Section: 5.5.2.2.2 Preparation phase
Content: Figure 5.5.2.2.2-1: UTRAN Iu mode to E-UTRAN Inter RAT HO, preparation phase 1. The source RNC decides to initiate an Inter-RAT handover to the E-UTRAN. At this point both uplink and downlink user data is transmitted via the following: Bearers between UE and source RNC, GTP tunnel(s) between source RNC, source SGSN (only if Direct Tunnel is not used), Serving GW and PDN GW. NOTE 1: The process leading to the handover decision is outside of the scope of this specification. 2. The source RNC sends a Relocation Required (Cause, Target eNodeB Identifier, CSG ID, CSG access mode, Source RNC Identifier, Source RNC to Target RNC Transparent Container) message to the source SGSN to request the CN to establish resources in the target eNodeB, Target MME and the Serving GW. The bearers that will be subject to data forwarding (if any) are identified by the target MME in a later step (see step 7 below). When the target cell is a CSG cell or a hybrid cell, the source RNC shall include the CSG ID of the target cell. If the target cell is a hybrid cell, the CSG access mode shall be indicated. 3. The source SGSN determines from the 'Target eNodeB Identifier' IE that the type of handover is IRAT Handover to E-UTRAN. The source SGSN selects the target MME as described in clause 4.3.8.3 on "MME Selection Function". The Source SGSN initiates the Handover resource allocation procedure by sending Forward Relocation Request (IMSI, Target Identification, CSG ID, CSG Membership Indication, MM Context, PDN Connections, SGSN Tunnel Endpoint Identifier for Control Plane, SGSN Address for Control plane, Source to Target Transparent Container, RAN Cause, MS Info Change Reporting Action (if available), CSG Information Reporting Action (if available), UE Time Zone, ISR Supported, Serving Network, Change to Report (if present)) message to the target MME. This message includes all EPS Bearer contexts corresponding to all the bearers established in the source system and the uplink Tunnel endpoint parameters of the Serving GW. If the information ISR Supported is indicated, this indicates that the source SGSN and associated Serving GW are capable to activate ISR for the UE. When ISR is activated the message should be sent to the MME that maintains ISR for the UE when this MME is serving the target identified by the Target Identification. RAN Cause indicates the Cause as received from source RNC. The Source to Target Transparent Container contains the value from the Source RNC to Target RNC Transparent Container received from the Source RNC. The old Serving Network is sent to target MME to support the target MME to resolve if Serving Network is changed. Change to Report flag is included by the source SGSN if reporting of change of UE Time Zone, or Serving Network, or both towards Serving GW / PDN GW was deferred by the source SGSN. The source SGSN shall perform access control by checking the UE's CSG subscription when CSG ID is provided by the source RNC. If there is no subscription data for this CSG ID or the CSG subscription is expired, and the target cell is a CSG cell, the source SGSN shall reject the handover with an appropriate cause unless the UE has emergency bearer services. The source SGSN includes the CSG ID in the Forward Relocation Request when the target cell is a CSG cell or hybrid cell. When the target cell is a hybrid cell, or if there are one or several emergency bearers and the target cell is a CSG cell, the CSG Membership Indication indicating whether the UE is a CSG member shall be included in the Forward Relocation Request message. This message includes all PDN Connections active in the source system and for each PDN Connection includes the associated APN, the address and the uplink tunnel endpoint parameters of the Serving GW for control plane, and a list of EPS Bearer Contexts. Prioritization of EPS Bearer Contexts is performed by the target core network node. The MM context contains security related information, e.g. UE Network capabilities and used UMTS integrity and ciphering algorithm(s) as well as keys, as described in clause 5.7.2 (Information Storage for MME). The target MME selects the NAS ciphering and integrity algorithms to use. These algorithms will be sent transparently from the target eNodeB to the UE in the Target to Source Transparent Container (EPC part). The MME establishes the EPS bearer(s) in the prioritized order. The MME deactivates, as provided in step 8 of the execution phase, the EPS bearers which cannot be established. The target MME shall determine the Maximum APN restriction based on the APN Restriction of each bearer context received in the Forward Relocation Request, and shall subsequently store the new Maximum APN restriction value. If SIPTO at the Local Network is active for a PDN connection in the architecture with stand-alone GW the source SGSN shall include the Local Home Network ID of the source cell in the PDN Connections corresponding to the SIPTO at the Local Network PDN connection. 4. The target MME determines if the Serving GW is to be relocated, e.g., due to PLMN change. If the Serving GW is to be relocated, the target MME selects the target Serving GW as described under clause 4.3.8.2 on "Serving GW selection function". The target MME sends a Create Session Request message (IMSI, MME Address and TEID, MME Tunnel Endpoint Identifier for Control Plane, MME Address for Control plane, PDN GW address(es) for user plane, PDN GW UL TEID(s) for user plane, PDN GW address for control plane, and PDN GW TEID(s) for control plane, the Protocol Type over S5/S8, Serving Network) per PDN connection to the target Serving GW. The Protocol Type over S5/S8 is provided to Serving GW which protocol should be used over S5/S8 interface. 4a. The target Serving GW allocates its local resources and returns them in a Create Session Response (Serving GW address(es) for user plane, Serving GW UL TEID(s) for user plane, Serving GW Address for control plane, Serving GW TEID for control plane) message to the target MME. 5. The target MME requests the target eNodeB to establish the bearer(s) by sending the message Handover Request (UE Identifier, S1AP Cause, KeNB, allowed AS Integrity Protection and Ciphering algorithm(s), NAS Security Parameters to E-UTRAN, EPS Bearers to be setup list, CSG ID, CSG Membership Indication, Source to Target Transparent Container). The NAS Security Parameters to E-UTRAN includes the NAS Integrity Protection and Ciphering algorithm(s), eKSI and NONCEMME are targeted for the UE. S1AP Cause indicates the RAN Cause as received from source SGSN. The Source to Target Transparent Container contains the value from the RAN Transparent Container received from the source SGSN. NOTE 2: The target MME derives K'ASME from CK and IK in the MM context and associates it with eKSI, as described in TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [41] and selects NAS Integrity Protection and Ciphering algorithm(s). The MME and UE derive the NAS keys and KeNB from K'ASME. If the MME shares an EPS security association with the UE, the MME may activate this native EPS security context by initiating a NAS SMC procedure after having completed the handover procedure. For each EPS bearer requested to be established, 'EPS Bearers To Be Setup' IE shall contain information such as ID, bearer parameters, Transport Layer Address, "Data forwarding not possible" indication, and S1 Transport Association. The target MME ignores any Activity Status Indicator within an EPS Bearer Context and requests the target eNodeB to allocate resources for all EPS Bearer Contexts received from the source side. The Transport Layer Address is the Serving GW Address for user data, and the S1 Transport Association corresponds to the uplink Tunnel Endpoint Identifier Data. "Data forwarding not possible" indication shall be included if the target MME decides the corresponding bearer will not be subject to data forwarding. The target MME shall include the CSG ID and CSG Membership Indication when provided by the source SGSN in the Handover Request message. The information about the selected NAS ciphering and integrity protection algorithm(s), KSI and NONCEMME will be sent transparently from the target eNodeB to the UE in the Target to Source Transparent Container, and in the message UTRAN HO Command from source RNC to the UE. This will then allow data transfer to continue in the new RAT/mode target cell without requiring a new AKA (Authentication and Key Agreement) procedure. More details are described in TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [41]. If the target cell is a CSG cell, the target eNodeB shall verify the CSG ID provided by the target MME, and reject the handover with an appropriate cause if it does not match the CSG ID for the target cell. If the target eNodeB is in hybrid mode, it may use the CSG Membership Status to perform differentiated treatment for CSG and non-CSG members. If the target cell is a CSG cell, and if the CSG Membership Indication is "non member", the target eNodeB only accepts the emergency bearers. 5a. The target eNodeB allocates the requested resources and returns the applicable parameters to the target MME in the message Handover Request Acknowledge (Target to Source Transparent Container, EPS Bearers setup list, EPS Bearers failed to setup list). The target eNodeB shall ignore it if the number of radio bearers in the Source to Target Transparent container does not comply with the number of bearers requested by the MME and allocate bearers as requested by the MME. Upon sending the Handover Request Acknowledge message the target eNodeB shall be prepared to receive downlink GTP PDUs from the Serving GW for the accepted EPS bearers. The target eNodeB selects AS integrity and ciphering algorithm(s). In addition to the information provided by the MME (eKSI, NAS Integrity Protection and Ciphering algorithm(s) and NONCEMME), the target eNodeB inserts AS integrity and ciphering algorithm(s) into the UTRAN RRC message, which is contained in the Target to Source Transparent Container. 6. If 'Indirect Forwarding' and relocation of Serving GW apply the target MME sends a Create Indirect Data Forwarding Tunnel Request message (Target eNodeB Address, TEID(s) for DL data forwarding) to the Serving GW. Indirect forwarding may be performed via a Serving GW which is different from the Serving GW used as the anchor point for the UE. 6a. The Serving GW returns a Create Indirect Data Forwarding Tunnel Response (Cause, Serving GW Address(es) and Serving GW DL TEID(s) for data forwarding) message to the target MME. 7. The target MME sends the message Forward Relocation Response (Cause, List of Set Up RABs, EPS Bearers setup list, MME Tunnel Endpoint Identifier for Control Plane, RAN Cause, MME Address for control plane, Target to Source Transparent Container, Address(es) and TEID(s) for Data Forwarding, Serving GW change indication) to the source SGSN. Serving GW change indication indicates whether a new Serving GW has been selected. The Target to Source Transparent Container includes the value from the Target to Source Transparent Container received from the target eNodeB. The IE 'Address(es) and TEID(s) for User Traffic Data Forwarding' defines the destination tunnelling endpoint for data forwarding in target system, and it is set as follows. If 'Direct Forwarding' or if 'Indirect Forwarding' but no relocation of Serving GW applies, then the IEs 'Address(es) and TEID(s) for Data Forwarding' contains the forwarding DL GTP-U tunnel endpoint parameters to the eNodeB received in step 5a. If 'Indirect Forwarding' and relocation of Serving GW apply the IEs 'Address(es) and TEID(s) for Data Forwarding' contains the DL GTP-U tunnel endpoint parameters to the Target eNodeB or to the forwarding Serving GW received in step 6a. 8. If "Indirect Forwarding" applies, the source SGSN shall send the message Create Indirect Data Forwarding Tunnel Request (Address(es) and TEID(s) for Data Forwarding (received in step 7)) to the Serving GW used for indirect forwarding. Indirect forwarding may be performed via a Serving GW which is different from the Serving GW used as the anchor point for the UE. 8a. The Serving GW returns the forwarding user plane parameters by sending the message Create Indirect Data Forwarding Tunnel Response (Cause, Serving GW Address(es) and TEID(s) for data forwarding). If the Serving GW doesn't support data forwarding, an appropriate cause value shall be returned and the Serving GW Address(es) and TEID(s) will not be included in the message.