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# Reply To: Minute Erlang Per drop

#64969
pix
Guest

hi fresh, fresher and freshest,

it shows the “density” of drops in the cell. In the end, it is just another way to estimate the call drop rate in the cell.
20 erlangs
10 drops
= 2 erl/drop = 120 minute-erl/drop

There is 1 drop every 2 hours of communication in the cell.

Now let’s assume that 1 call = 1 minute
There are 20 erlangs, that’s 20 hours = 1,200 minutes = 1,200 calls
CDR = 10/1,200 = 0.89%

There is a proportional relationship between min-erl/drop and the call drop rate. You could as well use the following formula :
drops / (erlang * 3600 / tch_average_duration [s])

the main difference is that if TCH are shorter than usual (due to HO for example), it means there are more calls in the cell, but still the same amount of drops : you drop rate decreases.
If TCH are longer than usual, the drop rate increases. But a “drop” KPI should not be impacted by TCH duration.

Whereas the minute-erlang per drop remains stable whatever the duration of the TCH.
It looks like the min-erlang per drop is a more objective approach than the call drop rate, especially in networks with a high amount of handovers. Problematic cells with high amount of HO have shorter TCH, therefore they have a better call drop rate than the subscribers are experiencing.

Well, while writing this post I convinced myself that erl/drop is useful :)) I am a manipulative master….

Regards 🙂
pix