RRC 5G UE -> gNB 3GPP TS 38.331

5G NR - UL Information Transfer MRDC

UL Information Transfer MRDC is the UE-to-network NR RRC wrapper used to carry MR-DC-related information in the uplink direction.

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	6.2.2
Direction	UE -> gNB	Message Type	MR-DC Information Transfer

Full message name	5G NR - UL Information Transfer MRDC
Protocol	RRC
Technology	5G
Direction	UE -> gNB
Interface	Uu
Signaling bearer / channel	SRB1 / SRB3 / UL-DCCH
Typical trigger	Used when the UE needs to send MR-DC-related information to the network.
Main purpose	Lets the UE deliver MR-DC-related information back to the network through a dedicated RRC container.
Main specification	3GPP TS 38.331, 6.2.2
Release added	Release 15
Procedures where used	MR-DC Coordination, Dual Connectivity Context Handling

What is UL Information Transfer MRDC in simple terms?

UL Information Transfer MRDC is the UE-to-network NR RRC wrapper used to carry MR-DC-related information in the uplink direction.

Lets the UE deliver MR-DC-related information back to the network through a dedicated RRC container.

Why this message matters

UL Information Transfer MRDC is an uplink RRC wrapper for MR-DC information.

Where this message appears in the call flow

MR-DC Coordination

Call flow position: Sent when the UE transfers MR-DC-related information upward.

Typical state: UE is in connected mode with dual-connectivity context.

Preconditions:

MR-DC-related context or coordination is active.

Next likely message: Network-side MR-DC handling or reconfiguration

Call flow position

Previous message(s): 5g-dl-information-transfer-mrdc, RRC Reconfiguration

Next message(s): Network-side MR-DC handling

Message direction and transport

Sender and receiver: UE -> gNB

Interface: Uu

Domain: Access-side radio control with MR-DC context

Signaling bearer: SRB1 / SRB3

Logical channel: UL-DCCH

Transport / encapsulation: Dedicated protected RRC signaling

Security context: Sent as protected connected-mode signaling.

Message Structure Overview

The wrapper is simple; the inner MRDC content is what matters.

ASN.1 for 5G NR - UL Information Transfer MRDC

ULInformationTransferMRDC ::= SEQUENCE {
  dedicatedMRDC-Message OCTET STRING
}

How to read this ASN.1

Engineers usually inspect this message together with the downlink MRDC transfer and later SCG or dual-connectivity behavior.

5G NR - UL Information Transfer MRDC - Example Dump

UL-DCCH-Message
  message: ulInformationTransferMRDC
    dedicatedMRDC-Message: present

How to read this dump

Correlate the uplink MRDC payload with later network response.

Important Information Elements

IE	Required	Description
`dedicatedMRDC-Message`	Yes	Carries the actual MR-DC-related content in the uplink wrapper.

Detailed field explanation

`dedicatedMRDC-Message`

Carries the actual MR-DC-related content in the uplink wrapper.

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 UE transferred the expected MRDC content.
Compare it with downlink MRDC information transfer if both exist.

Common Issues and Troubleshooting

The network never reacts to MR-DC information the UE should have sent.

Likely cause: The uplink MRDC transfer may be absent or malformed.

What to inspect: Check the dedicated MRDC payload and the later response.

Next step: Correlate it with dual-connectivity state and SCG behavior.

FAQ

What does UL Information Transfer MRDC do?

It carries UE-to-network MR-DC-related information inside a dedicated RRC wrapper.

Related message pages

Related Procedures

5G RRC Reconfiguration

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.