Numbering systems are designed to make contacting other radios easier for the terminal users. The numbering system provides a simple and optionally quicker (fewer digits to dial) means of dialling individual and group numbers
There are many different number schemes for Tier 3 radio systems, these can vary even from the same manufacturer. Each scheme segments the raw air interface numbering to make the terminal numbering easier for the user.
Air Interface numbering
All ETSI compliant Tier 3 systems use a common air interface numbering field. This is a 24 bit/3 byte field that can contain a single whole number from 0 to 16777215. In a Tier 2 system, this is the ident of the radio as seen by the user.
A dial string is a number a terminal user enters. This could be a full-length radio identity such as 80020201 or a short form version 201 (which gets transformed to 80020201 by the radio software. The full string will be broken down depending on the numbering scheme selected in the radio configuration.
E.g. 80020201 breaks down into Network Area Identity 800, Fleet Individual Identity 20 and Individual number 201 using the CPS-P3 number scheme.
SMC Gateway and Tier 3 numbering
The core nodes in the SMC Gateway work using the Air Interface identity. For Tier 2 systems this requires no further thought or interaction.
For Tier 3 systems we have provided a “Dialstring” node which converts between air interface and dial-string formats, including support for short dialling. Only where a user is going to view or enter a radio identity do you need to use the Dial-string node.
E.g. if your flow receives a text message and your flow replies with another text message the ident received is the same ident used to send the reply.
The “Dialstring” node works by looking for an ident or “dialstring” field in the incoming message and converts the value using the selected and configured dial scheme.
Air interface to dial-string mode
If the field has a valid whole number in it the node will convert this to a dial-string using the configured numbering scheme. In this case, the node will set a new “dialstring” field accordingly, and also np, fin and unit fields with the broken down elements of the dialstring.
Dial-string to air interface mode
If the incoming message has no ident or a non-numerical value, and it has a “dialstring” field the node will convert the “dialstring” value to an air interface and store it in the ident field.
Here are some of the more common numbering schemes and a brief note about each. Each element in a dial string is normally zero padded to meet a predetermined width – this width is shown with square brackets below:
Prefix / Ident
Network Prefix  / Fleet  / Unit/Group number [2 or 3]
Fleet is 2001-4999 for individuals and 5000-6050 for groups
Group number (two digits) 90-99
Unit number (three digits) 200-899
Group number (three digits) 900-998
Is air ident 71
Network Prefix  / Fleet  / Unit/Group number 
Fleet is 20-89
Where FIN is 20 to 41, Unit number 200-899
Where FIN is 42 to 89, Unit number 200-549
Group number 900-999
Is air ident 16515074