Figure AC.7.1-1depicts a signalling flow diagram for establishing a bootstrap data channel in a person-to-person use case. The MF anchors the bootstrap data channel, and the originating network is offering a bootstrap data channel to the remote peer as well for application download.
In the call flow the two 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 INVITE request with an initial SDP to the IMS AS, through P-CSCF and S-CSCF in the originating network. The initial SDP contains offers for the bootstrap data channel establishment request with bootstrap DC stream ID. In this example procedure, the SDP contains both bootstrap data channel offers for originating side and terminating side.
IMS AS validates user subscription data to determine whether the data channel call request should be notified to DCSF.
If the IMS AS determined, based on the user profile, that data channel call request needs to be notified to DCSF, the IMS AS selects a DCSF for this user based on local configuration or discovery and selection of a DCSF instance via NRF.
If the IMS AS determined, based on the user profile, that the data channel call request need not to be notified to DCSF, or DCSF decides that DC request is not allowed, the IMS AS proceeds with normal IMS procedures to setup the MMTel session without performing Data Channel bootstrapping, by deleting DC related media information and sending the updated SIP INVITE to the originating S-CSCF.
IMS AS notifies the DCSF of the DC call event by sending Nimsas_SessionEventControl_Notify (SessionEstablishmentRequestEvent, Session ID, Calling ID, Called ID, Session Case, Event initiator, Media InfoList, DC Stream ID) request to the DCSF.
After receiving the DC control request, the DCSF determines the policy about how to process the bootstrap data channel establishment request based on the related parameters in the Data Channel control request (e.g. CallingID, CalledID, DC Stream ID) and/or DCSF service specific policy.
Since the SessionEstablishmentRequestEvent indicates that served user is offered local bootstrap media, DCSF, based on its policies reserves originating side MDC1 media information, as well as the terminating side MDC1 remote bootstrap media (targeting remote UE), which are used to receive UE request for application downloading from MF or MRF.
DCSF invokes the Nimsas_MediaControl_MediaInstruction (Session ID, Media Instruction Set) operation based on its policies instructing the IMS AS how to set up bootstrap data channel with MF both for originating and terminating side. The MediaInstructionSet provided by the DSCF, includes its MDC1 media endpoint addresses created in step 5, DC Stream ID, and the replacement HTTP URL representing the application list offered via the MDC1 interface.
In this scenario, the DCSF instructs the IMS AS to terminate bootstrap data channel establishment request on originating MF, and initiate remote bootstrap data channel establishment request(targeting remote UE) as well as forwarding remote bootstrap data channel establishment request of served user (targeting remote DCSF) towards terminating network.
IMS AS invokes Nmf_MRM_Create(List of Media Termination Descriptors) service operation to instruct MF to allocate required data channel media resources. IMS AS request creation of two different Media Terminations, one representing the local bootstrap media to be terminated and the other representing the remote bootstrap media to be offered to remote UE. Each Media Termination includes information required to allocate resources in both Mb and the MDC1 interfaces. The MF responds with the negotiated data channel media resource information to IMS AS. If MRF is used, IMS AS uses Mr'/Cr to the MRF to reserve data channel media resources.
IMS AS responds to the MediaInstruction request received in step 6. The response may include the atomic success result of operation and also includes negotiated data channel media resource information for MDC1.
IMS AS sends the INVITE which includes the updated SDP offer adding media information of MF or MRF via the originating S-CSCF to remote network side and UE#2. In this scenario, the SDP offer for bootstrap data channel to UE#2 is included.
UE#2 and terminating network returns an 18X response with the SDP answer to bootstrap data channel to originating network. According to the received SDP answer, MF or MRF may update data channel media resource information for UE#2.
The bootstrap data channels have been established between originating MF or MRF and UE#1/UE#2. The UEs send application request messages to MF or MRF to request a data channel application or an application list if multiple DC applications are available, via the established bootstrap data channel with its data channel capabilities. The MF or MRF replaces the root URL with the replacement URL received in steps 8 and forwards the message to received media point of DCSF. The DCSF provides the application list and proper data channel applications further to UE#1 and UE#2 based on their data channel capabilities and their choices through MF or MRF.
The bootstrap data channels have also been established between terminating MF or MRF and UE#1/UE#2. The data channel application is requested and downloaded to UE#1 and UE#2 from terminating DCSF
Steps 20-23 may be executed after step 14, if the SDP answer in 200 OK to the PRACK and UPDATE messages contain the information required to establish bootstrap data channels.