Rosetta Stone for the Digital Modes

Same idea, six different names. Digital voice looks like six protocols to learn. It is closer to six concepts, each wearing six costumes — and nobody tells you which costume is which.

Why This Page Exists

A newcomer to digital voice is handed a vocabulary: Color Code, DG-ID, RAN, NAC, CAN. Five terms, five modes, and no indication that they are all the same thing.

They are. Every one of them is the digital descendant of CTCSS — a code that says this transmission is for this system, and lets a radio ignore everything else. Once you know that, five terms collapse into one idea, and you have four fewer things to learn.

The whole of digital voice works like this. There are perhaps six concepts underneath all six modes. What varies is almost entirely the words.

This page is a translation table. It does not teach you any mode — the mode guides do that. It teaches you that when a DMR operator says “talkgroup” and a D-STAR operator says “reflector module,” they are describing the same room.

Concept One — Who You Are

Every transmission has to say who sent it. Every mode does this. They disagree entirely about what form that answer takes.

DMR	D-STAR	C4FM	NXDN	P25	M17
DMR ID a number	Callsign	Callsign	Unit ID a number	Radio ID a number	Callsign encoded as the address

The split down the middle is numbers versus callsigns, and it has one enormous consequence: a number has to be issued by somebody.

That is the entire reason RadioID.net exists. If the network routes on numbers, someone must hand out the numbers and prevent collisions. If the network routes on callsigns, nobody needs to — the callsign was already issued, by your licensing authority, years ago.

The registry is not a policy choice. It is a mathematical consequence of the identity format. Modes that use numbers need a registry. Modes that use callsigns do not. Everything else about registration follows from that one fork.

Concept Two — What Lets You In

This is the row that causes more confusion than any other, because people mistake it for the row above.

DMR	D-STAR	C4FM	NXDN	P25	M17
Color Code	—	DG-ID	RAN	NAC	CAN

Five different names. One idea. All of them are CTCSS wearing a digital hat.

The job is always the same: a repeater or a radio ignores traffic that does not carry the matching code. It is not security — anyone can set the code, and it is not secret. It is a filter, so that two systems sharing a frequency do not open each other’s squelch.

The trap: this is a gate, not a badge. It says nothing about who you are. An operator who tells you their DG-ID is their “Fusion ID” has crossed row one and row two — and that mistake is extremely common.

D-STAR is the odd one out with no access code at all. Its gating happens through callsign routing and gateway registration instead.

Concept Three — The Room You Are Talking In

Where does your voice go once it leaves the repeater? Every mode has an answer, and this is where the words diverge most violently.

DMR	D-STAR	C4FM	NXDN	P25	M17
Talkgroup a number	Reflector + module a letter	Room, or DG-ID depending on the network	Talkgroup a number	Talkgroup a number	Reflector + module a letter

Three modes call it a talkgroup and address it with a number. Two call it a reflector module and address it with a letter. And C4FM — C4FM is the reason this page needed writing.

Look at where DG-ID appears. It is in row two and row three. On some systems it gates access; on others it also selects a destination. That is not a mistake in this table — it is a genuine double duty in the protocol, and it is precisely why C4FM operators and DMR operators talk past each other about what DG-ID “is.”

Concept Four — The Voice Itself

Underneath every digital voice mode is a vocoder — the thing that turns speech into bits. This row explains more about the digital voice world than any other.

DMR	D-STAR	C4FM	NXDN	P25	M17
AMBE+2	AMBE	AMBE+2	AMBE+2	IMBE	Codec 2

Read that row and half the mysteries of digital voice resolve at once:

Why some bridges are easy. DMR, C4FM and NXDN all speak AMBE+2. Bridging between them does not require changing the voice at all — the bits pass straight through.
Why D-STAR is awkward. It uses the older AMBE, not AMBE+2. Different codec, so the audio must be decoded and re-encoded.
Why P25 is the odd one out — and why that no longer costs you anything. IMBE is a different vocoder entirely; nothing else on this list speaks it, so bridging P25 always means transcoding. But IMBE's patent has expired and free software vocoders exist — so unlike D-STAR, P25 costs nothing extra to bridge. Different, but not expensive.
Why M17 is the odd one out — and why it exists. Codec 2 is free and open from the ground up. Every other codec on this row is proprietary; the AMBE family is also still licensed, which is why transcoding D-STAR, DMR, C4FM or NXDN so often requires a hardware dongle. (P25's IMBE is the exception — proprietary, but its patent has expired, so it can be done in software.) M17 was built so the row would never need a dongle at all.

This single row is why transcoding is hard, why AMBE dongles exist, and why the open-source community built a codec of its own. It is the hinge the entire digital voice world turns on.

Concept Five — How the Channel Is Divided

Two radios cannot occupy the same space at the same time. Every mode has to solve that, and there are only two answers.

Mode	Method	What it means
DMR	TDMA	Two conversations take turns in one channel — the two timeslots. This is why DMR, alone among these modes, has timeslots at all.
D-STAR	FDMA	One conversation, one channel. No slots.
C4FM	FDMA	One conversation, one channel. No slots.
NXDN	FDMA	One conversation, one channel — but an unusually narrow one.
P25	FDMA	Phase 1, as used on the amateur bands. One conversation, one channel.
M17	FDMA	One conversation, one channel. No slots.

Why does DMR have two timeslots and nobody else does? Because DMR chose TDMA and everything else chose FDMA. A timeslot is not a digital voice concept — it is a DMR concept. If you have been trying to find the timeslot setting on your Fusion radio, this is why you cannot: there isn’t one, and there was never meant to be.

The Master Table

Everything above, on one screen. This is the part to bookmark.

Concept	DMR	D-STAR	C4FM	NXDN	P25	M17
Who you are	DMR ID	Callsign	Callsign	Unit ID	Radio ID	Callsign
What lets you in	Color Code	—	DG-ID	RAN	NAC	CAN
The room you’re in	Talkgroup	Reflector + module	Room / DG-ID	Talkgroup	Talkgroup	Reflector + module
The vocoder	AMBE+2	AMBE	AMBE+2	AMBE+2	IMBE	Codec 2
Channel access	TDMA	FDMA	FDMA	FDMA	FDMA	FDMA
Registry needed	Yes	Gateway reg.	No	Yes	Yes — DMR’s	No

The Traps

A translation table is only half the job. The other half is knowing where the words actively mislead you — where two modes use the same word for different things, which is far more dangerous than using different words for the same thing.

“Radio ID” means two completely different things

In P25, the Radio ID is your identity — the number that says who you are, and on the amateur bands it is your DMR ID. In C4FM, the Radio ID is a factory-burned serial number identifying the hardware, which you cannot change and which is not your identity at all. Same two words. Opposite meanings.

DG-ID does two jobs

It appears in the access-code row and the destination row. Depending on the system, it gates, it routes, or both. No other mode’s access code does this, and it is the single most common source of C4FM confusion.

“Reflector” is not one thing

A D-STAR reflector, an M17 reflector, a YSF reflector and an XLX reflector are all called reflectors, and they are not interchangeable. They speak different protocols and, in most cases, different vocoders. The word describes a role — a server that fans one transmission out to many listeners — not a standard.

Not every “ID” is a registration

C4FM asks for no registration. M17 asks for none. P25 asks for one but it is DMR’s. D-STAR asks for a registration but issues no number. Only DMR and NXDN follow the pattern a newcomer expects — go to a website, get a number — and it is a mistake to assume the others work the same way.

The Bottom Line

Six modes. Six vocabularies. Roughly six ideas underneath.

Learn the ideas and the vocabularies stop mattering. When someone says NAC, you hear access code. When someone says Unit ID, you hear identity. When someone says reflector module, you hear the room. The mode stops being a wall and becomes a dialect — and dialects are easy, once you know they are dialects.