RRC 5G gNB -> UE 3GPP TS 38.331

5G NR - Paging

Paging is the NR RRC message used by the network to notify an idle-mode or inactive-mode UE that downlink signaling or service activity requires the UE's attention.

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.3.1, 6.3.2
Direction	gNB -> UE	Message Type	Paging / Mobility Management

Full message name	5G NR - Paging
Protocol	RRC
Technology	5G
Direction	gNB -> UE
Interface	Uu
Signaling bearer / channel	Broadcast paging transport / PCCH
Typical trigger	Triggered when the network needs to reach a UE in RRC_IDLE or RRC_INACTIVE for mobile-terminated data, NAS signaling, system information change notification, or warning messages.
Main purpose	Alerts the UE to resume monitoring and re-enter active signaling when the core network or radio network needs to deliver data, NAS signaling, public warning information, or mobility-related paging.
Main specification	3GPP TS 38.331, 5.3.1, 6.3.2
Release added	Release 15
Procedures where used	5G Paging Procedure, Idle Mode UE Reachability, Inactive Mode UE Reachability, System Information Change Notification
Related timers	UE paging monitoring behavior follows the configured paging cycle and DRX-related broadcast settings, Paging response timing is usually analyzed together with the resume or setup procedure rather than a dedicated timer inside Paging itself
Related cause values	Paging does not carry reject causes, Failures are usually inferred from missed paging occasions, wrong UE identity matching, bad DRX configuration, or a failed resume or setup after paging

What is Paging in simple terms?

Paging is the NR RRC message used by the network to notify an idle-mode or inactive-mode UE that downlink signaling or service activity requires the UE's attention.

Alerts the UE to resume monitoring and re-enter active signaling when the core network or radio network needs to deliver data, NAS signaling, public warning information, or mobility-related paging.

Why this message matters

Paging is the 5G NR RRC message the network uses to tell an idle or inactive UE that it needs to wake up and continue signaling.

Where this message appears in the call flow

Idle Mode Paging

Call flow position: Used when the UE is camped in RRC_IDLE and the network needs to reach it.

Typical state: UE is not connected and is monitoring paging occasions according to broadcast configuration.

Preconditions:

The UE has valid SIB1 and paging configuration.
The UE is registered and reachable in the tracking area.
The network has data or signaling for the UE.

Next likely message: RRC Setup Request or NAS signaling continuation through access

Inactive Mode Paging

Call flow position: Used when the UE is in RRC_INACTIVE and the network needs to trigger resume behavior.

Typical state: UE has inactive context and monitors paging according to the configured cycle.

Preconditions:

The UE holds a valid inactive context.
Paging identity and radio context remain valid.

Next likely message: RRC Resume Request

System Information Change / Warning Notification

Call flow position: Used when paging is leveraged to notify UEs about SI changes or warning-related action.

Typical state: UE is idle or inactive and must react to a cell-wide notification.

Preconditions:

The UE is monitoring the relevant paging occasions.

Next likely message: System information reacquisition or warning-related handling

Call flow position

Previous message(s): System Information Block 1 (SIB1), RRC Release, RRC Inactive state monitoring

Next message(s): RRC Resume Request, RRC Setup Request, 5G Paging Procedure

Message direction and transport

Sender and receiver: gNB -> UE

Interface: Uu

Domain: Access-side radio control for idle and inactive UE reachability

Signaling bearer: Broadcast paging transport

Logical channel: PCCH

Transport / encapsulation: RRC paging message carried on PCCH and scheduled on PDSCH using P-RNTI

Security context: Paging is not a dedicated SRB message. It is broadcast to the relevant paging occasion and interpreted using UE identity and paging context.

Message Structure Overview

Paging is compact and operationally focused. Its main job is to wake the correct UE or notify it that it must take the next step.
For engineering work, the key questions are whether the page was sent in the expected occasion, whether the UE identity matches, and whether the UE responded with resume or new access.
Paging is rarely debugged in isolation. It should be correlated with SIB1 paging configuration, UE state, core-network trigger, and the following resume or setup procedure.

ASN.1 for 5G NR - Paging

PCCH-Message ::= SEQUENCE {
  message CHOICE {
    c1 CHOICE {
      paging Paging,
      ...
    },
    ...
  }
}

Paging ::= SEQUENCE {
  pagingRecordList        SEQUENCE (SIZE (1..maxNrofPageRec)) OF PagingRecord,
  systemInfoModification  ENUMERATED {true} OPTIONAL,
  etws-Indication         ENUMERATED {true} OPTIONAL,
  ...
}

PagingRecord ::= SEQUENCE {
  ue-Identity             PagingUE-Identity,
  ...
}

How to read this ASN.1

In practice, engineers usually care less about the full ASN.1 tree and more about the pagingRecordList, the UE identity used for matching, and any system-information-modification indication.

Decoded Message Dump

PCCH-Message
  message: c1
    paging
      pagingRecordList
        [0]
          ue-Identity
            ng-5G-S-TMSI: 0x4A72C311
      systemInfoModification: absent

How to read this dump

The first practical check is whether the paged UE identity matches the UE under investigation.
If the UE does not react, confirm that the page landed in the correct paging occasion and that the UE was actually monitoring it.
When system information changes are involved, systemInfoModification can explain why the UE reacquires broadcast information instead of immediately resuming user traffic.

Important Information Elements

IE	Required	Description
`pagingRecordList`	Yes	Contains one or more paging records identifying the UE or UEs being paged.
`ue-Identity`	Yes	The identity used by the UE to determine whether the page is intended for it.
`cn-UE-PagingIdentity / ng-5G-S-TMSI`	Optional	Commonly inspected identity information used to correlate the page with NAS and core-network context.
`accessType / paging cause context`	Optional	Helps explain whether the paging is linked to service activity, signaling reachability, or warning-related behavior.
`systemInfoModification`	Optional	Indicates that the UE should reacquire system information because the broadcast information changed.

Detailed field explanation

`pagingRecordList`

Contains one or more paging records identifying the UE or UEs being paged.

Presence: Required

`ue-Identity`

The identity used by the UE to determine whether the page is intended for it.

Presence: Required

`cn-UE-PagingIdentity / ng-5G-S-TMSI`

Commonly inspected identity information used to correlate the page with NAS and core-network context.

Presence: Optional

`accessType / paging cause context`

Helps explain whether the paging is linked to service activity, signaling reachability, or warning-related behavior.

Presence: Optional

`systemInfoModification`

Indicates that the UE should reacquire system information because the broadcast information changed.

Presence: Optional

What to check in logs and traces

Confirm the UE is really in RRC_IDLE or RRC_INACTIVE when the page is sent.
Check SIB1 paging-related configuration such as paging cycle assumptions and monitoring occasions.
Verify that the P-RNTI scheduling and paging occasion align with the expected UE monitoring window.
Inspect the UE identity in pagingRecordList and confirm it matches the target UE.
Correlate the page with the following UE behavior: RRC Resume Request, RRC Setup Request, or no response.
If the UE misses the page, compare radio conditions, DRX behavior, identity mapping, and core-network trigger timing.

Common Issues and Troubleshooting

The network sends paging but the UE does not respond.

Likely cause: The UE may have missed the paging occasion, the identity may not match, or radio conditions may be too poor.

What to inspect: Check pagingRecordList, paging occasion timing, P-RNTI scheduling, and UE idle or inactive monitoring behavior.

Next step: Correlate the page with SIB1 configuration and confirm whether the UE should have been awake in that paging occasion.

The UE receives paging but resume fails.

Likely cause: Paging itself may be correct, but the following resume or access attempt fails.

What to inspect: Check whether the UE sent RRC Resume Request or RRC Setup Request and what failed next.

Next step: Move from the Paging analysis into the resume, setup, and NAS traces.

Paging behavior is inconsistent across cells.

Likely cause: Broadcast paging configuration or tracking-area context may differ across cells.

What to inspect: Compare SIB1 paging configuration, cell timing, and UE reachability context.

Next step: Validate whether the paging issue is cell-specific, UE-specific, or core-trigger related.

Detailed explanation

5G NR - Paging Explained

Paging is the 5G NR RRC message the network uses to reach a UE that is in RRC_IDLE or RRC_INACTIVE. It tells the UE that something important happened and that it should wake up, react, and continue the next signaling step.

For beginners, the simple meaning is: Paging is how the network gets an idle or inactive UE’s attention.
For experienced engineers, Paging is the radio-side reachability signal that must be correlated with SIB1 paging configuration, UE identity, core trigger timing, and the next resume or setup step.

What is Paging in simple terms?

Paging is a broadcast-style RRC message sent on the PCCH. The message itself is short. It does not carry full session information. Its job is to tell the correct UE that it has been paged and needs to respond.

In practical terms, Paging helps answer:

did the network try to reach the UE?
did the correct UE identity appear in the paging record?
did the UE respond with resume or fresh access?

Why this message matters

Paging matters because many service problems begin here:

mobile-terminated data does not arrive
the UE does not resume from inactive mode
the network pages repeatedly with no response
a paging issue gets confused with a later resume or setup failure

Where this message appears in the call flow

A simplified paging path is:

UE is in RRC_IDLE or RRC_INACTIVE.
The network has data or signaling for the UE.
The gNB sends Paging on the UE’s paging occasion.
The UE responds with RRC Resume Request or starts fresh access.

Mini sequence:

UE                          gNB / AMF
|                            |
|   idle / inactive          |
|<-- Paging -----------------|
|--- RRC Resume Request ---->|
|   or                       |
|--- RRC Setup Request ----->|

So Paging sits between reachability trigger and resume or setup behavior.

Message direction and transport

sender: gNB
receiver: target UE within the paging occasion
interface: Uu
signaling channel: PCCH
radio scheduling context: scheduled with P-RNTI
security context: not a dedicated SRB message

Important Information Elements

IE	Why it matters
`pagingRecordList`	Main list of paged UEs.
`ue-Identity`	Lets the UE determine whether the page is for it.
`ng-5G-S-TMSI` or related paging identity	Key field to correlate with core and NAS context.
`systemInfoModification`	Explains SI-change notification behavior.

Example message dump

PCCH-Message
  message: c1
    paging
      pagingRecordList
        [0]
          ue-Identity
            ng-5G-S-TMSI: 0x4A72C311
      systemInfoModification: absent

FAQ

What is Paging in 5G NR?

Paging is the NR RRC message used by the network to notify an idle or inactive UE that it needs to wake up for signaling, data delivery, or a broadcast-related action.

Who sends the 5G Paging message?

The gNB sends Paging over the radio interface to UEs monitoring the relevant paging occasions.

On which channel is Paging sent?

Paging is carried on PCCH and scheduled using the paging radio network temporary identifier, or P-RNTI.

What comes after Paging?

That depends on UE state. In inactive mode it often leads to RRC Resume Request. In idle mode it may lead to new access and RRC Setup Request.

Why would a UE miss Paging?

Common reasons include wrong paging occasion timing, poor radio conditions, DRX or monitoring issues, or identity mismatch.

Does Paging carry reject causes?

No. Paging does not carry reject causes. Engineers infer problems from the absence of response or the failure of the following resume or setup procedure.

Summary

Paging is the NR RRC message used by the network to notify an idle-mode or inactive-mode UE that downlink signaling or service activity requires the UE's attention.

Advanced Engineer Notes

Paging analysis is strongest when radio, core, and UE-state context are checked together rather than treating the page as only a PCCH decode.
A correct page with a bad follow-on resume should not be diagnosed as a paging failure.
In many real cases, the root cause is not the presence of Paging itself but identity mismatch, wrong paging occasion assumptions, or poor correlation between RAN and core reachability context.

LTE / 5G / Variant Comparison

Paging in RRC_IDLE versus RRC_INACTIVE

In idle mode, Paging often leads into fresh access and setup. In inactive mode, Paging more often leads into RRC Resume Request using the stored inactive context.

Paging versus dedicated RRC messages

Paging is a reachability notification on PCCH. It is not a dedicated SRB-based control message like RRC Setup, RRC Reconfiguration, or Security Mode Command.

Related message pages

Related Procedures

Related Tools

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.