This Technical Report provides background information, motivations, concepts and requirements regarding an extended Network Assisted Cell Change (NACC) feature for external cell change support. Cell change between GERAN and UTRAN cells is outside the scope of this report, although consideration has been taken in order to allow an easier extensibility to that case. The extension is based on the Release 4 version of the NACC feature where the mobile station is only supported by the NACC when performing internal cell re-selection, i.e. within a BSC. The extension of the feature is for GERAN just affecting BSS and for the core network the SGSN and signalling links between these network nodes. To support cell changes between GERAN and UTRAN, also the Um and the Uu interfaces are affected. The evolved Release 4 NACC proposal as described in this TR provides the basis for the detailed Stage 2 and stage 3 specification work. The feature will be developed in a phased approach and a longer-term vision is presented in the report. The focus of the TR is to:

• Define the requirements on different nodes
• Specify the requirements for the interfaces
• Propose a plan for the work item project
• Evaluation of what does and does not need to be standardised

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