LTE RRC CSFB Parameters Request CDMA2000

Message Fact Sheet

Protocol	lte-rrc	Network	lte
Spec	3GPP TS 36.331	Spec Section	5.3.5, 6.2.2
Direction	eNodeB -> UE	Message Type	Interworking / CSFB

Full message name	LTE RRC CSFB Parameters Request CDMA2000
Protocol	LTE-RRC
Technology	LTE
Direction	eNodeB -> UE
Interface	Uu
Signaling bearer / channel	SRB1 / DL-DCCH
Typical trigger	Triggered when the network needs cdma2000 CS fallback parameters before continuing the fallback branch.
Main purpose	Starts the cdma2000 CSFB parameter exchange branch so the UE can return the requested information in CSFBParametersResponseCDMA2000.
Main specification	3GPP TS 36.331, 5.3.5, 6.2.2
Release added	Release 8
Procedures where used	cdma2000 CS fallback preparation

What is LTE RRC CSFB Parameters Request CDMA2000 in simple terms?

Downlink LTE RRC message used to request cdma2000-related CS fallback parameter handling from the UE.

Starts the cdma2000 CSFB parameter exchange branch so the UE can return the requested information in CSFBParametersResponseCDMA2000.

Why this message matters

CSFB Parameters Request CDMA2000 is the LTE network asking the UE for cdma2000 fallback-related parameters.

Where this message appears in the call flow

cdma2000 CSFB parameter request

LTE flow showing CSFB Parameters Request CDMA2000 followed by a UE response — The eNodeB requests cdma2000 fallback-related parameters before the UE returns them in the response message.

Call flow position: Network request sent before the UE returns cdma2000 fallback-related parameters.

Typical state: The LTE side is preparing a cdma2000 fallback or interworking branch.

Preconditions:

The UE is in connected mode.
cdma2000 CS fallback handling is relevant.

Next likely message: CSFBParametersResponseCDMA2000

cdma2000 fallback preparation

LTE flow showing CSFB Parameters Request CDMA2000 used during fallback preparation — This request belongs to the fallback preparation branch rather than the later execution step.

Call flow position: Preparation message used before the network decides how to continue the cdma2000 branch.

Typical state: The network is gathering UE-side fallback parameters rather than executing fallback immediately.

Preconditions:

The cdma2000 fallback path is being prepared.

Next likely message: Later fallback continuation or mobility command

Call flow position

Previous message(s): RRCConnectionReconfiguration

Next message(s): CSFBParametersResponseCDMA2000, Later cdma2000 CS fallback continuation

Message direction and transport

Sender and receiver: eNodeB -> UE

Interface: Uu

Domain: Access-side radio control with cdma2000 CSFB interworking

Signaling bearer: SRB1

Logical channel: DL-DCCH

Transport / encapsulation: Protected connected-mode LTE RRC signaling

Security context: Sent as protected connected-mode signaling.

Message Structure Overview

This is a request message that starts the cdma2000 CSFB parameter exchange.

ASN.1 for LTE RRC CSFB Parameters Request CDMA2000

CSFBParametersRequestCDMA2000 ::= SEQUENCE {
  criticalExtensions CHOICE {
    c1 CHOICE {
      csfbParametersRequestCDMA2000-r8 NULL,
      spare3 NULL,
      spare2 NULL,
      spare1 NULL
    },
    criticalExtensionsFuture SEQUENCE {}
  }
}

How to read this ASN.1

The main value is its position in the cdma2000 fallback preparation branch.

LTE RRC CSFB Parameters Request CDMA2000 - Example Dump

DL-DCCH-Message
  message c1 : csfbParametersRequestCDMA2000-r8

How to read this dump

This message is mostly procedural. The follow-up response carries the useful parameter payload.

Important Information Elements

IE	Required	Description
`criticalExtensions`	Yes	Carries the CSFBParametersRequestCDMA2000 branch.

Detailed field explanation

`criticalExtensions`

Carries the CSFBParametersRequestCDMA2000 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 message appears before the expected cdma2000 parameter response.
Check whether the branch later leads into fallback preparation or interworking continuation.

Common Issues and Troubleshooting

cdma2000 fallback preparation stalls before the network gets the needed UE-side parameters.

Likely cause: The parameter request or its response may be missing from the branch.

What to inspect: Check whether CSFB Parameters Request CDMA2000 appears and whether the response follows.

Next step: Read the branch as fallback preparation, not as the actual mobility execution step.

FAQ

What is CSFB Parameters Request CDMA2000 in LTE?

It is the downlink LTE RRC message the network uses to request cdma2000 CS fallback-related parameters from 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.