2 The six working groups and the line between them

2.1 One radio, six kinds of question

Ask six honest engineers what has to be agreed before a phone works on a strange network, and you get six different lists.

What exactly is transmitted, and when? What do the two ends say to each other once they can hear? What do two base stations say to each other about a phone moving between them? How strong may the transmitter be? How do we prove a particular phone actually does all this?

RAN is split along exactly those lines, and the split is visible in the documents each group holds.

2.2 RAN1 — the signal itself

RAN1 is the layer 1 group: what is sent over the air, in what shape, at what moment. It holds 66 active documents RAN1 ^[1].

Four of them describe the 5G air interface between them: 38.211 for channels and modulation, 38.212 for channel coding, 38.213 for control procedures and 38.214 for data procedures TS 38.211 TS 38.212 TS 38.213 TS 38.214.

In TS 38.300 this is the material of clause 5, the physical layer — waveform, numerology, transport channels and the procedures that live below everything else §5.

2.3 RAN2 — what the two ends say

RAN2 is layer 2 and layer 3: the radio protocols, meaning what the phone and the base station say to each other once the radio works. 62 active documents RAN2 ^[2].

Its central document is 38.331, which defines every message of the radio connection. Under it sit the three layer-2 protocols: 38.321, 38.322 and 38.323 TS 38.331 TS 38.321 TS 38.322 TS 38.323.

RAN2 also owns 38.300 itself, the overall description this course reads, and 36.331, the same connection protocol for 4G TS 38.300 TS 36.331.

In the document, that is clauses 6 and 7 — layer 2 and the radio connection protocol §6 §7.

2.4 RAN3 — the wires between the boxes

RAN3 owns the interfaces: how one base station talks to another and to the core network. 168 active documents, the second largest working group RAN3 ^[3].

It holds 38.401, the architecture description, and three interface protocols — 38.413 towards the core, 38.423 between base stations, and 38.473 inside a base station that has been split into parts TS 38.401 TS 38.413 TS 38.423 TS 38.473.

TS 38.300 sketches those interfaces in clause 4.3 and then hands each one to a document of its own §4.3.

2.5 RAN4 — what can be measured

RAN4 is the measurable side: transmit power, receiver sensitivity, how fast a phone has to find a neighbouring cell. 427 active documents, more than any other group in RAN RAN4 ^[4].

Three documents carry most of that weight: 38.101-1 says what a phone's radio must do, 38.104 what a base station's radio must do, and 38.133 sets the radio resource management requirements TS 38.101-1 TS 38.104 TS 38.133.

2.6 RAN5 — the exam board

RAN5 does mobile terminal conformance testing: the test cases a phone has to pass. 84 active documents RAN5 ^[6].

Four of them mark out the exam. 38.508-1 holds the common test settings, 38.521-1 the radio transmission tests, 38.523-1 the protocol tests and 38.533 the radio management tests TS 38.508-1 TS 38.521-1 TS 38.523-1 TS 38.533.

RAN5 is the opposite shape to RAN4: 72 of its 84 documents are specifications, not study reports ^[7]. An exam board writes rules, not essays.

2.7 RAN6 — the closed room

RAN6 held the GSM radio work. It has 54 active documents and no meetings since 2020 RAN6 ^[8].

Its last meeting was a single day, held by telephone, on 2020-10-26 3GPPRAN6#18-Decision Teleconference.

The old work did not vanish with it. The renumbered GSM documents are held by the plenary, not by RAN6 — 179 active documents from the 3G and GSM series ^[9].

2.8 The line, in one table

Group	The question it answers	A document that marks it
RAN1	What is sent over the air?	38.211
RAN2	What do the two ends say?	38.331
RAN3	What do the boxes say to each other?	38.423
RAN4	How well must the radio perform?	38.133
RAN5	How is a phone proved to comply?	38.523-1
RAN6	The old GSM radio (closed)	—

2.9 Where the line is not obvious

Two things about the split catch people out.

The overall description is written by one group about everybody's work. TS 38.300 belongs to RAN2, yet its clause 5 is the physical layer, which is RAN1's, and its clause 4.3 is the interfaces, which are RAN3's TS 38.300 §5 §4.3. Owning the map is not owning the ground.

The closed group kept its own documents. RAN6 still holds 54 active ones ^[8], and the plenary holds 179 from the 3G and GSM series together — the register does not say how many of those 179 are GSM ^[9]. So a GSM number does not mean "no working group behind it".

That is why the groups meet in the same week and write letters to each other, which is the subject of How a radio feature travels from a question to a rule. First, though, What the numbers say about size and output puts sizes on all six.