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# Reply To: T200 optimal value

#61106
Zbigniew
Guest

Hi Pix,

here are some results for a single Nokia cell (daily values):

DAY SDCCH Assign SDCCH Radio Fail SDCCH Radio Fail [%] T200
1 16088 506 3,15 220
2 16231 537 3,31 220
3 13879 372 2,68 300
4 12639 298 2,36 400
5 17751 218 1,23 500
6 15540 208 1,34 600
7 13732 203 1,48 700
8 14836 274 1,85 800
9 14867 296 1,99 900
10 14717 143 0,97 1000
11 12800 101 0,79 1100
12 15288 133 0,87 1200
13 22190 129 0,58 1260

I agree with your calculation that improvements are only possibly in “steps” of 51er frames.

In your example you wrote that the MS is able to ack in frames 15,16,17,18. So the minimum timer value must be 18 frames = 82 ms.
But I think that in the opposite direction (in case the BTS has to ack L2 messages) the timer must be set to greater values:

MS sends in frames 15,16,17,18
BTS acks in frames 1,2,3,4

The minimum timer value will then be 51-15+4=40 frames = 184 ms

The strange thing is that the Siemens default value (145 ms) is below that minimum. The Nokia default value (220 ms) seems to fit if the ack has to be sent in the same 51er frame.

Which are the default values for T200 in Alacatel ? Which average SDCCH Radio Failure Rate do you see in your network ?

Tnank you for this interesting discussion !

Zbigniew