Section: 5.19.2a Impacts to Handover Procedures
Content: When DCNs are used, the impacts to the handover procedures are captured as below. - Forward Relocation Request message: When MME changes during handover, in the step where Forward Relocation Request message is sent from the Source MME/SGSN to Target MME/SGSN, the source MME/SGSN also includes the UE Usage Type, if available, in the message. This applies to the following clauses and step: - 5.5.1.2.2 S1-based handover, normal: Step 3 - 5.5.2.1.2 Preparation phase (E-UTRAN to UTRAN Iu mode Inter RAT handover): Step 3 - 5.5.2.2.2 Preparation phase (UTRAN Iu mode to E-UTRAN Inter RAT handover): Step 3 - 5.5.2.3.2 Preparation phase (E-UTRAN to GERAN A/Gb mode Inter RAT handover): Step 3 - 5.5.2.4.2 Preparation phase (GERAN A/Gb mode to E-UTRAN Inter RAT handover): Step 3 - Selection of new SGW: In the step, subsequent to the Forward Relocation Request message, in which the target MME/SGSN determines if the Serving GW is to be relocated, if the target MME/SGSN supports DCN, the target MME/SGWN also determines if the existing Serving GW supports the DCN for the UE based on UE Usage Type of the UE, locally configured operator's policies as well as UE related context information available at the target network, e.g. information about roaming. This applies to the following clauses and step: - 5.5.1.2.2 S1-based handover, normal: Step 4 - 5.5.2.1.2 Preparation phase (E-UTRAN to UTRAN Iu mode Inter RAT handover): Step 4 - 5.5.2.2.2 Preparation phase (UTRAN Iu mode to E-UTRAN Inter RAT handover): Step 4 - 5.5.2.3.2 Preparation phase (E-UTRAN to GERAN A/Gb mode Inter RAT handover): Step 4 - 5.5.2.4.2 Preparation phase (GERAN A/Gb mode to E-UTRAN Inter RAT handover): Step 4 - Handover from service area where DCN is not used to an area where DCN is supported: When handover occurs from a service area where DCN is not used to a service area where DCN is supported and the MME or SGSN changes, the target MME or SGSN obtains the UE Usage Type information from the HSS during the subsequent TAU or RAU procedure. If the target MME/SGSN determines that the Serving GW does not support the UE Usage Type, the target MME/SGSN triggers the Serving GW relocation as part of the handover procedures described in clause 5.5. If the target MME or SGSN does not serve the UE Usage type, the handover procedure should complete successfully and then the target MME or SGSN may use the procedure in clause 5.19.3 Step 5 onwards, to change the serving DCN of the UE.