NG-C (NG-Control-plane) is the acronym for a protocol used by NG-RAN nodes for signaling with the AMF (Advanced Mobile Front End). It’s the protocol of choice for communication between gNBs and the AMF. The protocol has several facets, but its most significant feature is its ability to support the separation of control and user planes.
It is a logical interface, meaning that it is based on a logical model of the entity it controls. It is also a point-to-point interface, meaning that it has a physical connection. The transport network layer is based on IP transport, and signaling PDUs are transported using the point-to-point transmission. The SCTP layer provides guaranteed delivery of application layer messages and is added on top of IP for reliable transport of signaling messages.
The NG-C protocol stack is shown in Figure 7.3.6-1. It contains the NG Control-plane Interface, the NG Session Setup, the NG User-plane Interface, the UE Positioning protocol, and the NG CP to UP transition. The NG Session Setup, for example, involves establishing a TNL address for gNB, and a UPGW address for gNB. Moreover, it establishes a link between the gNB and the UPGW.
The NG Session Setup is the most important of the NG-RAN-to-NG-C transitions. It establishes a TNL address for gNB, a UPGW address for gNB, and context for related resources in gNB. It is the first step in a process that will eventually lead to the successful transfer of NG traffic between gNBs. It is also the first step in a process that will ultimately lead to the gNB triggering an eLTE eNB. The UE Positioning protocol has a role to play in the transition, but it’s not the only reason for it’s existence. The NG-C also facilitates the exchange of configuration parameters between NG-RAN nodes and the AMF.
The NG-C interface has one other notable feature: It’s the NG CP to UP transition. This is a logical interface between gNB and UPGW, and the NG CP to NG-C transition is the most impressive. It’s a one-to-many relation between NG-RAN nodes and AMFs from different manufacturers.
What is 5G interface?
Unlike 4G, 5G networks will use dedicated technologies to support a wide range of industry applications. This will help the networks to reach a broader audience. However, not all applications will be suitable for 5G. In order to achieve this, the network infrastructure will need to evolve. A fundamental new capability of 5G is network slicing. These slices allow the network operator to divide resources and make efficient resource usage a reality.
There are three main types of network slices:
- Logical end-to-end network slices.
- Virtualized end-to-end network slices.
- Dedicated User Plane Functions (UPFs).
Each slice has a predetermined service level agreement and traffic characteristics. These slices are managed through a policy control framework.
The core architecture of 5G is based on the NG-RAN. The gNB is the main entity of the NG-RAN. The gNB provides NR user plane terminations and control plane terminations. The gNB may also be divided into gNB-central units and gNB-distributed units.
The gNB is connected to the 5G Core through a series of interfaces. The primary interface is the N4 interface, which acts as a conduit for PDU usage reporting to the SMF. The N4 interface also provides a path for traffic steering towards the UPF.
The User Plane Function transports IP data traffic between the UE and the external network. The UE also connects to the Evolved Packet Core. The User Plane Function provides an authentication and policy control framework and an access and mobility management function.
The Network Access and Mobility Function is the gatekeeper for the 5G Core. It accesses the UE and decides whether it can register with the network. The NSA mode allows devices to access the network and receive a downlink speed of 200 Mbps over 4G LTE.
The Nudm Service-Based Interface is a highly automated means of accomplishing several tasks. It manages subscription information and dynamic subscriber sessions. Among the other functions, it provides access to the 5GC Network Functions to obtain information about the UE.
The Network Access and Mobility Function is responsible for policing the network and making lawful intercepts. It will be used to establish connections to gNodeB.
5G Access and Mobility Management Function
NG-C (NG Core) and NG-RAN (NG Radio Access Network) are two network interfaces used by 5GC to establish the communication channel with UEs. In addition to establishing a connection, these interfaces also support separation of control plane and user plane.
NG-C interfaces are divided into Transport Network Layer and Radio Network Layer. The transport layer transmits packets between NG-RAN and 5GC. The radio network layer supports synchronization, signal quality measurement, and UE mobility management. The lower part of the figure is based on LTE and 3G, while the upper section is modeled after 4G.
The first Registration message sent by the UE represents the UE’s initial registration request. The UE indicates the registration mode, which must be compatible with 4G and 5G. Once the UE connects to the target gNB, the source node determines whether it needs a handover. It may then forward user plane traffic to the SMF or buffer it. In case the user plane traffic is not buffered, the SMF may forward it to the UPF.
The gNodeB is a brand-new macrocell installed in a Network Service Provider infrastructure. This node registers to the network and terminates the N1/N2 interfaces with the AMF. It may be configured to use a specific PCF. The gNodeB also provides NR user plane terminations. This node serves as the gateway between NG-RAN and the 5GC. It is also the intermediate point for all control messages sent by the UE to the gNodeB. If the UE requires information from the gNodeB, it can request the AMF. The gNodeB then selects the AMF if necessary.
The 5GC’s control plane functions have a different structure and separate separation of AMF and SMF. They interact in Service-Based Architecture. The SMF maintains a record of QoS Flows and converts PCC rules into QoS Profiles. It also ensures synchronization between CP functions.
The NGAP protocol is the standard protocol used for communication between NG-RAN nodes and the gNodeB. It also supports paging, warning message transmission, and AMF management. It is relevant for both 3GPP and non-3GPP networks.
