參數(shù)資料
型號： 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)管理器自動柜員機（異步傳輸模式緩沖器管理器）
文件頁數(shù)： 9/61頁
文件大?。?/td> 551K
代理商： PXB 4330 E
PXB 4330 E
ABM Buffer Configuration
Semiconductor Group
9
Application Note 11.98
If there is a cell in that queue it is immediately forwarded due to the higher priority of the
real time queue versus that of the WFQ mux.
Queues with Weight Factor
These queues are for VBR-rt and all sorts of non-real time traffic such as VBR-nrt, ABR,
GFR and UBR.
For this example VBR-rt is VBR.1 and VBR-nrt are VBR.2 and VBR.3 (VBR.1,2,3
according to [
6
]).
a) Real time traffic
All VCs with VBR.1 traffic can be assigned to one queue which has the maximum
weight factor w=1. This weight factor ensures that a cell in this queue is forwarded
with the highest priority to the WFQ multiplexer. Therefore this queue acts almost
like a second real time queue directly connected at a second input of the priority
mux. It has a lower priority than the real time queue for the CBR traffic (equivalent
diagram depicted through dashed lines, see
Figure 2
).
b) Non real time traffic
Each VC with VBR-nrt traffic (VBR.2 and VBR.3), ABR and GFR traffic is usually
assigned an individual queue to guarantee a minimum service rate (SCR for VBR-
nrt and MCR for ABR and GFR). This configuration is called per-VC queuing.
In order to reduce the required number of queues, more than one VBR-nrt
connection can be assigned to one queue. The weight assigned to the queue must
guarantee the sum of SCRs of the connections. PCR limiting is not possible in this
case. Fairness can still be guaranteed, though if VBR traffic is policed before
entering the ABM (e.g. by the using the PXB 4350 ALP device). Connection
isolation is assured to a certain degree, however CDV increases and MBS of
individual connections might be exceeded.
For ABR and GFR, connection isolation between the different users of a queue can
not be guaranteed, as it would require accurate policing of these traffic classes. A
malicious user could consume all the available buffer space and cause cell losses
for other users.
Optionally each queue can be PCR limited, which is shown in figure
2
with a bubble
in front of the VBR.2 queue (i.e. RateFactor(15:0) of that queue has a value greater
than zero).
In comparison UBR has no guaranteed rate, therefore all VCs with UBR traffic in an
individual scheduler can flow into one queue which has the minimum weight
w=1/15360. This weight ensures that an UBR cell is forwarded with the lowest
priority of all queues of the WFQ mux. Thus this queue acts like it would be
connected directly at the lowest input of the priority mux (equivalent diagram
depicted through dashed lines in
Figure
2
). Note that fairness between UBR
connections can only be achieved with per-VC queuing.
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