5 Releases 8 and 9: emergency calls, continuity and the fixed-network merge

5.1 Where the work piled up

Rel-8 carries 64 IMS rows in the work plan ^[8] and Rel-9 carries 45 ^[9]. The register holds a row count for each of the 16 releases IMS work is spread over ^[10].

Across all sixteen, no release carries more than Rel-8's 64. The next largest is Rel-12, at 60 ^[11].

That is a lot of rows for two releases, and the reason is that four different demands landed on IMS at roughly the same point in the plan.

• The mobile network's data side was being rebuilt, and IMS had to sit on it.

• Regulators wanted emergency calls to work over packet access, not only over the circuit side.

• Operators wanted a service to survive when the user moved between networks — and to survive when a piece of the IMS itself stopped answering.

• A body of fixed-network specifications written outside 3GPP was brought in and had to be maintained inside it.

5.2 Emergency calls over the packet network

IMS_EMER_GPRS_EPS is the widest row in these two releases by the number of groups on it: four rows in the plan, and ten groups listed, the IETF among them IMS_EMER_GPRS_EPS. It is marked Rel-9 and was opened by SP-080844 at plenary SP-42 SP-080844.

Its objective is short and names the three radio accesses it had to cover ^[1].

The justification is the more interesting half, because it is one of the few places in this register where a work item says out loud that the reason is the law ^[2].

The row names ten documents it would change, and the shape of that list is the point.

TS 23.167, the IMS emergency sessions specification TS 23.167, sits beside TS 23.401 and TS 23.402, the packet core's own architecture documents TS 23.401 TS 23.402, and beside TS 22.101 TS 22.101.

An emergency call is not a feature you can add inside IMS alone. TS 23.167 says so in its own scope, which covers emergency services in IMS including emergency services for eCall ^[12].

The row also names TR 23.869 — the study of IMS emergency calls over GPRS and EPS — among the documents it touches TR 23.869. Study first, then specification, is the ordinary path and it recurs three times in this chapter alone.

19 documents in the store carry this acronym ^[13]. As everywhere in this course, that is a floor set by when the store began labelling documents, not a measure of the argument.

5.3 One service, wherever you happen to be

IMS_SCC — IMS Services Centralization and Continuity — is a Rel-9 row across CT1, SA1 and SA2, opened by SP-080633 at plenary SP-41 IMS_SCC SP-080633. Its justification explains itself by naming what Rel-8 had already produced ^[3].

Two ideas, and they are worth keeping apart.

Centralization is IMS controlling the delivery of a service even when the call itself is running over the circuit side. Its specification is TS 23.292, whose scope is about delivering consistent services to the user regardless of the access type they are attached to TS 23.292 ^[14].

Continuity is a session carrying on while the ground moves underneath it. Its specification is TS 23.237, and its scope is one sentence: the architectural requirements and procedures for delivery of IMS Service Continuity TS 23.237 ^[15].

The SA1 half of the work item's objective is quoted too, and it is a plain requirements job: identification of additional IMS Centralized Services requirements ^[16].

5.4 What happens when the IMS itself stops answering

The third demand is the one nobody puts in a brochure. A network element fails, and every session it was holding has to be recovered.

Rel-8 wrote the procedures for one such failure. eIMS_RP, "Completion of IMS Restoration Procedures", is the Rel-9 row opened to finish the job — four rows across CT1, CT3 and CT4, opened by CP-091050 at plenary CP-46 eIMS_RP CP-091050.

That quotation is a compact lesson in how 3GPP work actually moves. A study is run — TR 23.820, the study of IMS restoration procedures TR 23.820. Part of it becomes a specification, TS 23.380 TS 23.380. The part that did not fit in the release is picked up by a new work item in the next one.

The objective says the same in one sentence ^[17], and the specification's own scope says what "restoration" means here: procedures to handle an S-CSCF or a P-CSCF service interruption with minimum impact on the service to the end user ^[18].

The register carries no expansion for S-CSCF or P-CSCF, so this course does not give one.

What it can say is that TS 23.380 has been reopened by later work several times: its catalogue row lists IMS_RES-CT, 5GS_Ph1-IMSo5G, eIMS5G_SBA and FS_IMS_RES among the work items whose documents change it TS 23.380. Falling over is a permanent subject.

5.5 The protocol chain gets heavy

IMSProtoc2, the second phase of the IETF protocol alignment work introduced in Releases 6 and 7: interworking, messaging, and a stream that never stopped, is marked Rel-8 and spreads over five rows IMSProtoc2. It was opened by CP-080794 at plenary CP-42 CP-080794.

Its objective names the job in one line ^[5].

Its justification opens by looking back at where the whole subject started ^[6].

248 documents carry this acronym ^[19], and its rows name TS 24.229 as a document it changes TS 24.229 — which is why that one specification has attracted more paper than anything else in this register.

5.6 Security, borders and corporate networks

Three more Rel-8 and Rel-9 rows are worth naming, because each one marks a boundary IMS had to be given.

Security. IMS-Sec, "Security Enhancements for IMS", is a Rel-8 row across CT1, CT4 and SA3, opened by SP-070496 at plenary SP-36 IMS-Sec.

Its objective is to study security requirements for common IMS and find solutions to meet them ^[20] — and note "common IMS" appearing there, the same phrase the TISPAN rows below use.

The border between two networks. IMS_IBCF is a Rel-9 row across CT3 and CT4 covering the Ix interface between the interconnection border control function and the transition gateway IMS_IBCF, opened by CP-090019 at plenary CP-43.

Its objective is to define the necessary detailed stage 2 and stage 3 specification for Ix, and the row names TS 29.238, TS 29.235 and TS 29.162 among its targets ^[21] TS 29.238 TS 29.235 TS 29.162.

Its objective is also a small lesson in how 3GPP splits a job. After naming the job it goes straight into "For CT3:" and the detailed stage 2 procedures that group has to write ^[21].

One interface, two groups on the row, three rows in the plan — the work item description hands each group its own part before a line of text is written.

Businesses. IMS_Corp, "IMS System enhancements for corporate network access", is a Rel-8 row spread over six rows and six groups, opened by SP-080095 at plenary SP-39 IMS_Corp.

That last clause is the interesting one: a corporate network that holds the IMS subscription while owning and managing its own users. The row names TS 23.228 and TS 24.229 among the documents it changes, so the change reached both the architecture and the protocol IMS_Corp.

5.6.1 Four rows, and not one document between them

Something about these three rows is worth stopping on. IMS-Sec, IMS_IBCF and IMS_Corp each have zero documents against them in the store, and eIMS_RP above has zero as well IMS-Sec IMS_IBCF IMS_Corp eIMS_RP.

Nobody wrote a specification with no paper. What the zero records is the floor explained in How this subject is cut out of the work plan: the store's earliest IMS upload stamp is 2015-01-23 ^[22], and these items ran before the store was labelling documents by work item.

So the counts in this chapter split cleanly in two. IMSProtoc2 has 248 and IMS_EMER_GPRS_EPS has 19 because those acronyms went on being used after the floor. The zeros are not silence; they are the edge of the record.

5.7 The fixed networks arrive

The largest structural change in Rel-8 is not a feature at all. A body of fixed-network specifications written under the name TISPAN was brought into 3GPP and had to be looked after there.

Three rows record it, and their titles say it plainly:

• IMS_Comm_Doc, "Documentation of TISPAN NGN R1 and R2 in 3GPP SA2", Rel-8, opened by SP-070823 and aimed at TS 23.228, TS 23.167 and TS 23.204 IMS_Comm_Doc TS 23.204.

• IMS_Comm_Mtce8, "Maintenance of TISPAN release 2 common IMS", Rel-8, opened by SP-070916 and aimed at TS 23.506 and TS 23.521 IMS_Comm_Mtce8 TS 23.506 TS 23.521.

• IMS_Comm_Mtce7, "SA1,SA2 part of Maintenance of TISPAN release 1 common IMS", which the plan marks Rel-7 rather than Rel-8, opened by SP-080501 and aimed at TS 22.173, TS 23.406 and TS 23.417 among others IMS_Comm_Mtce7 TS 23.406 TS 23.417.

The specifications themselves carry the word in their own catalogue titles — TS 23.506 and TS 23.417 both begin "TISPAN" TS 23.506 TS 23.417. The register says nothing about what TISPAN was or why the transfer happened, so neither does this course.

What it does show is the size of the housekeeping. Three rows exist purely to document and maintain text that arrived from outside.

Between them they name TS 22.173, TS 23.228, TS 23.167, TS 23.204, TS 23.406, TS 23.417, TS 23.506 and TS 23.521 as documents they touch IMS_Comm_Mtce7 IMS_Comm_Mtce8 IMS_Comm_Doc.

Two of those are the central IMS documents themselves — the stage 2 description and the emergency sessions specification TS 23.228 TS 23.167. Taking in somebody else's specifications was not a filing exercise on the side; it reached the documents at the middle of the subject.

5.8 One idea, several acronyms

A last habit of these two releases is worth naming, because it makes searching this subject much easier once you have seen it.

Emergency calling is not one acronym. Three more sit beside IMS_EMER_GPRS_EPS, and all three are marked Rel-9:

• IMS_EMER_GPRS_EPSC1, the CT1 stage 3 work IMS_EMER_GPRS_EPSC1

• IMS_EMER_GPRS_EPS-Sec, the security aspects IMS_EMER_GPRS_EPS-Sec

• IMS_EMER_GPRS_EPS-SRVCC, voice call continuity for emergency calls IMS_EMER_GPRS_EPS-SRVCC

Continuity is the same. IMS-Cont, "IMS Service Continuity", is a Rel-8 row of its own, sitting behind the Rel-9 IMS_SCC that quoted it IMS-Cont.

So the acronym is a handle on a piece of work, not a name for a subject. Looking for everything 3GPP did about emergency calls in IMS means following a family of acronyms and not one of them, which is exactly why How this subject is cut out of the work plan counts 177 acronyms and refuses to call that a count of pieces of work.

5.9 Where to read on

For emergency sessions, open TS 23.167 TS 23.167. For continuity and centralization, TS 23.237 and TS 23.292 TS 23.237 TS 23.292. For what happens when something fails, TS 23.380 TS 23.380 and the study behind it, TR 23.820 TR 23.820.

And for the boundary that decides what any of the counts in this chapter mean, How this subject is cut out of the work plan is the chapter to reread — the release field says what a row is for, and never when anybody worked on it.