Understanding 5G Network Architecture: NR, RAN, and Protocol Stack

This document outlines the architecture of 5G networks, including its key elements, and the 5G NR (New Radio) architecture as per the 3GPP document published in December 2017.

Generic 5G Network Architecture

Figure 1: 5G network architecture

The generic 5G network architecture leverages a flat IP concept, enabling diverse Radio Access Networks (RANs) to utilize a single Nanocore for communication.

Supported RANs include: GSM, GPRS/EDGE, UMTS, LTE, LTE-Advanced, WiMAX, WiFi, CDMA2000,EV-DO,CDMA One, IS-95.

The flat IP architecture uses symbolic names to identify devices, unlike hierarchical architectures that rely on IP addresses. This approach reduces the number of network elements in the data path, leading to cost savings and minimized latency.

A 5G aggregator consolidates traffic from all RANs and routes it to the gateway, typically located at the BSC/RNC.

5G mobile terminals are equipped with different radio interfaces for each Radio Access Technology (RAT) to support various spectrum access and wireless technologies.

Another vital component is the 5G nanocore, which incorporates nanotechnology, cloud computing, and an All-IP architecture. Cloud computing uses the internet and remote servers to manage user data and applications, allowing users to access applications without installation and retrieve files from any computer with internet access.

Global content service providers support applications such as Search engines, Education, Public portals, Private portals, Government services, Medical services, Transportation and Banking.

5G NR Architecture (3GPP Standard)

The following figure-2 shows the overall architecture of 5G NR as defined in 3GPP TS 38.300 specification.

As shown, the gNB node provides NR user plane and control plane protocol terminations towards the UE (i.e., 5G terminal device like smartphone, tablet, laptop, etc.) and is connected via the NG interface to the 5GC. The ng-eNB node provides E-UTRA (i.e., LTE) user plane and control plane protocol terminations towards the UE and connects to the 5GC via the NG interface. AMF stands for Access and Mobility Management Function, and UPF stands for User Plane Function.

3GPP TS 38.401 describes 5G NR user and control planes and the RAN architecture, including interfaces (NG, Xn, and F1) and their interaction with the radio interface (Uu).

5G smartphones interact with 5G-RAN over the Uu radio interface, while 5G RAN interacts with the 5GC (5G Core Network).

The protocols over Uu and NG interfaces are categorized into user plane and control plane protocols. User plane protocols implement the actual PDU Session service, carrying user data through the access stratum. Control plane protocols manage PDU Sessions and connections between the UE and the network, covering service requests, transmission resource control, and handover procedures. The mechanism for transparent transfer of NAS messages is also included.

The NG-RAN consists of a set of gNBs connected to the 5GC through the NG interface. A gNB can support FDD, TDD, or dual-mode operation. gNBs can be interconnected via the Xn interface. A gNB may consist of a gNB-CU and one or more gNB-DUs, connected via the F1 interface. NG, Xn, and F1 are logical interfaces.

The 5GC (5G Core) network architecture is highly flexible, modular, and scalable. It offers numerous functions, including network slicing, to meet diverse customer requirements. It incorporates distributed cloud, NFV (Network Functions Virtualization), and SDN (Software Defined Networking).

5G Protocol Stack

Figure 5: 5G protocol stack

The 5G protocol stack consists of the following layers:

• OWA Layer (Open Wireless Architecture): Functions as the physical and data link layers of the OSI model.
• Network Layer: Routes data from the source IP device to the destination IP device/system, divided into lower and upper network layers.
• Open Transport Layer: Combines the functionality of the transport and session layers.
• Application Layer: Marks data in the required format, encrypts and decrypts data, and selects the best wireless connection for a given service.

5G NR Radio Protocol Architecture

Figure 6: 5G NR radio protocol stack

The radio protocol architecture of 5G NR (New Radio) as defined in 3GPP TS 38.300. Protocol layers at UE and gNB side are shown in the figure for both user plane and control plane functionalities.