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

The group and what stage 3 means · chapter 3 of 14 · 7 minutes

3 What CT1 owns — 229 documents and the six that matter

The shape of CT1's specification list, the families inside it, and why six documents out of 229 take the most change documents.

3.1 What "owning a specification" means here

A specification, in this world, is one numbered document that 3GPP publishes: TS 24.501, TR 24.860. Every one of them is assigned to exactly one working group, and that group is the only one that may change its text.

Two kinds exist. A TS — technical specification — is the buildable kind: it tells you what to make. A TR — technical report — studies a question and does not oblige anybody to build anything.

CT1 has 237 documents listed against it [1]. 229 of those are active [2] and 8 are not [3].

Of the active ones, 199 are technical specifications [4] and 30 are technical reports [5].

3.2 Where the numbers fall

3GPP numbers documents by series, and the series says roughly what kind of thing it is. CT1's list is concentrated: 175 of the 229 sit in the 24 series [6] and 16 in the 23 series [7].

The rest are scattered across other series, and the register does not count those, so no number for them appears here.

It does hold each one as its own entry, and reading a few tells you something the counts do not: TR 21.904 on device capability requirements TR 21.904, TR 27.903 on synchronization standards TR 27.903, TR 29.846 on multicast procedures TR 29.846.

Older numbering survives on the same shelf. TS 04.08, "Mobile radio interface layer 3 specification" TS 04.08, TS 03.68 for voice group calls TS 03.68 and TS 09.08 TS 09.08 are still on CT1's list, next to documents numbered in the modern style.

3.3 Which Release a document has reached

A Release is a numbered edition of the whole 3GPP system. A specification gets a fresh version for each Release it is carried into, so the Release columns tell you how much of the shelf is still moving forward.

Release Active CT1 specifications with a version in it
Rel-18 149 [8]
Rel-19 154 [9]
Rel-20 31 [10]

The three columns cannot be added together: 149 plus 154 plus 31 is far more than 229, so the same document is being counted in more than one row. Read them as three snapshots of one shelf at three moments, not as three groups of documents.

The small Rel-20 number is what a Release looks like early in its life: 31 of the 229 already carry a Rel-20 version, and the catalogue says nothing about whether work has begun on the rest.

3.4 The six that absorb the work

A change request, always written CR, is one proposed edit to a published specification: one document, one problem, one set of replacement paragraphs. It is the unit of work in CT1, and counting CRs per specification shows where the effort actually goes.

Over the whole record:

Specification Change documents
TS 24.501 15623 [11]
TS 24.301 5422 [12]
TS 24.229 3413 [13]
TS 23.122 2447 [14]
TS 24.379 2364 [15]
TS 24.554 2064 [16]

TS 24.501 stands far ahead of the next document. It is the 5G NAS protocol TS 24.501, and it is why the middle of this course is about that document alone.

Behind it come five more:

3.5 The last twelve months look different

Take the same count over the twelve months to 2026-08-04 and the order changes, which is the most useful single comparison in this chapter:

Specification Change documents in the year
TS 24.301 499 [17]
TS 24.501 498 [18]
TS 24.369 430 [19]
TR 24.860 165 [20]
TS 24.554 162 [21]
TS 23.122 144 [22]
TS 24.543 143 [23]
TS 24.548 125 [24]

Two documents in that list are not in the all-time one at all.

TS 24.369 is "Ambient IoT Non-Access-Stratum (AIoT NAS) protocol for 5G System (5GS); Stage 3" TS 24.369 — third busiest in the year, absent from the all-time top six because it is young.

TR 24.860 is "Study on NAS protocol for 6G System" TR 24.860, and it is a report rather than a specification, which is what the beginning of a generation looks like on a document shelf.

3.6 The families on the shelf

The counts do not say what the documents are about; the titles in the register do. Reading along them, recurring families appear.

That spread is why the group's name has three parts. Mobility, call control and session management are not one subject; they are three, and CT1 carries all three.

3.7 What can be read here, and what cannot

157 of the 229 active CT1 specifications have parsed text on this machine [25]. For those, a clause can be quoted and opened. For the rest, the register holds the number, the type, the title and which Releases have a version — and nothing else.

That is also true of every specification here in one further respect: the register carries no publication date, no version date and no version number for any of them. Where those limits matter is What this record cannot tell you.

The next four chapters open the one document at the top of both tables: TS 24.501 — two protocols living in one document.

Where the numbers in this chapter come from

  1. 237 specifications listed against CT1 rows in the pygppe specification catalogue, table spec where wg='C1', read 2026-08-04
  2. 229 active CT1 specifications rows in the pygppe specification catalogue, table spec where wg='C1' and active='yes', read 2026-08-04
  3. 8 CT1 specifications no longer active rows in the pygppe specification catalogue, table spec where wg='C1' and active<>'yes', read 2026-08-04
  4. 199 active CT1 technical specifications (TS) rows in the pygppe specification catalogue, table spec where wg='C1' and active='yes' and type='TS', read 2026-08-04
  5. 30 active CT1 technical reports (TR) rows in the pygppe specification catalogue, table spec where wg='C1' and active='yes' and type='TR', read 2026-08-04
  6. 175 active CT1 specifications in the 24 series rows in the pygppe specification catalogue, table spec where wg='C1' and active='yes' and specnum starts with '24', read 2026-08-04
  7. 16 active CT1 specifications in the 23 series rows in the pygppe specification catalogue, table spec where wg='C1' and active='yes' and specnum starts with '23', read 2026-08-04
  8. 149 active CT1 specifications have a Rel-18 version distinct specnum in the catalogue table spec_version joined to spec where wg='C1', active='yes' and release='Rel-18', read 2026-08-04
  9. 154 active CT1 specifications have a Rel-19 version distinct specnum in the catalogue table spec_version joined to spec where wg='C1', active='yes' and release='Rel-19', read 2026-08-04
  10. 31 active CT1 specifications have a Rel-20 version distinct specnum in the catalogue table spec_version joined to spec where wg='C1', active='yes' and release='Rel-20', read 2026-08-04
  11. 15623 CT1 documents change 24.501 (Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.501'; rank 1 of the whole group, read 2026-08-04
  12. 5422 CT1 documents change 24.301 (Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.301'; rank 2 of the whole group, read 2026-08-04
  13. 3413 CT1 documents change 24.229 (IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.229'; rank 3 of the whole group, read 2026-08-04
  14. 2447 CT1 documents change 23.122 (Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='23.122'; rank 4 of the whole group, read 2026-08-04
  15. 2364 CT1 documents change 24.379 (Mission Critical Push To Talk (MCPTT) call control; Protocol specification), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.379'; rank 5 of the whole group, read 2026-08-04
  16. 2064 CT1 documents change 24.554 (Proximity-services (ProSe) in 5G System (5GS) protocol aspects; Stage 3), over the whole record rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.554'; rank 6 of the whole group, read 2026-08-04
  17. 499 CT1 documents change 24.301 (Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.301' and uploaded >= '2025-08-04'; rank 1 of the whole group, read 2026-08-04
  18. 498 CT1 documents change 24.501 (Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.501' and uploaded >= '2025-08-04'; rank 2 of the whole group, read 2026-08-04
  19. 430 CT1 documents change 24.369 (Ambient IoT Non-Access-Stratum (AIoT NAS) protocol for 5G System (5GS); Stage 3), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.369' and uploaded >= '2025-08-04'; rank 3 of the whole group, read 2026-08-04
  20. 165 CT1 documents change 24.860 (Study on NAS protocol for 6G System), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.860' and uploaded >= '2025-08-04'; rank 4 of the whole group, read 2026-08-04
  21. 162 CT1 documents change 24.554 (Proximity-services (ProSe) in 5G System (5GS) protocol aspects; Stage 3), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.554' and uploaded >= '2025-08-04'; rank 5 of the whole group, read 2026-08-04
  22. 144 CT1 documents change 23.122 (Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='23.122' and uploaded >= '2025-08-04'; rank 6 of the whole group, read 2026-08-04
  23. 143 CT1 documents change 24.543 (Data delivery management - Service Enabler Architecture Layer for Verticals (SEAL); Protocol Specification;), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.543' and uploaded >= '2025-08-04'; rank 7 of the whole group, read 2026-08-04
  24. 125 CT1 documents change 24.548 (Network Resource Management - Service Enabler Architecture Layer for Verticals (SEAL); Protocol specification), in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and crspec='24.548' and uploaded >= '2025-08-04'; rank 8 of the whole group, read 2026-08-04
  25. 157 of 229 active CT1 specifications have parsed text on this machine folders under /var/www/whatthespec.net/data/friendlyspec/json/<specnum without dots> that match an active CT1 specification, counted 2026-08-04

Every source this course is built on

Check yourself

Answers appear when you pick one, with where they come from.

Q3.1 How many CT1 specifications are active?

Q3.2 Which specification has attracted the most CT1 change documents over the whole record?

Q3.3 How many of the 229 active CT1 specifications sit in the 24 number series?

Q3.4 What is the difference between a TS and a TR?

Q3.5 How many active CT1 specifications have a Rel-20 version?

This chapter was written against TS 24.501 version 20.0.0, and built from a source register generated 2026-08-04. A newer version of the document may say something else.