5G • RAN
Default DRB
Default Data Radio Bearer
Pre-established radio bearer carrying any unmapped or newly established QoS Flows within a PDU Session.
Technical Explanation
Each PDU Session configures at least one Default DRB. If a user packet arrives with a QFI that has no specific mapping rule configured in the SDAP entity, the packet is automatically routed across the Default DRB to guarantee immediate transport without dropping data.
Key Functions
- Guarantees transport for newly created or unmapped QoS Flows
- Prevents packet drops during dynamic application session startup
- Established during initial PDU Session setup
Specifications
3GPP TS 37.324
Interfaces
Uu
Related 5G Concepts
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