8.3.5 GSM to UMTS Handover with Iu on IP
23.2053GPPBearer-independent circuit-switched core networkRelease 17Stage 2TS
If IuCS on IP is supported by the MSC server, the Core Network side procedures described in clauses 8.3.1, 8.3.2, 8.3.3, 8.3.4 shall apply. For the access bearer termination, the exchange of IP addresses via call control procedures is described in this clause.
Before the MSC server starts the access bearer assignment, the MSC server requests the MGW to prepare for the access bearer using the Prepare_IP_Transport procedure. The MSC server requests the MGW to provide an IP Transport address and UDP Port and provides the MGW with the bearer characteristics. For speech calls, the MSC server shall provide the MGW with the speech coding information and conditionally GTT related information in accordance with 3GPP TS 23.226 [28] for the bearer. For a non-speech call the MSC server also provides the MGW with a PLMN Bearer Capability [4]. After the MGW has replied with the IP address and UDP Port the MSC server requests access bearer assignment using the provided IP address and UDP Port in accordance with 3GPP TS 25.413 [26]. The IP addresses and UDP Ports of the MGW and the RNC are exchanged via the RANAP procedures. If the bearer transport is IP and IuUP mode is Transparent, when the MSC receives the RANAP Iu Relocation Request response, it shall send the RNC IP address and UDP Port to the MGW Access bearer termination using the Modify_IP_Transport_Address procedure.
If the bearer transport is IP and IuUP mode is Support, the MGW shall use the source IP address and UDP Port of the IuUP Init packet received from the radio access network as the destination address for subsequent downlink packets.
The sequence is shown in figure 8.3.5/1.
Figure 8.3.5/1 GSM to UMTS Handover with Iu on IP