Question: What is the maximum number of Data Radio Bearers supported over NB-IoT, and what does this imply about the number of PDU sessions that can have active user plane resources at the same time?
Option 1: One Data Radio Bearer, implying only one PDU session can have active user plane resources.
Option 2: Two Data Radio Bearers, implying a maximum of two PDU sessions can have active user plane resources at the same time.
Option 3: Three Data Radio Bearers, implying a maximum of three PDU sessions can have active user plane resources at the same time.
Option 4: Four Data Radio Bearers, implying a maximum of four PDU sessions can have active user plane resources at the same time.
Explanation: According to the QoS model for NB-IoT, a maximum of two Data Radio Bearers are supported. This implies that at most two PDU sessions can have active user plane resources at the same time.