A.2 Introduction

24.1473GPPConferencing using the IP Multimedia (IM) Core Network (CN) subsystemRelease 16Stage 3TS

A.2.1 General

This annex breaks down the signalling flows for establishing sessions into a number of individual procedures, following the same principles as 3GPP TS 23.228 [3] subclause 5.4.9.

For the purposes of the present document, a further breakdown has been necessary, and therefore a number of signalling flows have been given an (a) or (b) suffix, so that the signalling flows for establishing sessions where configuration independence is applied may be distinguished from those where it is not, e.g.:

– (MO#1a) Mobile origination, roaming, without I-CSCF providing configuration independence.

– (MO#1b) Mobile origination, roaming, with I-CSCF in home network providing configuration independence.

A.2.2 Key required to interpret signalling flows

The key to interpret signalling flows specified in 3GPP TS 24.228 [4] subclause 4.1 applies with the additions specified below:

– #### represents the contents in the headers are not shown and does not impact the implementation of the flows.

As in 3GPP TS 24.228 [4], in order to differentiate between SIP methods and other protocol messages, the message name is preceded with the associated protocol for all non-SIP messages.

Each flow table contains descriptions for headers where the content of the header is new to that flow, as is already performed in 3GPP TS 24.228 [4].

However, 3GPP TS 24.228 [4] includes extensive descriptions for the contents of various headers following each of the tables representing the contents of the flows. Where the operation of the header is identical to that shown in 3GPP TS 24.228 [4], then such text is not reproduced in the present document.

Additional text may also be found on the contents of headers within 3GPP TS 24.228 [4] in addition to the material shown in the present document.

A.2.3 Overview of signalling flows related to PSI routeing

The flows in this annex reflect examples for some of the PSI specific routing scenarios. This subclause gives a list of the PSI scenarios and indicates which flows specifically cover them:

1) User originating a dialog towards a PSI.

a) PSI is hosted by the originating users home network.

i) S-CSCF of originating user can directly route towards the AS hosting the PSI.

This case is shown in subclauses A.3.2.1 and A.4.4.1.

ii) PSI is statically pre-configured, i.e. S-CSCF of the originating user routes towards the S-CSCF assigned to the PSI, which afterwards routes towards the AS hosting the PSI.

This case is not covered by the present document.

b) PSI is hosted by a network different from the originating users home network.

i) PSI can be resolved directly by the S-CSCF located in the originating users home network.

This case is shown in subclauses A.4.2.1.2 and A.5.2.1.

ii) S-CSCF in originating users home network can only resolve an I-CSCF of the network that is hosting the PSI.

– I-CSCF can directly route towards the AS hosting the PSI.

This case is shown in subclauses A.3.2.2 and A.4.2.1.1.

– PSI is statically pre-configured, i.e. I-CSCF routes first to S-CSCF in the network that hosts the PSI, the S-CSCF afterwards routes towards the AS hosting the PSI.

This case is not covered by the present document.

2) Dialog originates from a PSI.

a) AS routes directly to the I-CSCF of the terminating users home network.

This case is shown in subclause A.4.3.1.3.

b) AS routes first to a S-CSCF in the network hosting the PSI, which then routes to the I-CSCF of the terminating users home network.

This case is shown in subclause A.4.3.1.4.

3) Dialog originating from a PSI and terminating at a different PSI.

This case is not covered by the present document.