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

What CT1 is and what it makes · chapter 1 of 4 · 3 minutes

1 Who writes the words your phone actually sends

What CT1 is, who sits in the room, and why an agreement like this one has to be written by a committee rather than by a company.

Built from §1

1.1 Why any of this has to be written down

Before your phone carries a byte of anybody's data, it has a conversation. It tells the network who it is, the network asks it to prove that, the two settle on the keys they will use, and only then is a data connection built.

That conversation is made of named messages with fixed contents. A phone built by one company and a network built by another have to agree in advance on every name, on what goes in each message, and on what to do when one arrives damaged.

No single company can settle that. The agreement has to exist in writing before any of the products do, and it has to be written by all of them at once.

1.2 The group that settles it for the core network

CT1 is a working group of 3GPP, and the name the record gives it says what it is about: CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1). Three jobs — keeping track of a phone as it moves, setting up calls TS 24.229, and building and tearing down the data connections it uses §1.

It sits under a parent group called CT. The record lists four other CT working groups by name — CT3, CT4, CT5 and CT6 — without saying which of them still meet, so that is a list of names, not proof that all four are running. CT1 itself grew out of an older group called CN1, which closed and became CT1.

Three different stores spell the group three different ways, which matters the moment you go looking for it: C1 in the specification catalogue, C1- in front of every document number, and "3GPP CT 1" in the meeting calendar.

1.3 Who is in the room

415 different organisations put at least one document to CT1 in the twelve months to 2026-08-04 [1]. The three busiest were Huawei, HiSilicon with 447 documents [2], Ericsson with 338 [3] and Nokia with 317 [4].

The name in each of those is the name printed on the document, not a company in a company register: "Huawei, HiSilicon" is one string, and nobody has tidied it.

Four people hold office, and the record gives none of them an end date [5]:

Post Who For Since
Chair Lena Chaponnière Qualcomm Incorporated 2025-04-12 [6]
Vice Chair Behrouz Aghili Apple Inc 2025-05-24 [7]
Vice Chair Sung Hwan Won Nokia Corporation 2025-05-24 [8]
Secretary Nevenka Biondic 3GPP Support 2025-10-07 [9]

Forty-four terms of office are on record in the same file [10], so the leadership can be followed back — but the register this course reads carries only the four above by name.

1.4 It does not work alone either

A liaison statement is a letter from one working group to another: a question, an answer, or a warning that something has changed. In the twelve months to 2026-08-04, CT1 sent 108 of them [12] and received 135 [13].

Counting only the letters that went to or came from a single group, RAN2 got 44 of the outgoing ones, more than anybody else [14], and SA2 sent 39 of the incoming ones, again more than anybody else [15].

Those two are the groups CT1 deals with most. Its subject touches theirs constantly, so a decision here turns into a letter there.

Where the numbers in this chapter come from

  1. 415 different organisations put a document to CT1 in the twelve months to 2026-08-04 distinct source in the pygppe document database, table tdoc where meeting starts with 'C1-' and uploaded >= '2025-08-04', read 2026-08-04
  2. 447 CT1 documents from Huawei, HiSilicon in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-', uploaded >= '2025-08-04' and source='Huawei, HiSilicon'; rank 1 of 6, read 2026-08-04
  3. 338 CT1 documents from Ericsson in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-', uploaded >= '2025-08-04' and source='Ericsson'; rank 2 of 6, read 2026-08-04
  4. 317 CT1 documents from Nokia in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-', uploaded >= '2025-08-04' and source='Nokia'; rank 3 of 6, read 2026-08-04
  5. 4 CT1 office holders have no end date on record rows with Group='C1' and an empty End field in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  6. CT1 Chair: CHAPONNIERE, Lena the row with Group='C1', Position='Chair' and no End date in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  7. CT1 Vice Chair: AGHILI, Behrouz the row with Group='C1', Position='Vice Chair' and no End date in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  8. CT1 Vice Chair: WON, Sung Hwan the row with Group='C1', Position='Vice Chair' and no End date in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  9. CT1 Secretary: BIONDIC, Nevenka the row with Group='C1', Position='Secretary' and no End date in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  10. 44 CT1 terms of office are on record rows with Group='C1' in /var/www/whatthespec.net/data/database/api/officials.jsn, read 2026-08-04
  11. 105699 CT1 documents on record rows in the pygppe document database, table tdoc where meeting starts with 'C1-', read 2026-08-04
  12. 108 CT1 documents of kind 'LS out' uploaded on or after 2025-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and tdoctype='LS out' and uploaded >= '2025-08-04', read 2026-08-04
  13. 135 CT1 documents of kind 'LS in' uploaded on or after 2025-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-' and tdoctype='LS in' and uploaded >= '2025-08-04', read 2026-08-04
  14. 44 outgoing liaison statements to RAN2 in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-', uploaded >= '2025-08-04', tdoctype='LS out' and the other group is 'RAN2', read 2026-08-04
  15. 39 incoming liaison statements from SA2 in the twelve months to 2026-08-04 rows in the pygppe document database, table tdoc where meeting starts with 'C1-', uploaded >= '2025-08-04', tdoctype='LS in' and the other group is 'SA2', read 2026-08-04

Every source this course is built on

Check yourself

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

Q1.1 What kind of body is CT1?

Q1.2 How many different organisations put at least one document to CT1 in the twelve months to 2026-08-04?

Q1.3 Which group did CT1 send the most letters to in that year?

Q1.4 Whom does TS 24.501 say it applies to?

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.