Figure AC.7.2.1-1 depicts a signalling flow diagram for establishing an application data channel in a person-to-person use case. In this scenario, the MF is not used to anchor the Application data channel.
In the call flow the UEs have already established an IMS audio session and the originating UE is updating the IMS audio/video session to an IMS data channel session.
IMS session and bootstrap data channel have been established as described in Figure AC.7.1-1. Each UE (UE#1 and UE#2) may have bootstrap data channels established with both originating MF and terminating MF. Selected data channel application has been downloaded to UE#1 and possibly UE#2.
UE#1 initiates a Person-to-Person Application Data Channel for the selected application. The UE#1 sends the SIP reINVITE request with an updated SDP to IMS AS, through originating network P-CSCF and S-CSCF. The updated SDP contains the bootstrap data channel information, as well as the requested application data channel and the associated DC application binding information, according to clause AC.5 and TS 26.114.
The IMS AS notifies the DCSF, via Nimsas_SessionEventControl_Notify (MediaChangeRequest Event, Calling ID, Called ID, Session ID, Event Direction, Media Info List) of the media change request event.
After receiving the session event notification, the DCSF determines the policy about how to process the application data channel establishment request based on the related parameters (i.e. associated DC application binding information) in the notification and/or DCSF service specific policy.
The DCSF determines that the added application data channel media descriptor of the SDP offer takes UE#2 as target endpoint and does not require anchoring on the local MF.
UE#2 and terminating network returns a 200 OK response with SDP answer for application data channel to originating network. UE#2 may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC.
The application data channel between UE#1 and UE#2 is established. In this example, it is not anchored in MF.
If the DCSF receives a notification for a media change request event for an application request that is initiated from the remote UE, if the local policy does not allow the remote UE to use an application, the DCSF may use the Nimsas_MediaControl_MediaInstruction service operation to instruct IMS AS to reject the offered media.