zl50400 Zarlink Semiconductor, zl50400 Datasheet - Page 37

• Manufacturer Part Number: zl50400
• Description: Lightly Managed/unmanaged 9-port 10/100 M Ethernet Switch
• Manufacturer: Zarlink Semiconductor

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.
As Table 7 illustrates, the six traffic types may each have their own distinct properties and applications. As shown,
classes may receive bandwidth assurances or latency bounds. In the table, P3, the highest transmission class,
requires that all frames be transmitted within 1 ms, and receives 50% of the 100 Mbps of bandwidth at that port.
Best-effort (P0) traffic forms a fourth class that only receives bandwidth when none of the other classes have any
traffic to offer. It is also possible to add a fourth class that has strict priority over the other three; if this class has
even one frame to transmit, then it goes first. In the ZL50400, each RMAC port will support two total classes, and
the MMAC 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.
Table 7 shows that different types of applications may be placed in different boxes in the traffic table. 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
There are two basic pieces to QoS scheduling in the MMAC port of ZL50400: strict priority (SP) or weighted fair
queuing (WFQ). The only configuration for a RMAC and CPU port is strict priority between the queues.
Highest
transmission
priority, P3
Middle
transmission
priority, P2
Low transmission
priority, P1
Total
Two QoS Configurations
Goals
50 Mbps
37.5 Mbps
12.5 Mbps
100 Mbps
(user defined)
TotalAssured
Bandwidth
Table 7 - Two-dimensional World Traffic
Apps: phone calls, circuit
emulation.
Latency: < 1 ms.
Drop: No drop if P3 not
oversubscribed.
Apps: interactive apps, Web
business.
Latency: < 4-5 ms.
Drop: No drop if P2 not
oversubscribed.
Apps: emails, file backups.
Latency: < 16 ms desired, but
not critical.
Drop: No drop if P1 not
oversubscribed.
Zarlink Semiconductor Inc.
Low Drop Probability
ZL50400
(low-drop)
37
Apps: training video.
Latency: < 1 ms.
Drop: No drop if P3 not
oversubscribed; first P3 to drop
otherwise.
Apps: non-critical interactive apps.
Latency: < 4-5 ms.
Drop: No drop if P2 not
oversubscribed; firstP2 to drop
otherwise.
Apps: casual web browsing.
Latency: < 16 ms desired, but not
critical.
Drop: No drop if P1 not
oversubscribed; first to drop
otherwise.
High Drop Probability
(high-drop)
Data Sheet