As mentioned in my post about Digital Voice, the various technologies available all have their quirks and differences along with the many things they have in common.

A common feature between most of these systems is the notion of Talk Groups, to use DMR terminology. In simplex operation or on a standalone repeater system, Talk Groups allow separate groups of radio users to operate on the same frequency or frequency pair without hearing messages from other groups, and without their messages being heard by those other groups.

On an internet-linked repeater system, a Talk Group can made available on different repeaters or gateways anywhere in the world, creating a wide-area virtual channel.

It's common on DMR systems to have a handful of Talk Groups configured on a repeater or gateway, meaning that it will transmit when traffic for that Talk Group arrives from the internet. End radio users can select which talk group they wish to listen to on their radio.

During a recent conversation on OARC's #digital-voice text chat I noted my experience that Yaesu's System Fusion lacked the ability to have multiple Talk Groups ('Rooms' in Yaesu's terminology, Reflectors in general amateur parlance) presented in this way, it only appearing to have the ability to switch which single Room was available using the Wires-X interface on the radio, or the "YSF Link Manager" feature in the Pi-Star DV Dashboard.

Jonathan Naylor (G4KLX), developer of MMDVMHost and many amateur radio digital voice tools, interjected that it was in fact possible do this, using DG-IDs.

DG-IDs are, I found, a bit of an underdocumented feature. The operating manual for my FT-991a includes the following description:

By matching the transmit DG-ID number to the uplink DG-ID number set in the DR-2X/XE System Fusion II digital repeater club, you can access the DR-2X/XE digital repeater used in the club. For communication only between transceivers in a group of friends, you can all match the same DG-ID number; then only your friend's voices will be heard.

The latter part of that is fairly understandable, and is similar to how Talk Groups can be used in DMR Simplex operation to separate groups of users, as described earlier. The first part is less clear to me.

A bit of internet searching led me to a description of a linked repeater system making use of the DG-ID system to allow users to choose whether their transmissions would be repeated by the repeater they were communicating with, or by every linked repeater in the group.

I also found discussion of part of the YSFClients suite that I had not looked at before - DGIdGateway. This work by Jonathan provides what I would describe as a routing service between a given DG-ID and various System Fusion services.

The sample DGIdGatway.ini offers an insight into what it can do - associating DG-IDs with YSFGateway, YSFParrot instances, various YSF2XXX bridges, and specific individual reflectors.

From the example, I set up my own hotspot and radio with these DG-IDs

1. YSFGateway
2. YSFParrot
3. DV Scotland YSF Reflector (Static)
4. Online Amateur Radio Club YSF Reflector (Static)
5. FreeStar UK YSF Reflector (Dynamic)
6. CQ-UK YSF Reflector (Dynamic)
7. SDF ARC Talk Group (Static)
8. Scotland Chat Talk Group (Static)

With the DG-ID set to 0, my radio operates as I have come to expect and I can either use the Wires-X menu or the Pi-Star DV Dashboard to change Reflectors.

By setting it to 1 through 7, my radio receives messages for the Reflector or Talkgroup selected, ignoring other traffic. The Static entries will always receive traffic from the internet, while the Dynamic ones require an initial local transmission to activate, and will remain active for a few minutes after the last local or internet transmission has been received. FreeStar and CQ-UK can busy at times so I'd prefer not to have them enabled all the time.

Usefully, the Pi-Star DV Dashboard will show DG-IDs associated with transmissions, so it is possible to observe where activity is taking place on DG-IDs other than the one selected on the radio.

DG-IDs 6 and 7 make use of the YSF2DMR bridge software to connect to talkgroups on the BrandMeister DMR network. It would also be possible to have additional DG-IDs configured to link to talkgroups on other DMR networks, or indeed networks for other protocols for which a YSF2XXX bridge is available.

I have a post in the works about how my MMDVM hotspot is configured which will include more detail on how I went about setting up DGIdGateway.