5G NGAP Uplink RAN Status Transfer Message

Message Fact Sheet

Protocol	ngap	Network	5g
Spec	3GPP TS 38.413	Spec Section	RAN Status Transfer procedure and UE Mobility Management procedures
Direction	Source NG-RAN -> AMF	Message Type	Mobility Management Message

Full message name	Uplink RAN Status Transfer
Protocol	NGAP
Technology	5G
Direction	Source NG-RAN -> AMF
Interface	N2 / NG-C
Signaling bearer / channel	UE-associated NGAP signaling / SCTP carried NGAP initiatingMessage
Typical trigger	The source NG-RAN has active handover state and needs to pass PDCP/RAN status upward so the target NG-RAN can continue packet handling through the paired Downlink RAN Status Transfer.
Main purpose	Transfers source-side RAN and PDCP state to AMF so the AMF can relay it to the target NG-RAN, reducing packet loss, duplication, and reordering during handover.
Main specification	3GPP TS 38.413, RAN Status Transfer procedure and UE Mobility Management procedures
Release added	Release 15
Procedures where used	Uplink RAN Status Transfer, Downlink RAN Status Transfer, N2 handover, Lossless handover continuity, PDCP status transfer handling

What is Uplink RAN Status Transfer in simple terms?

Uplink RAN Status Transfer is an NGAP Mobility Management message sent by the source NG-RAN node to the AMF during handover. It transfers RAN/PDCP status information so that the target NG-RAN can continue data transmission without loss, supporting lossless or seamless handover.

Transfers source-side RAN and PDCP state to AMF so the AMF can relay it to the target NG-RAN, reducing packet loss, duplication, and reordering during handover.

Why this message matters

Uplink RAN Status Transfer is the source NG-RAN sending PDCP/RAN status to AMF so the target side can continue packet delivery during handover.

Where this message appears in the call flow

Lossless handover status transfer

5G NGAP flow showing Source NG-RAN sending Uplink RAN Status Transfer to AMF and AMF forwarding status to Target NG-RAN with Downlink RAN Status Transfer — Status relay: the source NG-RAN sends PDCP/RAN status upward to AMF, and AMF forwards it to the target NG-RAN with the paired Downlink RAN Status Transfer.

Call flow position: The source NG-RAN sends this message upward to AMF while handover is in progress and source-side PDCP/RAN status must be preserved.

Typical state: The UE is moving from source to target, and the source side has status information needed by the target side for packet continuity.

Preconditions:

A handover branch is active.
Source NG-RAN has UE-associated NGAP context and active data state.
The handover requires status transfer for lossless or seamless continuity.
AMF UE NGAP ID and RAN UE NGAP ID identify the correct source-side UE context.

Next likely message: AMF forwards the transparent container to the target NG-RAN using Downlink RAN Status Transfer

Paired downlink status transfer

5G NGAP flow showing AMF relaying source-side Uplink RAN Status Transfer information to target NG-RAN using Downlink RAN Status Transfer — Paired relay: Uplink RAN Status Transfer provides source-side status to AMF, and Downlink RAN Status Transfer delivers that same status toward the target NG-RAN.

Call flow position: This is the upstream half of the RAN status transfer pair.

Typical state: AMF receives source-side status and then delivers it to the target side.

Preconditions:

The transparent container is present.
The target side has or is establishing the UE handover context.

Next likely message: Downlink RAN Status Transfer

Path switch distinction

5G NGAP diagram showing RAN Status Transfer for PDCP continuity and Path Switch Request for core user-plane route switching — Troubleshooting distinction: RAN Status Transfer handles PDCP continuity, while Path Switch Request changes the core user-plane route after target access.

Call flow position: This message supports packet continuity before or around the wider mobility completion branch.

Typical state: PDCP/RAN status is transferred separately from core user-plane route switching.

Preconditions:

Engineers distinguish status transfer from later Path Switch Request handling.

Next likely message: Handover Notify or Path Switch Request depending on handover progress

Call flow position

Previous message(s): Handover Command, Handover preparation, Active source-side data flow

Next message(s): Downlink RAN Status Transfer, Target-side PDCP status application, Handover Notify

Message direction and transport

Sender and receiver: Source NG-RAN -> AMF

Interface: N2 / NG-C

Domain: UE mobility management and lossless handover status continuity

Signaling bearer: UE-associated NGAP signaling

Logical channel: SCTP carried NGAP initiatingMessage

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

Security context: The message preserves radio-user-plane continuity during handover. It does not authenticate the UE, switch the core user-plane path, or create a new UE context.

Message Structure Overview

UPLINK RAN STATUS TRANSFER is a source-NG-RAN-to-AMF initiatingMessage in the NGAP mobility management set.
The message carries a mandatory RAN Status Transfer Transparent Container.
The transparent container is the operational payload and contains source-side PDCP/RAN status information.
AMF UE NGAP ID and RAN UE NGAP ID are mandatory because status must be mapped to the exact UE handover context.
AMF normally relays the received status to the target NG-RAN using DOWNLINK RAN STATUS TRANSFER.
The message preserves data continuity; it does not switch the core user-plane path.

ASN.1 for Uplink RAN Status Transfer

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

UplinkRANStatusTransfer-IEs NGAP-PROTOCOL-IES ::= {
  { AMF UE NGAP ID, mandatory } |
  { RAN UE NGAP ID, mandatory } |
  { RAN Status Transfer Transparent Container, mandatory },
  ...
}

RAN Status Transfer Transparent Container ::= OCTET STRING

How to read this ASN.1

Decode the UE identity pair first, then inspect the RAN Status Transfer Transparent Container. The container is where PDCP sequence state, DL/UL status, and forwarding continuity information are carried.

Uplink RAN Status Transfer - Example Dump

NGAP-PDU
  initiatingMessage
    procedureCode: id-UplinkRANStatusTransfer
    criticality: ignore
    value: UplinkRANStatusTransfer
      protocolIEs:
        - id: id-AMF-UE-NGAP-ID
          value: 0x10A1
        - id: id-RAN-UE-NGAP-ID
          value: 0x0041
        - id: id-RANStatusTransferTransparentContainer
          value:
            drb-status:
              drbID: 4
              pdcp-dl-count: <opaque value>
              pdcp-ul-count: <opaque value>
              receive-status-of-ul-pdcp-sdus: <opaque bitmap>

How to read this dump

Treat this as a teaching example based on the expected message structure, not as a captured network trace.
The transparent container is mandatory and is the most important operational field.
Correlate this message with the paired Downlink RAN Status Transfer before concluding that target-side status was delivered.
Path Switch Request is a separate routing procedure and should not be treated as a substitute for PDCP status transfer.

Important Information Elements

IE	Required	Description
`Message Type`	Yes	Identifies the NGAP PDU as UPLINK RAN STATUS TRANSFER.
`AMF UE NGAP ID`	Yes	Mandatory AMF-side UE identifier used to correlate the status transfer with the correct handover context.
`RAN UE NGAP ID`	Yes	Mandatory source NG-RAN-side UE identifier used to bind the transferred status to the source-side UE context.
`RAN Status Transfer Transparent Container`	Yes	Mandatory payload carrying PDCP/RAN status information such as sequence-number and forwarding state used for lossless handover.

Detailed field explanation

`Message Type`

Identifies the NGAP PDU as UPLINK RAN STATUS 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.

`AMF UE NGAP ID`

Mandatory AMF-side UE identifier used to correlate the status transfer with the correct handover context.

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.

`RAN UE NGAP ID`

Mandatory source NG-RAN-side UE identifier used to bind the transferred status to the source-side UE context.

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.

`RAN Status Transfer Transparent Container`

Mandatory payload carrying PDCP/RAN status information such as sequence-number and forwarding state used for lossless handover.

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 UPLINK RAN STATUS TRANSFER appears during a handover branch.
Confirm direction is source NG-RAN to AMF.
Match AMF UE NGAP ID and RAN UE NGAP ID to the active handover context.
Verify that RAN Status Transfer Transparent Container is present and non-empty.
Check that AMF follows with Downlink RAN Status Transfer toward the target NG-RAN.
Correlate PDCP sequence, packet duplication, packet loss, and reordering symptoms with the transferred status.
Keep this analysis separate from Path Switch Request, which changes the user-plane routing path.

Common Issues and Troubleshooting

Packet loss appears during a handover that should be lossless.

Likely cause: Uplink RAN Status Transfer may be missing, delayed, malformed, or not paired with Downlink RAN Status Transfer.

What to inspect: Check for the source-side message, decode the transparent container, and verify the paired AMF-to-target message.

Next step: Fix source status generation or AMF relay before tuning generic mobility timers.

Packets arrive out of sequence after handover.

Likely cause: PDCP sequence information inside the transparent container may be inconsistent or applied to the wrong target context.

What to inspect: Compare PDCP counts, DRB status, and UE identity mapping between source and target.

Next step: Correct status-container handling or UE context correlation.

Downlink RAN Status Transfer is missing after the uplink message.

Likely cause: AMF did not relay the transparent container or target-side context correlation failed.

What to inspect: Trace AMF handling between Uplink RAN Status Transfer and the expected Downlink RAN Status Transfer.

Next step: Investigate AMF mobility relay behavior and target UE context availability.

Engineers confuse RAN Status Transfer with Path Switch.

Likely cause: Status continuity and core user-plane path switching are being merged into one troubleshooting bucket.

What to inspect: Separate PDCP/RAN status transfer from Path Switch Request and Path Switch Request Acknowledge.

Next step: Use RAN Status Transfer for continuity issues and Path Switch for routing or UPF path issues.

The status transfer is mapped to the wrong UE.

Likely cause: AMF UE NGAP ID or source-side RAN UE NGAP ID does not match the handover branch being analyzed.

What to inspect: Correlate UE IDs across Handover Command, Uplink RAN Status Transfer, Downlink RAN Status Transfer, Handover Notify, and Path Switch Request.

Next step: Resolve UE identity correlation before interpreting packet behavior.

LTE / 5G / Variant Comparison

Compared with Downlink RAN Status Transfer

UPLINK RAN STATUS TRANSFER sends status from source NG-RAN to AMF. DOWNLINK RAN STATUS TRANSFER delivers that status from AMF to target NG-RAN.

Compared with Path Switch Request

RAN Status Transfer carries PDCP/RAN status for continuity. Path Switch Request changes the core user-plane routing path after target access.

Compared with Handover Command

Handover Command tells the source side to execute handover. Uplink RAN Status Transfer preserves source-side packet-status information for the target.

FAQ

What is Uplink RAN Status Transfer in NGAP?

It is the source-NG-RAN-to-AMF NGAP message used during handover to transfer RAN and PDCP status information for lossless data continuity.

Who sends Uplink RAN Status Transfer?

The source NG-RAN node sends Uplink RAN Status Transfer to the AMF.

What is inside the transparent container?

The RAN Status Transfer Transparent Container carries PDCP/RAN status information such as sequence-number state, DL/UL status, and forwarding-related information.

Why is Uplink RAN Status Transfer needed during handover?

It helps the target NG-RAN continue packet handling with the right PDCP state, reducing packet loss, duplication, and reordering.

How is Uplink RAN Status Transfer different from Path Switch Request?

Uplink RAN Status Transfer carries PDCP/RAN status for continuity. Path Switch Request switches the core user-plane path after target-side access.

What happens if Uplink RAN Status Transfer is missing?

If the handover branch requires lossless status transfer, a missing message can contribute to packet loss, duplication, sequence gaps, or target-side reordering issues.

How does it relate to Downlink RAN Status Transfer?

Uplink RAN Status Transfer sends status from the source NG-RAN to AMF. Downlink RAN Status Transfer is the paired AMF-to-target message that delivers that status to the target NG-RAN.

References

3GPP TS 38.413 - NGAP Mobility Management procedures
3GPP TS 38.413 - RAN Status Transfer procedure
3GPP TS 38.413 - Uplink RAN Status Transfer
3GPP TS 38.413 - Downlink RAN Status Transfer

Related message pages

Related Procedures

N2 handover

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.