| Protocol | rrc | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 38.331 | Spec Section | 5.3.5, 6.2.2 |
| Direction | gNB to UE | Message Type | Control-plane signaling |
| Full message name | 5G NR - RRC Reconfiguration |
|---|---|
| Protocol | RRC |
| Technology | 5G |
| Direction | gNB to UE |
| Interface | Uu |
| Signaling bearer / channel | SRB1 / DL-DCCH |
| Typical trigger | Bearer setup, measurement updates, mobility execution, or secondary-cell configuration changes while the UE is already connected. |
| Main purpose | Update the UE with new radio parameters, DRBs, measurement objects, mobility rules, or secondary cell changes. |
| Main specification | 3GPP TS 38.331, 5.3.5, 6.2.2 |
| Release added | See specification history |
| Procedures where used | PDU Session Establishment, Measurement Reporting, Connected Mode Handover |
| Related timers | T304 in handover-related cases |
Reconfigures the UE radio connection after setup, including bearers, measurements, and mobility.
Update the UE with new radio parameters, DRBs, measurement objects, mobility rules, or secondary cell changes.
RRCReconfiguration is the main message the gNB uses to change a UE's radio behavior after the connection is already up.
Call flow position: Connected-mode radio update used to add or modify radio resources after the initial setup phase.
Typical state: UE is already in RRC_CONNECTED.
Preconditions:
Next likely message: RRCReconfigurationComplete
Call flow position: Mobility-related configuration step that can prepare or execute connected mobility.
Typical state: UE is in connected mode with measurement and mobility handling active.
Preconditions:
Next likely message: RRCReconfigurationComplete
Previous message(s): Connected-state RRC/NAS procedure context
Next message(s): RRCReconfigurationComplete
Security context: Typically delivered after AS security is active, so integrity and ciphering context should be considered during trace analysis.
RRCReconfiguration ::= SEQUENCE {
rrc-TransactionIdentifier RRC-TransactionIdentifier,
criticalExtensions CHOICE {
rrcReconfiguration RRCReconfiguration-IEs,
criticalExtensionsFuture SEQUENCE {}
}
}
RRCReconfiguration-IEs ::= SEQUENCE {
radioBearerConfig RadioBearerConfig OPTIONAL,
secondaryCellGroup OCTET STRING OPTIONAL,
measConfig MeasConfig OPTIONAL,
lateNonCriticalExtension OCTET STRING OPTIONAL,
nonCriticalExtension SEQUENCE {} OPTIONAL
}
In practice, the important question is which optional configuration blocks are populated and whether they match the current procedure, UE capabilities, and target radio behavior.
DL-DCCH-Message ::= {
message c1 : rrcReconfiguration : {
rrc-TransactionIdentifier 1,
criticalExtensions rrcReconfiguration : {
measConfig {
measObjectToAddModList {
{
measObjectId 1,
measObjectNR {
ssbFrequency 631968,
ssbSubcarrierSpacing kHz30
}
}
}
}
}
}
}
| IE | Required | Description |
|---|---|---|
radioBearerConfig | Optional | Adds, modifies, or releases SRBs and DRBs. |
measConfig | Optional | Configures measurement objects, report rules, and gap settings. |
mobilityControlInfo | Optional | Carries target cell details when the reconfiguration is used for handover. |
secondaryCellGroup | Optional | Delivers secondary cell configuration for advanced radio features. |
radioBearerConfigAdds, modifies, or releases SRBs and DRBs.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
measConfigConfigures measurement objects, report rules, and gap settings.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
mobilityControlInfoCarries target cell details when the reconfiguration is used for handover.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
secondaryCellGroupDelivers secondary cell configuration for advanced radio features.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Likely cause: Unsupported or inconsistent configuration in one of the optional blocks.
What to inspect: Decode each populated section and compare with UE capability and serving-cell context.
Next step: Compare with a known-good reconfiguration trace or simplify the configuration to isolate the failure.
Likely cause: The mobility-related configuration may not match target-cell preparation.
What to inspect: Check mobilityControlInfo, target frequency, PCI, and related measurement assumptions.
Next step: Validate target cell preparation and neighbor configuration.
RRC Setup creates the first connected-mode control configuration, while RRC Reconfiguration handles later connected-state changes such as DRBs, measurements, mobility, and secondary-cell updates.
No. It is a general-purpose connected-state update message and is also used for bearer setup and measurements.
Because the gNB uses this message to arm the UE with the measurement logic needed for mobility decisions.
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.