8.3 Re-selection between GERAN/UTRAN/E-UTRAN and GAN modes

3GPP43.318Generic Access Network (GAN)Release 17Stage 2TS

8.3.1 Rove-in (from GERAN/UTRAN/E-UTRAN mode to GAN mode)

This procedure is applicable only if GAN service is available, a MS is not in NC2 mode (as defined in 3GPP TS 45.008 [18]) and has an MS preference for:

– GAN-only;

– GAN-preferred or;

– GERAN/UTRAN/E-UTRAN-preferred and the MS cannot find a suitable GERAN, UTRAN or E-UTRAN cell to camp on.

Following successful GAN registration, the Access mode in the MS is switched to GAN mode. GA-CSR or GA-RRC entity in the MS reports to the NAS, the NAS-related system information received in the GAN Registration Procedure. The NAS considers the GANC allocated cell ID, as the current serving cell.

While in GAN mode, an MS in GERAN/UTRAN, UTRAN or E-UTRAN-preferred mode may perform GERAN/UTRAN, UTRAN or E-UTRAN cells monitoring according to 3GPP TS 45.008 and follow the behaviours according to 3GPP TS 23.122.

While in GAN mode, the GERAN-RR, UTRAN RRC and E-UTRAN RRC entities are detached from the RR-SAP in the MS, as a result the entities do not:

– inform NAS about any GERAN/UTRAN/E-UTRAN cell re-selection and/or the change of system information of the current camping cell;

– inform NAS about any newly found PLMN over GERAN, UTRAN or E-UTRAN; and

– act on any paging request message received over GERAN, UTRAN or E-UTRAN.

Rove-in may be applied to support CS call re-establishment following the loss of an RR connection in GSM or to support packet service re-establishment following abnormal TBF release with cell reselection in GPRS. The support for call re-establishment is indicated to the MS in the GAN system information.

8.3.2 Rove-out (from GAN mode to GERAN/UTRAN/E-UTRAN mode)

This procedure is applicable when MS detaches from the generic IP access network, and its mode selection is GAN‑preferred or when MS finds a suitable GERAN/UTRAN/E-UTRAN cell for camping on, and its mode selection is GERAN/UTRAN/E-UTRAN-preferred.

When the MS detaches from the generic IP access network, depending on prevailing circumstances the MS may be able to deregister first with the GANC.

For the GAN-preferred and GERAN/UTRAN/E-UTRAN-preferred mode selections, the MS detaches GA-CSR or GA-RRC from the RR-SAP and re-attaches GERAN-RR, UTRAN RRC or E-UTRAN RRC to RR-SAP and restores normal GERAN-RR, UTRAN RRC or E-UTRAN RRC functionality.

For the GAN-only mode selection, GA-CSR or GA-RRC remains attached to NAS and the MS stays in GAN mode (in "No Service" condition).