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.
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 TS 26.114.
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 or MRF. If MF or MRF needs to anchor application data channel, DCSF would have used the Nimsas_MediaControl service operation to instruct IMS AS to allocate data channel media resources of the MF or MRF.
UE#2 and terminating network returns a 200 OK response with SDP answer for application data channel to originating network. Based on the received DC application binding information in the SDP offer of the re-INVITE, 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.