| Protocol | nas | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 24.501 | Spec Section | 8.2.29 |
| Direction | UE to AMF | Message Type | 5GMM signaling |
| Full message name | 5G NAS - UL NAS Transport |
|---|---|
| Protocol | NAS |
| Technology | 5G |
| Direction | UE to AMF |
| Interface | N1 |
| Signaling bearer / channel | NAS signaling / Dedicated NAS message, commonly transported via UL Information Transfer on the access side |
| Typical trigger | Sent when the UE needs to forward a payload through NAS transport handling rather than through a standalone top-level 5GMM message. |
| Main purpose | Transports a contained NAS or application-related payload from the UE to the network without defining a standalone new top-level procedure for every use case. |
| Main specification | 3GPP TS 24.501, 8.2.29 |
| Release added | Release 15 |
| Procedures where used | Payload delivery over NAS, Protected 5GMM signaling, Core-facing transport of embedded information |
UL NAS Transport is the NAS wrapper message the UE uses to send a payload upward toward the core when the NAS procedure needs to carry additional information transparently.
Transports a contained NAS or application-related payload from the UE to the network without defining a standalone new top-level procedure for every use case.
UL NAS Transport is the UE using NAS as a wrapper to send another piece of information up to the network.
Call flow position: UE-to-network transport step used when an inner payload must be delivered through NAS signaling.
Typical state: The UE already has a valid NAS relationship and is using UL NAS Transport as a wrapper rather than starting a new standalone outer procedure.
Preconditions:
Next likely message: DL NAS Transport or procedure-specific network handling
Call flow position: Supplementary UE uplink transport step inside a broader mobility-management or session-related interaction.
Typical state: The outer NAS exchange is stable, but the message meaning depends mainly on the transported payload.
Preconditions:
Next likely message: Payload-specific response or transport continuation
Previous message(s): Registration Accept, Security Mode Complete, Protected NAS procedure state
Next message(s): DL NAS Transport, Procedure-specific core response, 5GMM Status
Security context: Often appears in an already established NAS security context, so engineers should inspect both the outer transport wrapper and the inner payload meaning.
This message is not typically analyzed as ASN.1 on the wire. It is usually read as a NAS or protocol field structure instead.
UL NAS Transport follows NAS 24.501 IE structure and is not an ASN.1 message.
UL NAS Transport
Extended Protocol Discriminator: 5G Mobility Management
Security Header Type: Integrity protected and ciphered
Message Type: UL NAS Transport
Payload Container Type: N1 SM information
Payload Container: 2e0101c1ff...
PDU Session ID: 10
| IE | Required | Description |
|---|---|---|
Payload container type | Yes | Tells you what kind of embedded content the message is carrying and therefore how the inner payload should be interpreted. |
Payload container | Yes | Carries the actual transported content, which often matters more than the outer UL NAS Transport wrapper. |
PDU Session ID | Optional | May be present when the transported payload is related to a specific session context. |
Additional information | Optional | Scenario-dependent container extensions that refine how the payload should be handled. |
Payload container typeTells you what kind of embedded content the message is carrying and therefore how the inner payload should be interpreted.
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.
Payload containerCarries the actual transported content, which often matters more than the outer UL NAS Transport wrapper.
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.
PDU Session IDMay be present when the transported payload is related to a specific session context.
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.
Additional informationScenario-dependent container extensions that refine how the payload should be handled.
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.
Likely cause: The wrapper may be correct while the embedded payload is malformed, unsupported, or not accepted by the network.
What to inspect: Decode the payload container type and the inner payload before concluding that the NAS transport itself failed.
Next step: Correlate with the matching DL NAS Transport or later core response to see whether the inner request was understood.
Likely cause: UL NAS Transport is a transport wrapper, so reading only the outer message hides the real procedure semantics.
What to inspect: Focus on the payload container type, the payload container contents, and any session identifiers.
Next step: Map the inner payload to its actual procedure instead of treating UL NAS Transport as the whole story.
It carries an embedded payload from the UE toward the network using NAS transport handling.
Usually no. It is often a wrapper, and the real procedure meaning comes from the transported payload.
Start with the payload container type and then decode the inner payload.
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.