Why Terminal IDs?

In the case of callsign routing, D-Star transmissions are routed to the destination call sign through the global network.
Each radio amateur usually has only one individual call sign with which he can be qrv.
There are situations where you would like to do different things with several devices.

This is not only with D-Star so, who knows Packet radio, knows there the SSID (= Second Station ID), with which one can establish several connections in parallel.
The terminal ID at D-Star has a similar function.

For example, if you want to use a device with 70cm of voice QSO, parallel to a 23cm device to establish a data connection, then you have to use two different "callsigns", so that the D-Star router can distinguish the two devices. Otherwise, the router would after a data exchange the call sign to 23cm suspect and also there the voice data, which actually belong to 70cm.

This can happen if you have 2 devices connected in parallel on 2 different D-Star inputs qrv, whether this is 2 radios on different gateways, or a radio and a DV dongle.
D-Star routing always routes traffic to the location where the addressed call sign has been heard for the last time.

In D-Star, a call signal always consists of 8 characters, 7 for the actual call sign (with fewer digits filled with spaces) and the 8th for an ID.
The actual call sign contains only the basic call sign, no attachments like "-p", "-m" etc. with D-Star!
The ID can be a space "" / Space, or a letter AZ.
Digits should not be used here according to the Icom specification.
This ID is never empty, with D-Star callsign always all 8 digits are occupied, possibly with spaces.

When registering, you must always register an entry with a space.
Unfortunately the Icom software of the registration server does not do this automatically, unfortunately we have no influence on it.

Before everybody thinks he has to provide IDs for all his devices or even use changing IDs for a single device, an important disadvantage is pointed out:

If a station addresses a transmission directly in the URCALL, the transmission only arrives if the complete call sign incl. The ID fits.
An addressing to "DL5DI" (space as ID) will not reach "DL5DI M" and vice versa! (unless "DL5DI M" hears where "DL5DI" was last qrv).
For the D-Star router, callsigns with different IDs (the space is also an ID!) Are different destinations, which he remembers separately!