By Yannick Lair and Georg Mayer

A platform for mission critical (MC) communications and MC Services has been a key priority of 3GPP in recent years and is expected to evolve into the future by taking more requirements, from different sectors of the global critical communications industry, on board.

This article provides an overview of what was achieved so far in the MC domain within 3GPP and also gives an outlook of what can be expected in the near future. We plan to create a more detailed paper on MC Services, which will summarize the use cases and functional aspects of Rel-13, Rel-14 and upcoming Rel-15, later this year.

Driven by the 3GPP release schedule, the mission critical related functionalities have been phased across them, each release encompassing a complete set of standards for equipment vendors and operators to phase their implementations and deployments, based on market demands.

Early Mission Critical Enablers

Prior to Rel-13, 3GPP standardized functionality that was later to serve as an enabler for MC Services. For example, MC Services benefit from the use of multicast bearers in LTE due to the standardisation of eMBMS and Group Communication System Enablers (GCSE). Additionally, D2D Proximity Based Services (ProSe) was enhanced to support public safety use.

This allows public safety operators to determine whether critical communications occur on-network using the LTE network infrastructure, or off-network without the use of the LTE network infrastructure, or both.

Mission Critical Push to Talk in 3GPP Rel-13

3GPP entered the application domain by standardizing Mission Critical Push to Talk (MCPTT) in Rel-13, completed in 2016. To provide organizational support and focus a new working group - SA6 - was established in order to complete the new application related work in concert with other 3GPP working groups in less than one and a half years - by March 2016.

By achieving this challenging goal, 3GPP not only honoured its commitment to the mission critical industries but also demonstrated its ability to take on new, application related work and to complete it within a set timeline.

Mission Critical Services in 3GPP Rel-14

MCPTT was the first major step in a series of MC Services and functionalities demanded by the market. In Rel-14, completed in 2017, 3GPP added additional MC Services and enhancements to its repertoire of standardized applications, specifically:

• Enhancements to MCPTT
• MCData
• MCVideo
• General framework which facilitates standardizing additional MC Services

The Rel-14 work on MC Services required not only a large set of new protocol additions and new security functionality, but also enhancements to the MCPTT Rel-13 specifications to enable reuse of common functionality across MC Services. Given the tight timeline for Rel-14 and with an eye on the upcoming 5G work, the MC Services were split into smaller, self-contained features in order to allow 3GPP to finish the majority of them in Rel-14, by September 2017, and to complete the remaining features in Rel-15, due to be completed in June 2018.

The MC Services introduced in Rel-14 offer stand-alone functionality that enriches the existing base of MC Services. The set of features included was carefully chosen so that implementers need not have to wait for the completion of additional standardized functionality in Rel-15. The Rel-14 MCVideo and MCData specifications therefore offer equipment vendors as well as network operators a consistent and fully specified set of standards, ready for initial implementation and deployment.

A detailed list of the functionalities completed in Rel-14 and Rel-15 respectively, can be found at the end of this article.

Mission Critical Services and Industry Specific Requirements in 3GPP Rel-15 and beyond

All 3GPP working groups have already started work on Rel-15, the first release of the 5G system. In addition, 3GPP is also working on service requirements for Rel-16, the second release of the 5G system.

In Rel-15, the MC Services are further evolved. In addition to that, 3GPP is currently evaluating and studying further MC related topics for Rel-15 and beyond, in particular:

• Interconnection between 3GPP defined MC systems
• Interworking between the 3GPP defined MC system and legacy systems such as TETRA or P25, for voice and short data service
• MC Service requirements from railway industries
• MBMS APIs for MC Services
• MC Service requirements from maritime industries

Conformance test standards for MC Services are also being developed within 3GPP. The initial set of test specifications on conformance testing Rel-13 MCPTT, is expected to be available by the end of 2017. Subsequently, conformance test specifications for Rel-14 and Rel-15 feature sets will be developed.

Mission Critical Services – Detailed List of Rel-13, Rel-14 and Rel-15 Functionalities

Rel-13 MCPTT (completed 2016)

• User authentication and service authorization
• Configuration
• Affiliation and de-affiliation
• Group calls on-network and off-network (within one system or multiple systems, pre-arranged or chat model, late entry, broadcast group calls, emergency group calls, imminent peril group calls, emergency alerts)
• Private calls on-network and off-network (automatic or manual commencement modes, emergency private calls)
• MCPTT security
• Encryption (media and control signalling)
• Simultaneous sessions for call
• Dynamic group management (group regrouping)
• Floor control in on-network (within one system or across systems) and in off-network
• Pre-established sessions
• Resource management (unicast, multicast, modification, shared priority)
• Multicast/Unicast bearer control, MBMS (Multimedia Broadcast/Multicast Service) bearers
• Location configuration, reporting and triggering
• Use of UE-to-network relays

Rel-14 MC Services (completed 2017)

MC Services Common Functionalities:

• User authentication and service authorization
• Service configuration
• Affiliation and de-affiliation
• Extended Location Features
• (Dynamic) Group Management
• Identity management
• MC Security framework
• Encryption (media and control signalling)

MCPTT Enhancements:

• First-to-answer call setup (with and without floor control)
• Floor control for audio cut-in enabled group
• Updating the selected MC Service user profile for an MC Service
• Ambient listening call
• MCPTT private call-back request
• Remote change of selected group

MCVideo, Common Functions plus:

• Group Call (including emergency group calls, imminent peril group calls, emergency alerts)
• Private Call (off-network)
• Transmission Control

MCData, Common Functions plus:

• Short Data Service (SDS)
• File Distribution (FD) (on-network)
• Transmission and Reception Control
• Handling of Disposition Notifications
• Communication Release

Rel-15 MC Services (in progress)

MC Services Common Functionalities Enhancements:

• Enhanced MCPTT group call setup procedure with MBMS bearer
• Enhanced Location management, information and triggers
• Interconnection between 3GPP defined MC systems
• Interworking with legacy systems

MCPTT Enhancements:

• Remotely initiated MCPTT call
• Enhanced handling of MCPTT Emergency Alerts
• Enhanced Broadcast group call
• Updating pre-selected MC Service user profile
• Temporary group call - user regroup
• Functional alias identity for user and equipment
• Multiple simultaneous users

MCVideo Additions:

• Video push
• Video pull
• Private call (on-network)
• Broadcast Group Call
• Ambient Viewing Call
• Capability information sharing
• Simultaneous Sessions
• Use of MBMS transmission
• Emergency and imminent peril private communications
• Primary and Partner MC system interactions for MCVideo communications
• Remote video parameters control capabilities

MCData Additions:

• MCData specific Location
• Enhanced Status
• Accessing list of deferred communications
• Usage of MBMS
• Emergency Alert
• Data streaming
• File Distribution (FD) (off-network)
• IP connectivity

MCPTT Conformance Tests (so far only for Rel-13 MCPTT)

Timeline for MC Services and 3GPP Releases

Release 13

• Mission Critical Push to Talk (MCPTT) completed in March 2016

Release 14

• MCPTT Improvements completion 09/2017
• MCData completion 09/2017
• MCVideo completion 09/2017

Release 15 and beyond

• MCPTT Improvements completion 06/2018
• MCData completion 06/2018
• MCVideo completion 06/2018
• Railways (FRMCS) study ongoing in SA6,normative work completion ~06/2018
• Interconnection between systems study completed,normative work completion ~06/2018
• Interworking with legacy systems study completed,normative work completion ~06/2018
• Maritime communications study ongoing in SA1
• Railways (FRMCS2) study and normative work ongoing in SA1
• MBMS APIs for MC Services study ongoing in SA6 

Further Reading:

3GPP Mission Critical Specifications (selected):

Stage 1 – Requirements

• TS 22.280 - MCS Common Requirements
• TS 22.179 - MCPTT over LTE requirements
• TS 22.281 - MCVideo over LTE requirements
• TS 22.282 - MCData over LTE requirements
• TS 22.289 – Mobile Communication Systems for Railways
• TR 22.819 - Study on Maritime Communication Services over 3GPP system

Stage 2 – Functional Architecture and Procedures

• TS 23.280 – MC Common Architecture
• TS 23.379 – MCPTT Architecture and Flows
• TS 23.281 – MCVideo Architecture and Flows
• TS 23.282 – MCData Architecture and Flows
• TS 33.180 – MC Services Security aspects
• TS 23.283 – MC Interworking between LTE-based systems and non-LTE-based systems
• TR 23.790 - Study on application architecture for the Future Railway Mobile Communication System (FRMCS)

Stage 3 – Protocols

• TS 24.379 – MCPTT Call Control
• TS 24.380 – MCPTT Media Plane
• TS 24.481 – MCS Group Management
• TS 24.482 – MCS Identity Management
• TS 24.483 – MCS Management Object (MO)
• TS 24.484 – MCS Configuration Management
• TS 24.281 – MCVideo signalling protocol
• TS 24.581 – MCVideo media plane control
• TS 24.282 – MCData signalling protocol
• TS 24.582 – MCData media plane control
• TR 24.980 - Minimum requirements for support of MCPTT over the Gm

Conformance Testing (so far only for Rel-13 MCPTT)

• TS 36.579-1 Mission Critical Push To Talk (MCPTT) over LTE; Part 1: Common test environment
• TS 36.579-2 Mission Critical Push To Talk (MCPTT) over LTE; Part 2: User Equipment (UE) Protocol conformance specification
• TS 36.579-3 Mission Critical Push To Talk (MCPTT) over LTE; Part 3: MCPTT Server Application conformance specification
• TS 36.579-4 Mission Critical Push To Talk (MCPTT) over LTE; Part 4: Test Applicability and Implementation Conformance Statement (ICS) proforma specification
• TS 36.579-5 Mission Critical Push To Talk (MCPTT) over LTE; Part 5: Abstract test suite (ATS)

The authors want to thank Ricky Kaura, Dean Prochaska, Frank Korinek, Suresh Chitturi, Erik Guttman, Luisa Marchetto, Zhang Ling, Francois Piroard, Andrew Howell, William Janky, Kevin Flynn as well as the rapporteurs of the indicated work items for their input to this article.