參數(shù)資料
型號(hào)： MVTX2603
廠商： Zarlink Semiconductor Inc.
英文描述： Unmanaged 24-Port 10/100 Mb + 2-Port 1 Gb Ethernet Switch
中文描述： 非托管的24端口的10/100 Mb 2端口千兆以太網(wǎng)交換機(jī)1
文件頁(yè)數(shù)： 28/109頁(yè)
文件大?。?/td> 803K
代理商： MVTX2603
MVTX2603
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
MVTX2603, we do not enforce a fair bandwidth partition by dropping strict priority traffic. To summarize, dropping to
enforce 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 MVTX2603 provides the user with a WFQ option with the understanding that delay assurances can
not be provided if the incoming traffic pattern is uncontrolled. The user sets four WFQ “weights” (eight for Gigabit
ports) 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 MVTX2603 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, queue P0 for a 10/100
port (and queues P0 and P1 for a Gigabit port) 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 MVTX2603, 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 MVTX2603.
Shaping is limited to the two Gigabit ports only, and only to class P6 (the second highest priority). This means that
class P6 will be the class used for EF traffic. If shaping is enabled for P6, then P6 traffic must be scheduled using
strict priority. With reference to Table 8 only the middle two QoS configurations may be used.
Peak rate is set using a programmable whole number, no greater than 64. 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 MVTX2603 at a rate always less than 500 Mbps and averaging no greater than 250 Mbps. See
Programming QoS Registers Application Note for more information.
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 we do have global resource management, we do nothing to prevent this situation locally. We
assume SP traffic is policed at a prior stage to the MVTX2603.
相關(guān)PDF資料
PDF描述
MVTX2603AG Unmanaged 24-Port 10/100 Mb + 2-Port 1 Gb Ethernet Switch
MVTX2604 Managed 24-Port 10/100 Mb + 2 Port 1 Gb Ethernet Switch
MVTX2604AG Managed 24-Port 10/100 Mb + 2 Port 1 Gb Ethernet Switch
MVTX2801 Unmanaged 4-Port 1000 Mbps Ethernet Switch
MVTX2801AG Unmanaged 4-Port 1000 Mbps Ethernet Switch
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MVTX2603A 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Unmanaged 24 port 10/100Mb + 2 port 1Gb Ethernet switch
MVTX2603AG 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Unmanaged 24-Port 10/100 Mb + 2-Port 1 Gb Ethernet Switch
MVTX2603AG2 制造商:Microsemi Corporation 功能描述:
MVTX2604 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Managed 24-Port 10/100 Mb + 2 Port 1 Gb Ethernet Switch
MVTX2604A 制造商:未知廠家 制造商全稱:未知廠家 功能描述:MVTX260x Physical Port Control
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