5G NGAP Downlink Non UE Associated NRPPa Transport Message

Message Fact Sheet

Protocol	ngap	Network	5g
Spec	3GPP TS 38.413	Spec Section	Downlink Non UE Associated NRPPa Transport message
Direction	AMF -> NG-RAN	Message Type	NRPPa / Positioning Transport

Full message name	Downlink Non UE Associated NRPPa Transport
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	AMF or a positioning-related core function has non-UE-associated NRPPa information to transport toward NG-RAN.
Main purpose	Transports non-UE-associated NRPPa signalling toward NG-RAN, supports positioning procedures not bound to one UE, carries an encoded NRPPa-PDU as a transparent payload, can include routing context for positioning entities, and separates NGAP transport from NRPPa positioning interpretation.
Main specification	3GPP TS 38.413, Downlink Non UE Associated NRPPa Transport message
Release added	Release 15
Procedures where used	Non-UE-associated NRPPa Transport, 5G positioning procedures, NR positioning support, N2 positioning signalling relay, NRPPa payload troubleshooting

What is Downlink Non UE Associated NRPPa Transport in simple terms?

Downlink Non UE Associated NRPPa Transport is the NGAP positioning transport message sent by the AMF to the NG-RAN node to carry non-UE-associated NRPPa signalling.

Transports non-UE-associated NRPPa signalling toward NG-RAN, supports positioning procedures not bound to one UE, carries an encoded NRPPa-PDU as a transparent payload, can include routing context for positioning entities, and separates NGAP transport from NRPPa positioning interpretation.

Why this message matters

Downlink Non UE Associated NRPPa Transport is the AMF sending a positioning payload to NG-RAN without a specific UE context. The absence of UE IDs is the point, not a decode error.

Where this message appears in the call flow

Non-UE-associated NRPPa Transport

Call flow position: AMF sends this non-UE-associated initiatingMessage when NRPPa positioning signalling must be delivered toward NG-RAN without binding it to one UE context.

Typical state: NG-RAN receives the transparent NRPPa-PDU and handles it as non-UE-associated positioning signalling.

Preconditions:

The positioning signalling is node-level, general, or otherwise not tied to a UE-associated NGAP context.
AMF has an encoded NRPPa-PDU to relay toward NG-RAN.
Routing context is available if required by the deployment.

Next likely message: Uplink Non UE Associated NRPPa Transport

No UE identity context

5G NGAP diagram showing Routing ID and NRPPa-PDU without AMF UE NGAP ID or RAN UE NGAP ID — Non-UE-associated transport omits UE IDs; NRPPa-PDU is decoded as NRPPa.

Call flow position: This message intentionally omits AMF UE NGAP ID and RAN UE NGAP ID.

Typical state: Trace analysis should not expect UE ID correlation fields in this transport branch.

Preconditions:

The procedure does not require a specific UE-associated NGAP context.
Any needed routing is carried by routing context and the NRPPa payload.

Next likely message: Correct non-UE-associated interpretation

Transparent NRPPa payload handling

5G NGAP comparison showing UE-associated NRPPa transport with UE IDs and non-UE-associated transport without a UE context — Use the non-UE-associated branch when the positioning signalling is not tied to one UE.

Call flow position: NGAP provides transport and optional routing context; the NRPPa content is decoded by NRPPa logic, not by NGAP.

Typical state: Engineers separate the NGAP transport envelope from the positioning message inside NRPPa-PDU.

Preconditions:

NRPPa-PDU is present and decodable by the analyzer.
The decoder supports the relevant NRPPa release and payload type.

Next likely message: NRPPa procedure continuation

Call flow position

Previous message(s): AMF has a non-UE-associated NRPPa payload for NG-RAN, No UE-associated NGAP context is required

Next message(s): NG-RAN processes the NRPPa-PDU, Uplink Non UE Associated NRPPa Transport

Message direction and transport

Sender and receiver: AMF -> NG-RAN

Interface: N2 / NG-C

Domain: NRPPa positioning transport

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 Non UE Associated NRPPa Transport carries positioning signalling that is not tied to one UE-associated NGAP context. Validate routing and payload handling according to operator positioning policy.

Message Structure Overview

Downlink Non UE Associated NRPPa Transport is an AMF-to-NG-RAN non-UE-associated initiatingMessage.
It does not carry AMF UE NGAP ID or RAN UE NGAP ID.
NRPPa-PDU is the main payload and is interpreted using NRPPa, not NGAP.
Routing ID can support correct routing of positioning signalling when present or required by the deployment.
The likely reverse or follow-up path is Uplink Non UE Associated NRPPa Transport.

ASN.1 for Downlink Non UE Associated NRPPa Transport

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

DownlinkNonUEAssociatedNRPPaTransport-IEs NGAP-PROTOCOL-IES ::= {
  { ID id-RoutingID  CRITICALITY reject TYPE RoutingID  PRESENCE optional } |
  { ID id-NRPPa-PDU  CRITICALITY reject TYPE NRPPa-PDU  PRESENCE mandatory },
  ...
}

How to read this ASN.1

Read this as a non-UE-associated NGAP envelope around an encoded NRPPa payload. There are no AMF UE NGAP ID or RAN UE NGAP ID fields to correlate.

Downlink Non UE Associated NRPPa Transport - Example Dump

NGAP-PDU
  initiatingMessage
    procedureCode: id-DownlinkNonUEAssociatedNRPPaTransport
    criticality: ignore
    value: DownlinkNonUEAssociatedNRPPaTransport
      protocolIEs:
        - id: id-RoutingID
          value: <optional routing context>
        - id: id-NRPPa-PDU
          value: <encoded NRPPa positioning payload>

How to read this dump

Treat this as a teaching example based on the expected message structure, not as a captured network trace.
Do not look for AMF UE NGAP ID or RAN UE NGAP ID in this non-UE-associated message.
NRPPa-PDU is opaque to NGAP and must be decoded using NRPPa rules.

Important Information Elements

IE	Required	Description
`Message Type`	Yes	Identifies the NGAP PDU as DOWNLINK NON UE ASSOCIATED NRPPA TRANSPORT.
`Routing ID`	Optional	Routing information for positioning transport when used by the involved positioning entities.
`NRPPa-PDU`	Yes	Encoded NRPPa payload carried transparently by NGAP.

Detailed field explanation

`Message Type`

Identifies the NGAP PDU as DOWNLINK NON UE ASSOCIATED NRPPA TRANSPORT.

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.

`Routing ID`

Routing information for positioning transport when used by the involved positioning entities.

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.

`NRPPa-PDU`

Encoded NRPPa payload carried transparently by NGAP.

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.
Confirm the message is non-UE-associated.
Check that NRPPa-PDU is present and decodable.
Check Routing ID when it is present or expected by the deployment.
Look for Uplink Non UE Associated NRPPa Transport when a response or follow-up is expected.
Use an analyzer that can decode the NRPPa payload rather than only showing opaque bytes.

Common Issues and Troubleshooting

An engineer expects AMF UE NGAP ID or RAN UE NGAP ID in the message.

Likely cause: The message is being confused with UE-associated NRPPa transport.

What to inspect: Check the top-level message name and confirm it is Non UE Associated.

Next step: Use Routing ID and NRPPa payload context instead of UE ID correlation.

The downlink non-UE transport appears but the positioning procedure does not continue.

Likely cause: The NRPPa-PDU may be malformed, unsupported by the decoder or node, or routed incorrectly.

What to inspect: Check Routing ID if present, then decode NRPPa-PDU with NRPPa support enabled.

Next step: Separate NGAP transport and routing from the inner NRPPa procedure failure.

NRPPa payload is shown only as opaque bytes.

Likely cause: The analyzer may decode NGAP but not the embedded NRPPa release or message type.

What to inspect: Verify analyzer NRPPa support, release settings, and payload handoff from NGAP to NRPPa decoding.

Next step: Use a decoder profile that supports the relevant NRPPa payload.

Routing appears inconsistent across positioning messages.

Likely cause: Routing ID or positioning entity mapping may not match the expected transport path.

What to inspect: Compare Routing ID values across downlink and uplink non-UE-associated NRPPa transport messages.

Next step: Validate routing configuration between positioning-related core functions, AMF, and NG-RAN.

A UE-associated transport is expected instead.

Likely cause: The procedure may actually be tied to a specific UE context.

What to inspect: Check whether AMF UE NGAP ID and RAN UE NGAP ID are required for the procedure.

Next step: Use UE-associated NRPPa transport for UE-specific positioning branches.

LTE / 5G / Variant Comparison

Compared with Uplink Non UE Associated NRPPa Transport

Downlink Non UE Associated NRPPa Transport carries non-UE-associated NRPPa from AMF to NG-RAN. Uplink Non UE Associated NRPPa Transport carries the reverse direction from NG-RAN to AMF.

Compared with UE-associated NRPPa transport

UE-associated transport includes AMF UE NGAP ID and RAN UE NGAP ID. Non-UE-associated transport does not include UE IDs and is used for node-level or general positioning signalling.

Compared with Location Reporting

Location Reporting messages are UE-related NGAP location reporting procedures. NRPPa Transport carries encoded NRPPa positioning signalling as a payload.

FAQ

What is Downlink Non UE Associated NRPPa Transport in NGAP?

It is the AMF-to-NG-RAN NGAP message used to carry non-UE-associated NRPPa positioning signalling.

Who sends this message?

The AMF sends Downlink Non UE Associated NRPPa Transport to the NG-RAN node.

Why are AMF UE NGAP ID and RAN UE NGAP ID not present?

They are not present because this is a non-UE-associated message and is not tied to a specific UE-associated NGAP context.

What does NRPPa-PDU contain?

NRPPa-PDU contains the encoded NRPPa positioning message. NGAP transports it but does not interpret the positioning contents.

How is this different from UE-associated NRPPa transport?

UE-associated transport includes UE identifiers and is used for UE-specific positioning. Non-UE-associated transport omits UE IDs and is used for node-level or general positioning signalling.

What is Routing ID used for?

Routing ID supports routing of NRPPa signalling between AMF, NG-RAN, and positioning-related entities when that routing context is used.

Does NGAP decode the positioning payload?

No. NGAP carries NRPPa-PDU transparently. The payload must be decoded according to NRPPa specifications.

How do you troubleshoot non-UE-associated NRPPa transport?

Confirm AMF-to-NG-RAN direction, verify that no UE IDs are expected, check Routing ID if used, confirm NRPPa-PDU presence, and decode the payload with an NRPPa-aware analyzer.

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.