5G Core Network Functions

As a follow up from our previous post on 5G Core Network (5GC) and system architecture, today I’d like to touch upon the 5G network functions (NFs) that are related to core network. As we’ll see, some of them look very similar to the corresponding functions in the previous generations’ core networks (CN). This of course is not surprising, as the network always has to carry out some basic functions such as: communicate with the UE, store its subscription and credentials, allow access to external networks & services, provide security and manage the network access and mobility. However, we will also see some new functions, that were not present before, which are needed to enable the new network paradigms like slicing and service-based networking.

Service-Based Architecture (SBA)

To describe the CN functions themselves, let’s firstly look at the system architecture from 3GPP SA2 on the following figure.

Figure 1: 5G System: Service-based architecture (SBA) [1]

We can see that part of this architecture, looks like good old LTE/3G with similar nodes and interfaces (lower part of the picture). However, the upper part of the figure (5GC Control Plane), has a “bus” and service-based interface exhibited by individual function. This creates a so-called Service Based Architecture (SBA), in which, one CP network function (e.g. SMF) allows any other authorized NFs to access its services. According to [1], the NFs within 5GC Control Plane, shall only use service-based-interfaces for their interactions.

Note: If you want to revisit the “good-old” reference point architecture representation for 5G, read our other blog on the general 5GC aspects: [5G CN Overview]. Yes, the 5G system architecture with reference points is there.

Network Functions (NFs)

Ok, let’s discuss a bit of the 5GC network functions themselves and what functionalities do they support (note that not all functionalities of individual functions are present). 

• Access and Mobility Management function (AMF) supports: Termination of NAS signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. (AMF has part of the MME functionality from EPC world)
• Session Management function (SMF) supports: session management (session establishment, modification, release), UE IP address allocation & management, DHCP functions, termination of NAS signalling related to session management, DL data notification, traffic steering configuration for UPF for proper traffic routing. (AMF has part of the MME and PGW functionality from EPC world)
• User plane function (UPF) supports: packet routing & forwarding, packet inspection, QoS handling, acts as external PDU session point of interconnect to Data Network (DN), and is an anchor point for intra- & inter-RAT mobility. (UPF has part of the SGW & PGW functionality from EPC world)

... to read the complete article that includes info about all other NFs (including, PCF, AUSF, UDM, AF, NEF, NRF and NSSF), and concluding remarks, visit our blog post @ 5G Core Network Functions.

To read the previous post on 5G Core Network Overview, see: 5G Core Network - A Short Overview

To check all our posts on 5G-related topics see: Grandmetric Blog - 5G



References/resources

[1] 3GPP TS 23.501 V15.0.0 (2017-12) System Architecture for the 5G System (Stage 2)