School of Specs CT1 — the group that writes what your…Overview

TS 24.501 · version 20.0.0 · 1340 clauses · Overview · 40 minutes

CT1 — the group that writes what your phone says

CT1 is the 3GPP working group that writes the exact conversation between a phone and the core network: which message is sent, what is in it, how long the phone waits for an answer. Its biggest document is TS 24.501, and it has been changed more than any other document the group owns. This course is for somebody who has to follow a conversation about CT1 and know what to look up afterwards — not for somebody who works in it. Every number here was read out of a file or a database, and every claim points at either a clause of TS 24.501 or an entry in the group's source register. The last chapter is about what that record cannot tell you, which matters as much as the rest.

Start at chapter 1 Sit the final test Look at the document first

This course was written against TS 24.501 version 20.0.0, and built from a source register generated 2026-08-04.

Same subject, different depth: quick start · in depth

The document, all of it

One block per clause of TS 24.501, in the order they appear, sized by how much text the clause holds. Lit blocks are taught in this course.

Open the whole of TS 24.501 as a page

The chapters

Part 1 Where the group sits

  1. 1 The group that writes what your phone says What 3GPP CT WG1 is, who runs it today, and why the conversation between a phone and the core network has a working group of its own. 6 min
  2. 2 Architecture and protocol — what stage 2 and stage 3 mean Why the same piece of 5G is described twice, what the second description adds, and how to tell which of the two documents you are holding. 6 min

Part 2 What it produces

  1. 3 What the group owns, and what it actually works on The shape of CT1's 229 active documents, and the handful of them that soak up most of the group's work. 6 min
  2. 4 Inside TS 24.501, the document at the centre How the group's largest specification is laid out, from scope to change history, and which clause answers which kind of question. 6 min

Part 3 How the work gets done

  1. 5 How a change request becomes published text The path from one company's proposed edit to a new version number, read off the change history of TS 24.501 itself. 5 min
  2. 6 How a CT1 meeting runs, in real numbers Five days, six hundred documents and six outcome words — what the record of a CT1 meeting actually contains. 5 min
  3. 7 Following the group yourself, and what the record cannot tell you Where to look, in what order, and the twelve things this record does not contain — which matters as much as what it does. 5 min

Testing yourself

Every question at once

35 questions, chapter by chapter, on one page — for revision after you have read the course.

Open all the questions

The final test

15 questions drawn across the whole course, marked at the end. 70 per cent to pass, and every miss says which chapter to go back to.

Sit the final test

What this course is built on

Chapters
7
Words written for you
7,455
Clauses covered
1203 of 1340
Figures from the document
45
Abbreviations
201
Published versions
69
Checked sources
354
Sources this course cites
115

The document · Words · History · Documents around it · Every source