Also known as: DMR Tier III, DMR Tier 3
DMR Tier III is the trunked tier of the DMR standard. It adds a control channel and trunking signalling so many talkgroups can share a pool of two-slot TDMA channels, assigned on demand.12
Overview
Where Tier II is conventional, Tier III is a full trunked-radio system. Radios register (affiliate) and request calls over a dedicated control channel, which issues channel grants pointing them to a traffic channel and slot. Tier III (TS 102 361-4) is a standardised, multi-vendor trunking layer; Motorola’s Capacity Plus and Hytera’s Connect Plus are proprietary alternatives that trunk DMR outside the strict Tier III specification, so a decoder has to recognise which signalling dialect a given system speaks.
Technical characteristics
| Property | Value |
|---|---|
| Access | Two-slot TDMA + dedicated control channel |
| Signalling | CSBK control messages |
| Channel | 12.5 kHz |
| Modulation | 4FSK, 9600 bps |
| Vocoder | AMBE+2 |
| Squelch / identity | color code, talkgroup, source ID |
The control channel continuously broadcasts CSBK messages — system announcements, registration acknowledgements, and channel grants — and the same CSBK format also carries short data and SMS-style messaging. A radio idles on the control channel, requests a call, and is directed to a free traffic channel/slot; when the call ends the resources return to the pool.
History
Tier III trunking was standardised by ETSI (TS 102 361-4) to give DMR a multi-site, high-capacity option competing with P25 and TETRA in the commercial market at lower equipment cost.12
Deployment
Used by larger commercial, utility, transport, and campus operators needing trunked capacity at lower cost than TETRA or P25. Some networks instead run vendor trunking (Capacity Plus, Connect Plus) where the vendor’s own infrastructure keeps the deployment within one ecosystem.
Decoding it with GopherTrunk
GopherTrunk locks the Tier III control channel, decodes the CSBK channel grants, follows them to the assigned channel and slot, and decodes the AMBE+2 voice — reading the color code and talkgroup per call. It also handles the common vendor trunking dialects. See Status.
Sources
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Digital mobile radio — Wikipedia, for the ETSI DMR tiers, including the trunked Tier III with its control channel and CSBK signalling. ↩ ↩2
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DMR Association — the DMR manufacturer association, for the TS 102 361-4 trunking standard and Tier III’s relationship to vendor trunking modes. ↩ ↩2