For this end-to-end session flow, we assume the originator is a UE located within the service area of the network operator to whom the UE is subscribed. The UE has already established an IM CN session and is generating an invite to add another media (e.g. video to a voice call) to the already established session. Note that the invite to add media to an existing session could be originated by either end. The invite, and subsequent flows, are assumed to follow the path determined when the initial session was established. Any I-CSCFs that were included in the initial session would be included in this session.
The originating party addresses a destination that is a subscriber of the same network operator.
The destination party is a UE located within the service area of the network operator to which it is subscribed.
The flow presented here assumes that Policy and Charging Control is in use.
Depending on the bearer establishment mode selected for the IP-CAN session, resource reservation shall be initiated either by the UE or by the IP-CAN itself. UE#2 initiates the resource reservation procedures for the resources necessary for this additional media as shown in Figure 5.33. Otherwise, the IP-CAN initiates the reservation of required resources after step 9.
Depending on the bearer establishment mode selected for the IP-CAN session, resource reservation shall be initiated either by the UE or by the IP-CAN itself. After determining the offered set of media streams for this additional media, in step #15 above, UE#1 initiates the reservation procedures for the additional resources needed for this new media as shown in Figure 5.33. Otherwise, the IP-CAN#1 initiates the reservation of required resources after step 13.
When the terminating side has successfully reserved the needed resources, it sends the "reservation successful" message to UE#1 along the signalling path established by the INVITE message. The message is sent first to P-CSCF#1.