What is NSA?
5G Non-Standalone (NSA) is the first-wave 5G deployment architecture where the 5G NR gNB (Secondary Node) operates in conjunction with an existing 4G LTE eNB (Master Node), using the 4G EPC as the core network. NSA enabled operators to deploy 5G rapidly without the significant investment of a new 5G Core network.
How Does NSA Work?
The primary NSA mode is EN-DC (Option 3x): the LTE eNB handles all RRC control signalling (anchored to EPC via S1-MME), while the 5G gNB adds a Secondary Cell Group for user plane throughput only. The UE must maintain LTE coverage at all times to use 5G NSA. The eNB and gNB coordinate via the X2/Xn interface for data splitting and resource management.
Use Cases
The dominant 5G deployment model for operators worldwide from 2019 onwards, delivering 5G data rates over existing 4G infrastructure investments. Being progressively complemented or replaced by SA as operators deploy 5GC.
3GPP / Standards Reference
3GPP TS 37.340 (Multi-RAT Dual Connectivity), TS 23.401, Release 15
Related Terms
SA | EN-DC | eNB | gNB | EPC | NR | LTE
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