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LTE Generic Error Handling Procedure Call Flow

call-flow LTE | Failure | Troubleshooting

LTE Generic Error Handling Procedure is the LTE failure-handling branch used when a procedure cannot continue normally and the network or UE has to reject, report, or classify the problem.

This page focuses on the failure path itself rather than the earlier success flow that should have happened before it.

Introduction

Generic error handling is the fallback failure path used when a procedure breaks, but the exact LTE failure family is still not clear. It sits above the more specific branches and helps sort the trace before deeper analysis starts.

Use this page when the trace clearly shows a broken procedure, but it is still unclear whether the problem belongs to unknown content, missing content, encoding trouble, or a later reject or timeout branch.

What Is LTE Generic Error Handling Procedure in Simple Terms?

What starts the procedure: A procedure receives invalid, unsupported, or otherwise unusable content and cannot continue normally.
What the UE and network want to achieve: Classify the procedure break and send the analysis into the correct specific failure branch.
What success looks like: The failure is classified correctly and the next analysis step becomes clear.
What failure means: The wrong failure branch is assumed and the real problem is hidden under generic symptoms.

Why this procedure matters

Many LTE failures look similar at the symptom level. Correctly classifying the failure type early prevents time being lost on the wrong branch.

Quick Fact Sheet

Procedure name	LTE Generic Error Handling Procedure
Domain	Generic LTE protocol failure handling
Main trigger	A procedure receives invalid, unsupported, or otherwise unusable content and cannot continue normally.
Start state	A wider LTE procedure is already in progress and something has gone wrong or become invalid
End state	The invalid branch is rejected, ignored, or routed to a more specific failure category
Main nodes	UE, eNB, MME / network side
Main protocols	RRC, NAS, procedure context
Main success outcome	The failure branch is clearly identified and the next corrective action is possible
Main failure outcome	The real break point stays unclear or the wrong failure branch is assumed
Most important messages	Rejects, ignore rules, later release or retry behavior
Main specs	TS 36.331, TS 24.301

LTE Generic Error Handling Procedure — Click the diagram to open the full-size in a new tab.

Preconditions

A wider LTE procedure is already underway or has just failed.
The network and UE still have enough context to reject, report, or classify the failure.
The trace includes the messages immediately before and after the failure branch.

Nodes and Interfaces

Nodes involved

Node	Role in this procedure
UE	Detects the condition, rejects the invalid branch, or reports failure context after the earlier problem.
eNB	Carries the LTE radio side and receives failure or reject behavior from the UE.
MME / network side	Interprets the reject, timeout, or failure report and decides the next correction or release step.

Interfaces used

Interface	Path	Role
LTE Uu	UE <-> eNB	Carries the reject or failure-report signaling seen on the radio side.
S1-MME	eNB <-> MME	Carries the wider procedure context behind the failure or reject branch.

End-to-End Call Flow

UE / network        Procedure context
|--invalid condition detected---->|
|--apply generic error rule------>|
|--reject / ignore / release----->|

Major Phases

Phase	What happens
1. Detect the abnormal condition	A procedure step is found to be invalid or unusable.
2. Decide the handling category	The network or UE decides whether the problem is generic or belongs to a more specific branch.
3. Apply the handling rule	The procedure is rejected, ignored, released, or redirected to a later analysis path.

Step-by-Step Breakdown

Step 1: Notice the abnormal procedure state

Sender -> receiver: UE or network side

Message(s): Procedure-specific message or condition

Purpose: Recognize that the current branch cannot continue normally.

State or context change: The wider procedure is now on a failure path instead of a success path.

Note: This is the point where later troubleshooting should stop assuming a normal progression.

Step 2: Map the failure to a handling type

Sender -> receiver: UE or network side

Message(s): Generic error classification

Purpose: Decide whether the issue is missing content, unknown content, encoding trouble, or another class of failure.

State or context change: The failure now has a usable category for later analysis.

Note: This is the most important reasoning step in the whole generic error path.

Step 3: Apply the chosen handling rule

Sender -> receiver: Procedure side -> peer or internal handling

Message(s): Reject, ignore, release, or retry decision

Purpose: Finish the failure-handling branch according to the detected category.

State or context change: The procedure is no longer trying to continue normally.

Note: The visible error response is often less important than the category decision behind it.

Important Messages

Message	Protocol	Direction	Purpose in this procedure	What to inspect briefly
Attach Reject	NAS	Network -> UE	Useful example of a hard failure outcome after generic or specific analysis.	Check whether the reject is the real root cause or only the visible result of an earlier error category.
Security Mode Reject	NAS	UE -> Network	Useful example of a UE-side reject after a procedure becomes unacceptable.	Check whether the reject came from content validity, security mismatch, or an earlier error condition.

Important Parameters to Inspect

Parameter	What it is	Where it appears	Why it matters	Common issues
Failure category	The class of failure being applied to the broken procedure.	Failure analysis stage	Explains which specific branch should be opened next.	The trace is read with the wrong failure category.
First invalid condition	The earliest point where the branch stopped being acceptable.	Message before reject or timeout	Shows the real break point instead of the later visible reject only.	The visible reject is blamed while the true break point is earlier.
Handling rule	Whether the condition should be ignored, rejected, released, or retried.	Failure branch	Explains why the procedure ended the way it did.	The output looks surprising because the handling rule was not identified.
Procedure context	The wider attach, security, mobility, or bearer branch where the failure occurred.	Full trace context	Prevents the generic failure from being read in isolation.	The failure is analyzed without the wider procedure context.
Retry or release behavior	What happened after the failure classification.	Later messages	Shows whether the system tried to recover or ended the procedure completely.	The trace is cut too early and misses the actual failure outcome.

Successful Completion

Success in this page means the failure has been classified correctly enough that the next troubleshooting step is obvious.

Common Failures and Troubleshooting

Symptom	Likely cause	Where to inspect	Relevant message(s)	Relevant interface(s)	Likely next step
Trace shows a reject but the real cause is unclear	The visible reject is only the final effect of an earlier invalid condition.	The message immediately before the reject and the wider procedure context.	Reject message and earlier procedure message	NAS or RRC plus context	Go backward one or two messages and classify the earlier abnormal condition first.
Same symptom appears in multiple procedures	A generic symptom is being reused across different LTE branches.	Procedure family, trigger, and the first invalid condition.	Procedure-specific	Procedure-specific	Separate the symptom from the procedure family before choosing the next page.

What to Check in Logs and Traces

Find the first invalid condition before reading the later reject.
Classify the failure category before drilling into cause values.
Keep the wider procedure context visible while reading the failure branch.

Related sub-procedures

Related message reference pages

Related troubleshooting pages

Notes

This page is a classification layer. It helps choose the correct specific failure branch rather than replacing the deeper, more specific failure pages.

FAQ

What is LTE generic error handling?

It is the high-level failure-classification path used when a procedure cannot continue and the exact failure type still needs to be identified.

Should this page be read before the specific failure pages?

Yes, when the trace shows a break but the exact failure category is not yet obvious.