School of Specs IMS — the call as an internet sessionOverview

858 checked sources · Overview · 45 minutes

IMS — the call as an internet session

IMS — the IP Multimedia Subsystem — is how a mobile network sets a call up and carries it as an internet session. It is not a young subject: its work plan rows spread over 16 releases, Rel-5 to Rel-20, 345 rows under 177 acronyms, and fourteen groups have IMS documents on the record. Most of the paperwork is upkeep rather than invention: of the 4939 IMS meeting documents in the local record, 3509 are change requests, and 1680 of them change one single document, TS 24.229. This course is for somebody who has to follow a conversation about that work — what IMS is in its own documents' words, how it was rebuilt for each new kind of network, which group does which part, what is written down, and what is running now. Every number points at the register entry it was read from, and the last chapter is about what the record cannot say: it carries no IMS document earlier than 2015, and the work started in Release 5.

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: quick start · in depth

The chapters

Part 1 What IMS is, and where it came from

  1. 1 What IMS is, in the words of its own documents Four documents define the subject between them — the requirements, the architecture, the call model and the protocol — and this chapter reads their opening clauses side by side. 6 min
  2. 2 The founding: Release 5 and the ring of work around it One work plan row called IMS, the paper that opened it, the thirteen rows that surround it in Release 5, and why the document record cannot see any of it. 7 min
  3. 3 Rebuilt for every new network: circuits, LTE, the browser, 5G The pattern that makes this subject unlike a young one — every new way of carrying IP sends the same system back to the drawing board, from circuit networks in Release 6 to the 5G core in Releases 15 to 17. 7 min

Part 2 Who does the work, and what they write

  1. 4 Who does the work: fourteen groups, and a core-network shape The fourteen groups with IMS documents on record, how much each one has filed, what that shape says about the subject, and the two counting traps in the numbers. 7 min
  2. 5 What they write: the IMS family of specifications The 241 documents this work touches, sorted into the two that are IMS, the family around them, the studies, and the 5G core documents that had to be edited. 7 min

Part 3 Where it stands, and how to follow it

  1. 6 Maintenance, and what is running now Why 3509 of the 4939 documents are change requests, why one work item has been reopened in every release since Rel-7, and what sits on the table for Rel-19 and Rel-20. 7 min
  2. 7 Following it yourself, and what the record cannot tell you Search by the work item acronym and never by the title, and know the eleven things this record is silent about before you lean on it. 7 min

Testing yourself

Every question at once

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

Open all the questions

The final test

12 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
8,834
Checked sources
858
Sources this course cites
193

Every source