LTE RRC MCG Failure Information r16

Message Fact Sheet

Protocol	lte-rrc	Network	lte
Spec	3GPP TS 36.331	Spec Section	5.6, 6.2.2
Direction	UE -> eNodeB	Message Type	Failure Reporting

Full message name	LTE RRC MCG Failure Information r16
Protocol	LTE-RRC
Technology	LTE
Direction	UE -> eNodeB
Interface	Uu
Signaling bearer / channel	SRB1 / UL-DCCH
Typical trigger	Triggered when the UE detects failure affecting the master cell group branch.
Main purpose	Lets the network know that the master cell group branch failed so recovery, investigation, or release handling can continue with the right failure focus.
Main specification	3GPP TS 36.331, 5.6, 6.2.2
Release added	Release 16
Procedures where used	MCG failure reporting, Dual connectivity recovery

What is LTE RRC MCG Failure Information r16 in simple terms?

Uplink LTE RRC message used by the UE to report master cell group failure information.

Lets the network know that the master cell group branch failed so recovery, investigation, or release handling can continue with the right failure focus.

Why this message matters

MCG Failure Information r16 tells the network that the master cell group failed.

Where this message appears in the call flow

MCG failure reporting

LTE flow showing MCG Failure Information r16 after master cell group failure — When the master cell group fails, the UE reports it so the network can move into the correct master-side recovery branch.

Call flow position: UE report sent when the master cell group is judged to have failed.

Typical state: The network can distinguish master-side failure from secondary-side failure and apply the right recovery path.

Preconditions:

An MCG context exists.
The UE detected an MCG-related failure.

Next likely message: Recovery handling or release

Master-side recovery investigation

LTE flow showing MCG Failure Information r16 before later master-side recovery handling — The message helps separate MCG-side failure handling from SCG-side failure recovery and narrows the later troubleshooting branch.

Call flow position: UE report sent before the network decides how to recover from the master-side failure.

Typical state: The message marks the failure as centered on the master branch instead of only the secondary branch.

Preconditions:

The failing condition is tied to the master cell group.

Next likely message: Later master-side recovery or reconfiguration

Call flow position

Previous message(s): Connected dual-connectivity continuation

Next message(s): Recovery handling, RRCConnectionReconfiguration, RRCConnectionRelease

Message direction and transport

Sender and receiver: UE -> eNodeB

Interface: Uu

Domain: Access-side radio control and master-cell failure reporting

Signaling bearer: SRB1

Logical channel: UL-DCCH

Transport / encapsulation: Protected LTE RRC signaling in connected mode

Security context: Sent as protected connected-mode signaling.

Message Structure Overview

MCGFailureInformation-r16 is a master-side failure report used to narrow the failure domain.

ASN.1 for LTE RRC MCG Failure Information r16

MCGFailureInformation-r16 ::= SEQUENCE {
  criticalExtensions CHOICE {
    c1 CHOICE {
      mcgFailureInformation-r16 MCGFailureInformation-r16-IEs,
      spare3 NULL,
      spare2 NULL,
      spare1 NULL
    },
    criticalExtensionsFuture SEQUENCE {}
  }
}

How to read this ASN.1

Read this message mainly to distinguish master-cell failure from SCG-side failure.

LTE RRC MCG Failure Information r16 - Example Dump

UL-DCCH-Message
  message c1 : mcgFailureInformation-r16 : {
    criticalExtensions c1 : mcgFailureInformation-r16 : {
      failureType-r16 t310-Expiry
    }
  }

How to read this dump

The first practical read is the failure domain: master-side rather than secondary-side.

Important Information Elements

IE	Required	Description
`failureType-r16`	Yes	Indicates the reported master-cell-group failure type.

Detailed field explanation

`failureType-r16`

Indicates the reported master-cell-group failure type.

Presence: Required

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.

What to check in logs and traces

Check whether the failing branch is the master cell group.
Inspect the reported failure type.
Compare the message with any SCG-side failure reports in the same trace.

Common Issues and Troubleshooting

The main connected branch looks unstable, not just the secondary branch.

Likely cause: The UE may have reported MCG Failure Information r16 for a master-side problem.

What to inspect: Check the message timing, failure type, and the later recovery or release branch.

Next step: Separate master-side failure handling from SCG-specific failure analysis.

FAQ

What is MCG Failure Information r16 in LTE?

It is the uplink LTE RRC message the UE uses to report master cell group failure information.

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.