Identity Response is the NAS message the UE sends after Identity Request to provide the specific identity type the network asked for, such as SUCI, IMEI, IMEISV, or another requested identifier.
Message Fact Sheet
Protocol
nas
Network
5g
Spec
3GPP TS 24.501
Spec Section
8.2.11
Direction
UE to AMF
Message Type
5GMM signaling
Full message name
5G NAS - Identity Response
Protocol
NAS
Technology
5G
Direction
UE to AMF
Interface
N1
Signaling bearer / channel
NAS signaling / Dedicated NAS message, commonly transported via UL Information Transfer
Typical trigger
Sent immediately after the UE receives Identity Request and extracts the identity type the AMF wants.
Main purpose
Returns the requested UE identity so the AMF can continue registration, service handling, authentication, or another 5GMM procedure.
Main specification
3GPP TS 24.501, 8.2.11
Release added
Release 15
Procedures where used
5G Initial Registration, Service Request, Mobility Registration Update
Related timers
T3570
What is Identity Response in simple terms?
Identity Response is the NAS message the UE sends after Identity Request to provide the specific identity type the network asked for, such as SUCI, IMEI, IMEISV, or another requested identifier.
Returns the requested UE identity so the AMF can continue registration, service handling, authentication, or another 5GMM procedure.
Why this message matters
Identity Response is the UE answering the network's identity question so the NAS procedure can continue.
Where this message appears in the call flow
5G Initial Registration
Call flow position: UE reply step after Identity Request when the network needs a more explicit or alternate identity before continuing.
Typical state: Registration is paused until the UE returns the requested identity.
Preconditions:
The AMF has already sent Identity Request.
The UE can provide the requested identity form.
Next likely message: Authentication Request or Registration Reject
Service Request
Call flow position: Identity clarification response when service recovery cannot continue on the basis of the identity already available.
Typical state: The network needs identity confirmation before restoring or continuing service handling.
Preconditions:
The network has requested a specific UE identity.
Next likely message: Service Accept, Authentication Request, or Service Reject
Domain: Core-side mobility management signaling with access-side NAS transport dependency
Signaling bearer: NAS signaling
Logical channel: Dedicated NAS message, commonly transported via UL Information Transfer
Transport / encapsulation: NAS 5GS message carried end-to-end between UE and AMF
Security context: Can appear before full NAS security is active because it often belongs to early registration identity exchange.
Message Structure Overview
Identity Response is a short NAS 5GMM reply whose main value is the actual identity value returned by the UE.
In trace analysis, engineers correlate this message directly with the preceding Identity Request and the next authentication or reject decision.
ASN.1 Message Syntax for 5G NAS - Identity Response
This message is not typically analyzed as ASN.1 on the wire. It is usually read as a NAS or protocol field structure instead.
Identity Response follows NAS 24.501 encoding rather than ASN.1 syntax.
5G NAS - Identity Response - Example Dump
Identity Response
Extended Protocol Discriminator: 5G Mobility Management
Security Header Type: Plain NAS
Message Type: Identity Response
Mobile Identity
Type of identity: SUCI
SUPI format: IMSI
MCC: 001
MNC: 01
Routing Indicator: 1234
How to read this dump
The important check is whether the UE returned the same identity type the network requested.
Engineers usually compare this response against the prior Identity Request and the next Authentication Request or Reject.
Important Information Elements
IE
Required
Description
Mobile identity
Yes
Carries the specific identity value requested by the network, such as SUCI, IMEI, or IMEISV.
Detailed field explanation
Mobile identity
Carries the specific identity value requested by the network, such as SUCI, IMEI, or IMEISV.
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 which identity type the network requested in Identity Request.
Check that the UE returned the matching identity type in Identity Response.
Verify whether the response is plain or protected NAS and whether that fits the procedure stage.
Correlate the response with the next network decision such as Authentication Request or Registration Reject.
Common Issues and Troubleshooting
The UE sends Identity Response but registration still does not progress.
Likely cause: The returned identity may not match what the AMF requested or the AMF may still reject the identity context.
What to inspect: Compare the requested identity type with the returned mobile identity contents and check the immediate next NAS message.
Next step: Move analysis to Authentication Request or Registration Reject to see how the network evaluated the returned identity.
Identity exchange repeats even after Identity Response.
Likely cause: The response may be malformed, incomplete, or not acceptable for the expected procedure context.
What to inspect: Check identity encoding, identity type, and whether the uplink NAS transport path delivered the message cleanly.
Next step: Compare with a known-good trace and verify that the UE can provide the identity format the network expects.
FAQ
What does Identity Response do in 5G?
It returns the specific UE identity the network asked for in Identity Request so the NAS procedure can continue.
Is Identity Response usually protected?
It can appear before full NAS security is established because identity exchange often happens early in registration.
What should happen after Identity Response?
The network usually continues with Authentication Request, though a reject or another branch is also possible depending on the returned identity and core evaluation.
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.