What is TETRA radio?

What does TETRA stand for?

TETRA stands for Terrestrial Trunked Radio, a digital trunked mobile radio standard that ETSI developed for professional users. The first ETSI standards, adopted in January 1996, still spelled it Trans-European Trunked Radio. Public safety agencies, transport operators, utilities, governments, armed forces and industry run TETRA today.12

"Trunked" means the network hands out channels on demand from a shared pool instead of giving each group its own frequency. ETSI says TETRA scales from single-site local coverage to multi-site wide-area and nationwide networks.1 It is one of several types of two-way radio; makers of TETRA radios include Motorola Solutions and Hytera.

How does TETRA work?

A TETRA carrier is 25 kHz wide and split in time into four channels, so four calls share one carrier. Radios normally work through the network's base stations and switching (trunked mode). They can also talk radio to radio without any base station (direct mode), for example where there is no coverage.34

National regulators assign the exact frequencies.3 TETRA Release 2 added TEDS, a data mode on wider channels of 25, 50, 100 or 150 kHz with user bit rates from 30 to 400 kbit/s.6

Who uses TETRA?

TETRA serves public safety agencies first, along with transport operators, utilities, government and military users, oil and gas companies, and commercial and industrial fleets. In a July 2023 statement, ETSI and TCCA counted more than 120 countries using dedicated TETRA networks, from single sites to nationwide systems.17

National emergency networks are the best-known examples. Sweden's Rakel, Norway's Nødnett and Finland's Virve are TETRA networks linked across their borders.8 In Britain, the emergency services' Airwave network runs on TETRA.9 The wider picture, including P25 in North America, is on public safety radio.

How is TETRA different from DMR and PoC?

TETRA puts four channels on a 25 kHz carrier and is built for large trunked networks. DMR puts two on 12.5 kHz and is common in business fleets. A PoC radio uses no radio channel of its own: it sends voice over 4G/LTE data, so it reaches wherever the mobile network does.310

CEPT groups TETRA with other digital 25 kHz systems, and DMR, TETRAPOL and P25 with 12.5 kHz systems.6 The full PoC comparison with a direct radio network is in PoC vs DMR.

What is TETRAPOL?

TETRAPOL is a digital radio system for public safety that Matra began developing in 1988 and Airbus now sells. Unlike TETRA, it gives each channel its own frequency, 12.5 or 10 kHz wide depending on the project. Airbus lists nationwide TETRAPOL networks in Switzerland, the Czech Republic, Spain, Slovakia, Mexico and France.111213

The French Gendarmerie has used its TETRAPOL network, RUBIS, since 1992.15 The ISITEP final report calls TETRAPOL the other prevalent public safety technology in Europe and notes that it does not interoperate with TETRA over the air.14

How do TETRA and TETRAPOL networks work together across borders?

Networks connect through the Inter-System Interface (ISI), an ETSI standard that links two TETRA networks so radios can migrate between them and join individual and group calls across. The EU project ISITEP (2013–2016) built on it with IP gateways between national TETRA and TETRAPOL networks and tested them across European borders.161718

ISI is a family of ETSI standards: individual calls, group calls, short data and mobility management each have their own part, and the TETRA security standard covers key management across ISI.1619 Norway's DSB puts it simply: ISI enables communication between different networks and lets radio terminals migrate across them.8

ISITEP, "Inter System Interoperability for Tetra-TetraPol Networks", ran from 1 September 2013 to 31 December 2016 under the EU's security research program. Leonardo of Italy coordinated 18 partners from Belgium, Norway, Sweden, the Netherlands, Spain, Finland, France, Denmark, Italy and Greece. It cost €15.99 million, of which the EU paid €10.29 million.18 Its goals were ETSI ISI among national TETRA networks and ISI over IP gateways among TETRAPOL networks and between TETRAPOL and TETRA.18

The report calls the Norway–Sweden cooperation agreement of November 2016 the first real implementation of the ISITEP framework, and says Finland and Norway agreed to put the ISITEP ISI into operational use in 2017.14 In September 2019 the three-way link between Finland's Virve, Norway's Nødnett and Sweden's Rakel went live, a joint effort of DSB, Erillisverkot and MSB.8

How is TETRA moving to mission-critical LTE?

Operators are moving to 3GPP mission-critical services over 4G and 5G, starting with MCPTT, completed in Release 13 in March 2016. TETRA stays in use during the change. Interworking functions, introduced in 3GPP Release 15, link mission-critical users with TETRA, P25 and GSM-R, mainly for voice, messaging and location.2021

3GPP itself says the migration is not instantaneous and that many user groups will rely on narrowband networks for years.20 Its TETRA interworking specification does not define the interface inside the TETRA system, which is left to vendors; ISI is one of the alternatives it names.20 ETSI studied the scenarios in TR 103 565 in 2017.22

How commercial networks give responders priority is covered under commercial networks for public safety.

Is TETRA encrypted?

TETRA has air-interface encryption with the TEA algorithms, and end-to-end encryption as a separate service. In July 2023 researchers at Midnight Blue published TETRA:BURST, five vulnerabilities, two of them critical. ETSI and TCCA answered that they knew of no exploitation on operational networks and pointed to the newer TEA5–TEA7 algorithms.19277

Midnight Blue describes four TEA ciphers with 80-bit keys: TEA1 and TEA4 for commercial and export use, TEA2 and TEA3 for emergency services inside and outside Europe. It reported that TEA1 reduces the effective key so far that it can be brute-forced.27 ETSI does not regard that export-related limit as a backdoor, found no weakness in TEA2 and TEA3, and recommends patches, the move to TEA5–TEA7 and end-to-end encryption.7 In October 2022 ETSI said it had completed new air-interface encryption algorithms designed to withstand brute-force attack beyond 2040.28

How this relates to PoC radio

A PoC radio and a TETRA radio solve the same problem, a group talking at the press of a button, on different networks. TETRA runs on a dedicated network with its own frequencies and direct mode; a PoC radio rides on a mobile operator's LTE network and a push-to-talk service.

The two meet in three places. Mission-critical push-to-talk on LTE is where TETRA networks are heading.20 Push-to-talk platforms bridge app users to TETRA: TASSTA, for example, lists Sepura TETRA equipment among the radios its gateway connects. And some makers sell both, such as Motorola Solutions with DIMETRA (TETRA) next to its LTE radios.

For a team that does not run a national emergency network, the comparison that matters is usually PoC against a licensed radio network, covered in PoC vs DMR and 4G LTE walkie-talkies.

Questions

Sources

1. Terrestrial Trunked Radio and Critical Communications Evolution (TCCE) · ETSI
2. ETS 300 392-1 (1996): Trans-European Trunked Radio (TETRA), Voice plus Data, General network design · ETSI
3. ETSI EN 300 392-2 V3.8.1 (2016-08): TETRA Voice plus Data, Air Interface · ETSI
4. ETSI EN 300 396-1 V1.2.1 (2011-12): TETRA Direct Mode Operation, General network design · ETSI
5. ETSI TS 100 392-15 V1.5.1 (2011-02): TETRA frequency bands, duplex spacings and channel numbering · ETSI
6. ECC/DEC/(08)05: Harmonisation of frequency bands for digital PPDR narrow band and wide band radio in 380–470 MHz (amended 2019) · CEPT ECC
7. ETSI and TCCA statement on TETRA security algorithms research findings, 24 July 2023 · ETSI
8. Cross-border communication · DSB, Norway
9. Emergency Services Network: summary business case, 27 July 2026 · UK Home Office
10. ETSI TS 102 361-1 V2.7.1 (2026-05): Digital Mobile Radio (DMR), Air Interface protocol · ETSI