Node B, eNodeB, gNB and ng-eNB are network nodes that are part of the mobile radio access network. When you see the architecture of a 3G/4G mobile network, you are likely to come across the terms Node B and eNodeB. Mobile networks have evolved from 2G to 3G, 4G and 5G over the last few decades, and as a result, the network architecture has changed also. We now have two new terms called gNB and ng-eNB, but let’s start with some definitions first. We’ll touch upon ng-eN at the end of this post to avoid unnecessary confusion.
Node B, eNodeB and gNB are essential radio network components for 3G UMTS, 4G LTE and 5G NR mobile networks. Node B is the radio base station for UMTS networks (Universal Mobile Telecommunications System), eNodeB or eNB is the radio network node for LTE networks (Long Term Evolution), and gNB is the radio network node for 5G NR. These nodes are installed at the cell sites of mobile operators and can be seen as tall masts, also known as cellular towers.
What is Node B?
When the 2G GSM networks (Global System for Mobile Communications) started in the early 1990s, the wireless connectivity was enabled by the radio base stations also known as Base Transceiver Station or BTS. The word ‘transceiver’ suggests that the base station is capable of transmitting as well as receiving. When 3G UMTS networks came, the 3G base stations were assigned a new terminology ‘Node B’. Node B, sometimes also written as NodeB, uses WCDMA (Wideband Code Division Multiple Access) for the air interface to connect mobile phones to the mobile network. It is part of the 3G UMTS Radio Access Network or UTRAN (UMTS Terrestrial Radio Access Network). If a mobile operator wants to provide nationwide 3G network coverage, it needs to deploy a large number of Node Bs throughout the country.
Node Bs are controlled by another entity in the 3G radio network called the Radio Network Controller or RNC. The 2G equivalent of RNC in the GSM network is the Base Station Controller or BSC. When your cell phone screen shows 3G or H or H+ symbol next to the signal bar, you are being served by a Node B. As shown in the network diagram above, Node B and RNC collectively represent the 3G UMTS radio access network. The RNC then connects through a backhaul link to the SGSN (Serving GPRS Support Node) to establish a connection between the 3G radio access network and the 3G mobile core. You can check out this post to learn more about the radio network, and this post for more information on the mobile core network.
What is eNodeB?
The base stations in 4G LTE networks are called evolved Node B or eNodeB. In network architecture diagrams, eNodeB is often also abbreviated as eNB. eNodeB is an essential part of the 4G LTE radio network and is capable of performing network control functions in addition to creating mobile network coverage. If you look at the network diagram above, you may notice that the 4G radio network does not have a separate network controller entity. This is different from GSM and UMTS networks that have BSC and RNC respectively for network control tasks. It means that for LTE, eNodeB is able to perform the radio access functions that are equivalent of what Node B and RNC do together in 3G UMTS.
In line with the LTE standard, eNodeB employs separate radio access technologies for the uplink and the downlink. The communication between eNodeB and the cell phone uses Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink.
eNodeB also has the intelligence and ability to perform radio network control functions. As part of that, it represents the 4G LTE radio access network E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). It then connects to the 4G LTE core network, the Evolved Packet Core (EPC).
What about gNB and ng-eNB?
5G networks use a technology called New Radio or NR for the air interface. There are two ways in which 5G networks can be deployed; standalone mode and non-standalone mode. Standalone mode (SA) is where 5G networks operate completely on their own without any legacy network i.e. no 4G LTE network dependency. The non-standalone mode (NSA) is the more common one especially for early adoption of 5G where mobile operators add 5G NR to their existing 4G LTE infrastructure. You may read more about SA and NSA in this post, but the point relevant here is that NSA makes use of the LTE core network EPC (with some enhancements) whereas SA uses a new 5G core network called 5G Core or 5GC. In both cases, 5G uses a dedicated radio network for the air interface. The radio network for 5G NR is called Next-Generation Radio Access Network or NG-RAN.
Since NSA deployment takes advantage of the existing EPC for core network functions, it requires both LTE and NR radio networks to connect to the same EPC. 4G LTE networks can operate the same way they do today by allowing eNB to communicate with EPC for control plane as well as user plane. In other words, all the radio network functions, as well as user functions (e.g. mobile data, QoS etc.), take place through eNB. The 5G radio network node gNB operates slightly differently and is only used for user-level functions. The control plane for 5G is still managed by eNB as part of a concept called dual connectivity.
When 5G Core network is used instead of EPC, the connectivity for any 5G devices uses the gNB node for both user and control planes. Any 4G LTE devices, on the other hand, use ‘next-generation’ eNodeB instead of the regular eNodeB to be able to communicate with the 5G Core network. The next-generation eNodeB is abbreviated as ng-eNB.