Main protocols of the 5G Core network

Services provided by 5G NFs

  • The transport layer protocol is TCP
  • Transport layer security protection is assisted with TLS
  • Application layer protocol is HTTP/2
  • The serialization protocol is JSON
  • The openAPI 3.0.0 is adopted as the interface definition language.

Service based interface protocol stack

Application

HTTP/2

TLS

TCP

IP

L2


Protocols

To decrease the coupling between customer and servers, the RESTful framework is applied for the APIs design as follows :

The REST-style service operations implement the L2 of the Richardson maturity model.

Level 3 (HATEOAS) of the Richardson maturity model is optional. The SBI’s also assist procedures for overload control and message prioritisation. PFCP is used over the N4 interface for the separation of CP and UP in the 5GC. GTPv2 is utilized over the N26 interface for mobility between EPC and 5GC.

Functional split between radio and core

The gNB functions

  • Functions for radio resource management
  • IP header compression
  • Routing of user plane data towards UPFs
  • Routing of control plane information towards AMF
  • Connection setup and release
  • Scheduling and transmission of paging messages
  • Scheduling and transmission of system broadcast information

The AMF functions

  • The NAS signalling termination
  • The NAS signalling safety
  • The AS security control
  • Registration area management
  • Assist of intra-system and inter-system mobility
  • Access authentication
  • SMF selection

The UPF functions

Traffic usage reporting

Uplink classifier to assist routing traffic flows to a data network. Branching point to assist multi-homed PDU sessions.QoS handling for user plane e.g packet filtering, gating, UL/DL rate enforcement.

The SMF functions

  • Session management
  • UE IP address allocation & management
  • Selection and control of UP functions
  • Configure traffic steering at UPF to route traffic to the proper destination.
  • Control part of policy enforcement and QoS.
  • DL data notification

Functional split between NG-RAN & 5GC

NSA radio protocol architecture

Control plane

In EN-DC, the UE has a single RRC state, based on MN RRC and a single C-plane connection towards the CN.

CP architecture for EN-DC

User plane

In EN-DC , from a UE perspective, three bearer types exist : MCG bearer, SCG bearer and split bearer. For EN-DC, the network can configure either E-UTRA PDCP or NRPDCP for MCG bearers while NR PDCP is utilized for SCG and split bearers.

Architecture

SA radio protocol Architecture

Control plane protocol stack

Control plane

  • PDCP, RLC and MAC
  • RRC
  • NAS CP

User plane protocol stack

User plane

  • SDAP
  • PDCP
  • RLC and MAC