5.6 Network Assisted Cell Change
23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS
Network Assisted Cell Change (NACC) is a means that enables better performance for packet data services upon inter-cell change for those networks that do not support PS Handover. It reduces the service interruption time for UEs in active mode upon cell change by providing in the source cell, prior to the cell change, system information of a target cell allowing packet access.
Within the scope of this specification, NACC is applicable for inter-RAT cell changes from a source E‑UTRAN cell towards a target GERAN cell.
When the UE changes from a source E-UTRAN cell towards a target GERAN cell, the UE locally deactivates ISR by setting its TIN from "RAT-related TMSI" to "GUTI", if any EPS bearer context activated after the ISR was activated in the UE exists.
When the UE changes from a source E-UTRAN cell in connected mode towards a target GERAN cell from the same RA via Cell Change Order that is not for CS fallback and the ISR is active, the UE locally deactivates ISR by setting its TIN from "RAT-related TMSI" to "GUTI".
5.6.1 Architecture Principles for E-UTRAN to GERAN NACC
Introducing NACC from E‑UTRAN to GERAN follows the principles of the Network Assisted Cell Change between UTRAN and GERAN as described in TS 25.413 [22] and TS 23.060 [7]. It specifies the RAN Information Management (RIM) procedures as specified in clause 5.15 and depicted in figure 5.6‑1.
Figure 5.6-1: E-UTRAN to GERAN NACC basic network architecture
The support for the NACC from E‑UTRAN to GERAN has the following impacts on E‑UTRAN / GERAN architecture:
– Affected nodes: BSC, eNodeB, MME, SGSN;
– Affected network interfaces: Gb, Iu, S3, Gn, S1;
– Affected radio interfaces: Um and Uu.