At the early stage of 5G, 5G base stations (referred to as gNodeBs) defined in 3GPP specifications can be connected to a 4G core network (referred to as EPC). At the maturity stage of 5G, the EPC connected to 5G base stations is evolved to a 5G core network (abbreviated as 5GC and referred to as NGC in some protocols). Ultimately, 5G base stations can be directly connected to the 5GC, supporting all use cases of 5G. During network evolution, 4G base stations (referred to as eNodeBs) can be upgraded to eLTE base stations (referred to as eLTE eNBs), allowing connections to the 5GC. This prolongs the lifespan of and protects investments in eNodeBs.
Whether an architecture belongs to NSA networking or SA networking depends on the quantity of radio access technologies (RATs) that it involves. An architecture involving two RATs belongs to NSA networking, while an architecture involving only one RAT belongs to SA networking. NSA networking can be deployed using either of the following configurations, which differ in signaling anchors:
NSA NR: The gNodeB requires an eNodeB or eLTE eNB as the signaling anchor (also referred to as the control plane anchor) for 5G services.
NSA E-UTRA: The eLTE eNB requires a gNodeB as the signaling anchor for 4G services.
The EPC is connected to a radio access network (RAN) through S1 interfaces. It has no direct connection over the air interface, and therefore cannot detect in real time the radio condition changes on the RAN side. As a result, the EPC cannot dynamically adjust the amount of service data to be distributed based on the real-time radio condition changes. UEs are highly mobile. When they are moving, the radio condition continuously changes. However, the EPC cannot detect these changes in real time. It distributes 5G service data to the eNodeB and gNodeB based on the preset configurations (such as 4G and 5G cell capabilities). This causes user experience to deteriorate in the following two scenarios: When the 5G radio signal quality is good, the EPC does not increase the amount of data distributed to the gNodeB; when the 5G radio signal quality is poor, the EPC does not reduce the amount of data distributed to the gNodeB, causing a large number of packets to be lost.
