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參數(shù)資料
| 型號： | MVTX2802 |
| 廠商： | Zarlink Semiconductor Inc. |
| 英文描述： | Managed 4-Port 1000 Mbps Ethernet Switch |
| 中文描述： | 管理4端口1000 Mbps以太網(wǎng)交換機(jī) |
| 文件頁數(shù)： | 28/154頁 |
| 文件大?。?/td> | 1936K |
| 代理商： | MVTX2802 |
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MVTX2802
Data Sheet
28
Zarlink Semiconductor Inc.
7.4 Strict Priority and Best Effort
When strict priority is part of the scheduling algorithm, if a queue has even one frame to transmit, it goes first.
Two of our four QoS configurations include strict priority queues. The goal is for strict priority classes to be used
for IETF expedited forwarding (EF), where performance guarantees are required. As we have indicated, it is
important that strict priority traffic be either policed or implicitly bounded, so as to keep from harming other
traffic classes.
When best effort is part of the scheduling algorithm, a queue only receives bandwidth when none of the other
classes have any traffic to offer. Two of our four QoS configurations include best effort queues. The goal is for
best effort classes to be used for non-essential traffic, because we provide no assurances about best effort
performance. However, in a typical network setting, much best effort traffic will indeed be transmitted, and with
an adequate degree of expediency.
Because we do not provide any delay assurances for best effort traffic, we do not enforce latency by dropping
best effort traffic. Furthermore, because we assume that strict priority traffic is carefully controlled before
entering the MVTX2802AG, we do not enforce a fair bandwidth partition by dropping strict priority traffic. To
summarize, dropping to enforce quality of service (i.e. bandwidth or delay) does not apply to strict priority or
best effort queues. We only drop frames from best effort and strict priority queues when global buffer resources
become scarce.
7.5 Weighted Fair Queuing
In some environments – for example, in an environment in which delay assurances are not required, but precise
bandwidth partitioning on small time scales is essential - WFQ may be preferable to a delay-bounded
scheduling discipline. The MVTX2802AG provides the user with a WFQ option with the understanding that
delay assurances cannot be provided if the incoming traffic pattern is uncontrolled. The user sets eight WFQ
“weights” such that all weights are whole numbers and sum to 64. This provides per-class bandwidth
partitioning with error within 2%.
In WFQ mode, though we do not assure frame latency, the MVTX2802AG still retains a set of dropping rules
that helps to prevent congestion and trigger higher level protocol end-to-end flow control.
As before, when strict priority is combined with WFQ, we do not have special dropping rules for the strict priority
queues, because the input traffic pattern is assumed to be carefully controlled at a prior stage. However, we do
indeed drop frames from SP queues for global buffer management purposes. In addition, queues P1 and P0 are
treated as best effort from a dropping perspective, though they still are assured a percentage of bandwidth from
a WFQ scheduling perspective. What this means is that these particular queues are only affected by dropping
when the global buffer count becomes low.
7.6 Shaper
Although traffic shaping is not a primary function of the MVTX2802AG, the chip does implement a shaper for
expedited forwarding (EF). Our goal in shaping is to control the peak and average rate of traffic exiting the
MVTX2802AG. Shaping is limited to class P6 (the second highest priority). This means that class P6 will be the
class used for EF traffic. (By contrast, we assume class P7 will be used for control packets only.) If shaping is
enabled for P6, then P6 traffic must be scheduled using strict priority. With reference to Table 2, only the middle
two QoS configurations may be used.
Peak rate is set using a programmable whole number, no greater than 64 (register QOS-CREDIT_C6_Gn). For
example, if the setting is 32, then the peak rate for shaped traffic is 32/64
×
1000 Mbps = 500 Mbps. Average
rate is also a programmable whole number, no greater than 64, and no greater than the peak rate. For example,
if the setting is 16, then the average rate for shaped traffic is 16/64
×
1000 Mbps = 250 Mbps. As a
consequence of the above settings in our example, shaped traffic will exit the MVTX2802AG at a rate always
less than 500 Mbps, and averaging no greater than 250 Mbps.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MVTX2802AG | Managed 4-Port 1000 Mbps Ethernet Switch |
| MVTX2803 | Unmanaged 8-Port 1000 Mbps Ethernet Switch |
| MVTX2803AG | Unmanaged 8-Port 1000 Mbps Ethernet Switch |
| MVTX2804 | 8-Port 1000 Mbps Ethernet Distributed Switch |
| MVTX2804AG | 8-Port 1000 Mbps Ethernet Distributed Switch |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MVTX2802A | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Managed 4 port Gigabit Ethernet switch |
| MVTX2802AG | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Managed 4-Port 1000 Mbps Ethernet Switch |
| MVTX2803 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Unmanaged 8-Port 1000 Mbps Ethernet Switch |
| MVTX2803A | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Unmanaged 8 port Gigabit Ethernet switch |
| MVTX2803AG | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Unmanaged 8-Port 1000 Mbps Ethernet Switch |
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