5G • 5G-Advanced (Rel-18)
L4S for 5G-Advanced XR
Low Latency, Low Loss, Scalable Throughput Congestion Control
Integrates IETF L4S (DualQ and ECN) into 5G radio queues, enabling video servers to adjust bitrate instantaneously before queue buffers build latency.
Technical Explanation
Traditional TCP congestion control requires packets to drop or delay significantly before adjusting transmission rates. Rel-18 embraces L4S (Low Latency, Low Loss, Scalable Throughput), using Explicit Congestion Notification (ECN) marking inside gNodeB radio queues to signal congestion instantly without dropping packets, maintaining sub-5 ms queuing latency at maximum throughput.
Key Functions
- Eliminates queue-induced bufferbloat latency in cellular base stations
- Employs Explicit Congestion Notification (ECN) marking to signal instantaneous channel limits
- Allows cloud video encoders to adjust rendering bitrates in under 10 milliseconds
- Maintains ultra-low packet loss rates (<10^-5) alongside high link utilization
Specifications
3GPP TR 38.835, TS 23.501 (Rel-18)
Interfaces
Uu (RLC/MAC)N3 (UPF)N6
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