5G Paging Procedure Explained

Introduction

In 5G networks, the Paging Procedure is used by the network to locate a User Equipment (UE) when the device is in RRC Idle or RRC Inactive state.

When the network needs to deliver data or signaling messages to the UE, it sends a paging message to the base stations in the UE’s Tracking Area.

This ensures the UE can re-establish a connection and receive incoming services.

The paging procedure is defined by the 3rd Generation Partnership Project in:

• 3GPP TS 23.502 - 5G System Procedures
• 3GPP TS 38.300 - NR Architecture
• 3GPP TS 38.331 - RRC Protocol

Why Paging Is Needed

When a UE is idle or inactive, it does not maintain an active connection with the base station.

To deliver incoming traffic or signaling, the network must notify the UE through paging.

Typical scenarios include:

Network Elements Involved

UE (User Equipment)

Monitors paging messages periodically when in RRC Idle or RRC Inactive state.

gNB (Next Generation NodeB)

Broadcasts the paging message over the radio interface.

AMF (Access and Mobility Management Function)

Initiates the paging procedure when the network needs to contact the UE.

Interfaces Used

Paging Procedure Call Flow

Below is the simplified signaling sequence.

UE            gNB            AMF
 |             |              |
 |             |<--Paging-----|
 |<--Paging----|              |
 |             |              |
 |--RRC Resume / Service Request-->|

After receiving the paging message, the UE initiates a connection resume or service request procedure.

Step-by-Step Explanation

Step 1: Downlink Data Arrival

The core network receives data or signaling intended for the UE.

Since the UE is idle or inactive, the AMF initiates the paging procedure.

Important parameters to check

Engineers should verify:

• UE registration state
• UE tracking area list
• paging identity

Step 2: Paging Message Sent to gNB

The AMF sends a Paging message to all gNBs within the UE’s Tracking Area.

This message includes:

• UE paging identity
• paging cause
• tracking area information

Important parameters to check

Check:

• paging identity (5G-S-TMSI)
• paging cause
• tracking area configuration

Step 3: gNB Broadcasts Paging

Each gNB broadcasts the paging message over the radio interface.

The message is transmitted through the Paging Channel (PCH).

Important parameters to check

Verify:

• paging frame configuration
• DRX paging cycle
• paging occasions

Step 4: UE Detects Paging

The UE periodically wakes up according to its paging DRX cycle and monitors paging messages.

If the paging identity matches the UE, the device responds.

Important parameters to check

Check:

• UE paging cycle
• DRX configuration
• UE identity matching

Step 5: UE Responds to Paging

After detecting the paging message, the UE initiates one of the following procedures:

• RRC Resume (if in RRC Inactive state)
• Service Request (if in RRC Idle state)

Paging Channels in 5G

UE Paging Behavior

Troubleshooting Paging Issues

UE Not Responding to Paging

Possible causes:

• incorrect paging configuration
• UE not monitoring correct paging cycle
• radio coverage issues

Paging Delay

Possible reasons:

• large tracking area list
• high network load
• paging DRX cycle too long

Paging Message Not Received

Possible causes:

• incorrect cell configuration
• UE synchronization issues
• signaling errors

Key Messages in Paging Procedure

Relevant 3GPP Specifications

The Paging Procedure is defined by the 3rd Generation Partnership Project in:

• 3GPP TS 23.502 - 5G System Procedures
• 3GPP TS 38.300 - NR Architecture
• 3GPP TS 38.331 - RRC Protocol

Summary

The 5G Paging Procedure enables the network to locate and notify a UE when it is in idle or inactive state.

The process includes:

1. AMF initiating paging
2. gNB broadcasting paging messages
3. UE detecting the paging message
4. UE re-establishing connection through RRC Resume or Service Request

Paging ensures that incoming data and signaling can reach devices efficiently while minimizing radio resource usage.