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Understanding the fleet number etc. used in some DMR Tier 3

One of the steps in getting a MOTOTRBO radio onto another vendors DMR Tier 3 compliant system, is to convert the assigned Fleet Individual Identity (FFFGGNNN) into the DMR Air Interface Address (Radio ID).

Some vendors use a proposed Dialing Plan discussed in Annex E of ETSI TS 102-361 §4. This dialing plan uses a Fleet Individual Identity to create fleets and groups in the same vein as MPT1343 did for MPT1327 systems.
Capacity Max does not use this Fleet Individual Identity but rather the actual Air Interface Address defined in ETSI TS 102-361 §1 to §4 (i.e. the real number that is sent over the air). When another vendors radio makes a call on a DMR Tier 3 system, the radio will convert the displayed/dialed Fleet Individual Identity into an Air Interface Address.

Fortunately §E3.1.3.3 has a formula to convert the Fleet Individual Identity to the Air Interface Address:

  • For dialled digits 20 to 41 AI MS address = (NP – 328) × 8000h + (FIN – 20) × 700 + (IN – 200) + 100001h
  • For dialled digits 42 to 89 AI MS address = (NP – 328) × 8000h + (FIN – 42) × 350 + (IN – 200) + 103C29h

The h suffix on some of the numbers means Hexadecimal so you need to convert those numbers into decimal before doing the calculation.
NP means Network Prefix; FIN is Fleet Individual Number; and IN Individual Number.

In §E. a formula is given to convert the Group Number into the Group ID (the real Group Number):

  • Group ID = (NP – 328) × 8000h + (FGN – 20) × 100 + (GN – 900) + 100001h.

Again, h means Hexadecimal and (as you can guess) FGN means Fleet Group Number.

The dialing plan described in Annex E is only Informative so the implementation is not compulsory and entirely up to the vendors own interpretation.
As mentioned above, Capacity Max avoids any potential complication by simply using the Air Interface ID – this is the same ID used if the radio were operating on a conventional channel.