eNB vs gNB
An eNB (eNodeB) is the LTE base station. It runs the LTE radio, it belongs to the E-UTRAN, and it connects to the Evolved Packet Core (EPC) over the S1 interface, with X2 links to neighbouring eNBs for handovers and dual connectivity.
A gNB (gNodeB) is the 5G NR base station. It runs the NR radio, it belongs to the NG-RAN, and it connects to the 5G Core (5GC) over the NG interface, with Xn links to neighbouring gNBs. Unlike the eNB, a gNB can be split into CU, DU and RU so the higher protocol layers, the lower layers, and the radio sit on separate hardware.
Two hybrids cross the line and trip people up. An ng-eNB is an LTE radio node that connects to the 5GC (so it sits inside the NG-RAN). An en-gNB is an NR node bolted onto an LTE eNB and the EPC — the secondary node in EN-DC, the usual flavour of non-standalone 5G.
| Aspect | eNB (LTE) | gNB (5G NR) |
|---|---|---|
| Network it belongs to | E-UTRAN (the LTE access network) | NG-RAN (the 5G access network); an ng-eNB also lives here |
| Core network it connects to | EPC, over the S1 interface (S1-MME + S1-U) | 5GC, over the NG interface (NG-C to the AMF + NG-U to the UPF) |
| Interface to neighbouring base stations | X2 | Xn (XnAP for signalling) |
| Radio waveform | OFDMA downlink, SC-FDMA (DFT-s-OFDM) uplink | CP-OFDM both ways; DFT-s-OFDM still available on the uplink for cell-edge UEs |
| Architecture | Monolithic — one node holds the full stack | Can be disaggregated into CU, DU and RU (the CU itself splits into CU-CP and CU-UP) |
| Subcarrier spacing | Fixed 15 kHz | Flexible numerology: 15/30/60/120 kHz (µ = 0–3), picked per band |
| Antennas and beamforming | Up to 8 layers; FD-MIMO added in later releases, mostly sub-6 GHz | Massive MIMO with many elements; analogue/hybrid beamforming, and effectively mandatory at FR2 |
| User-plane protocol stack | PDCP / RLC / MAC / PHY | Adds SDAP on top of PDCP to map QoS flows onto data radio bearers |
| Max channel bandwidth | 20 MHz per carrier; wider only with carrier aggregation | 100 MHz per carrier in FR1, 400 MHz per carrier in FR2 |
| Internal split interfaces | None defined — internal vendor design | F1 between CU and DU; E1 between CU-CP and CU-UP; fronthaul (eCPRI / O-RAN 7.2x) to the RU |
| 3GPP origin | Release 8 onward | Release 15 onward |
| Hybrid variants | en-gNB — an NR node that attaches to an eNB and the EPC as the EN-DC secondary node | ng-eNB — an LTE radio node that attaches to the 5GC inside the NG-RAN |
The interface rename: S1/X2 became NG/Xn
The names changed for a reason, not just for marketing. An eNB faces the EPC over S1, which splits into S1-MME (control, to the MME) and S1-U (user plane, to the Serving Gateway). Between eNBs you get X2, used for handovers and for the LTE side of dual connectivity.
A gNB faces the 5GC over NG, which splits into NG-C (control, to the AMF) and NG-U (user plane, to the UPF). Between gNBs you get Xn, carrying XnAP signalling for mobility and secondary-node coordination.
So the pattern is clean: S1 → NG to the core, X2 → Xn between base stations. The catch is the ng-eNB. It is an LTE radio node, but because it connects to the 5GC it uses NG and Xn, not S1 and X2. The interface tells you which core you are talking to, not which radio you are running.
CU, DU and RU: why the gNB can be split
An eNB is one box that owns the whole protocol stack, from RRC down to the RF. A gNB does not have to be. 3GPP defined a higher-layer split so the gNB can be disaggregated:
- CU (Central Unit) — RRC, SDAP and PDCP. It can be centralised, and it splits again into CU-CP (control plane) and CU-UP (user plane), linked by the E1 interface.
- DU (Distributed Unit) — RLC, MAC and the higher PHY. It sits closer to the cell site and connects to the CU over the F1 interface.
- RU (Radio Unit) — the low PHY and the RF, connected to the DU over fronthaul (eCPRI, or the O-RAN 7.2x split).
One CU can serve several DUs, and one DU can serve several RUs, which is what makes Cloud RAN and O-RAN deployments work. An eNB has no standardised internal interfaces — any split inside it is the vendor's own affair — so you cannot mix and match LTE CUs and DUs from different suppliers the way the gNB split is meant to allow.
ng-eNB and en-gNB: the hybrids that confuse everyone
These two look almost like typos of each other, and they mean opposite things. Read the prefix as "which core".
An en-gNB is an NR node attached to the EPC. It is the secondary node in EN-DC, where the phone keeps its control link on an LTE eNB (the master) and adds an NR carrier for data. This is non-standalone (NSA) 5G — Option 3 — and it reuses the existing 4G core, which is why operators could launch 5G speeds before deploying a 5GC. The en-gNB does not talk to the 5GC at all.
An ng-eNB is the mirror image: an LTE radio node attached to the 5GC. It runs E-UTRA on the air but connects to the 5G core over NG, so it counts as part of the NG-RAN alongside gNBs. You see it in standalone-core deployments that still want LTE radio coverage feeding the 5GC, such as some NG-RAN dual-connectivity options (NGEN-DC).
Quick rule: en-gNB = NR radio → EPC; ng-eNB = LTE radio → 5GC. The hybrid's radio is in the suffix, its core is in the prefix.
The bottom line
The gNB is the 5G evolution of the eNB — same job (run the radio, schedule users, anchor mobility), new core, new interface names, a richer protocol stack with SDAP, flexible numerology, massive MIMO, and the option to split into CU/DU/RU.
But this is not a clean switchover. The two coexist for years. In NSA the eNB stays the anchor and an en-gNB adds NR data on top of the EPC; with DSS the same band carries LTE and NR side by side; and where the 5GC is in place, an ng-eNB can feed LTE radio into it. So in most live networks you are not choosing eNB or gNB — you are running both, with the ng-eNB and en-gNB bridging the gap between the 4G and 5G worlds.
Frequently asked questions
- What's the difference between an eNB and a gNB?
- An eNB is the LTE base station: it runs the LTE radio, belongs to the E-UTRAN, connects to the EPC over S1, and links to other eNBs over X2. A gNB is the 5G NR base station: it runs the NR radio, belongs to the NG-RAN, connects to the 5GC over NG, and links to other gNBs over Xn. The gNB also adds the SDAP protocol layer, flexible numerology, wider carriers, massive MIMO, and the option to be split into CU, DU and RU.
- What is an en-gNB, and how is it different from an ng-eNB?
- An en-gNB is an NR node that connects to the 4G EPC. It is the secondary node in EN-DC (non-standalone 5G), where an LTE eNB stays the master and the en-gNB adds an NR carrier for extra data. An ng-eNB is the opposite: an LTE radio node that connects to the 5G Core over NG, so it sits inside the NG-RAN. Read the prefix as the core: en-gNB goes to the EPC, ng-eNB goes to the 5GC.
- Can an eNB be upgraded to a gNB?
- Not by a config change — NR is a different air interface, so it needs NR baseband and, on many bands, new radios. Whether it is a software upgrade or a hardware swap depends on the vendor and the band. Some modern radios are multi-mode and can run NR on the same hardware (this is what makes DSS possible), but the eNB and gNB remain separate logical nodes with different cores and interfaces even when they share a cabinet.
- Do eNBs and gNBs work together?
- Yes, that is exactly how most early 5G runs. In EN-DC (the basis of NSA), the phone keeps its control link on an LTE eNB and gets an NR carrier from an en-gNB at the same time, with the X2 interface coordinating the two. DSS goes further and lets LTE and NR share one band on the same hardware. So eNB and gNB routinely operate side by side rather than one replacing the other.
Related terms
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