FAILRESTART-1 Failure during the start of an alert that affects individual cells within eNBs

Description

Cell broadcast fails in one cell of an eNB upon starting the alert. The alert starts correctly in other cells of the same eNB.

The affected eNB will provide to the MME the list of cells in which the broadcast is running. The MME compares this list with the one sent and checks for missing cells. The MME reports back to the CBC the list of eNBs that failed broadcast the message in all their cells.

Reported list in failure message

This TC is tricky and the outcome is likely to be specific to each MME implementation. The standard provides two methods for the MME to inform about failures in cell broadcasting in eNBs:

1. WRITE-REPLACE WARNING INDICATION

   If indication messages are enabled for CBS, then the MME shall report the list of eNBs that fail to broadcast in ALL their cells. This method provides eNB level granularity.

   In principle, this does not cover the case of this TC, in which the eNB activates broadcast in some cells but fails to activate in others (e.g. a 3 sectors eNB requested to broadcast in all the sectors but can only start the broadcast in two and fails in the third one).

2. FAILURE INDICATION

   This method provides cell level granularity. The MME can use this method to cover the cases of this TC in which an eNB activates broadcast in some cells but fails to activate it in other cells.

Pre-requisites

• Define an alert area that includes at least two cells controlled by the same eNB. It may include cells in other eNBs as well.
• Dispose the conditions for the broadcast to fail in one cell of the eNB that controls at least two cells of the alert area.

TIP

A possible way to execute this test case in a real LTE network is to congest the broadcasting resources of one cell by having multiple messages broadcasted in parallel in this cell.

Steps to execute

1. CBE sends CAP Alert message with:
   • A single info element. I.e. only one message in one language.
   • alertinfo.language.code set to the value of the local language (e.g. sl-SI for Slovenian).
   • alertinfo.instruction.text content of the alert message in local language. Using a very long message that fills the 15 pages might help to trigger a failure.
   • Time information that allows the CBC to calculate the repetition period and the number of repetitions.
   • Alert area that is inside the area controlled by a single MME. I.e. only one MME needs to be involved in this test.

Information flow

Result

Verify that:

1. The message sequence completes as one of the two options shown in the flow above. Option 1 is only possible if indication messages are supported and enabled in the MME.
2. The failure event is logged by the CBC.
3. If the CBC is configured to raise an alarm in this case, then an alarm is raised.
4. If the CBE - CBC interface provides the means for conveying information about this type of failures, then the CBC sends this information to the CBE.