Question: What is the primary source from which a UE (User Equipment) derives the value for its `VarGnbID` variable in a 5G NR (New Radio) network?
Option 1: From the Tracking Area Update Accept message sent by the MME (Mobility Management Entity)
Option 2: From the leftmost bits of the Cell Identity in the Master Information Block (MIB)
Option 3: From the System Information Block Type 2 (SIB2) containing the cell's access restrictions
Option 4: From the first PLMN-IdentityInfo IE of PLMN-IdentityInfoList in System Information Block Type 1 (SIB1)
Explanation: In a 5G NR network, the UE's `VarGnbID` variable is populated from the first PLMN-IdentityInfo IE within the PLMN-IdentityInfoList found in SIB1, specifically using parts of the Cell Identity to derive the GnbID, crucial for identifying and managing UE-gNB connections. SIB1, broadcast by gNBs, provides essential cell access information to UEs.