Call drop analysis .1 Principles

With this feature, you can obtain information about call drops. This information can help analyse the call drop scenarios and fine-tune the network.

The data available includes:

• RSL layer 3 history:

It gives a maximum of 63 last treated Abis RSL and BTS internal messages at the BTS at TDMA level. This allows you to determine in which phase of the communication the call drop occurred. For each message, it gives the message type and the BTS state when the message was treated.

• LAPDm history:

It gives a maximum of 16 LAPDm frames exchanged between the MS and the BTS (uplink and downlink) on SAPI 0 of the main channel. For each message, it gives the channel and the N3 message type if any.

• Connection context:

It gives last average measurements available in L1M for the communication, and last received (enhanced) measurement report.

This allows you to check the radio characteristics of the communication.

The role of the BTS in the Call Drop Analysis feature is to provide the relevant information for the analysis to be done at the OMC-R.

When the call drop is detected by the BTS, the BTS systematically sends the data it owns to the BSC to help in analysing the call drop.

When the Call Drop is detected by the BSC, the BSC requests information through a RF_CHAN_REL message. The request can be for one or more items of information.

This feature is guaranteed only with a BSC 3000.

GSM-R dropped calls are not analyzed.

1.12.9.2 Interoperability with other features

Call path/call path trace The features Call path/Call path trace and Call Drop analysis both use a lot of memory space on the BSC and the SDO.

Both features can be activated at the same time, but in that case, it is recommended that the operator activates only a few cells at a time on the same BSC (to avoid congestion on the BSC and the SDO).

Switch Interference Matrix (16411) The Switch Interference Matrix stores a lot of data on the BSC disk. Due to disk space limitation on the BSC, it is forbidden to activate the Switch Interference Matrix and the Call Drop analysis features simultaneously.

When activating the Call Drop Analysis on a cell, the OMC-R/W-NMS checks the flag interferenceMatrixRunning. If the cell is still running the Interference Matrix measurements, then the callDropActivation parameter cannot be set to enabled (that is, the Call Drop Analysis feature cannot be activated).

1.12.9.3 Benefits

The feature provides the operator with a means to analyze call drops and thus to optimize the RF network.

On cells where the call drop ratio is too high, the operator can activate the feature and analyze the call drops. This enables time and cost efficient RF network optimization according to the call drops causes.

1.12.9.4 Activation

The class 3 OMC-R parameter callDropActivation (on the bts object) is used to enable or disable the feature. If enabled, the operator can select:

• drops on TCH communications

• drops on SDCCH communications

• drops on both TCH and SDCCH communications 1.12.9.5 File naming conventions

For the file naming conventions on the SDO, see NTP < 130 >.

1.12.9.6 Post-processing of data collected

The feature 28796 (Call drop analysis post-processing), introduced in V16.0, provides a tool to process the data collected by the call drop analysis (CDA) feature. This tool is available on the OMC-R but not on the WNMS.

The purpose of tool is to help extract and process information to:

• Characterize the conditions when the call drop occurred.

• Sort the different types of call drops.

• Create user customized reports and graphs to identify call drop causes.

• Provide statistics for each kind of call drop or group of call drops respecting the same criteria (filter choice) for a selected NE (cell, group of cells).

Using the tool With the tool, the user can select/transfer the CDA data from the server (SDO) where it is stored to the PC on which the tool is installed, and then process the data.

For performance reasons, it is recommended not to run the RMD (Radio measurement distribution), CDA (Call drop analysis), and IM (Interference matrix) post-processing tools at the same time.

For more details of the post-processing tool, see NTP < 006 >.

There are three phases:

• transferring data

• selecting data

• post-processing the data

Transferring data The data can be transferred in one of the following ways:

• Manually

A file explorer window helps the user to select the files or folder to be retrieved. The user can select one or more SDO servers and/or retrieve one or more days data from these SDOs.

• Semi-automatically

Using a profile name, the user can launch the data retrieval by pressing a button. From the profile, the tool knows the SDO server to connect to and all CDA data not present on the user’s PC is retrieved.

• Automatically

A job scheduler helps the user to set the time, date, and the periodicity of the data retrieval. This operation can be set only if the PC on which the tool is installed is connected (that is, it is not in offline mode). The job scheduler definition is associated with a profile.

Selecting data Examples of data selection are:

• Select data from one or more SDOs.

• Select data based on: BSCIC, Cell Id, LAC.

• Select data for a period (one or more days selected with start and end date).

• Select data for a time of the day (whole day or a specific time period).

Post-processing data Examples of post-processing for CDA data are:

• Filter the data with user-defined filters.

• Display the total number of signalling and traffic drops per cell.

• Export CDA data in csv (comma-separated values) format.

• Export CDA data in HTML format.

• Display statistical reports (general drops, radio drops, intercell HO drops, intracell HO drops, system drops etc.).

• Compare graphs for the same cell at different dates.

1.12.10 Generating an Interference Matrix