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CHAPTER 5 SAR FUNCTION
233
31
0
alpha
- 0 -
16
15
Nubr_th
11
beta1
beta2
2
3
6
5
12
8
7
- 0 -
Nubr_th:
Number of UBR service VCs. Nubr_th is used as the threshold value in calculation of the band
allocated to UBR.
Initial value after a reset:
0
alpha:
Used for ABR internal congestion control. Sets the proportion by which the rate will be reduced
in response to internal congestion. (See
Section 5.8.6
.)
Initial value after a reset:
0
beta2:
β
2, that is, the ratio of bands to be assigned to the UBR when the number of actual active UBR
VCs is greater than Nubr_th
β
2 = 1/2
beta2
Initial value after a reset:
0
beta1:
β
1, that is, the ratio of bands to be assigned to the UBR when the number of actual active UBR
VCs is less than Nubr_th
β
1 = 1 - 1/2
beta1
Initial value after a reset:
7
The bands to be assigned to the UBR are obtained using the following:
if (n_ubr = 0) then
C
ABR
= C
ABR+UBR
C
UBR
= 0
if (0 < n_ubr < Nubr_th) then
C
ABR
= (C
ABR+UBR
- sum of MCR)*
β
1 + sum of MCR
C
UBR
= (C
ABR+UBR
- sum of MCR)*(1 -
β
1)
if (n_ubr
≥
Nubr_th) then
C
ABR
= (C
ABR+UBR
- sum of MCR)*
β
2 + sum of MCR
C
UBR
= (C
ABR+UBR
- sum of MCR)*(1 -
β
2)
n_ubr:
Actual active UBR VCs
C
ABR
:
ABR band
C
UBR
:
UBR band
C
ABR+UBR
:
ABR and UBR bands (value in the AUB register)
sum of MCR: MCR total
β
1:
β
1 = 1 - 1/2
beta1
β
2:
β
2 = 1/2
beta2
The ranges of the values set for the parameters in the above expressions are:
β
1:
(0, 0.5, 0.75, 0.85, 0.9375, 0.96875, 0.984375, 0.9921875)
β
2:
(1, 0.5, 0.25, 0.125, 0.0625, 0.03125, 0.015625, 0.0078125)
Nubr_th:
(0 to 65,535)