6
N7
N10
N11

3.3  Abbreviationsp. 16

For the purposes of the present document, the abbreviations given in TR 21.905 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.
APN
Access Point Name
ARP
Allocation and Retention Priority
BM‑SC
Broadcast Multicast Service Centre
CHAP
Challenge-Handshake Authentication Protocol
CSCF
Call Server Control Function
DL
Downlink
DPF
Direct Provisioning Function
E-UTRAN
Evolved Universal Terrestrial Radio Access Network
E2EE
End to End Encryption
ECGI
E-UTRAN Cell Global Identifier
EPC
Evolved Packet Core
EPS
Evolved Packet System
GBR
Guaranteed Bit Rate
GCS AS
Group Communication Service Application Server
GCSE_LTE
Group Communication Service Enabler over LTE
GRUU
Globally Routable User agent URI
HLR
Home Location Register
HSS
Home Subscriber Server
HTTP
Hyper Text Transfer Protocol
I-CSCF
Interrogating CSCF
ICE
Interactive Connectivity Establishment
IM CN
IP Multimedia Core Network
IMPI
IP Multimedia Private Identity
IMPU
IP Multimedia PUblic identity
IMS
IP Multimedia Subsystem
ITSI
Individual TETRA Subscriber Identity
LMR
Land Mobile Radio
MBMS
Multimedia Broadcast and Multicast Service
MBSFN
Multimedia Broadcast multicast service Single Frequency Network
MC
Mission Critical
MC ID
Mission Critical user identity
MCPTT
Mission Critical Push To Talk
MCPTT AS
MCPTT Application Server
MCPTT group ID
MCPTT group identity
MCPTT ID
MCPTT user identity
NAT
Network Address Translation
PAP
Password Authentication Protocol
P-CSCF
Proxy CSCF
PCC
Policy and Charging Control
PCRF
Policy and Charging Rules Function
PLMN
Public Land Mobile Network
ProSe
Proximity-based Services
PSI
Public Service Identity
PTT
Push To Talk
QCI
QoS Class Identifier
QoS
Quality of Service
RAN
Radio Access Network
RF
Radio Frequency
RSI
Radio Set Identity
S-CSCF
Serving CSCF
SAI
Service Area Identifier
SDF
Service Data Flow
SIP
Session Initiated Protocol
SSL
Secure Sockets Layer
TLS
Transport Layer Security
TMGI
Temporary Mobile Group Identity
UM
Unacknowledged Mode
URI
Uniform Resource Identifier
USB
Universal Serial Bus
WLAN
Wireless Local Area Network
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4  Introductionp. 17

The MCPTT service supports communication between several users (i.e. group call), where each user has the ability to gain access to the permission to talk in an arbitrated manner. The MCPTT service also supports private calls between two users.
The MCPTT architecture utilises the common functional architecture to support mission critical services over LTE defined in TS 23.280 and aspects of the IMS architecture defined in TS 23.228, the Proximity-based Services (ProSe) architecture defined in TS 23.303, the Group Communication System Enablers for LTE (GCSE_LTE) architecture defined in TS 23.468 and the PS-PS access transfer procedures defined in TS 23.237 to enable support of the MCPTT service.
The MCPTT UE primarily obtains access to the MCPTT service via E-UTRAN, using the EPS architecture defined in TS 23.401. Certain application functions of MCPTT service such as dispatch and administrative functions can be supported using either MCPTT UEs in E-UTRAN or using MCPTT UEs via non-3GPP access networks.
MCPTT UEs that use non-3GPP access can only support a subset of the functionality specified in this specification that is supported by the non-3GPP access network.
The MCPTT system provides the function to support interworking with LMR systems defined in TS 23.283.
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5  Architectural requirementsp. 17

5.1  Media routing requirementsp. 17

The voice media flow for a private call shall be routed according to one of the following two options:
  1. Option 1:
    1. Through the primary MCPTT system if both users in the call belong to the same organisation; or
    2. Through the primary MCPTT system of both users, if the users in the call do not belong to the same organisation.
  2. Option 2: The voice media flow may be routed locally, under the control of the primary MCPTT system, through an entity allowing the duplication of the media flow to the primary MCPTT system of each user.
The voice media flow for a group call shall be routed to the group home MCPTT system.
The routing of media flow shall be end-to-end from transmitter to receiver(s), except for the MCPTT control function.
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5.2  Requirements for user identity managementp. 17

To allow for confidentiality of user identities in various cases of business relationship as defined in clause 6, the MCPTT application may provide public user identities to the MCPTT UE, to be used by MCPTT UE for MCPTT services.

5.3  MCPTT group affiliation and MCPTT group de-affiliationp. 18

MCPTT group affiliation shall be as specified in clause 5.2.5 of TS 23.280. In addition, the following requirements shall be fulfilled by the MCPTT service for MCPTT users affiliated to MCPTT groups:
  • MCPTT users receive notifications for MCPTT group call setup and invitations for their affiliated MCPTT group(s).
  • MCPTT users receive media and events from their affiliated MCPTT group(s).

5.4  MCPTT call requirementsp. 18

5.4.1  Generalp. 18

The on-network MCPTT service shall support the use of pre-established sessions.

5.4.2  Group call requirementsp. 18

The MCPTT service shall support the chat group (restricted) call model for MCPTT group call.
The MCPTT service shall support the pre-arranged group call model for MCPTT group call.

5.5  GCS AS requirements for the MCPTT servicep. 18

The GCS AS architecture requirements for MC services are specified in TS 23.280.

5.6  Group selectionp. 18

The following functionalities shall be supported by the MCPTT service.
  1. The MCPTT user shall select an affiliated group to initiate a new group call or transmit media in an existing group call.
  2. An authorized MCPTT user (e.g., dispatcher) may remotely force or request to change other on-network MCPTT users' selected MCPTT group to a particular affiliated group.

5.7  Bearer managementp. 18

5.7.1  Generalp. 18

The MCPTT UE shall use the APNs as defined in subclause 5.2.7.0 of TS 23.280.

5.7.2  EPS bearer considerationsp. 18

The EPS bearer considerations specified in subclause 5.2.7.2 of TS 23.280 shall apply.

5.7.3  EPS unicast bearer considerations for MCPTTp. 18

For an MCPTT call session request, resources shall be requested utilising interaction with dynamic PCC. The MCPTT system shall request resources over Rx to a PCRF. The dedicated bearer for voice shall utilise the QCI value of 65 (as specified in TS 23.203) and the bearer for MCPTT-4 reference point messaging shall utilise the QCI value of 65 or the QCI value of 69 (as specified in TS 23.203). The request of resources over Rx shall include an application identifier for MCPTT in order for the PCRF to evaluate the correct QCI.
The UE is required to support at minimum one UM bearer which is used for MCPTT voice (see Annex A in TS 36.331).
Depending on operator policy:
  • the MCPTT system may be able to request modification of the priority (ARP) of an existing bearer without the need to initiate a new dedicated GBR bearer; or
  • the EPS bearers for MCPTT call may enable pre-emption of lower priority EPS bearers if the maximum number of UM bearers has been reached in favour of MCPTT initiated EPS bearer, if the EPS bearer used for MCPTT call has higher priority level (ARP) than the UM bearer(s) used for other application(s) and if the bearers for non MCPTT application are pre-emptable. In this case, the EPS bearer for MCPTT call pre-empts one of the existing EPS bearers when the maximum number of bearers is established for other applications.
The EPS bearer for MCPTT emergency call shall have highest priority level among MCPTT call types. The EPS bearer for MCPTT imminent peril call shall have higher priority level than one for MCPTT call.
To ensure that the MCPTT service always has access to a dedicated bearer for MCPTT media, a pre-established session may be setup that includes a request for resources at the first MCPTT group affiliation.
This means that the PCC may multiplex MCPTT media streams from multiple concurrent MCPTT calls into one EPS bearer on one shared network priority regardless of MCPTT call priority.
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5.7.4  MBMS bearer managementp. 19

The MBMS bearer management for MC services is specified in subclause 5.2.7.1 of TS 23.280.

5.8  MCPTT system interconnect requirementsp. 19

The architecture for interconnect between MCPTT systems is specified, allowing the affiliation of MCPTT users from an MCPTT system with MCPTT groups defined in another MCPTT system. When both MCPTT systems are served by different networks, interconnect of signalling and media is achieved using the interfaces defined for interconnect between PLMNs.

6  Involved business relationshipsp. 19

The description of the involved business relationships for the MCPTT service is contained in clause 6 of TS 23.280.

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