5G • RAN
BSR
Buffer Status Report
MAC Control Element sent by UE to inform the gNodeB of the total data volume awaiting transmission in uplink buffers.
Technical Explanation
Because the gNodeB scheduler cannot observe UE buffer occupancy directly, the UE transmits Buffer Status Reports (BSR). BSR formats include Short BSR (for 1 logical channel group), Long BSR (for multiple LCGs), and Truncated BSR. BSR is triggered by new high-priority data arrival, periodic timers, or padding capacity.
Key Functions
- Notifies gNodeB of buffer volumes awaiting uplink transmission
- Organized across up to 8 Logical Channel Groups (LCGs)
- Triggers gNodeB dynamic uplink scheduling allocations
Specifications
3GPP TS 38.321
Interfaces
Uu
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