1 What CT1 is, and the three names it answers to

1.1 The problem a group like this exists to solve

A phone made in one country has to be switched on in another, on a network it has never seen, built by a different vendor, and be let in within a second or two. Nothing about that works unless both sides already agree, to the bit, on what the first message looks like.

Somebody has to write that agreement down, keep it correct as the system grows, and settle the arguments about what a sentence in it means. In 3GPP that job belongs to CT1.

Its own long name in the tooling that mirrors it is "CT1 — Mobility, call control, session management" CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1). Those three words are the job description: knowing where a device is, setting up a call, setting up a connection to a data network.

1.2 Where it sits

CT1 is a working group, which in 3GPP means a body that owns documents and meets to change them. It sits under a parent group called CT, and the register lists four other CT working groups by name — CT3, CT4, CT5 and CT6 CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1).

That is a list of names and nothing more. The entry does not say which of the four still meet, and some of them may not: this register was built for CT1 alone and holds no meeting, document or specification count for any of them. What it does and does not hold about the neighbours is The neighbours — and how little the record says about them.

The group grew out of an older one called CN1, which closed and became CT1 CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1). That rename is still visible: the long form the tooling uses ends with "ex-CN1", so a search for the old name finds the new group.

Four people hold office with no end date on record ^[1]:

Post	Who	For	Since
Chair	Lena Chaponnière	Qualcomm Incorporated	2025-04-12 [2]
Vice Chair	Behrouz Aghili	Apple Inc	2025-05-24 [3]
Vice Chair	Sung Hwan Won	Nokia Corporation	2025-05-24 [4]
Secretary	Nevenka Biondic	3GPP Support	2025-10-07 [5]

Forty-four terms of office are in the same file altogether ^[6], so the leadership can be followed back through it.

The register itself carries only the four current names, and no chapter of this course can name a past chair — that limit and the rest of them are What this record cannot tell you.

1.3 The three names, and why they bite

The same group is spelled three ways in three different stores, and all three are in the register CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1):

• C1 is what the specification catalogue puts in the "working group" column. Filtering that catalogue for CT1 means filtering for C1.

• C1- is the front of every document number the group produces: C1-262074, C1-261459. A number without that prefix is not a CT1 document.

• "3GPP CT 1", with a space, is the group's name in the meeting calendar.

1.4 How big it is

Four numbers give the shape of the group better than any description.

Documents. 105699 CT1 documents are on record ^[7], and the stored dates on them run from 2005 to 2026 ^[8]. 4235 of them arrived in the twelve months to 2026-08-04 ^[9].

2005 is where this database begins, not where the work began. CT1 grew out of CN1 CT1 — Mobility, call control, session management (WG1_mm-cc-sm_ex-CN1), and nothing CN1 filed is in here. Read every date in this course as the floor of a store, never as the start of the group.

Specifications. 237 documents are listed against the group ^[10], of which 229 are active ^[11] and 8 are not ^[12]. What is inside that pile is What CT1 owns — 229 documents and the six that matter.

Meetings. 184 are listed, held and planned together ^[13]; 172 had started by 2026-08-04 ^[14]; the earliest one the meetings database holds started 2005-04-25 ^[15] — the floor of that store, not CT1's first meeting. 133 of them have documents attached ^[16].

Contributors. 415 different organisations put at least one document to CT1 in the year ^[17]. The biggest single filer was "Huawei, HiSilicon" with 447 ^[18], ahead of Ericsson with 338 ^[19] and Nokia with 317 ^[20].

1.5 The document it is known by

One specification stands out of the 229: TS 24.501, "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3" TS 24.501. Over the whole record, 15623 CT1 documents propose changes to it ^[21] — more than to any other.

Its own scope names two protocols §1. One is mobility management, between the device and the AMF — the access and mobility management function, the core-network end of that conversation.

The other is session management, between the device and the SMF, the session management function that provides the device its connectivity to a data network.

Four boxes, one document. What those four have to do falls into three groups §4.1:

• supporting the mobility of the device, with the common procedures that go with it such as authentication and security;

• supporting session management, so the device gets and keeps a connection to a data network;

• carrying other things — short messages, positioning protocols, policy containers — inside NAS messages, because the path is already there and already protected.

The mobility half sums itself up in one line: its main function is to support the identification, security and mobility of a device, as well as generic message transport §5.1.1.

Everything else in this course either leads to that document — Stage 3 — the difference between a plan and a protocol, What CT1 owns — 229 documents and the six that matter — or comes out of it, in TS 24.501 — two protocols living in one document and the three chapters after it.

1.6 How to read the numbers in this course

Every figure on these pages came out of a file or a database on one machine on 2026-08-04, and every one of them is an entry you can open.

Each counted number carries a method: the exact question that produced it and the day it was asked.

"229 active CT1 specifications" is not an assertion — it is the answer to a stated query against a stated table on a stated date ^[11]. If the query was wrong, the method says so and you can see it.

The same holds for the meetings, the documents, the office holders and the specifications: each is a register entry with an address behind it. Nothing in this course is cited any other way, and there is deliberately no way to write a plain web address into one of these chapters.

The one thing the method cannot fix is a question the data was never asked. That list is long enough to have a chapter of its own, and it is What this record cannot tell you — read it before quoting anything from here in an argument.

1.7 Where this meets the rest of the course

What the group produces and how much of it there is: What CT1 owns — 229 documents and the six that matter. What "Stage 3" in that title actually promises: Stage 3 — the difference between a plan and a protocol.

How a proposal turns into a new version of the document: From a document number to a published version. How to follow any of it yourself, from a document number to the file area: Following CT1 yourself.