Question: In LTE networks, for RRC confidentiality protection between UE (User Equipment) and eNB (evolved Node B), what is the primary function of the 128-bit cipher Key KRRCenc in the PDCP (Packet Data Convergence Protocol) layer?
Option 1: To encrypt the bearer identity (BEARER) for secure radio bearer identification.
Option 2: To serve as the KEY input parameter for the 128-EEA algorithms, enabling confidentiality protection.
Option 3: To determine the direction of transmission (DIRECTION) for uplink or downlink data.
Option 4: To generate a static COUNT value for all bearers to simplify keystream generation.
Explanation: The 128-bit cipher Key KRRCenc plays a crucial role in the confidentiality protection mechanism by serving as the KEY input for the 128-EEA algorithms. This key, along with other parameters (bearer identity, direction of transmission, length of keystream required, and a bearer-specific COUNT), ensures that data exchanged between the UE and eNB is encrypted, thus maintaining confidentiality. The correct functioning of these algorithms relies on this key to securely encrypt the data.