03 April 2024

Harald Ludwig, chair, TCCA Technical Forum

Amidst all development within 3GPP, and the mission critical broadband features emerging, national TETRA network operators and users are investigating and preparing to adopt the new mission critical technologies. However, it is accepted that TETRA will be needed to work in parallel with the emerging critical broadband networks, and for that to happen there needs to be a mechanism put in place for the two networks to operate in harmony.

Since 2021, stakeholders in critical communications have been discussing if an interworking function (IWF) is to be made available in the market so it can be used for the communication between the existing narrowband TETRA systems and the 3GPP MCX services. These are mission critical Push-to-Talk (MCPTT), mission critical data (MCData) and mission critical video (MCVideo) collectively known as MCX, running on 4G/LTE and 5G bearers. As mission critical broadband technologies are deployed, this requirement for interworking with existing TETRA systems is becoming increasingly important.

To facilitate the adoption of MCX, and to enable communication between users on each system, a connection between the two types of technology is needed. A means to provide this bridging functionality is under development by ETSI to standardise into a logical IWF that will be located within the TETRA network infrastructure.

TCCA has produced a white paper that describes the relation between the IWF and the TETRA infrastructure from the perspective of operators and users. The focus is on the usage during transition and what the expected features needed from this perspective are. It designates priorities in a clear overview of 1) must-have, 2) nice to have and 3) not prioritised. Included are use cases which are reflections from operators considering how the IWF can be managed during operation.

The white paper puts into an operational perspective how TETRA operators and users might want to use an interworking functionality for pilots, proof of concepts, migration, hybrid deployment and, at a later stage, the transition towards MCX.

From an operator perspective there could be several phases in the IWF deployment cycle. These phases will be part of planning the national migration projects and will have variable durations, hence they indicate the business and use case for the IWF. The four main phases (which have overlaps) can be categorised as:

• Pre- IWF Planning Phase: the pre-migration phase defines the outlines for the migration and deployment, including the definition of the national or international project deliveries for the MCX services, requests for information, definitions on use cases, pilots, test setup, user configurations and establishment on a small scale as the proof of concept before rollout. What are the available options in the market for LMR operators and users to facilitate per today and near future in the core infrastructure or command and control centres to connect both systems? What is the preferred scenario to start migration and deploy the different architectures to keep the TETRA networks in operation during transition? Here, the possible solutions are validated as strategies to make plans on how to migrate. The basic features to have available in and across TETRA and MCX to be able to provide critical communications in a time of transition are considered.
• Interworking roll-out Phase: the scale-up of the agreed connections to maintain during migration. It is the deployment phase where there is a functioning IWF between the TETRA and MCX systems to guarantee business as usual for critical communications for and with the end users in both the systems. It will be dependent on the user, operator, or network as to how long this phase will be, depending on many factors that will be part of the national migration plan and roll out. These include budgets, expectations, end user agreements, investments and maturity of deployment of the future technologies. The needed interworking functionality could be in a range from basic simple communication between systems to more sophisticated deployment.
• Interworking Phase: a hybrid phase where both solutions need to coexist, interwork and gradually move end users from the TETRA system over to the new ecosystem on the MCX servers. Again, this phase will be coloured by national rollout plans and timelines and could define the extend of functionalities required from the old and new network and the IWF in between. This could span between the absolute needed minimum up to what new features need to be in place from day one on the MCX platforms. These requirements may vary per national scenario, so the usage of IWF functionality could differ in deployment per operator.
• Retirement Phase: if an operator is considering replacing an existing TETRA network with MCX, an optional Retirement Phase can be added. This is the downsizing or dismantling of the IWF functionality and the TETRA system once most of the users are migrated over to the MCX services.

With all planning ongoing for migration to a next generation infrastructure and ecosystem, it is likely that most of the major TETRA operators will go through these phases when making this transition to MCX, although there are exceptions and not all providers and operators will follow these phases.

The IWF was added to the 7th ETSI Plugtests™ event hosted in Malaga in November 2022 for the first time. A standardised and preferable certified TETRA IWF solution supporting the basic set of voice and data services should be available in the market to facilitate the transition so operators and network owners can start dimensioning future scenarios of making the transition from TETRA to MCX. The white paper ‘Service Overview: TETRA-MCX Interworking (TETRA IWF)’ can be read here