If the NRF is used for NF registration and discovery, the DCSF and the MF shall register their services at the NRF before providing services to consumers, and existing NRF based mechanism needs to be extended with DC specific profiles according to clause 4.17.1 of TS 23.502.
The DCSF profile includes NF type=DCSF and may include IMPU ranges for calling identities or called identities of users it serves.
The DCSF can update and deregister in the NRF after registration and the procedures are specified in clauses 4.17.2 and 4.17.3 of TS 23.502.
After registration in the NRF, the DCSF can be discovered by other consumer NFs as specified in clauses 4.17.4 and 4.17.5 of TS 23.502.
The MF profile includes NF type=MF and may include MF location information to select a local MF to minimize transmission delays in the media path.
The MF can update and deregister in the NRF after registration and the procedures are specified in clauses 4.17.2 and 4.17.3 of TS 23.502.
After registration in the NRF, the MF and its services can be discovered by other consumer NFs as specified in clauses 4.17.4 and 4.17.5 of TS 23.502.
According to clause 188.8.131.52 of TS 26.114, the UE can send a HTTP GET Request for the root ("/") URL through the bootstrap data channel which is replied with a data channel application describing the graphical user interface and the logic needed to handle any further data channel usage beyond the bootstrap data channel itself. The graphical user interface can e.g. contain a menu of applications, from which the user can choose one or several. The graphical user interface should be subscriber specific and contain only applications for which the user has subscribed to and is authorized to use. To provide the graphical user interface containing subscriber specific data channel applications via the bootstrap data channel to the UE, the DCSF, when receiving a call event notification including subscriber specific information and optionally stream ID from the IMS AS, creates the URL identifying the graphical user interface corresponding to the stream ID (if available) for this subscriber.
When a bootstrap data channel is established successfully, the bootstrap data channel shall be kept available during the IMS MMTel session, and it shall be terminated along with the release of the call.
The application data channel shall be terminated along with the release of the call or be terminated by closing this application separately. In the latter case, the UE triggers a SDP negotiation to release the application data channel.
The termination of application data channel shall not have any impact on the audio or video within the IMS sessions.
To enable the use of MRF as media resource function for IMS DC, there is a need to map the MF MRM SBI services, operations, and attributes to Mr'/Cr requests and responses. Table AC.7.8-1 defines a high level mapping between MF MRM SBI services, operation and Mr'/Cr Requests:
The IMS network and the UE need to mutually negotiate the capability of supporting IMS data channel mutually.
IMS data channel capability negotiation includes two aspects:
The network discovers the data channel capability of the UE.
The UE discovers the data channel capability of the network.
When the UE supporting IMS data channel registers on the IMS network, it includes the media feature tag as specified in TS 26.114 in the Contact header field of the initial REGISTER request to allow the home IMS network discovers its IMS data channel capability.
If the IMS network supports IMS data channel, the S-CSCF includes a Feature-Caps header field indicating its data channel capability in the 200 OK response to the initial and any subsequent REGISTER request, which is used by the UE to discover the IMS data channel capability of its home IMS network.
When the UE supporting IMS data channel initiates an IMS session, it includes the media feature tag as specified in TS 26.114 in the Contact header field of the initial INVITE or a re-INVITE request to remote UE, regardless of data channel media being part of the SDP or not.
The UE shall not include data channel media description in the SDP offer of the initial INVITE request or any subsequent re-INVITE, if the S-CSCF has not included the data channel capability indication in the Feature-Caps header field in the 200 OK response either to the REGISTER or subsequent REGISTER request.