16 Roles for collaborative sessions involving participants with different subscriptions

24.3373GPPIP Multimedia (IM) Core Network (CN) subsystem IP Multimedia Subsystem (IMS) inter-UE transferRelease 17Stage 3TS

16.1 Introduction

This clause specifies the collaborative session procedures in the case when users of different subscriptons participate in the collaborative session as controller or controllee.

16.2 SC UE

The procedures in subclause 11.2.1.1 apply.

16.3 SCC AS serving the collaborative session

Before sending the inter-UE transfer request towards the controllee UE, the SCC AS serving the collaborative session, shall act as follows:

1) if the Contact header field contains the address of the SCC AS, insert the media feature tag g.3gpp.iut-focus as described in annex B.3 into the Contact header field; or

2) if the Contact header field does not contain the address of the SCC AS, insert the feature-capability indicator g.3gpp.iut-focus into the Feature-Caps header field as described in IETF RFC 6809 [44].

If the SCC AS serving the collaborative session inserted the feature-capability indicator g.3gpp.iut-focus into the Feature-Caps header field in the inter-UE transfer request towards the controllee UE then the SCC AS serving the collaborative session shall include the feature-capability indicator g.3gpp.iut-focus into the Feature-Caps header field in any target refresh request and, in each 1xx or 2xx response to target refresh request sent to the controllee UE.

When the SCC AS in the home network of the controllee UE receives the inter-UE transfer request containing the media feature tag g.3gpp.iut-focus in the Contact header field or containing the feature-capability indicator g.3gpp.iut-focus in the Feature-Cap header field, it will forward the inter-UE transfer request to the controllee UE without applying inter-UE transfer functionality.

NOTE: The SCC AS in the home network of the controller UE takes full control of the collaborative session. Further SCC AS added in the home networks of controllee UEs do not influence the collaborative session call flows in a way which would cause additional signalling from/to the SCC AS in the home network of the controller UE. The SCC AS in the home network of the controller UE therefore does not need to distinguish whether a request is sent to / received from a controllee UE directly or via an SCC AS in the controllee UEs home network.