5G NSA (Non-Standalone)
5G deployment mode: 5G radio + LTE core. Phone latches onto a 4G cell for control-plane, on 5G for user-plane throughput. Pioneered 2019-2020 for carriers to deploy quickly without waiting for a full-5G core.
Trade-off vs SA: faster deployment (reuse existing 4G cores), lower-cost initial rollout, but no network slicing, no URLLC, higher latency. Most early 5G (2019-2022) was NSA. Carriers migrate gradually to SA: T-Mobile USA dropped NSA 2024, Verizon planning 2025-2026. Modern smartphones support both. Symptom of NSA: phone shows "5G" but is still on a 4G "anchor cell" — battery drain higher than SA. Modern: NSA still dominant globally (2024) despite SA roadmaps.