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参数资料
| 型号： | ZL50408GDG2 |
| 厂商： | CONEXANT SYSTEMS |
| 元件分类： | 网络接口 |
| 英文描述： | DATACOM, LAN SWITCHING CIRCUIT, PBGA208 |
| 封装： | 17 X 17 MM, 1.40 MM HEIGHT, LEAD FREE, MO-192, LBGA-208 |
| 文件页数： | 86/144页 |
| 文件大小： | 1779K |
| 代理商： | ZL50408GDG2 |
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ZL50408
Data Sheet
46
Zarlink Semiconductor Inc.
Once a frame has been scheduled, the TxQ manager reads the FCB information and writes to the correct port
control module. The detail of the QoS decision guideline is described in chapter 5.
6.2.5
Port Control
The port control module calculates the SRAM read address for the frame currently being transmitted. It also writes
start of frame information and an end of frame flag to the MAC TxFIFO. When transmission is done, the port control
module requests that the buffer be released.
6.2.6
TxDMA
The TxDMA multiplexes data and address from port control, and arbitrates among buffer release requests from the
port control modules.
7.0
Quality of Service and Flow Control
7.1
Model
Quality of service is an all-encompassing term for which different people have different interpretations. In general,
the approach to quality of service described here assumes that we do not know the offered traffic pattern. We also
assume that the incoming traffic is not policed or shaped. Furthermore, we assume that the network manager
knows his applications, such as voice, file transfer, or web browsing, and their relative importance. The manager
can then subdivide the applications into classes and set up a service contract with each. The contract may consist
of bandwidth or latency assurances per class. Sometimes it may even reflect an estimate of the traffic mix offered to
the switch. As an added bonus, although we do not assume anything about the arrival pattern, if the incoming traffic
is policed or shaped, we may be able to provide additional assurances about our switch’s performance.
A class is capable of offering traffic that exceeds the contracted bandwidth. A well-behaved class offers traffic at a
rate no greater than the agreed-upon rate. By contrast, a misbehaving class offers traffic that exceeds the
agreed-upon rate. A misbehaving class is formed from an aggregation of misbehaving microflows. To achieve high
link utilization, a misbehaving class is allowed to use any idle bandwidth. However, such leniency must not degrade
the quality of service (QoS) received by well-behaved classes.
Each traffic type may each have their own distinct properties and applications. Classes may receive bandwidth
assurances or latency bounds. For example, the highest transmission class may require that all frames receive
50% of the 100 Mbps of bandwidth at that port.
Best-effort (P0) traffic forms a class that only receives bandwidth when none of the other classes have any traffic to
offer. It is also possible to add a class that has strict priority over all others; if this class has even one frame to
transmit, then it goes first. In the ZL50408, each RMAC port will support two total classes, and the GMAC port will
support four classes. We will discuss the various modes of scheduling these classes in the next section.
In addition, each transmission class has two subclasses, high-drop and low-drop. Well-behaved users should rarely
lose packets. But poorly behaved users–users who send frames at too high a rate – will encounter frame loss, and
the first to be discarded will be high-drop. Of course, if this is insufficient to resolve the congestion, eventually some
low-drop frames are dropped, and then all frames in the worst case. For example, casual web browsing fits into the
category of high-loss, high-latency-tolerant traffic, whereas VoIP fits into the category of low-loss, low-latency traffic.
7.2
Two QoS Configurations
There are two basic pieces to QoS scheduling in the GMAC port of ZL50408: strict priority (SP) or weighted fair
queuing (WFQ). The only configuration for a RMAC and CPU port is strict priority between the queues.
7.2.1
Strict Priority
When strict priority is part of the scheduling algorithm, if a queue has any frame to transmit, it goes first. For RMAC
ports, this is an easy way to provide the different service. For all recognizable traffic, the bandwidth is guaranteed to
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相关代理商/技术参数 |
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|---|---|
| ZL50409 | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Managed 9-Port 10/100M Ethernet Switch |
| ZL50409GDC | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Managed 9-Port 10/100M Ethernet Switch |
| ZL50409GDC1 | 制造商:Microsemi Corporation 功能描述: |
| ZL50410 | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Managed 8-Port 10/100M + 1-Port 10/100/1000M Ethernet Switch |
| ZL50410GDC208 | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Managed 8-Port 10/100M + 1-Port 10/100/1000M Ethernet Switch |
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