data it receives from the core network Figure 10.4 - NSA DC bearers Let's define each of the terms from the diagram one by one: MCG bearer: The Master Cell Group (MCG) bearer in DC is a bearer whose radio protocol stack is only located in master nodeB and only uses the master nodeB resources. The S1-U connection to the SGW is terminated in the master node itself; the secondary node is not involved in the direct transport of data to the EPC. SCG bearer: The Secondary Cell Group (SCG) bearer in DC is a bearer whose radio protocol stack is only located in the secondary node to use secondary nodeB resources. In this case, there is an S1-U connection from the secondary node to the SGW; hence there is a direct path for data to pass to the EPC from the secondary nodeB. Split bearer: This is a combination of the previous two bearers, in which the bearer's radio protocol stack is located in both the master and the secondary nodeB. This pictorial representation of these split bearers will help to further enhance our understanding: A deep dive into NSA networks MCG Split SCG Split Bearer Bearer Bearer Bearer LTE/NR NR PDCP NR PDCP NR PDCP LTE RLC LTE RLC LTE RLC NR RLC NR RLC NR RLC LTE MAC NR MAC Figure 10.5 - Split bearers One practical use case of this scenario is the implementation of voice and data networks in a particular coverage area. This can be implemented using option 3x because the lightweight voice (Voice over LTE (VoLTE)) traffic can leverage 4G eNB and the heavy-weight data service is provided by the 5G NR. In this section, we were introduced to the basic concept of NSA networks and the terms related to it. In the next section, we will see the various options for NSA and Standalone (SA) networks. A deep dive into NSA networks In this section, we will dive deeper into the topic and also see the types of networks that can be deployed, which translates to the various options that a service provider may have if they introduce 5G in their network. This also highlights another aspect of the great flexibility in dep