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參數(shù)資料
| 型號： | MVTX2803 |
| 廠商： | Zarlink Semiconductor Inc. |
| 英文描述： | Unmanaged 8-Port 1000 Mbps Ethernet Switch |
| 中文描述： | 非托管8端口1000 Mbps以太網(wǎng)交換機(jī) |
| 文件頁數(shù)： | 22/127頁 |
| 文件大?。?/td> | 1706K |
| 代理商： | MVTX2803 |
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MVTX2803
Data Sheet
22
Zarlink Semiconductor Inc.
performance. However, in a typical network setting, much best effort traffic will be transmitted, and with an
adequate degree of expediency.
Because there is not any delay assurances for best effort traffic, enforcement of latency by dropping best effort
traffic is not provided. Furthermore, because it is assumed that strict priority traffic is carefully controlled before
entering the MVTX2803AG, a fair bandwidth partition by dropping strict priority traffic is not enforced. To
summarize, dropping to enforce quality of service (i.e. bandwidth or delay) does not apply to strict priority or
best effort queues. It only drops 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 MVTX2803AG 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 frame latency is not assured, the MVTX2803AG 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, there are no special dropping rules for the strict priority
queues, because the input traffic pattern is assumed to be carefully controlled at a prior stage. However, there
is 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 MVTX2803AG, the chip does implement a shaper for
expedited forwarding (EF). The goal in shaping is to control the peak and average rate of traffic exiting the
MVTX2803AG. 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, 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 4, 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 the example, shaped traffic will exit the MVTX2803AG at a rate always
less than 500 Mbps, and averaging no greater than 250 Mbps.
Also, when shaping is enabled, it is possible for a P6 queue to explode in length if fed by a greedy source. The
reason is that a shaper is by definition not work-conserving; that is, it may hold back from sending a packet
even if the line is idle. Though there is global resource management, nothing is done to prevent this situation
locally. This assumes SP traffic is policed at a prior stage to the MVTX2803AG.
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| MVTX2804 | 8-Port 1000 Mbps Ethernet Distributed Switch |
| MVTX2804AG | 8-Port 1000 Mbps Ethernet Distributed Switch |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| 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 |
| MVTX2803AG2 | 制造商:Microsemi Corporation 功能描述: |
| MVTX2804 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:8-Port 1000 Mbps Ethernet Distributed Switch |
| MVTX2804AG | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:8-Port 1000 Mbps Ethernet Distributed Switch |
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