5G NSA

5G NSA (5G Non-Standalone) is a 5G deployment in which 5G NR radio is added on top of an existing LTE network. The device connects to LTE first — the anchor — and the network then adds a 5G NR carrier for extra capacity, while control signaling and the core network remain 4G. It was the first form of 5G launched commercially, because operators could reuse their LTE core.

How 5G NSA works

The most common NSA architecture is Option 3x, built on EN-DC (E-UTRA–NR Dual Connectivity):

1. The device attaches to an LTE cell and registers with the 4G core (EPC), exactly as an LTE device would.
2. The LTE base station, acting as master node, asks the device to measure nearby 5G NR cells.
3. If an NR cell is good enough, the network adds it as a secondary node, and user data flows over LTE and NR together.
4. If NR coverage drops, the device keeps its LTE connection and loses only the NR leg.

Because NSA relies on LTE signaling, whether a device displays a 5G indicator can depend on operator configuration rather than on an active NR connection.

Limitations of NSA

• No 5G Core features: network slicing and other 5GC capabilities require 5G SA.
• Voice stays on LTE: calls use VoLTE on the anchor, not VoNR.
• Dependency on the anchor: if LTE is weak, NR cannot be used even where the NR signal is strong.
• Roaming: NSA roaming needs an LTE roaming agreement plus permission to use NR as a secondary RAT, and partners may support one without the other.

How to tell NSA from SA

Indicator	5G NSA	5G SA
Registration	LTE attach to the EPC	5G registration to the 5GC
Radio measurements	LTE RSRP plus NR SS-RSRP	NR SS-RSRP only
Modem RAT report	LTE with NR (EN-DC)	NR

See RSRP, RSRQ and SINR for what those measurements mean.

Why it matters for testing

NSA remains common in many markets, and its performance depends as much on the LTE anchor as on NR. Separating NSA from SA — and testing each explicitly — avoids blaming 5G for LTE problems or the reverse. SimCheck.ai tests can force 5G NSA or 5G SA and record the RAT and band in use — see quick tests.