1 - In Msg4 there is a MAC CE including UE Contention Resolution Identity that matches the one in Msg3 CCCH SDU, then the UE knows the Msg4 is for itself.
2 - After contention resolution UE gets a temporary identity C-RNTI, which is valid in the current cell only. C-RNTI is used in PDCCH scrambling and differ to other UE’s C-RNTI. Different UE’s PDCCH schedules different PDSCH, then UE can only receive its own message.
3 - PDU session establishment is session related procedure, no relation with RRC procedure. And a UE can maintain only one RRC connection at the same time.
4 - UL-CCCH1-Message carries 64 bits while UL-CCCH-Message carries 48 bits.
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