ZL50404
TotalAssured
Bandwidth
(user defined)
50 Mbps
Data Sheet
Goals
Highest
transmission
priority, P3
Low Drop Probability
(low-drop)
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.
High Drop Probability
(high-drop)
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.
Middle
transmission
priority, P2
37.5 Mbps
Low transmission
priority, P1
12.5 Mbps
Total
100 Mbps
Table 7 - Two-dimensional World Traffic
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 ZL50404, 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
Two QoS Configurations
There are two basic pieces to QoS scheduling in the MMAC port of ZL50404: strict priority (SP) or weighted fair
queuing (WFQ). The only configuration for a RMAC and CPU port is strict priority between the queues.
35
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
