ETSI TS 124 379 V17.15.0 (2026-03)

LTE; Mission Critical Push To Talk (MCPTT) call control; Protocol specification (3GPP TS 24.379 version 17.15.0 Release 17)

RTS/TSGC-0124379vhf0

General Information

• Status: Not Published
• Technical Committee: 3GPP CT 1 - MM/CC/SM [lu] (formely CN1)
• Current Stage: 8 - Draft receipt by ETSI Secretariat
• Completion Date: 10-Mar-2026

Standards Content (Sample)

TECHNICAL SPECIFICATION
LTE;
Mission Critical Push To Talk (MCPTT) call control;
Protocol specification
(3GPP TS 24.379 version 17.15.0 Release 17)

3GPP TS 24.379 version 17.15.0 Release 17 1 ETSI TS 124 379 V17.15.0 (2026-03)

Reference
RTS/TSGC-0124379vhf0
Keywords
LTE
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3GPP TS 24.379 version 17.15.0 Release 17 2 ETSI TS 124 379 V17.15.0 (2026-03)
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ETSI
3GPP TS 24.379 version 17.15.0 Release 17 3 ETSI TS 124 379 V17.15.0 (2026-03)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 21
1 Scope . 22
2 References . 22
3 Definitions, symbols and abbreviations . 25
3.1 Definitions . 25
3.2 Abbreviations . 28
4 General . 29
4.1 MCPTT overview . 29
4.2 URI and address assignments . 30
4.3 MCPTT speech . 31
4.4 Warning Header Field . 31
4.4.1 General . 31
4.4.2 Warning texts . 31
4.5 MCPTT session identity . 36
4.6 MCPTT priority calls and alerts . 37
4.6.1 MCPTT emergency group calls . 37
4.6.2 MCPTT emergency private calls . 38
4.6.3 MCPTT emergency alerts . 39
4.6.4 MCPTT imminent peril group call . 40
4.7 Communication security . 41
4.7.1 Media security . 41
4.7.2 Signalling security . 42
4.8 Protection of sensitive application data . 43
4.9 Pre-established session . 46
4.10 MCPTT client ID . 47
4.11 Off-network MCPTT . 47
4.12 Broadcast Group Calls . 47
5 Functional entities . 48
5.1 Introduction . 48
5.2 MCPTT client . 48
5.3 MCPTT server . 49
5.3.1 General . 49
5.3.2 Functional connectivity models . 50
5.3.3 Failure case . 52
5.3.4 Management of MBMS bearers . 52
5.4 MCPTT UE-to-network relay. 53
5.5 MCPTT gateway server . 53
5.5.1 General . 53
5.5.2 Functional connectivity models . 53
6 Common procedures. 54
6.1 Introduction . 54
6.2 MCPTT client procedures . 54
6.2.0 Distinction of requests at the MCPTT client . 54
6.2.0.1 SIP MESSAGE request . 54
6.2.1 SDP offer generation . 56
6.2.2 SDP answer generation . 57
6.2.3 Commencement modes . 58
6.2.3.1 Automatic commencement mode . 58
6.2.3.1.1 Automatic commencement mode for private calls . 58
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6.2.3.1.2 Automatic commencement mode for group calls . 59
6.2.3.2 Manual commencement mode . 59
6.2.3.2.1 Manual commencement mode for private calls . 59
6.2.3.2.2 Manual commencement mode for group calls . 59
6.2.4 Leaving an MCPTT session initiated by MCPTT client . 60
6.2.4.1 On-demand session case . 60
6.2.4.2 Pre-established session case . 60
6.2.5 Releasing an MCPTT session initiated by MCPTT client . 60
6.2.5.1 On-demand session case . 60
6.2.5.2 Pre-established session case . 61
6.2.6 Receiving an MCPTT session release request . 61
6.2.7 Void . 61
6.2.8 Priority call conditions . 61
6.2.8.0 General . 61
6.2.8.1 MCPTT emergency group call conditions . 62
6.2.8.1.1 SIP INVITE request or SIP REFER request for originating MCPTT emergency group calls . 62
6.2.8.1.2 Resource-Priority header field for MCPTT emergency group calls . 63
6.2.8.1.3 SIP re-INVITE request for cancelling MCPTT in-progress emergency group state . 63
6.2.8.1.4 Receiving a SIP 2xx response to a SIP request for a priority call . 64
6.2.8.1.5 Receiving a SIP 4xx response, SIP 5xx response or SIP 6xx response to a SIP request for a

priority group call . 64
6.2.8.1.6 Determining authorisation for initiating or cancelling an MCPTT emergency alert . 65
6.2.8.1.7 Determining authorisation for cancelling the in-progress emergency state of an MCPTT
group . 65
6.2.8.1.8 Determining authorisation for originating a priority group call . 65
6.2.8.1.9 SIP request for originating MCPTT imminent peril group calls . 66
6.2.8.1.10 Determining authorisation for cancelling an imminent peril group call . 67
6.2.8.1.11 SIP re-INVITE request for cancelling MCPTT in-progress imminent peril group state . 67
6.2.8.1.12 Resource-Priority header field for MCPTT imminent peril group calls . 67
6.2.8.1.13 Receiving a SIP INFO request in the dialog of a SIP request for a priority group call . 68
6.2.8.1.14 SIP re-INVITE request for cancelling the in-progress emergency group state of a group by a
third-party . 68
6.2.8.1.15 Retrieving Resource-Priority header field values . 69
6.2.8.1.16 Handling receipt of a SIP re-INVITE request for priority group call origination status within
a pre-established session . 70
6.2.8.1.17 Priority group call conditions upon receiving call release . 70
6.2.8.1.18 Emergency private call conditions upon receiving call release . 71
6.2.8.2 Request for an originating broadcast group call . 71
6.2.8.3 MCPTT emergency private call conditions . 71
6.2.8.3.1 Authorisations . 71
6.2.8.3.2 SIP request for originating MCPTT emergency private calls . 72
6.2.8.3.3 Resource-Priority header field for MCPTT emergency private calls . 73
6.2.8.3.4 Receiving a SIP 2xx response to a SIP request for an MCPTT emergency private call . 73
6.2.8.3.5 Receiving a SIP 4xx response, SIP 5xx response or SIP 6xx response to a SIP request for an

MCPTT emergency private call. 73
6.2.8.3.6 SIP re-INVITE request for cancelling MCPTT emergency private call state. 74
6.2.8.3.7 Receiving a SIP INFO request in the dialog of a SIP request for a priority private call. 75
6.2.8.3.8 SIP re-INVITE request for cancelling the MCPTT emergency private call state by a third-
party . 75
6.2.8.3.9 Retrieving a KMS URI associated with an MCPTT ID . 76
6.2.9 Location information . 76
6.2.9.1 Location information for location reporting . 76
6.3 MCPTT server procedures . 77
6.3.1 Distinction of requests sent to the MCPTT server . 77
6.3.1.1 SIP INVITE request . 77
6.3.1.2 SIP REFER request . 78
6.3.1.3 SIP MESSAGE request . 78
6.3.1.4 SIP SUBSCRIBE request . 83
6.3.2 Participating MCPTT Function. 84
6.3.2.1 Requests initiated by the served MCPTT user . 84
6.3.2.1.1 SDP offer generation . 84
6.3.2.1.2 SDP answer generation . 85
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6.3.2.1.3 Sending an INVITE request on receipt of an INVITE request . 85
6.3.2.1.4 Sending an INVITE request on receipt of a REFER request . 86
6.3.2.1.5 Response to an INVITE request . 87
6.3.2.1.6 Sending a SIP BYE request on receipt of a SIP BYE request . 88
6.3.2.1.7 Sending a SIP BYE request on receipt of a SIP REFER request . 89
6.3.2.1.8 Priority call conditions . 89
6.3.2.1.9 Generating a SIP re-INVITE request on receipt of a SIP re-INVITE request . 93
6.3.2.1.10 Sending a SIP INVITE request towards the non-controlling MCPTT function . 93
6.3.2.2 Requests terminated to the served MCPTT user . 95
6.3.2.2.1 SDP offer generation . 95
6.3.2.2.2 SDP answer generation . 95
6.3.2.2.3 SIP INVITE request towards the terminating MCPTT client . 95
6.3.2.2.4 Response to a SIP INVITE request . 96
6.3.2.2.5 Automatic Commencement Mode . 97
6.3.2.2.6 Manual Commencement Mode . 100
6.3.2.2.7 Void . 103
6.3.2.2.8 SIP BYE request towards the terminating MCPTT client . 103
6.3.2.2.9 Populate MIME bodies . 103
6.3.2.2.10 Generating a SIP re-INVITE request towards the terminating MCPTT client . 104
6.3.2.2.11 Generating a SIP MESSAGE request towards the terminating MCPTT client . 104
6.3.2.3 Void. 104
6.3.2.4 Request initiated by the participating MCPTT function . 104
6.3.2.4.1 Generating a SIP MESSAGE request for notification of entry into or exit from an emergency
alert area . 104
6.3.2.4.2 Generating a SIP MESSAGE request for notification of entry into or exit from a group
geographic area . 105
6.3.2.5 Handling of the no answer timer (TNP1) . 106
6.3.2.6 Generating a SIP MESSAGE request for call forwarding of a private call . 107
6.3.3 Controlling MCPTT function . 108
6.3.3.1 Request initiated by the controlling MCPTT function . 108
6.3.3.1.1 SDP offer generation . 108
6.3.3.1.2 Sending an INVITE request . 109
6.3.3.1.3 Receipt of a SIP response to a SIP INVITE request . 109
6.3.3.1.4 Void . 110
6.3.3.1.5 Sending a SIP BYE request . 110
6.3.3.1.6 Sending a SIP re-INVITE request for MCPTT emergency group call . 110
6.3.3.1.7 Sending a SIP INVITE request for MCPTT emergency group call . 111
6.3.3.1.8 Sending a SIP UPDATE request for Resource-Priority header field correction. 112
6.3.3.1.9 Generating a SIP re-INVITE request . 113
6.3.3.1.10 Generating a SIP re-INVITE request to cancel an in-progress emergency . 113
6.3.3.1.11 Generating a SIP MESSAGE request for notification of in-progress emergency or imminent
peril status change . 113
6.3.3.1.12 Populate mcptt-info and location-info MIME bodies for emergency alert . 114
6.3.3.1.13 Authorisations . 115
6.3.3.1.14 Generating a SIP 403 response for priority call request rejection . 120
6.3.3.1.15 Sending a SIP re-INVITE request for MCPTT imminent peril group call . 120
6.3.3.1.16 Handling the expiry of timer TNG2 (in-progress emergency group call timer) . 121
6.3.3.1.17 Validate priority request parameters . 121
6.3.3.1.18 Sending a SIP INFO request in the dialog of a SIP request for a priority call . 122
6.3.3.1.19 Retrieving Resource-Priority header field values . 122
6.3.3.1.20 Generating a SIP MESSAGE request to indicate successful receipt of an emergency alert or
emergency cancellation . 123
6.3.3.1.21 void . 124
6.3.3.1.22 void . 124
6.3.3.2 Requests terminated by the controlling MCPTT function . 124
6.3.3.2.1 SDP answer generation . 124
6.3.3.2.2 Receipt of a SIP INVITE request . 124
6.3.3.2.3 Sending a SIP response to a SIP INVITE request . 124
6.3.3.2.4 Receiving a SIP BYE request . 125
6.3.3.3 Handling of the acknowledged call setup timer (TNG1) . 126
6.3.3.4 Generating a SIP NOTIFY request . 128
6.3.3.5 Handling of the group call timer (TNG3) . 129
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6.3.3.5.1 General . 129
6.3.3.5.2 Interaction with the in-progress emergency group call timer (TNG2) . 129
6.3.3.6 Void. 130
6.3.4 Non-controlling MCPTT function of an MCPTT group . 130
6.3.4.1 Request initiated by the non-controlling MCPTT function of an MCPTT group . 130
6.3.4.1.1 SDP offer generation . 130
6.3.4.1.2 Sending an INVITE request towards the MCPTT client . 130
6.3.4.1.3 Sending a SIP INFO request . 131
6.3.4.1.4 Sending an INVITE request towards the controlling MCPTT function . 132
6.3.4.2 Requests terminated by the non-controlling MCPTT function of an MCPTT group . 133
6.3.4.2.1 SDP answer generation . 133
6.3.4.2.2 Sending a SIP response to the SIP INVITE request . 133
6.3.4.3 Generating a SIP NOTIFY request . 134
6.3.4.4 Void. 135
6.3.5 Retrieving and processing a group document . 135
6.3.5.1 General . 135
6.3.5.2 Rules for retrieving Group Document(s) . 135
6.3.5.3 Rules for joining a group session . 137
6.3.5.4 Rules for initiating a prearranged group session . 137
6.3.5.5 Determining the group members to invite . 139
6.3.6 Affiliation check . 139
6.3.7 Error handling . 140
6.3.7.1 Public service identity does not exist . 140
6.3.8 Session release policy . 140
6.3.8.1 Session release policy for group call . 140
6.3.8.2 Session release policy for private call . 140
6.4 Implicit floor request . 140
6.5 Handling of MIME bodies in a SIP message. 141
6.6 Confidentiality and Integrity Protection . 142
6.6.1 General . 142
6.6.1.1 Applicability and exclusions . 142
6.6.1.2 Performing XML content encryption . 142
6.6.1.3 Performing integrity protection on an XML body . 142
6.6.1.4 Verifying integrity of an XML body and decrypting XML elements . 143
6.6.2 Confidentiality Protection . 143
6.6.2.1 General . 143
6.6.2.2 Keys used in confidentiality protection procedures . 143
6.6.2.3 Procedures for sending confidentiality protected content . 144
6.6.2.3.1 MCPTT client . 144
6.6.2.3.2 MCPTT server . 144
6.6.2.3.3 Content Encryption in XML elements . 144
6.6.2.3.4 Attribute URI Encryption . 145
6.6.2.4 Procedures for receiving confidentiality protected content . 145
6.6.2.4.1 Determination of confidentiality protected content . 145
6.6.2.4.2 Decrypting confidentiality protected content in XML elements . 145
6.6.2.4.3 Decrypting confidentiality protected URIs in XML attributes . 146
6.6.2.5 MCPTT server copying received XML content . 146
6.6.3 Integrity Protection of XML documents . 147
6.6.3.1 General . 147
6.6.3.2 Keys used in integrity protection procedures . 149
6.6.3.3 Sending integrity protected content . 150
6.6.3.3.1 MCPTT client . 150
6.6.3.3.2 MCPTT server . 150
6.6.3.3.3 Integrity protection procedure . 150
6.6.3.4 Receiving integrity protected content. 151
6.6.3.4.1 Determination of integrity protected content . 151
6.6.3.4.2 Verification of integrity protected content. 151
6.7 Priority sharing . 151
6.8 Procedures at the MCPTT gateway . 151
6.8.1 General . 151
6.8.2 MCPTT gateway server acting as an exit point from an MCPTT system . 152
6.8.3 MCPTT gateway server acting as an entry point in an MCPTT system . 152
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6.8.4 Local policies enforcement . 153
7 Registration and service authorisation . 153
7.1 General . 153
7.2 MCPTT client procedures . 153
7.2.1 SIP REGISTER request for service authorisation . 153
7.2.1AA SIP REGISTER request without service authorisation . 154
7.2.1A Common SIP PUBLISH procedure . 155
7.2.2 SIP PUBLISH request for service authorisation and MCPTT service settings . 155
7.2.3 Sending SIP PUBLISH for MCPTT service settings only . 156
7.2.4 Determination of MCPTT service settings . 157
7.2.5 Receiving a CSK key download message . 158
7.3 MCPTT server procedures . 159
7.3.1 General . 159
7.3.1A Confidentiality and Integrity Protection . 159
7.3.2 SIP REGISTER request for service authorisation . 160
7.3.3 SIP PUBLISH request for service authorisation and service settings . 161
7.3.4 Receiving SIP PUBLISH request for MCPTT service settings only . 163
7.3.5 Receiving SIP PUBLISH request with "Expires=0" . 164
7.3.6 Subscription to and notification of MCPTT service settings . 164
7.3.6.1 Receiving subscription to MCPTT service settings . 164
7.3.6.2 Sending notification of change of MCPTT service settings . 165
7.3.7 Sending a CSK key download message . 165
7.4 Coding . 165
7.4.1 Extension of
...