6.4.10 Inter-system Handover: GSM/BSS to UTRAN

25.3033GPPInterlayer procedures in Connected ModeRelease 17TS

The handover from GSM/BSS to UTRAN for a dual-mode GSM MS / UMTS UE is illustrated in figure 39. On the network side, upon the reception of a HARD HANDOVER PROCEED 2 command through the RANAP protocol, the RRC layer performs admission control and radio resource allocation assigning an RNTI for the RRC connection and selecting radio resource parameters (such as transport channel type, transport format sets, etc). RRC configures these parameters on layer 1 and layer 2 to locally establish the DCH logical channel.

The selected parameters including the RNTI, were previously transmitted to UE via RANAP message HARD HANDOVER PROCEED 1 and GSM upgraded message HANDOVER COMMAND.

Upon reception of the HANDOVER COMMAND message, the GSM RR layer transmits the required parameters to the UMTS RRC layer using an RR-Data-IND primitive. UE RRC configures L1 and L2 using these parameters to locally establish the DCH logical channel. Layer 1 indicates to RRC when it has reached synchronisation. An RLC signalling link establishment is then initiated by the UE. A HANDOVER COMPLETE message is finally sent by the UE.

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Figure 39: GSM to UMTS inter-system handover