Home / Call Flows / LTE / UE Capability Transfer Procedure

LTE UE Capability Transfer Procedure Call Flow

call-flowLTE | E-UTRAN | RRC

LTE UE Capability Transfer is the connected-mode RRC procedure used when the eNB needs the UE to report its radio capability information before later control decisions such as configuration, bearer setup, carrier aggregation, or mobility-related behavior.

The core message pair is UE Capability Enquiry followed by UE Capability Information.

Introduction

The LTE UE Capability Transfer procedure does not create access or registration by itself. It gives the network the information needed to decide what the UE can actually support before later configuration is pushed.

The main nodes are UE and eNB. The procedure matters because a later configuration failure can begin with wrong, missing, or misread capability information here.

What Is LTE UE Capability Transfer in Simple Terms?

What starts the procedure: The eNB needs the UE's capability information before later radio decisions.
What the UE and network want to achieve: Report the supported features accurately so the network configures only what the UE can handle.
What success looks like: The eNB sends UE Capability Enquiry and the UE returns UE Capability Information.
What failure means: Capability reporting is missing, incomplete, or later configuration assumes support that was not really present.

Why this procedure matters

This is the reference point behind many later feature-dependent LTE behaviors, especially when configuration looks valid but still fails at the UE side.

Quick Fact Sheet

Procedure name	LTE UE Capability Transfer Procedure
Domain	Connected-mode LTE capability signaling
Main trigger	eNB needs UE capability information before later control decisions
Start state	UE is already in connected signaling and can exchange dedicated RRC messages
End state	eNB has the UE capability report needed for later configuration
Main nodes	UE, eNB
Main protocols	RRC
Main success outcome	The network receives usable capability containers and can continue with capability-aware control
Main failure outcome	Later configuration uses wrong assumptions or the capability report is incomplete
Most important messages	UE Capability Enquiry, UE Capability Information
Main specs	TS 36.331

LTE UE Capability Transfer procedure flow between UE and eNB — Click the diagram to open the full-size in a new tab.

Preconditions

The UE is already in connected mode and can exchange dedicated RRC messages.
The eNB has a reason to validate or refresh capability information.
The UE can build the capability containers requested by the network.

Nodes involved

Node	Role in this procedure
UE	Returns the requested capability information.
eNB	Requests and consumes the capability report for later control decisions.

Interfaces used

Interface or channel context	Path	Why it matters here
LTE Uu	UE <-> eNB	Carries the dedicated RRC exchange.
DCCH / SRB1	UE <-> eNB	Provides the connected signaling path used for enquiry and report.

End-to-end call flow

UE                          eNB
|                            |
|<- UE Capability Enquiry ---|
|                            |
|-- UE Capability Information ->|
|                            |
|   later configuration uses capability result   |

Major phases

Phase	What happens
1. Network requests report	The eNB asks for the UE capability information it needs.
2. UE builds response	The UE composes the requested capability containers.
3. Capability delivery	The report reaches the eNB for later control use.

Step-by-step breakdown

Step 1: UE Capability Enquiry

Sender -> receiver: eNB -> UE

Message(s): UE Capability Enquiry

Purpose: Ask the UE for capability information needed before later configuration.

State or context change: The UE knows which capability report the network expects.

Note: The enquiry content explains why later capability exchange appears at that moment.

Step 2: UE Capability Information

Sender -> receiver: UE -> eNB

Message(s): UE Capability Information

Purpose: Return the supported capability containers to the eNB.

State or context change: The eNB can now continue with capability-dependent control decisions.

Note: Later reconfiguration should be read against this message, not in isolation.

Important messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
UE Capability Enquiry	RRC	eNB -> UE	Requests the UE capability report.	Requested RAT or capability scope and timing within the larger procedure.
UE Capability Information	RRC	UE -> eNB	Returns the actual capability containers.	Container presence and whether later configuration matches the reported support.

Important parameters to inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Requested scope	The capability area the eNB wants to learn about.	UE Capability Enquiry	Explains why the network requested the report.	Enquiry too narrow for later feature use.
Capability containers	The actual reported capability data.	UE Capability Information	Forms the basis of later network decisions.	Missing container, decode gap, unexpected omission.
Transaction pairing	The relation between enquiry and information response.	Both messages	Confirms the right report belongs to the right request.	Merged attempts or wrong pairing in long traces.
Later configuration relation	The first feature-dependent action taken after the report.	After UE Capability Information	Shows whether the network used the report correctly.	Later configuration assumes unsupported feature.

Successful completion of the procedure

Success means the capability report reached the eNB and the later LTE control decision is consistent with what the UE actually reported.

Common failures in LTE UE Capability Transfer

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Later configuration fails unexpectedly	The network used capability assumptions that do not match the report.	UE Capability Information and later reconfiguration together.	UE Capability Information	LTE Uu	Check whether the feature was really declared as supported.
Capability report seems incomplete	Missing container, narrow enquiry, or decode limitation.	Enquiry scope and returned containers.	UE Capability Enquiry, UE Capability Information	LTE Uu	Decide whether the report is truly incomplete or only partially decoded.

What to check in logs and traces

Pair the enquiry and information messages correctly.
Inspect which capability containers were actually present.
Compare the report with the next configuration or feature action.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

3GPP Decoder

Notes

This procedure is easy to underestimate because it is short. Many later feature and bearer problems only make sense when the capability report is read first.

FAQ

What is LTE UE Capability Transfer?

It is the RRC procedure used to request and return the UE's radio capability information.

Which message starts it?

UE Capability Enquiry starts the exchange.

Why is it important?

Because later LTE configuration depends on what the UE reported here.