LTE RRC UL Information Transfer

Message Fact Sheet

Protocol	lte-rrc	Network	lte
Spec	3GPP TS 36.331	Spec Section	5.3.11, 6.2.2
Direction	UE -> eNodeB	Message Type	Dedicated Information Transfer

Full message name	LTE RRC UL Information Transfer
Protocol	LTE-RRC
Technology	LTE
Direction	UE -> eNodeB
Interface	Uu
Signaling bearer / channel	SRB1 / UL-DCCH
Typical trigger	The UE has uplink EPS NAS content that must be delivered to the network through the current LTE RRC connection.
Main purpose	Transfers UE-originated EPS NAS signaling transparently across LTE RRC so the network can receive attach requests, TAU requests, service requests, detach requests, or other NAS content through the current LTE RRC connection.
Main specification	3GPP TS 36.331, 5.3.11, 6.2.2
Release added	Release 8
Procedures where used	Initial access and attach continuation, Tracking area update continuation, Service request continuation, Connected-mode NAS signaling

What is LTE RRC UL Information Transfer in simple terms?

Uplink LTE RRC message used by the UE to carry NAS payloads toward the network over the LTE access stratum.

Transfers UE-originated EPS NAS signaling transparently across LTE RRC so the network can receive attach requests, TAU requests, service requests, detach requests, or other NAS content through the current LTE RRC connection.

Why this message matters

UL Information Transfer is the LTE RRC message that carries uplink NAS signaling from the UE to the network.

Where this message appears in the call flow

LTE initial access

Call flow position: Uplink NAS delivery step used after the dedicated RRC signaling path is active.

Typical state: UE is in connected mode and sends EPS NAS content through LTE RRC toward the network.

Preconditions:

The dedicated SRB1 path is active.
The UE has NAS content to send.

Next likely message: DLInformationTransfer or later LTE RRC / NAS continuation

Connected-mode NAS delivery

Call flow position: Transparent uplink NAS transport step used while the UE remains in connected mode.

Typical state: LTE RRC carries a NAS container without changing the basic role of NAS as the higher-layer control payload.

Preconditions:

SRB1 is active.
The UE remains in connected mode.
An EPS NAS procedure needs uplink signaling.

Next likely message: DLInformationTransfer or later NAS/RRC continuation

Call flow position

Previous message(s): DLInformationTransfer, Earlier NAS or RRC procedure context in connected mode

Next message(s): DLInformationTransfer, Later NAS or RRC procedure continuation

Message direction and transport

Sender and receiver: UE -> eNodeB

Interface: Uu

Domain: Access-side radio control carrying core-network NAS signaling

Signaling bearer: SRB1

Logical channel: UL-DCCH

Transport / encapsulation: RRC over DCCH on SRB1 carrying a dedicated NAS message container

Security context: This message appears after the dedicated signaling path is active and is used to carry NAS content through protected LTE RRC signaling.

Message Structure Overview

ULInformationTransfer is mainly a transport wrapper for an uplink NAS payload.
The useful read starts with the carried NAS content, not with the outer RRC message name alone.
This message is best read together with the related NAS procedure and the later downlink reply path.

ASN.1 for LTE RRC UL Information Transfer

ULInformationTransfer ::= SEQUENCE {
  rrc-TransactionIdentifier RRC-TransactionIdentifier,
  criticalExtensions CHOICE {
    c1 CHOICE {
      ulInformationTransfer-r8 ULInformationTransfer-r8-IEs,
      spare3 NULL,
      spare2 NULL,
      spare1 NULL
    },
    criticalExtensionsFuture SEQUENCE {}
  }
}

ULInformationTransfer-r8-IEs ::= SEQUENCE {
  dedicatedInfoType CHOICE {
    dedicatedInfoNAS DedicatedInfoNAS,
    ...
  },
  nonCriticalExtension ULInformationTransfer-v8a0-IEs OPTIONAL
}

How to read this ASN.1

The outer message is small. The real operational value comes from identifying the NAS container and reading the carried NAS procedure in context.

LTE RRC UL Information Transfer - Example Dump

UL-DCCH-Message
  message c1 : ulInformationTransfer : {
    rrc-TransactionIdentifier 4,
    criticalExtensions c1 : ulInformationTransfer-r8 : {
      dedicatedInfoType dedicatedInfoNAS : '072801...'H
    }
  }

How to read this dump

Start by confirming that the payload is dedicatedInfoNAS.
The next useful step is decoding the carried NAS payload and placing it in the active EPS procedure.
Do not stop at the outer RRC decode when the real meaning sits inside the NAS container.

Important Information Elements

IE	Required	Description
`rrc-TransactionIdentifier`	Yes	Transaction identifier for the LTE RRC message exchange.
`dedicatedInfoType`	Yes	Wrapper that identifies the payload type being carried by ULInformationTransfer.
`dedicatedInfoNAS`	Yes	NAS message container delivered transparently from the UE toward the network.
`lateNonCriticalExtension / nonCriticalExtension`	Optional	Release-extension branch for later additions.

Detailed field explanation

`rrc-TransactionIdentifier`

Transaction identifier for the LTE RRC message exchange.

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.

`dedicatedInfoType`

Wrapper that identifies the payload type being carried by ULInformationTransfer.

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.

`dedicatedInfoNAS`

NAS message container delivered transparently from the UE toward the network.

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.

`lateNonCriticalExtension / nonCriticalExtension`

Release-extension branch for later additions.

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 message appears on SRB1 / UL-DCCH.
Check that the payload is a NAS container.
Decode the carried NAS message and identify the active EPS procedure.
Correlate the message with the earlier RRC connection and paging or service context if relevant.
Follow the next downlink NAS or RRC continuation instead of reading the message in isolation.

Common Issues and Troubleshooting

ULInformationTransfer is present but the procedure meaning is unclear.

Likely cause: The outer RRC wrapper was read, but the carried NAS payload was not decoded or correlated with the EPS procedure.

What to inspect: Decode the NAS container and map it to attach, TAU, service request, detach, or other EPS signaling.

Next step: Move from the RRC wrapper into the NAS message reference path.

The UE sends ULInformationTransfer but no expected downlink continuation follows.

Likely cause: The problem may be in the carried NAS procedure, not in the transport wrapper itself.

What to inspect: Check the carried NAS message, the security state, and the expected downlink reply such as DLInformationTransfer.

Next step: Read the message inside the wider NAS request-response sequence.

The message appears after paging and the path looks radio-related.

Likely cause: ULInformationTransfer may simply be the LTE RRC transport path for the uplink NAS continuation after service return.

What to inspect: Check the NAS container first before assuming the problem is in radio configuration.

Next step: Treat the message as a bridge between LTE RRC and EPS NAS rather than a standalone radio action.

LTE / 5G / Variant Comparison

Compared with DLInformationTransfer

UL Information Transfer carries NAS payloads from the UE to the network. DLInformationTransfer carries NAS payloads from the network to the UE.

Compared with RRCConnectionSetupComplete

RRCConnectionSetupComplete ends the early setup branch and can include an initial NAS container. UL Information Transfer is the general connected-mode uplink NAS transport wrapper.

FAQ

What is UL Information Transfer in LTE?

It is the uplink LTE RRC message used to carry NAS payloads from the UE to the network.

What does UL Information Transfer carry?

It typically carries a dedicated NAS container, so the real procedure meaning comes from the NAS message inside it.

What should I inspect first in UL Information Transfer?

Start by confirming the NAS container and decoding the carried NAS payload.

Why is UL Information Transfer important in troubleshooting?

It marks the point where UE-originated EPS NAS signaling is delivered through LTE RRC, so problems often sit in the carried NAS procedure rather than in the outer wrapper.

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.