Selasa, 01 Desember 2009

Drop Call Analysis

From technical perspective, dropped calls show the number of

abnormal disconnection’s during call setup, SMS, supplementary

service activation or during conversation. They are a few different

counters for dropped calls, i.e. dropped calls due to low signal

strength, bad quality, too high timing advance and miscellaneous is

used to get an indication of the reason for possible bad performance.

From a subscriber point of view, dropped calls are those that

interrupt an ongoing conversation, i.e. a call dropped on the TCH. If the

call is dropped on the SDCCH the user simply re-dials again and

hopefully succeeds with the new call setup. For this analysis we will

focus on the drop call on the Traffic Channel (TCH).

TCH Drop call can be divided into a few categories:

1. Excessive Timing advance

2. Low Signal Strength – UL/DL/BL

3. BL Bad Quality – UL/DL/BL

4. Sudden Loss

5. Other reason (not standalone counter)

Dropped connection due to failure is counted in counter TFNDROP,

which step for the number of abnormally terminated connections.

These counters are incremented when the BSC send ‘CLEAR

REQUEST’ and when ‘CLEAR COMMAND’ message is received if the

code differs from the cause codes ‘CALL CONTROL’ and ‘Handover

successful’. If the ‘CLEAR REQUEST’ has been sent previously before

‘CLEAR COMMAND’, the counter will not step.

When a call is abnormally disconnected, that is ‘CLEAR REQUEST’ is

sent to the MSC, a check is made in the function Assignment or Handover if any of the

following urgency state existed. If more than one type of urgency state are indicated by

the locating procedure, the following priority (highest priority first) is used to determine

the type of urgency state:

1. Excessive Timing Advance (TA)

2. Low signal strength in downlink and/or uplink

3. Bad quality downlink and/or uplink

4. Sudden loss of connection

When type of urgency is determined, one of counters of this urgency

state is stepped.