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LTE Handover to CDMA2000 Call Flow

call-flow LTE | CDMA2000 | Inter-RAT | RRC

LTE handover to CDMA2000 is the outbound inter-RAT mobility path used when the UE leaves LTE and continues on the CDMA2000 side. It is one of the target-specific branches of LTE legacy interworking.

This page focuses on the LTE-to-CDMA2000 branch rather than the generic inter-RAT umbrella.

Introduction

The LTE side prepares the CDMA2000 branch, delivers Mobility From E-UTRA Command, and the UE continues on the target CDMA2000 system after leaving LTE.

Use this page when the destination technology is CDMA2000.

What Is Handover to CDMA2000 in Simple Terms?

  • What starts the procedure: The network chooses CDMA2000 as the target system.
  • What the UE and network want to achieve: Move connected service off LTE and continue on CDMA2000.
  • What success looks like: The UE exits LTE and starts the expected CDMA2000 branch.
  • What failure means: The target CDMA2000 continuation does not appear or does not complete.

Why this procedure matters

This page gives the target-specific CDMA2000 view of outbound LTE mobility.

Quick Fact Sheet

Procedure name LTE Handover to CDMA2000
Domain Outbound inter-RAT mobility from LTE to CDMA2000
Main trigger CDMA2000 selected as the target RAT
Start state UE is connected on LTE
End state UE continues on CDMA2000
Main nodes UE, source eNB, target CDMA2000 system
Main protocols LTE RRC and CDMA2000 target control signaling
Main success outcome Service leaves LTE and continues on CDMA2000
Main failure outcome Inter-RAT transition to CDMA2000 fails
Most important messages Mobility From E-UTRA Command and target continuation
Main specs TS 36.331 and CDMA2000 mobility specs
LTE Handover to CDMA2000 call flow
Click the diagram to open the full-size in a new tab.

Handover Concept

This illustration shows the basic handover concept used in this procedure: the UE leaves the serving side after the mobility decision and continues on the target side once the target path is ready.

Handover Concept Concept illustration of a UE moving from the serving side to the target side. Source eNB CDMA2000 UE moving to target Serving side Target side
Prepare target branch to Continue on CDMA2000. The target system becomes active if the move succeeds.
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Preconditions

  • The UE is connected on LTE.
  • CDMA2000 is selected as the target system.
  • The target continuation branch is prepared.

Nodes and Interfaces

Nodes involved

Node Role in this procedure
UE Receives the command and continues on CDMA2000.
Source eNB Delivers the outbound LTE command.
CDMA2000 system Takes over the service branch after LTE exit.

Interfaces used

Interface Path Role
LTE Uu UE <-> source eNB Carries the LTE exit command.
CDMA2000 target interface UE <-> target system Carries the target continuation after LTE exit.

End-to-End Call Flow

UE             Source eNB             CDMA2000
|<--Mobility From EUTRA Command--|      |
|==== leave LTE =======================>|
|----------- CDMA2000 continuation ----->|

Major Phases

Phase What happens
1. Prepare CDMA2000 branch The LTE side selects and prepares the target system.
2. Deliver exit command The source eNB sends the LTE-side move command.
3. Exit LTE The current LTE serving path ends.
4. Continue on CDMA2000 The target branch begins.

Step-by-Step Breakdown

Step 1: Target preparation

Sender -> receiver: LTE side

Message(s): Inter-RAT preparation

Purpose: Prepare the CDMA2000 continuation branch.

State or context change: The UE is still on LTE.

Note: This is the last preparation stage before LTE exit.

Step 2: Mobility command

Sender -> receiver: source eNB -> UE

Message(s): Mobility From E-UTRA Command

Purpose: Carry the CDMA2000 target payload toward the UE.

State or context change: The UE has the information it needs to leave LTE.

Note: This is the main LTE-side message to inspect.

Step 3: Exit LTE

Sender -> receiver: UE

Message(s): LTE exit execution

Purpose: Stop the source LTE serving path.

State or context change: LTE connected service ends.

Note: The next meaningful trace now belongs to CDMA2000.

Step 4: CDMA2000 continuation

Sender -> receiver: UE -> CDMA2000

Message(s): Target access and continuation

Purpose: Continue service on the target technology.

State or context change: CDMA2000 becomes active if the move succeeds.

Note: Interpret the next branch with the target-system procedure.

Important Messages

Message Protocol Direction Purpose in this procedure What to inspect briefly
Mobility From E-UTRA Command RRC source eNB -> UE Carries the CDMA2000 target move. Inspect the target-system payload and the LTE exit timing.

Important Parameters to Inspect

Parameter What it is Where it appears Why it matters Common issues
Target RAT CDMA2000 as the destination system. Mobility command Confirms this is the correct target-specific page. Wrong target assumption.
Exit timing The final LTE-side control timing. Air trace Useful for aligning LTE and CDMA2000 traces. Cross-system timing mismatch.
First target message The first visible CDMA2000 continuation message. Target trace Confirms whether the move reached the target system. Target branch missing.
Service expectation The service that should continue on the target. Mobility context Helps interpret the target branch. Wrong expectation about preserved service.
Recovery result What happened if entry failed. Later trace Shows whether another fallback branch appeared. Failure hidden as generic radio loss.

Successful Completion

Success means the UE leaves LTE and starts the expected CDMA2000 continuation branch.

Common Failures and Troubleshooting

Symptom Likely cause Where to inspect Relevant message(s) Relevant interface(s) Likely next step
LTE exit appears but CDMA2000 continuation does not The move left LTE but the target branch failed or never started. The LTE command and the first expected target-side message. Mobility From E-UTRA Command LTE Uu and target interface Check the target-side continuation immediately after the LTE exit.
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What to Check in Logs and Traces

  • Confirm that the target system in the command is CDMA2000.
  • Use the LTE exit timing as the correlation point into the target trace.
  • Check whether the first CDMA2000 control message appears after LTE exit.

Related Pages

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

Handover to CDMA2000 is a target-specific legacy branch. Treat the LTE command as the last LTE-side anchor before target continuation.

FAQ

What is LTE handover to CDMA2000?

It is the inter-RAT mobility path that moves connected service from LTE to CDMA2000.