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

What IMS is, and where it came from · chapter 2 of 4 · 4 minutes

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.

2.1 The first row of the work plan

The work plan is 3GPP's list of everything it has agreed to write, one row per group's share of a piece of work. Its first IMS row is a Release 5 item whose short name is plain IMS and whose title is "Provisioning of IP-based multimedia services". IMS

The plan points at one paper, SP-000216, recorded against meeting SP-8. SP-000216 The store holds no title for that paper and no days and no place for that meeting, so both can be cited and neither can be described.

The work item description behind it survives, and its reason is one sentence.

Its objective names what those requirements were for: concepts regarding general service requirements and service features for Release 2000, an evolved Release 99 plus IM services. [6]

Those services were to support multiple media components per call, on the multimedia call control standards that already existed.

2.2 Making it reach the network that was already there

Release 6 carries IMS-CCR-IWCS, "Interworking between IMS and CS networks". IMS-CCR-IWCS

Its objective is the same thing said flatly: to address the issue of interworking between the IM CN subsystem and CS networks, in order to support basic voice calls. [7]

2.3 The two releases that carry the most of it

Release 8 and Release 9 are the two biggest IMS releases in the work plan, at 64 rows and 45 rows. [8] [9] One of the things settled over that stretch was the emergency call.

IMS_EMER_GPRS_EPS, "Support for IMS Emergency Calls over GPRS and EPS", is a Release 9 item whose first objective is an update of requirements on the support of IMS emergency calls over GERAN, UTRAN and E-UTRAN access. IMS_EMER_GPRS_EPS [10]

2.4 Letting a browser in

IMS_WebRTC, "Web Real Time Communication access to IMS", is a Release 12 item, and its reason begins outside 3GPP altogether. IMS_WebRTC

What it set out to do was to specify service requirements for WebRTC clients to reach IMS, reusing IMS client security credentials and public identities where that made sense. [11]

2.5 Onto the 5G core

5GS_Ph1-IMSo5G, "IMS impact due to 5GS IP-CAN", is Release 15. 5GS_Ph1-IMSo5G

Read the second sentence twice. 5G did not take voice away from IMS: it became a new kind of IP connectivity underneath it.

Release 16 then rebuilt the joins between the two. eIMS5G_SBA was opened because a study had already reached conclusions on the service-based interactions between IMS and the 5G core, and those parts could be written without waiting for the parts still unfinished. [12]

543 documents carry that short name, more than any other IMS work item in this register. eIMS5G_SBA [13]

2.6 What Release 20 is asking

FS_enIMS_ARC, "Study on IMS Architecture Enhancement", is a Release 20 study owned by SA2. FS_enIMS_ARC

Its justification names generative artificial intelligence, large language models, AI agents, AI glasses and embodied robots, and points at a 6G requirements study running in SA1. [14]

2.7 Sixteen releases, and not one date

IMS work spreads over 16 releases, Rel-5 to Rel-20. [15]

Where the numbers in this chapter come from

  1. why IMS was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/1273/S1-000299/S1-000299.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its own title, 'Support of IP multimedia services', shares 3 words with the work plan name; the document store has no row for S1-000299, so the address here is the plenary paper SP-000216 that carried it
  2. why IMS-CCR-IWCS was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/2047/NP-030292/NP-030292.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with NP-030292, the document the work plan points at
  3. why IMS_WebRTC was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/580062/SP-130707_clean/SP-130707_clean.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with SP-130707, the document the work plan points at
  4. why 5GS_Ph1-IMSo5G was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/760029/CP-180094/CP-180094.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because it states the unique identifier of this work plan row
  5. what FS_enIMS_ARC set out to do the opening sentences of the objective of the work item description /var/www/whatthespec.net/data/data/wis/1100026/SP-251692 was SP-251656 was of SP-251638 was SP-251411_S2-2511300_was_S2-2511257_New SID on IMS architecture enhancement r02/SP-251692 was SP-251656 was of SP-251638 was SP-251411_S2-2511300_was_S2-2511257_New SID on IMS architecture enhancement r02.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because it states the unique identifier of this work plan row
  6. what IMS set out to do the opening sentences of the objective of the work item description /var/www/whatthespec.net/data/data/wis/1273/S1-000299/S1-000299.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its own title, 'Support of IP multimedia services', shares 3 words with the work plan name; the document store has no row for S1-000299, so the address here is the plenary paper SP-000216 that carried it
  7. what IMS-CCR-IWCS set out to do the opening sentences of the objective of the work item description /var/www/whatthespec.net/data/data/wis/2047/NP-030292/NP-030292.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with NP-030292, the document the work plan points at
  8. 64 IMS work plan rows are marked Rel-8 rows of table `item` in /var/www/whatthespec.net/data/database/api/wp.sqlite taken in by the acronym rule whose release field is exactly 'Rel-8', read 2026-08-05
  9. 45 IMS work plan rows are marked Rel-9 rows of table `item` in /var/www/whatthespec.net/data/database/api/wp.sqlite taken in by the acronym rule whose release field is exactly 'Rel-9', read 2026-08-05
  10. what IMS_EMER_GPRS_EPS set out to do the opening sentences of the objective of the work item description /var/www/whatthespec.net/data/data/wis/380064/SP-080844/SP-080844.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with SP-080844, the document the work plan points at
  11. what IMS_WebRTC set out to do the opening sentences of the objective of the work item description /var/www/whatthespec.net/data/data/wis/580062/SP-130707_clean/SP-130707_clean.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with SP-130707, the document the work plan points at
  12. why eIMS5G_SBA was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/840062/SP-190181_S2-1902837_eIMS5G_SBA WID/SP-190181_S2-1902837_eIMS5G_SBA WID.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because its name begins with SP-190181, the document the work plan points at
  13. 543 documents carry the work item eIMS5G_SBA rows of `tdoc` whose work item column names eIMS5G_SBA as a whole word, asked of /var/www/whatthespec.net/data/database/api/api.sqlite on 2026-08-05; the first and last meeting are those of its earliest and latest upload stamp
  14. why FS_enIMS_ARC was proposed the opening sentences of the justification of the work item description /var/www/whatthespec.net/data/data/wis/1100026/SP-251692 was SP-251656 was of SP-251638 was SP-251411_S2-2511300_was_S2-2511257_New SID on IMS architecture enhancement r02/SP-251692 was SP-251656 was of SP-251638 was SP-251411_S2-2511300_was_S2-2511257_New SID on IMS architecture enhancement r02.md, copied word for word, read 2026-08-05. That file was taken as this work item's own because it states the unique identifier of this work plan row
  15. IMS work items are spread over 16 releases, Rel-5 to Rel-20 distinct values of the release field over the 345 IMS work plan rows, read 2026-08-05. They are named in the order the field spells them and no date of any release is stored

Every source this course is built on

Check yourself

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

Q2.1 What did the first IMS work item set out to define?

Q2.2 Why was interworking with circuit switched networks opened in Release 6?

Q2.3 What made 3GPP open WebRTC access to IMS in Release 12?

Q2.4 How many 3GPP releases does IMS work spread over?

This chapter was built from a source register generated 2026-08-05. A fresher build of the register may hold different numbers.