LTE RRC Early Data Request-r15

Message Fact Sheet

Protocol	lte-rrc	Network	lte
Spec	3GPP TS 36.331	Spec Section	5.3.3, 6.2.2
Direction	UE -> eNodeB	Message Type	CP-EDT Access

Full message name	LTE RRC Early Data Request-r15
Protocol	LTE-RRC
Technology	LTE
Direction	UE -> eNodeB
Interface	Uu
Signaling bearer / channel	SRB0 / UL-CCCH
Typical trigger	The UE has a small NAS payload and the CP-EDT branch is allowed for the current access attempt.
Main purpose	Combines early access intent with the initial NAS payload so small data can be sent without a full ordinary setup path.
Main specification	3GPP TS 36.331, 5.3.3, 6.2.2
Release added	Release 15
Procedures where used	Control Plane Early Data Transmission, Small Data Access
Related timers	T300

What is LTE RRC Early Data Request-r15 in simple terms?

Uplink LTE RRC message used by the UE to request control-plane early data transmission.

Combines early access intent with the initial NAS payload so small data can be sent without a full ordinary setup path.

Why this message matters

RRC Early Data Request-r15 is the LTE message the UE uses to start the control-plane early data branch with a small NAS payload.

Where this message appears in the call flow

Control-plane early data transmission

Call flow position: UE entry message for the CP-EDT access branch.

Typical state: UE is idle and is trying to send small data without a normal full setup branch.

Preconditions:

The UE has already completed the early access prerequisites.
The NAS payload is ready for early delivery.

Next likely message: RRCEarlyDataComplete-r15 or reject handling

Small mobile-originated data from idle

Call flow position: Early access branch used when a small NAS payload is the main trigger.

Typical state: UE is still on the early CCCH path.

Preconditions:

The small-data branch is permitted in the serving context.

Next likely message: RRCEarlyDataComplete-r15

Call flow position

Previous message(s): Random access completion, Broadcast information acquisition

Next message(s): RRCEarlyDataComplete-r15, RRCConnectionReject

Message direction and transport

Sender and receiver: UE -> eNodeB

Interface: Uu

Domain: Access-side early data control

Signaling bearer: SRB0

Logical channel: UL-CCCH

Transport / encapsulation: RRC over CCCH on the CP-EDT entry path

Security context: Sent before normal connected-mode AS security activation on the early data entry path.

Message Structure Overview

RRCEarlyDataRequest-r15 is an early-access request plus NAS payload container.
The main reading points are the establishment cause and the presence of the small NAS payload.

ASN.1 for LTE RRC Early Data Request-r15

RRCEarlyDataRequest-r15 ::= SEQUENCE {
  criticalExtensions CHOICE {
    c1 CHOICE {
      rrcEarlyDataRequest-r15 RRCEarlyDataRequest-r15-IEs,
      spare3 NULL,
      spare2 NULL,
      spare1 NULL
    },
    criticalExtensionsFuture SEQUENCE {}
  }
}

RRCEarlyDataRequest-r15-IEs ::= SEQUENCE {
  establishmentCause-r15 EstablishmentCause,
  dedicatedInfoNAS-r15   DedicatedInfoNAS,
  nonCriticalExtension   SEQUENCE {} OPTIONAL
}

How to read this ASN.1

Read this message as the CP-EDT entry request plus the first NAS payload.

LTE RRC Early Data Request-r15 - Example Dump

UL-CCCH-Message
  message c1 : rrcEarlyDataRequest-r15 : {
    criticalExtensions c1 : rrcEarlyDataRequest-r15 : {
      establishmentCause-r15 mo-Data,
      dedicatedInfoNAS-r15 '271101'H
    }
  }

How to read this dump

Check the establishment cause and the presence of dedicatedInfoNAS-r15.
Correlate the message with the later early-data completion outcome.

Important Information Elements

IE	Required	Description
`s-TMSI-r15`	Optional	Temporary UE identity used when available on the early data path.
`establishmentCause-r15`	Yes	Shows why the early access was requested.
`dedicatedInfoNAS-r15`	Yes	NAS payload carried on the control-plane early data branch.

Detailed field explanation

`s-TMSI-r15`

Temporary UE identity used when available on the early data path.

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.

`establishmentCause-r15`

Shows why the early access was requested.

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-r15`

NAS payload carried on the control-plane early data branch.

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 the access is really the CP-EDT branch.
Check the establishment cause.
Check whether RRCEarlyDataComplete-r15 follows.

Common Issues and Troubleshooting

The UE attempts small data from idle but the early-data branch does not complete.

Likely cause: The CP-EDT entry may have started correctly but the network did not accept or finish the branch.

What to inspect: Check this request, the carried NAS payload, and whether RRCEarlyDataComplete-r15 or reject handling appears.

Next step: Treat the issue as an early-data access problem rather than a normal full setup problem.

FAQ

What is RRCEarlyDataRequest-r15 in LTE?

It is the LTE RRC message the UE uses to start the control-plane early data branch and carry the first NAS payload.

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.