Question: Under what condition does the network initiate the security mode command procedure to a UE (User Equipment) in RRC_CONNECTED state, specifically in relation to the establishment of Signaling Radio Bearers (SRBs)?
Option 1: When both SRB1 and SRB2 are established.
Option 2: After multicast MRBs (Media Resource Bearers) and/or DRBs (Data Radio Bearers) are set up.
Option 3: Simultaneously with the establishment of the first DRB.
Option 4: When only SRB1 is established, prior to the setup of SRB2, multicast MRBs, and/or DRBs.
Explanation: Initiating the security mode command when only SRB1 is established ensures a basic level of security is implemented early on, even before additional bearers (SRB2, multicast MRBs, and/or DRBs) are set up, prioritizing securing the initial signaling pathway between the network and UE.