D-STAR is a digital voice and data system for amateur radio. This guide explains the basics using Icom's official introduction, and how it fits with the Australian band plan.
1What D-STAR is
D-STAR stands for "Digital Smart Technologies for Amateur Radio" and is an open standard set by the JARL (Icom).
DV (digital voice): 4.8 kbps, with up to 950 bps of simultaneous low-speed data such as your call sign, short messages and GPS position (D-PRS).
DD (digital data): 128 kbps, which Icom says is "available with ID-1 only".
2Repeaters, simplex and the gateway
You can use a D-STAR repeater locally with no internet involved, and D-STAR radios can also talk directly to each other on simplex. A repeater's internet gateway lets calls be routed to remote repeaters; for that, Icom says "The D-STAR repeater call sign and IP address must be registered to the gateway server."
Repeaters running the dplus software can also link to another repeater or a group of repeaters via a reflector; Icom's example is "REF0010C".
3Where D-STAR sits in the band plan
On 2m, digital repeaters use Block C (12.5 kHz channels: outputs 144.8875–145.0625 MHz, inputs 145.4875–145.6625 MHz), and analogue or digital repeaters can use Blocks A and B. The digital voice call channel on 70cm is 439.200 MHz (WIA band plan).
DD mode needs about 128 kbps of wide bandwidth, which doesn't fit the 2m (under 25 kHz) or 70cm (under 16 kHz) channel limits. In practice that suggests DD would mean the 23cm band in Australia, which needs a Standard or Advanced qualification. That's an inference from the band plan bandwidths, not something the band plan states for D-STAR directly.
4Finding Australian D-STAR repeaters
Search the WIA Repeater Directory for your area and check the notes for D-STAR repeaters, or ask a local club. This guide doesn't list repeater counts or default reflector links, because those couldn't be verified.