1.1 Solutions to High TCH Call Drop Rate
Before analyzing the causes of high TCH call drop rates, you should find out the
difference between the actual TCH call drop rate and the expected value. You
should also find out the impact of the problems and the related KPIs.
You can analyze the distribution of call drops based on the traffic measurement. If
a certain type of call drop accounts for a large proportion of total call drops, you
can locate the fault by performing the corresponding procedure. If no obvious
causes are found, you can perform the procedures shown in Ошибка! Источник
ссылки не найден.. The following table lists the mapping between the traffic
measurement counters and the troubleshooting procedures.
Traffic Measurement Counter
Troubleshooting Procedure
M3100A (T200 expiry)
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M3101A (radio link failure)
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M3101D (radio resource unavailable)
1.1.1 Checking the Hardware
CM333 (Abis terrestrial link
failure)
1.1.2 Checking the Transmission
M314 (device failure)
1.1.1 Checking the Hardware
The following sections describe the solutions to high TCH call drop rates.
The traffic measurement counters and KPIs in this document are the same as
those in the BSC6000V9R8C01B051 version.
1.1.1 Checking the Hardware
If a TRX or a combiner is faulty or if an RF cable is incorrectly connected, seizing
the TCH becomes difficult, and thus the TCH call drop rate increases. See
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You can check whether hardware is faulty by viewing BTS alarms or viewing the
hardware state on the Site Device Panel of the LMT. Table 1-1 lists the major BSC
alarms related to hardware failures.
Table 1-1 Major BSC alarms related to hardware failure
Alarm ID
Alarm Name
1000
LAPD_OML Fault Alarm
2204
TRX Communication Alarm
4414
TRX VSWR Alarm
3606
DRU Hardware Alarm
In addition, you can locate the fault by checking the traffic measurement related to
hardware failures.
Cause
BSC Level
Cell Level
Equipment
failure
Access Measurement per BSC
in BSC Measurement:
KPI Measurement per Cell:
Available TCHs per BSC
Available TCHs
Configured TCHs per BSC
Configured TCHs
Available TCHs per BSC
TRX Measurement per Cell:
TCH Availability
Number of configured TRXs in a
cell
Number of available TRXs in a
cell
Call Drop Measurement per Cell
in Call Measurement:
Call Drops due to Equipment
Failure (TCH)
1.1.2 Checking the Transmission
Poor transmission quality, unstable transmission links, or insufficient resources on
the Abis and A interface may lead to the increase of the TCH call drop rate. You
can check the transmission conditions by viewing the alarms related to
transmission. If a large number of transmission alarms are generated, you can
infer that transmission failure has occurred. Then, you should check the
transmission connections. See Ошибка! Источник ссылки не найден..
Table 1-2 BSC alarms related to transmission
Alarm ID
Alarm Name
1000
LAPD_OML Fault Alarm
11270
LAPD Alarm
11278
E1 Local Alarm
11280
E1 Remote Alarm
20081
Loss of E1/T1 Signals (LOS)
20082
E1/T1 Frame Out-of-Synchronization (LOF)
In addition, you can locate the fault by checking the traffic measurement related to
transmission failures.
Cause
BSC Level
Cell Level
Transmission failure
LAPD Measurement in
BSC Measurement
Channel Activation
Measurement per Cell in Call
Measurement:
CHAN ACTIV NACK
Messages Sent by BTS
Channel Activation Timeouts
Call Drop Measurement per
Cell in Call Measurement:
Measurement of Call Drops
Due to Abis Terrestrial Link
Failure