School of Specs IMS — the call as an internet sessionQuick start

858 checked sources · Quick start · 15 minutes

IMS — the call as an internet session

IMS is the part of a mobile network that sets a call up and carries it as an internet session instead of as a circuit. 3GPP opened the work in Release 5 and is still writing it for Release 20: 345 rows of the work plan under 177 named pieces of work, touching 241 specifications, with 4939 meeting documents in the local record. Four short chapters — what IMS is in the words of its own documents, where it came from and why it keeps being rebuilt, who writes it, and where to go and read it. Every number here was read out of a file or a database on this machine, and the last chapter says plainly what that record cannot tell anybody, starting with the first ten years of the work, which it does not hold at all.

Start at chapter 1 The whole thing on one page Sit the final test

This course was built from a source register generated 2026-08-05.

Same subject, different depth: overview · in depth

The chapters

Part 1 What IMS is, and where it came from

  1. 1 What IMS is: a call carried as an internet session What IMS is in the words of its own documents — the name their definitions clause uses, what each of the three rungs says it is for, and the four terms everything else is built on. 4 min
  2. 2 Where it came from, and why it keeps being rebuilt Release 5 opened it, Release 6 made it reach the old telephone network, Release 12 let a browser in, Release 15 and 16 put it on the 5G core, and Release 20 is asking what it needs for AI and 6G. 4 min

Part 2 Who builds it, and where to read it

  1. 3 Who writes it, and what the paperwork looks like The groups that share IMS between them, how much each has filed, and why most of the pile is change requests to documents that already exist. 4 min
  2. 4 Where to read it yourself, and what the record cannot say The four documents to open first, the four Release 20 papers a reader can follow today, and the questions this record is honestly unable to answer. 4 min

Testing yourself

Every question at once

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

Open all the questions

The final test

10 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
4
Words written for you
2,865
Checked sources
858
Sources this course cites
67

Every source