RRC 5G gNB -> UE 3GPP TS 38.331

5G NR - DL Information Transfer

DL Information Transfer is the NR RRC message the network uses to send upper-layer information, most commonly NAS messages, to the UE over the established RRC connection.

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.6.1, 6.3.2
Direction	gNB -> UE	Message Type	Dedicated Information Transfer / NAS Transport

Full message name	5G NR - DL Information Transfer
Protocol	RRC
Technology	5G
Direction	gNB -> UE
Interface	Uu
Signaling bearer / channel	SRB1 or SRB2 / DCCH
Typical trigger	Sent when the network needs to deliver NAS signaling such as registration responses, authentication content, mobility management, or session-related information after the RRC connection exists.
Main purpose	Provides the radio-side RRC container that carries NAS or other dedicated upper-layer information from the network toward the UE.
Main specification	3GPP TS 38.331, 5.6.1, 6.3.2
Release added	Release 15
Procedures where used	5G Initial Registration, 5G Authentication Procedure, 5G PDU Session Establishment, 5G Mobility Registration Update
Related timers	DL Information Transfer itself does not define a standalone transaction timer, Timing is usually analyzed through the NAS procedure it carries, such as registration, authentication, or session management
Related cause values	DL Information Transfer does not carry reject causes, Failures are usually inferred from missing NAS payload, transport issues, or no corresponding UE-side continuation

What is DL Information Transfer in simple terms?

DL Information Transfer is the NR RRC message the network uses to send upper-layer information, most commonly NAS messages, to the UE over the established RRC connection.

Provides the radio-side RRC container that carries NAS or other dedicated upper-layer information from the network toward the UE.

Why this message matters

DL Information Transfer is the 5G NR RRC message the network uses to send NAS information down to the UE after the RRC connection is already established.

Where this message appears in the call flow

Initial Registration

Call flow position: Used after the AMF processes UE-originated NAS information and needs to send a NAS response back.

Typical state: UE is connected and capable of dedicated RRC signaling.

Preconditions:

RRC setup is complete.
The network has NAS payload to send.

Next likely message: UL Information Transfer, NAS continuation in the UE, or later procedure-specific signaling

Authentication and Security Signaling

Call flow position: Used when the network sends NAS authentication or related NAS content toward the UE.

Typical state: UE is connected and waiting for network-driven upper-layer signaling.

Preconditions:

Core-network authentication or related NAS handling is active.

Next likely message: UL Information Transfer carrying the UE NAS response

PDU Session and Mobility Signaling

Call flow position: Relevant when the network sends session-related or mobility-related NAS information to the UE.

Typical state: UE is connected and upper-layer signaling must reach the UE through RRC.

Preconditions:

Relevant NAS signaling has been generated by the network.

Next likely message: UL Information Transfer or internal UE NAS handling depending on the procedure

Call flow position

Previous message(s): UL Information Transfer, NAS processing in AMF, Core-network procedure continuation

Next message(s): UL Information Transfer, NAS handling in the UE, Core-network procedure continuation

Message direction and transport

Sender and receiver: gNB -> UE

Interface: Uu

Domain: Access-side radio control bridging core-network signaling toward the UE

Signaling bearer: SRB1 or SRB2

Logical channel: DCCH

Transport / encapsulation: Dedicated RRC signaling on DCCH carrying DL dedicated NAS information or other upper-layer payloads

Security context: Dedicated UE-specific AS-protected signaling once access security is active in connected mode.

Message Structure Overview

DL Information Transfer is a lightweight wrapper message. Its main engineering value is the NAS or upper-layer payload it carries.
For most traces, the first question is which NAS message is inside the dedicatedNAS-Message container.
This message should be interpreted together with the NAS procedure and the following UE response, not as an isolated RRC event.

ASN.1 for 5G NR - DL Information Transfer

DL-DCCH-Message ::= SEQUENCE {
  message CHOICE {
    c1 CHOICE {
      dlInformationTransfer DLInformationTransfer,
      ...
    },
    ...
  }
}

DLInformationTransfer ::= SEQUENCE {
  criticalExtensions CHOICE {
    dlInformationTransfer DLInformationTransfer-IEs,
    ...
  }
}

DLInformationTransfer-IEs ::= SEQUENCE {
  dedicatedNAS-Message       DedicatedNAS-Message,
  lateNonCriticalExtension   OCTET STRING OPTIONAL,
  ...
}

How to read this ASN.1

At the RRC level, DL Information Transfer is simple. The important practical question is what NAS payload sits inside dedicatedNAS-Message and how that payload relates to the current core-network procedure.

Decoded Message Dump

DL-DCCH-Message
  message: c1
    dlInformationTransfer
      criticalExtensions
        dlInformationTransfer
          dedicatedNAS-Message
            7E 00 56 34 20 01 02 A1 ...

How to read this dump

The outer RRC decode is usually short.
The key trace step is to decode the NAS payload carried inside dedicatedNAS-Message.
If the NAS payload is missing, malformed, or does not match the expected procedure stage, the whole downlink signaling path can fail.

Important Information Elements

IE	Required	Description
`dedicatedNAS-Message`	Yes	The main payload container used to carry NAS information from the network toward the UE.
`lateNonCriticalExtension`	Optional	Optional extension field for later release additions.
`payload container context`	Optional	Operationally important because engineers usually care more about the carried NAS message than the outer RRC wrapper.

Detailed field explanation

`dedicatedNAS-Message`

The main payload container used to carry NAS information from the network toward the UE.

Presence: Required

`lateNonCriticalExtension`

Optional extension field for later release additions.

Presence: Optional

`payload container context`

Operationally important because engineers usually care more about the carried NAS message than the outer RRC wrapper.

Presence: Optional

What to check in logs and traces

Check which NAS procedure is expected at the moment DL Information Transfer is sent.
Verify that dedicatedNAS-Message is present and decodes to the expected NAS message.
Correlate the downlink RRC transfer with NGAP and AMF-side handling.
If the UE does not continue the procedure, check whether the payload reached the UE correctly and was interpreted in the expected state.
Separate an RRC transport issue from a NAS rejection or UE-side NAS handling issue.
Compare the carried NAS message with the current registration, mobility, or session state.

Common Issues and Troubleshooting

DL Information Transfer is sent but the UE does not continue the procedure.

Likely cause: The NAS payload may be malformed, unexpected for the current UE state, or not interpreted correctly.

What to inspect: Check the dedicatedNAS-Message content and correlate with UE NAS state and the previous uplink signaling.

Next step: Debug the carried NAS procedure before assuming a pure RRC failure.

The network appears to respond, but the UE behaves as if nothing was received.

Likely cause: The DL Information Transfer may not have been delivered correctly, or the UE may not accept the payload in the current state.

What to inspect: Check downlink RRC traces, radio delivery, and UE NAS decode behavior.

Next step: Trace the message end-to-end from AMF to NGAP to RRC to UE NAS handling.

The following UL response does not match the downlink content.

Likely cause: The wrong NAS payload may have been delivered, or the UE interpreted it differently than expected.

What to inspect: Decode the NAS payload inside DL Information Transfer and compare it with the subsequent UL Information Transfer or UE action.

Next step: Validate UE NAS state and payload contents before changing radio-layer assumptions.

Detailed explanation

5G NR - DL Information Transfer Explained

DL Information Transfer is the 5G NR RRC message the network uses to send NAS or other upper-layer information down to the UE after a dedicated RRC connection already exists.

For beginners, the simple meaning is: this is how the network sends important core-network signaling down through the radio connection.
For experienced engineers, DL Information Transfer is usually the downlink RRC wrapper around a NAS message and should be debugged together with the carried NAS payload and the matching NGAP/core traces.

What is DL Information Transfer in simple terms?

DL Information Transfer is a dedicated gNB-to-UE RRC message carried on DCCH. The message itself is usually simple. Its main value is the payload inside it.

In practical terms, DL Information Transfer helps answer:

what NAS message did the network send?
did that NAS payload reach the UE correctly?
did the UE continue the expected procedure?

Why this message matters

DL Information Transfer matters because many registration, authentication, mobility, and session procedures depend on it:

NAS signaling must reach the UE correctly
the UE must process the payload in the correct state
the following uplink NAS response depends on it

Where this message appears in the call flow

A simplified signaling path is:

The network has NAS information to send.
gNB sends DL Information Transfer.
UE processes the carried NAS payload.
UE continues the procedure, often with UL Information Transfer.

Mini sequence:

AMF                gNB                 UE
|----- NAS ------->|                   |
|                  |-- DL Info ------->|
|                  |   Transfer        |
|<----- next NAS / UL Information Transfer ---|

So DL Information Transfer sits between core-network response generation and UE-side NAS procedure continuation.

Message direction and transport

sender: gNB
receiver: UE
interface: Uu
signaling bearer: SRB1 / SRB2
signaling channel: DCCH
security context: dedicated protected signaling

Important Information Elements

IE	Why it matters
`dedicatedNAS-Message`	Main carried payload.
`lateNonCriticalExtension`	Optional later-release extension field.
NAS payload contents	Usually the real troubleshooting focus.

Example message dump

DL-DCCH-Message
  message: c1
    dlInformationTransfer
      criticalExtensions
        dlInformationTransfer
          dedicatedNAS-Message
            7E 00 56 34 20 01 02 A1 ...

FAQ

What is DL Information Transfer in 5G NR?

DL Information Transfer is the NR RRC message the network uses to send NAS or other upper-layer information to the UE after the RRC connection is established.

Who sends DL Information Transfer?

The gNB sends DL Information Transfer to the UE.

What does DL Information Transfer usually carry?

Most commonly it carries a dedicated NAS message related to registration, authentication, mobility, service, or session procedures.

What comes after DL Information Transfer?

Usually UE-side NAS handling and often a corresponding UL Information Transfer carrying the next NAS response.

Is DL Information Transfer mainly an RRC message or a NAS wrapper?

In practice it is mostly an RRC wrapper around NAS payload.

Why is DL Information Transfer useful in troubleshooting?

Because it helps engineers confirm whether the correct NAS payload reached the UE and whether the following failure is radio-side, UE-side, or core-side.

Summary

DL Information Transfer is the NR RRC message the network uses to send upper-layer information, most commonly NAS messages, to the UE over the established RRC connection.

Advanced Engineer Notes

This message is often best treated as an RRC wrapper around NAS rather than as a complex RRC procedure on its own.
Many troubleshooting cases that look like RRC problems are really NAS payload or UE-side interpretation problems inside DL Information Transfer.
Always correlate DL Information Transfer with the matching NGAP, AMF, and following UE NAS response.

LTE / 5G / Variant Comparison

DL Information Transfer versus UL Information Transfer

DL Information Transfer carries NAS or upper-layer payload from the network to the UE. UL Information Transfer carries the corresponding payload from the UE toward the network.

DL Information Transfer versus RRC Setup

RRC Setup establishes dedicated radio control context. DL Information Transfer is the general dedicated wrapper used later to carry NAS or upper-layer payloads down to the UE.

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.