參數(shù)資料
型號(hào)： PXB 4330 E
廠商： SIEMENS AG
英文描述： ATM Buffer Manager(異步傳輸模式緩沖器管理器)
中文描述： 緩沖區(qū)管理器自動(dòng)柜員機(jī)（異步傳輸模式緩沖器管理器）
文件頁數(shù)： 44/61頁
文件大小： 551K
代理商： PXB 4330 E
PXB 4330 E
Semiconductor Group
44
Application Note 11.98
The guaranteed buffer space for rt-traffic is selected to e.g. 512 cells. Therefore the
highest BufNrtMax threshold (in general BufNrtEPD thresholds are below the
corresponding BufNrtMax; otherwise it would make no sense) has to be chosen in a
manner to ensure space for these 512 cells. Thus BufNrtMax of VBR.2(nrt) is set to
65024 cells.
TrafClassMax of both rt-traffic classes is set to 256 cells to prevent one rt-traffic class
from occupying all 512 guaranteed cells.
The threshold SbMaxEpdCi case a) + b) (see [
1
], page 52) is intended to be used as
global buffer occupation control per scheduler e.g. in case a scheduler is not served due
to failure of the associated PHY (as the buffer space occupied by this scheduler without
limitation would grow very fast and take the whole buffer). Overbooking is
recommended, so in this example the value of SbMaxEpdCi case a) or b) is set to 50%
of total buffer. If only 2 schedulers are used it should be set e.g. to 75% per scheduler in
order to reach overbooking.
QMaxEPD of both rt-traffic classes is set to Max. threshold for at least 256 cells in order
to enable the usage of the buffer space given by the respective TrafClassMax.
QCICLP1 is not used by CBR.1 and VBR.1(rt) as for this traffic classes the conformance
definition for PCR and SCR applies for CLP=0+1 cells (see [
6
]). Hence QCICLP1 has to
be set to maximum value 3FF
H
.
Non-Real-Time Traffic
VBR.2(nrt) and VBR.3(nrt)
BufNrtMax of VBR.2 is set to 65024 cells to ensure the guaranteed buffer space (512
cells) for rt-traffic. BufNrtMax of VBR.3 is arbitrarily chosen to 58368 cells (10% below
VBR.2). For both traffic classes these are only PPD thresholds. EPD thresholds are not
useful as VBR-traffic is already policed.
TrafClassMax normally should be chosen between 50-80% of the global buffer. In this
example they were set to 32768 cells (= 50%). During longer periods where only VBR.2
or VBR.3 traffic arrives the global buffer occupation is limited by the respective
TrafClassMax. As these thresholds (= TrafClassMax of VBR.2 and VBR.3) are lower
than the BufNrtMax/BufNrtEPD thresholds of GFR and UBR, still arriving GFR/UBR cells
(after a longer period with only VBR.2/VBR.3 traffic) can be buffered. Supposing
TrafClassMax of VBR.2 and VBR.3 were set to 80% (= 52224 cells) then both
BufNrtEPD thresholds of GFR and UBR are exceeded and if VBR.2 or VBR.3 has
occupied it’s maximum allowed buffer space represented by TrafClassMax every new
arriving GFR or UBR cell is discarded (although free buffer space is available on
condition that the whole remaining buffer space isn’t still occupied by the other traffic
classes).
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