5G NGAP Downlink RAN Configuration Transfer Message

Message Fact Sheet

Protocol	ngap	Network	5g
Spec	3GPP TS 38.413	Spec Section	Downlink RAN Configuration Transfer message
Direction	AMF -> NG-RAN	Message Type	RAN Configuration Transfer

Full message name	Downlink RAN Configuration Transfer
Protocol	NGAP
Technology	5G
Direction	AMF -> NG-RAN
Interface	N2 / NG-C
Signaling bearer / channel	Non-UE-associated NGAP signaling / SCTP carried NGAP initiatingMessage
Typical trigger	The AMF has received RAN configuration transfer information, usually through Uplink RAN Configuration Transfer, and needs to deliver it toward the target NG-RAN node.
Main purpose	Delivers RAN configuration transfer information to NG-RAN, supports indirect RAN-to-RAN configuration exchange, carries source and target RAN context plus transparent configuration content, helps with SON or inter-node coordination, and is different from AMF Configuration Update or RAN Configuration Update.
Main specification	3GPP TS 38.413, Downlink RAN Configuration Transfer message
Release added	Release 15
Procedures where used	RAN Configuration Transfer, Inter-node RAN coordination, SON-related information transfer, Indirect RAN-to-RAN configuration exchange, RAN topology or neighbour coordination

What is Downlink RAN Configuration Transfer in simple terms?

Downlink RAN Configuration Transfer is the NGAP message sent by the AMF to the NG-RAN node to deliver RAN configuration transfer information received from another RAN node.

Delivers RAN configuration transfer information to NG-RAN, supports indirect RAN-to-RAN configuration exchange, carries source and target RAN context plus transparent configuration content, helps with SON or inter-node coordination, and is different from AMF Configuration Update or RAN Configuration Update.

Why this message matters

Downlink RAN Configuration Transfer is the AMF delivering a RAN-to-RAN configuration transfer container down to the target NG-RAN.

Where this message appears in the call flow

RAN Configuration Transfer

Call flow position: AMF sends this non-UE-associated initiatingMessage when RAN configuration transfer content must be delivered toward the target NG-RAN node.

Typical state: Target NG-RAN receives the SON Configuration Transfer container and processes the RAN-specific transfer content.

Preconditions:

A source NG-RAN has sent RAN configuration transfer information.
The AMF can identify the target NG-RAN node.
The transfer is intended to use the core-network path rather than a direct inter-RAN interface.

Next likely message: Target NG-RAN RAN-side handling

Indirect RAN-to-RAN coordination

5G NGAP diagram showing SON Configuration Transfer carrying source RAN identity, target RAN identity, and transparent transfer information toward the receiving NG-RAN — SON Configuration Transfer is the mandatory container for source, target, and transparent RAN-side content.

Call flow position: The message provides the AMF-to-NG-RAN delivery leg of an indirect RAN-to-RAN coordination path.

Typical state: The AMF relays the transfer container without treating it as its own configuration update.

Preconditions:

Source and target RAN context is present in the transfer container.
The transparent content is valid for the receiving NG-RAN.

Next likely message: Receiving NG-RAN interprets the transparent content

Transfer versus update distinction

5G NGAP comparison showing RAN Configuration Transfer as AMF-relayed RAN-to-RAN content and configuration update as local AMF or RAN configuration refresh — Use transfer for RAN-to-RAN coordination content; use update procedures for local AMF or RAN configuration refresh.

Call flow position: Use this transport-style procedure when AMF forwards RAN-originated transfer content, not when the AMF updates NG-RAN about AMF-side configuration.

Typical state: Trace analysis separates Downlink RAN Configuration Transfer from AMF Configuration Update and RAN Configuration Update.

Preconditions:

The payload belongs to a RAN-to-RAN transfer context.
The message is non-UE-associated and carries SON Configuration Transfer.

Next likely message: Correct RAN configuration transfer interpretation

Call flow position

Previous message(s): Uplink RAN Configuration Transfer, AMF received SON Configuration Transfer, Target NG-RAN needs the transferred information

Next message(s): Target NG-RAN processes the transfer content, RAN-side coordination or SON handling continues

Message direction and transport

Sender and receiver: AMF -> NG-RAN

Interface: N2 / NG-C

Domain: RAN configuration transfer and inter-node coordination

Signaling bearer: Non-UE-associated NGAP signaling

Logical channel: SCTP carried NGAP initiatingMessage

Transport / encapsulation: NGAP over SCTP/IP between AMF and NG-RAN

Security context: Downlink RAN Configuration Transfer is non-UE-associated and delivers RAN-side configuration transfer content. Validate source, target, and transparent container handling before treating the transfer as successfully delivered.

Message Structure Overview

Downlink RAN Configuration Transfer is an AMF-to-NG-RAN non-UE-associated initiatingMessage.
SON Configuration Transfer is the key mandatory container.
The container can carry source RAN node identity, target RAN node identity, and transparent SON or RAN configuration information.
The receiving NG-RAN interprets the RAN-specific content.
The paired uplink path is Uplink RAN Configuration Transfer.

ASN.1 for Downlink RAN Configuration Transfer

DownlinkRANConfigurationTransfer ::= SEQUENCE {
  protocolIEs ProtocolIE-Container { {DownlinkRANConfigurationTransfer-IEs} },
  ...
}

DownlinkRANConfigurationTransfer-IEs NGAP-PROTOCOL-IES ::= {
  { ID id-SONConfigurationTransfer  CRITICALITY ignore  TYPE SONConfigurationTransfer  PRESENCE mandatory },
  ...
}

How to read this ASN.1

Read this as a non-UE-associated NGAP envelope around a SON Configuration Transfer container. The AMF forwards RAN-originated transfer content rather than sending its own AMF Configuration Update.

Downlink RAN Configuration Transfer - Example Dump

NGAP-PDU
  initiatingMessage
    procedureCode: id-DownlinkRANConfigurationTransfer
    criticality: ignore
    value: DownlinkRANConfigurationTransfer
      protocolIEs:
        - id: id-SONConfigurationTransfer
          value:
            sourceRANNodeID: <source RAN node identity>
            targetRANNodeID: <target RAN node identity>
            sONInformation: <transparent RAN configuration transfer information>

How to read this dump

Treat this as a teaching example based on the expected message structure, not as a captured network trace.
SON Configuration Transfer is the main payload to inspect.
Do not confuse this forwarded transfer container with AMF Configuration Update or RAN Configuration Update.

Important Information Elements

IE	Required	Description
`Message Type`	Yes	Identifies the NGAP PDU as DOWNLINK RAN CONFIGURATION TRANSFER.
`SON Configuration Transfer`	Yes	Carries source and target RAN information plus transparent RAN configuration transfer content intended for the receiving NG-RAN.

Detailed field explanation

`Message Type`

Identifies the NGAP PDU as DOWNLINK RAN CONFIGURATION TRANSFER.

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.

`SON Configuration Transfer`

Carries source and target RAN information plus transparent RAN configuration transfer content intended for the receiving NG-RAN.

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

Confirm the direction is AMF to NG-RAN.
Check that SON Configuration Transfer is present.
Confirm the message follows a matching Uplink RAN Configuration Transfer when expected.
Validate source and target RAN identities.
Confirm the transparent transfer content is decoded, exported, or forwarded correctly.
Check whether the receiving NG-RAN processes the transfer content.
Confirm the trace is not being interpreted as AMF Configuration Update or RAN Configuration Update.

Common Issues and Troubleshooting

The downlink transfer is missing after an uplink transfer.

Likely cause: The AMF may not have resolved a valid target NG-RAN, policy may block forwarding, or the uplink container may be malformed.

What to inspect: Check the source uplink transfer, AMF target selection, and SON Configuration Transfer validation.

Next step: Separate source encoding and AMF forwarding behavior before blaming the receiving NG-RAN.

The receiving NG-RAN ignores the transfer.

Likely cause: The target RAN identity may not match the receiving node or the transparent content may not be valid for that RAN side.

What to inspect: Compare source and target identities with the expected RAN nodes and review the transparent container content.

Next step: Correct the identity mapping or regenerate the transfer container.

The transparent container is shown as opaque bytes.

Likely cause: The analyzer may decode NGAP but not the embedded SON or RAN configuration transfer content.

What to inspect: Verify decoder support for SON Configuration Transfer details and export the container when deeper RAN-side decoding is needed.

Next step: Use an analyzer or RAN-side tool that understands the transparent content.

Engineers troubleshoot it as AMF Configuration Update.

Likely cause: Both messages are AMF-to-NG-RAN and mention configuration, but their procedures are different.

What to inspect: Check whether the key IE is SON Configuration Transfer or AMF configuration update IEs.

Next step: Use AMF Configuration Update analysis only when the AMF is updating NG-RAN about AMF-side configuration.

LTE / 5G / Variant Comparison

Compared with Uplink RAN Configuration Transfer

Uplink RAN Configuration Transfer sends RAN configuration transfer content from NG-RAN to AMF. Downlink RAN Configuration Transfer delivers relayed content from AMF to NG-RAN.

Compared with AMF Configuration Update

AMF Configuration Update tells NG-RAN about AMF-side configuration. Downlink RAN Configuration Transfer forwards RAN-originated transfer information to NG-RAN.

Compared with RAN Configuration Update

RAN Configuration Update refreshes AMF-side knowledge of the sending NG-RAN. Downlink RAN Configuration Transfer delivers transferred information from another RAN-side source.

FAQ

What is Downlink RAN Configuration Transfer in NGAP?

It is the AMF-to-NG-RAN NGAP message used to deliver RAN configuration transfer information received from another RAN node.

Who sends Downlink RAN Configuration Transfer?

The AMF sends Downlink RAN Configuration Transfer to the NG-RAN node.

Is this message UE-associated?

No. Downlink RAN Configuration Transfer is a non-UE-associated NGAP message.

What does SON Configuration Transfer contain?

SON Configuration Transfer contains source and target RAN context plus transparent SON or RAN configuration information intended for the receiving NG-RAN.

How is it related to Uplink RAN Configuration Transfer?

Uplink RAN Configuration Transfer sends the transfer content upward to the AMF. Downlink RAN Configuration Transfer delivers the relayed content downward toward NG-RAN.

How is it different from AMF Configuration Update?

AMF Configuration Update carries AMF-side configuration information. Downlink RAN Configuration Transfer forwards RAN-originated configuration transfer content to NG-RAN.

How is it different from RAN Configuration Update?

RAN Configuration Update updates AMF about the reporting NG-RAN's configuration. Downlink RAN Configuration Transfer delivers transferred information from another RAN-side source.

How do you troubleshoot RAN Configuration Transfer issues?

Confirm AMF-to-NG-RAN direction, verify SON Configuration Transfer presence, match it with the uplink transfer when expected, validate source and target RAN identities, and check receiving NG-RAN handling.

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.