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Demystifying Control Plane Protocols in 5G Networks

Demystifying Control Plane Protocols in 5G Networks
Demystifying Control Plane Protocols in 5G Networks


In the intricate landscape of 5G networks, the control plane plays a pivotal role in orchestrating the signaling between various network entities. This article delves into the technical intricacies of control plane protocols specified by 3GPP, shedding light on their functions, message encapsulation, and interfaces.

Control Plane Protocol Stack In 5G Networks

At the heart of the control plane protocol stack lies the Radio Resource Control (RRC) layer, responsible for signaling between the User Equipment (UE) and the Base Station. RRC messages traverse through Signaling Radio Bearers (SRBs), utilizing logical channels like the Common Control Channel (CCCH) and Dedicated Control Channel (DCCH).

PDCP, RLC, MAC, and Layer I

  • Packet Data Convergence Protocol (PDCP): Ensures ciphering and integrity protection.

  • Radio Link Control (RLC): Offers transmission modes, including Transparent and Acknowledged, ensuring reliable data transfer.

  • Medium Access Control (MAC): Prioritizes and multiplexes logical channel data, supporting Hybrid Automatic Repeat Request (HARQ) for fast re-transmissions.

  • Layer I: Handles physical layer processing, including channel coding, interleaving, and modulation.

Interfaces and Protocol Stacks

Various interfaces like Xn, F1, FI, and NG facilitate control plane data transfer between Base Stations and network entities like Centralized Units (CU) and User Plane (UP). These interfaces utilize specific protocol stacks tailored for efficient signaling.

Non-Access Stratum (NAS) Control Plane

The NAS control plane protocol stack handles signaling between the UE and the Access and Mobility Management Function (AMF) or Session Management Function (SMF). Utilizing NGAP over SCTP for message encapsulation, NAS messages traverse the IP layer, facilitating mobility and session management.

NAS Message Categories

NAS messages are categorized into Mobility Management and Session Management, catering to various network procedures like registration, authentication, session establishment, and release.

Message Encapsulation and Transfer

RRC messages, UL Information Transfer, and DL Information Transfer encapsulate NAS messages for transmission between the UE and Base Station. Similarly, NGAP messages facilitate NAS message transfer between the Base Station and AMF/SMF.


Understanding the intricate web of control plane protocols in 5G networks is crucial for network architects and engineers. By dissecting the protocol stack, message categories, and interfaces, this article provides a comprehensive overview of the control plane's functioning in modern telecommunications infrastructure.


The technical content of this article is based on specifications provided by 3GPP.

Here are the reference links to the relevant 3GPP specifications mentioned in the article:

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