UE Radio Capability ID Mapping Response is the NGAP message sent by the NG-RAN node to the AMF to return the result of a UE Radio Capability ID Mapping Request.
Message Fact Sheet
Protocol
ngap
Network
5g
Spec
3GPP TS 38.413
Spec Section
UE Radio Capability Management messages and UE Radio Capability ID Mapping Response (Release 18 baseline)
NG-RAN has processed a UE Radio Capability ID Mapping Request and returns the mapping result to the AMF.
Main purpose
Returns the result of capability ID mapping, helps AMF avoid unnecessary full capability transfer, synchronizes capability ID knowledge between NG-RAN and AMF, and supports later UE context, mobility, and capability-related procedures.
Main specification
3GPP TS 38.413, UE Radio Capability Management messages and UE Radio Capability ID Mapping Response (Release 18 baseline)
Release added
Release 15
Procedures where used
UE Radio Capability ID Mapping, UE Radio Capability Management, Capability ID synchronization, AMF capability storage
What is UE Radio Capability ID Mapping Response in simple terms?
UE Radio Capability ID Mapping Response is the NGAP message sent by the NG-RAN node to the AMF to return the result of a UE Radio Capability ID Mapping Request.
Returns the result of capability ID mapping, helps AMF avoid unnecessary full capability transfer, synchronizes capability ID knowledge between NG-RAN and AMF, and supports later UE context, mobility, and capability-related procedures.
Why this message matters
UE Radio Capability ID Mapping Response is the gNB's answer to AMF's request to resolve a capability ID. It may return the ID context or full capability information.
Where this message appears in the call flow
UE Radio Capability ID Mapping
Response branch: NG-RAN processes the requested capability ID and returns mapping context.
Call flow position: NG-RAN sends this response after processing an AMF-requested capability ID mapping request.
Typical state: AMF receives the mapping result and updates capability identity or capability information context.
Preconditions:
A matching UE Radio Capability ID Mapping Request was sent by the AMF.
AMF UE NGAP ID and RAN UE NGAP ID identify the same UE-associated NGAP context.
NG-RAN processed the requested UE Radio Capability ID.
Next likely message: AMF capability ID storage or later capability-dependent procedure
Capability ID synchronization
The response may confirm a capability ID or include full UE Radio Capability information when needed.
Call flow position: The response helps AMF and NG-RAN agree on capability identity, or supplies full capability information when needed.
Typical state: Capability ID and full capability information are stored or reconciled by AMF.
Preconditions:
Optional UE Radio Capability ID is decoded if present.
Optional UE Radio Capability is decoded if full capability information is returned.
Next likely message: Synchronized capability context
Transport / encapsulation: NGAP over SCTP/IP between NG-RAN and AMF
Security context: The message can return or confirm a UE Radio Capability ID and may include full UE radio capability information if ID mapping alone is insufficient.
Message Structure Overview
UE Radio Capability ID Mapping Response is an NG-RAN-to-AMF response in UE Radio Capability Management.
AMF UE NGAP ID and RAN UE NGAP ID correlate the response with the request.
UE Radio Capability ID may confirm or return the handled capability identifier.
UE Radio Capability may be included when full capability context is needed.
Criticality Diagnostics may appear for protocol-level diagnostics.
ASN.1 for 5G NGAP - UE Radio Capability ID Mapping Response
UERadioCapabilityIDMappingResponse ::= SEQUENCE {
protocolIEs ProtocolIE-Container { {UERadioCapabilityIDMappingResponse-IEs} },
...
}
UERadioCapabilityIDMappingResponse-IEs NGAP-PROTOCOL-IES ::= {
{ ID id-AMF-UE-NGAP-ID CRITICALITY reject TYPE AMF-UE-NGAP-ID PRESENCE mandatory } |
{ ID id-RAN-UE-NGAP-ID CRITICALITY reject TYPE RAN-UE-NGAP-ID PRESENCE mandatory } |
{ ID id-UERadioCapabilityID CRITICALITY ignore TYPE UERadioCapabilityID PRESENCE optional } |
{ ID id-UERadioCapability CRITICALITY ignore TYPE UERadioCapability PRESENCE optional } |
{ ID id-CriticalityDiagnostics CRITICALITY ignore TYPE CriticalityDiagnostics PRESENCE optional },
...
}
How to read this ASN.1
Decode both UE identifiers first, then inspect whether the response returned a UE Radio Capability ID, full UE Radio Capability information, or diagnostics. The exact operational meaning depends on the matching Mapping Request.
5G NGAP - UE Radio Capability ID Mapping Response - Example Dump
Treat this as a teaching example based on the expected message structure, not as a captured network trace.
The response must be correlated with a preceding UE Radio Capability ID Mapping Request.
UE Radio Capability ID and UE Radio Capability are optional result/context fields.
Do not confuse this with UE Radio Capability Check Response, which reports compatibility through IMS Voice Support Indicator.
Important Information Elements
IE
Required
Description
Message Type
Yes
Identifies the NGAP PDU as UE RADIO CAPABILITY ID MAPPING RESPONSE.
AMF UE NGAP ID
Yes
Mandatory AMF-side UE identifier used to correlate the response with the original mapping request.
RAN UE NGAP ID
Yes
Mandatory NG-RAN-side UE identifier used to bind the response to the radio-side UE context.
UE Radio Capability ID
Optional
Optional returned or confirmed capability identifier handled by NG-RAN.
UE Radio Capability
Optional
Optional full UE radio capability information returned when ID mapping alone is insufficient or full context is needed.
Criticality Diagnostics
Optional
Optional protocol diagnostics for IE handling or mapping-response processing.
Detailed field explanation
Message Type
Identifies the NGAP PDU as UE RADIO CAPABILITY ID MAPPING RESPONSE.
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 response with the original mapping request.
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 NG-RAN-side UE identifier used to bind the response to the radio-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.
UE Radio Capability ID
Optional returned or confirmed capability identifier handled by NG-RAN.
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.
UE Radio Capability
Optional full UE radio capability information returned when ID mapping alone is insufficient or full context is needed.
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.
Criticality Diagnostics
Optional protocol diagnostics for IE handling or mapping-response processing.
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.
What to check in logs and traces
Confirm the response follows a matching UE Radio Capability ID Mapping Request.
Confirm direction is NG-RAN node to AMF.
Match AMF UE NGAP ID and RAN UE NGAP ID to the original request.
Decode UE Radio Capability ID if present.
Decode UE Radio Capability if full capability information is returned.
Check Criticality Diagnostics if present.
Do not confuse the response with Info Indication or Check Response.
Common Issues and Troubleshooting
Mapping response appears without a request.
Likely cause: The matching request may be missing from the trace window, filtered out, or correlated with a different UE context.
What to inspect: Search for UE Radio Capability ID Mapping Request with matching AMF UE NGAP ID and RAN UE NGAP ID.
Next step: Do not interpret the response until the request and capability ID context are known.
Mapping result is confused with compatibility result.
Likely cause: UE Radio Capability ID Mapping Response is being confused with UE Radio Capability Check Response.
What to inspect: Check whether the response carries UE Radio Capability ID or UE Radio Capability rather than IMS Voice Support Indicator.
Next step: Use Check Response for compatibility and Mapping Response for ID resolution.
AMF does not store returned capability information.
Likely cause: Returned UE Radio Capability may be ignored, malformed, or associated with the wrong UE context.
What to inspect: Decode UE Radio Capability and verify UE ID correlation.
Next step: Confirm AMF storage behavior and capability context update.
Capability ID remains unresolved.
Likely cause: The response may not include enough mapping context, or the requested ID may not be known to NG-RAN.
What to inspect: Compare the request's UE Radio Capability ID with the response fields.
Next step: Fall back to full capability information or repeat mapping with a valid ID if needed.
Info Indication and Mapping Response are mixed in trace analysis.
Likely cause: Both can carry capability context, but their triggers differ.
What to inspect: Check whether the message is an NG-RAN-initiated indication or a response to AMF's mapping request.
Next step: Analyze Info Indication as reporting and Mapping Response as request/response result.
LTE / 5G / Variant Comparison
Compared with UE Radio Capability ID Mapping Request
Mapping Request asks NG-RAN to map or resolve a capability ID. Mapping Response returns the result.
Compared with UE Radio Capability Info Indication
Info Indication is NG-RAN-initiated capability reporting. ID Mapping Response is the answer to AMF's mapping request.
Compared with UE Radio Capability Check Response
Check Response reports compatibility or IMS voice support. ID Mapping Response reports capability ID mapping result.
FAQ
What is UE Radio Capability ID Mapping Response in NGAP?
It is the NG-RAN-to-AMF response message used to return the result of a UE Radio Capability ID Mapping Request.
Who sends UE Radio Capability ID Mapping Response?
The NG-RAN node sends UE Radio Capability ID Mapping Response to the AMF.
What message triggers this response?
It is triggered by a preceding UE Radio Capability ID Mapping Request from the AMF.
Does this message carry full UE Radio Capability?
It can include UE Radio Capability when full capability information is needed for the mapping result, but that field is optional.
How is it different from UE Radio Capability Info Indication?
Info Indication is NG-RAN-initiated reporting. ID Mapping Response is a response to AMF's mapping request.
How is it different from UE Radio Capability Check Response?
Check Response reports compatibility, especially IMS voice support. ID Mapping Response reports capability ID mapping result.
What should be checked when troubleshooting mapping response issues?
Find the matching Mapping Request, match both UE NGAP IDs, decode returned UE Radio Capability ID or UE Radio Capability, and inspect Criticality Diagnostics if present.
Can this message include Criticality Diagnostics?
Yes. Criticality Diagnostics may be included for protocol-level IE handling or mapping-response diagnostics.
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.
