Digital Mobile Radios also referred to as DMR are two-way radio technologies released in 2005 by the European Telecommunication Standards Institute as a cheaper alternative to analogue radios. 

Tier-1, Tier-2 & Tier-3 DMR

Tier 1, an entry level tier which is cost effective and ideal for smaller businesses.

Tier 2, introducing trunking to the technology which incorporates applications.

Tier-3, Frequency and channel capacity are pooled and shared between users.