TCH DR vs Call DR

[vasa08]

Dear Experts,

I need your help in understanding a difference between two KPIs - TCH Drop Rate and Call Drop Rate. See, in my operator we calculate only TCH Drop Rate as number of TCH drops / number of successful TCH assignments.
But in all GSM optimization books I saw it's recommended to calculate Call Drop Rate (or Dropped Call Rate) KPI and if I understood it correctly - CDR for a cell_A is equal to number of TCH drops in Cell_A / number of calls which were finished in Cell_A.

Is it correct?

So, main difference between KPIs is their denominators. In Call Drop Rate formula denominator is number of successful TCH assignments minus all outgoing HO from a cell. It means that CDR shows problems on the concrete cell (cell_A in my example).

So, what's a meaning to calculate TCH Drop Rate?

I will appreciate for your answers!

[RF engineer]

Dear Experts,

I need your help in understanding a difference between two KPIs - TCH Drop Rate and Call Drop Rate. See, in my operator we calculate only TCH Drop Rate as number of TCH drops / number of successful TCH assignments.
But in all GSM optimization books I saw it's recommended to calculate Call Drop Rate (or Dropped Call Rate) KPI and if I understood it correctly - CDR for a cell_A is equal to number of TCH drops in Cell_A / number of calls which were finished in Cell_A.

Is it correct?

So, main difference between KPIs is their denominators. In Call Drop Rate formula denominator is number of successful TCH assignments minus all outgoing HO from a cell. It means that CDR shows problems on the concrete cell (cell_A in my example).

So, what's a meaning to calculate TCH Drop Rate?

I will appreciate for your answers!

From this you can see if the drops is come from normal assignment or handover.

BR

[vasa08]

From this you can see if the drops is come from normal assignment or handover.
BR

Sorry, didn't understand you. I can see if drops come from handovers using TCH drops distrubution (TCH drop due to radiolink, TCH drop due to inter cell handover etc.). Still didn't understand a meaning of TCH Drop call rate calculation - why do we need this KPI?

[scumbie]

Basically ....the TCH drop rate you are calculating is assuming the number of incoming and outgoing handovers for that cell are equal (which is rarely the case).

Now to get a true value of the drop rate for a cell :

CDR(cell_level)= (TN_DROP/N_CALLS) x 100%

Where:

CDR(cell_level)- Call drop rate for that cell
TN_DROPS - Total number of dropped connections
N_CALLS- Number of calls terminated in a cell


Now to explain further N_CALLS:

I_CALLS - Number of initiated calls in a cell
Inc- Sum of all incoming handovers to a cell
Outg - Sum of all outgoing handover from a cell

Therefore:
N_CALLS= I_CALLS+ IncHO-OutgHO


If your network employs Assignment to Other feature you need to also consider

AW - Number of successful assignments to worse cell
AB - Number of successful assignments to better cell

so N_CALLS become:

N_CALLS= I_CALLS+ Inc(HO-AB-AW)-Outg(HO-AB-AW)


Below is the formula for N_CALL if you are using E******* BSC:

N_CALLS=TFCASSALL + TFCASSALLSUB +THCASSALL +THCASSALLSUB + (SUMIHOSUCC-SUMIABSUCC-SUMIAMSUCC) - (SUMOHOSUCC-SUMOABSUCC-SUMOAWSUCC).


I know its a lot of info, I hope it helps

scumbie

[vasa08]

Now to get a true value of the drop rate for a cell :

CDR(cell_level)= (TN_DROP/N_CALLS) x 100%

Where:

CDR(cell_level)- Call drop rate for that cell
TN_DROPS - Total number of dropped connections
N_CALLS- Number of calls terminated in a cell


Now to explain further N_CALLS:

I_CALLS - Number of initiated calls in a cell
Inc- Sum of all incoming handovers to a cell
Outg - Sum of all outgoing handover from a cell

Therefore:
N_CALLS= I_CALLS+ IncHO-OutgHO

scumbie

scumbie, thanks a lot for the explanation! Now is clear with CDR. But again, what's meaning to calculate TCH Drop Rate, which is

TDR(cell_level)= (TN_DROP/[I_CALLS + IncHO]) x 100%

What does this KPI tell me about a cell? Should a RF optimization engineer analyze TCH drop rate?

Sorry if questions look stupid, I'm a beginner in optimization.

[ludali]

Hello,

It appears that in your formula for TCH Drop there is an assumption that calls terminating on a particular cells are either those initiated on it or due to incoming HO (thereby excluding outgoing HO).

I have been in a situation like that before and I reconcile the two cases in this way:


For my understanding of RNO and for the purpose of getting a true picture (and thereby identifying issues and resolving them), I consider CDR.
TCH Drop Rate should only be used to comply with requirements of operator (who may need the KPI calculated in that way even though it's not as logical to) only.

Note that with TCH Drop Rate, assignments due to Handover (incoming or outgoing is assumed balanced, i.e. incoming HO - outgoing HO = 0).

BR,

Ludali

[Processor]

In my humble opinion you are referring to the same thing except its a vendor based KPI else in GSM standards you can only have a call drop when on a TCH channel, hence, can be referred to as TCH drop.

Someone should please correct me if i'm wrong.:D

[RF engineer]

Sorry, didn't understand you. I can see if drops come from handovers using TCH drops distrubution (TCH drop due to radiolink, TCH drop due to inter cell handover etc.). Still didn't understand a meaning of TCH Drop call rate calculation - why do we need this KPI?

Dear
Sure you can use the drop distribution but some times vendor gives you alot of KPIs that make you confusing you can use your KPI like CSSR none of the world vendor have unique Formula .

so if you compare the CDR and TCH drop you can see it comes from normal assignment or HO.

BR