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參數(shù)資料
| 型號(hào)： | MVTX2604AG |
| 廠商： | ZARLINK SEMICONDUCTOR INC |
| 元件分類： | 網(wǎng)絡(luò)接口 |
| 英文描述： | Managed 24-Port 10/100 Mb + 2 Port 1 Gb Ethernet Switch |
| 中文描述： | DATACOM, LAN SWITCHING CIRCUIT, PBGA553 |
| 封裝： | 37.50 X 37.50 MM, 2.33 MM HEIGHT, MS-034, HSBGA-553 |
| 文件頁(yè)數(shù)： | 37/173頁(yè) |
| 文件大?。?/td> | 2097K |
| 代理商： | MVTX2604AG |
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MVTX2604
Data Sheet
39
Zarlink Semiconductor Inc.
7.6 Shaper
Although traffic shaping is not a primary function of the MVTX2604, 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 MVTX2604.
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 7, 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 MVTX2604 at a rate always less than 500 Mbps and averaging no greater than 250 Mbps. See
Programming QoS Register 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 MVTX2604.
7.7 Rate Control
The MVTX2604 provides a rate control function on its 10/100 ports. This rate control function applies to the
outgoing traffic aggregate on each 10/100 port. It provides a way of reducing the outgoing average rate below full
wire speed. Note that the rate control function does not shape or manipulate any particular traffic class.
Furthermore, though the average rate of the port can be controlled with this function, the peak rate will still be full
line rate.
Two principal parameters are used to control the average rate for a 10/100 port. A port’s rate is controlled by
allowing, on average, M bytes to be transmitted every N microseconds. Both of these values are programmable.
The user can program the number of bytes in 8-byte increments and the time may be set in units of 10 ms.
The value of M/N will, of course, equal the average data rate of the outgoing traffic aggregate on the given 10/100
port. Although there are many (M,N) pairs that will provide the same average data rate performance, the smaller the
time interval N, the “smoother” the output pattern will appear.
In addition to controlling the average data rate on a 10/100 port, the rate control function also manages the
maximum burst size at wire speed. The maximum burst size can be considered the memory of the rate control
mechanism; if the line has been idle for a long time, to what extent can the port “make up for lost time” by
transmitting a large burst This value is also programmable, measured in 8-byte increments.
Example: Suppose that the user wants to restrict Fast Ethernet port P’s average departure rate to 32 Mbps – 32%
of line rate – when the average is taken over a period of 10 ms. In an interval of 10 ms, exactly 40000 bytes can be
transmitted at an average rate of 32 Mbps.
So how do we set the parameters The rate control parameters are contained in an internal RAM block accessible
through the CPU port (See Programming QoS Registers application note and Processor interface application note).
The data format is shown below.
As we indicated earlier, the number of bytes is measured in 8-byte increments, so the 16-bit field “Number of bytes”
should be set to 40000/8, or 5000. In addition, the time interval has to be indicated in units of 10 ms. Though we
want the average data rate on port P to be 32 Mbps when measured over an interval of 10 ms, we can also adjust
the maximum number of bytes that can be transmitted at full line rate in any single burst. Suppose we wish this limit
63:40
39:32
31:16
15:0
0
Time interval
Maximum burst size
Number of bytes
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MVTX2801 | Unmanaged 4-Port 1000 Mbps Ethernet Switch |
| MVTX2801AG | Unmanaged 4-Port 1000 Mbps Ethernet Switch |
| MVTX2802 | Managed 4-Port 1000 Mbps Ethernet Switch |
| MVTX2802AG | Managed 4-Port 1000 Mbps Ethernet Switch |
| MVTX2803 | Unmanaged 8-Port 1000 Mbps Ethernet Switch |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MVTX2801 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Unmanaged 4-Port 1000 Mbps Ethernet Switch |
| MVTX2801A | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Unmanaged 4 port Gigabit Ethernet switch |
| MVTX2801AG | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Unmanaged 4-Port 1000 Mbps Ethernet Switch |
| MVTX2802 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:Managed 4-Port 1000 Mbps Ethernet Switch |
| 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 |
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