 routing scheme can be summarised as follows: User Plane Detailed Planning Control plane Fully meshed MSS Core network area subnetworks User plane Figure 4.31 Distributed network architecture call initiation from the user equipment via the originating RNC to the MSS and setup confirmation from the terminating RNC; topology database query and user plane analysis; MGW selection and resource reservation request sending; bearer connection establishment; RAB assignment request and access side bearer establishment between the MGW and the RNC; alerting and call connection. The user plane can be routed via the ATM and IP core network. ATM resources can be reserved by BICC signalling. IP resource reservation is handled by BICC or SIP. User Plane Signalling Bearer establishment can be achieved with the following signalling protocols: RANAP With the Iu-CS interface, the user plane is always established using the RNC. Therefore, the BIWF (bearer interworking function) address (RANAP: transport layer address) and binding ID (RANAP: Iu transport association) are reserved from the chosen MGW and delivered to the RNC using the RANAP assignment request message. Currently only the AAL2 type of user plane connection is allowed in the Iu- CS interface. The binding ID is the connector factor of RANAP/BICC signalling at the control plane and AAL signalling at the user plane. The binding ID is needed in AAL2 PVC (permanent virtual connection). Core Network Planning and Optimisation BICC (Binding ID) RAB (Binding ID) H.248 (Binding ID) H248 (Binding ID) AAL2 setup (Binding ID) MGW 1 AAL2 setup (Binding ID) MGW 2 SVC setup (Binding ID) Figure 4.32 Reservation of a binding ID Resources reservation has two phases, the reservation of the binding ID (Figure 4.32) and the signalling part. The MSS asks the MGW to reserve a binding ID. The binding ID is returned to the MSS, which sends it to the RNC or the other MSS. That reserved binding ID is then received in the AAL2 or UNI signalling setup and it is detected that the binding ID is reserved 