DMR Tier I, II and III: how they differ and what amateurs use

The DMR (Digital Mobile Radio) standard is defined in the ETSI TS 102 361 series of documents and is split into three tiers — Tier I, Tier II and Tier III. Each one describes a distinct class of systems with different requirements for licensing, network topology and capabilities. Understanding these tiers is critically important for anyone who wants to grasp the basics of DMR and choose the right equipment.

Tier I — the licence-free segment for consumer use

Tier I is the simplest tier of the standard, intended for consumer and light commercial applications. The key feature: Tier I devices operate without an individual licence in direct mode (simplex, no repeater) at a power of no more than 0.5 W. The antenna on such devices is built in and non-removable.

In Europe, Tier I is assigned to the 446 MHz band (the 446.1–446.2 MHz segment) — the same stretch as analogue PMR446, but in a digital form. Digital Tier I radios often combine analogue PMR446 and digital channels: typically 8 analogue and 16 digital (thanks to TDMA, two slots per frequency channel). The transmit timer is limited to 180 seconds, and repeaters and telephone gateways are not supported.

Tier I is suited to tourists, small businesses (warehouses, shops) and short-term coordination over short distances. For amateur radio in the classic sense — with repeaters, large coverage areas and network routing — it is not intended.

Tier II — conventional licensed systems, the backbone of amateur DMR

It is Tier II that people mean when the conversation turns to amateur DMR, to repeaters, to global networks like BrandMeister and DMRplus — and to the DMRhub network itself.

Tier II operates in licensed bands from 66 to 960 MHz. The key technology is TDMA (Time Division Multiple Access) with two time slots in a single 12.5 kHz radio channel. This means that two independent voice channels run simultaneously on one carrier frequency. The TDMA frame length is 60 ms: two 30 ms slots with guard intervals.

How the two time slots work

Picture a train with two tracks in a single tunnel: instead of building a second tunnel (a second frequency), TDMA lets two "trains" alternate at high speed without getting in each other's way. Time slot 1 and time slot 2 are effectively two separate radio links on one frequency. On a repeater this makes it possible to run two independent QSOs or route them to different talkgroups.

In addition to the two time slots, each Tier II channel is characterised by a Color Code (CC, the equivalent of CTCSS in the analogue world) — a value from 0 to 15 that uniquely identifies a repeater or hotspot and protects against accidental interference from other systems on the same frequency. Read more about this parameter in the article /tech/color-code.

Tier II modes: direct and via a repeater

Tier II supports both simplex (direct communication) without any infrastructure and operation through a repeater (base station). It is the availability of the repeater mode that sets Tier II apart from Tier I in a fundamental way: a repeater extends the coverage area, connects to an IP network and can route traffic to the desired talkgroup — local, regional or international. Compare the available modes in more detail in the article /tech/dmr-vs-rezhimy.

Hundreds of thousands of repeaters worldwide run on Tier II, including Russian DMR repeaters. A hotspot (a low-power personal repeater connected to the internet) is also a Tier II device; it is precisely these hotspots that connect to DMRhub.

Tier III — trunking for large systems

Tier III consists of trunked systems. Unlike Tier II, where each repeater operates on a fixed pair of frequencies, trunking automatically assigns a free channel from a pool when a call is initiated: the user does not select a channel manually, the system controller does it. Tier III is aimed at large corporate and government structures: transport companies, utilities, security and emergency agencies. The frequency range is the same — 66–960 MHz, and licensing is mandatory.

In amateur radio, Tier III is virtually never encountered: it requires substantial infrastructure and trunking controllers whose cost and complexity are out of all proportion to typical ham projects. Amateurs simply do not need it — everything required for full operation is covered by Tier II.

Comparison table: Tier I, II and III

Why Tier II is the amateur's choice

The amateur radio community settled on Tier II for a number of compelling reasons:

• Two time slots — a repeater simultaneously serves two QSOs or routes the slots to different talkgroups (for example, slot 1 — a regional group, slot 2 — an international one).
• Color Code and addressing — every call contains the source and destination Radio ID, which makes it possible to build addressable networks and place private calls.
• IP routing — Tier II systems are designed from the ground up to connect to an IP network through the repeater controller. This is exactly how all the major global networks and our DMRhub operate.
• Affordable equipment — a huge selection of Tier II-compatible radios from Baofeng, Retevis, TYT, Hytera, Motorola. More in the review of the best DMR radios.
• Hotspots — compact personal "mini-repeaters" (MMDVM, Pi-Star, SharkRF and others) that connect to the internet and provide access to the global network even from your home. They all run on Tier II.

Tier II and DMRhub: how they work together

The DMRhub network is built on Tier II. When you register a hotspot or radio, the system assigns you a DMR ID — a unique 7-digit number embedded in every packet under the Tier II protocol. Call routing between hotspots happens through our server: radio → hotspot (Tier II TDMA, 12.5 kHz) → internet → DMRhub server → another hotspot → the recipient's radio.

A talkgroup in DMRhub is a Tier II concept: a group of subscribers that can be subscribed to a time slot statically or activated dynamically with a single call. Exactly how static and dynamic subscriptions work is covered in the article /tech/talkgroup-static-dynamic. The Color Code of each hotspot in the network is also a Tier II parameter — it is set during configuration in your personal dashboard.

To enter the network through a hotspot, you do not need a repeater within radio range: the hotspot is itself a Tier II node with a power of a few tens of mW, enough to work within a single room or a car.