![](http://datasheet.mmic.net.cn/200000/ZL50418GKG2_datasheet_15116876/ZL50418GKG2_59.png)
ZL50418
Data Sheet
59
Zarlink Semiconductor Inc.
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.
8.2
Four QoS Configurations
There are four basic pieces to QoS scheduling in the ZL50418: strict priority (SP), delay bound, weighted fair
queuing (WFQ), and best effort (BE). Using these four pieces, there are four different modes of operation as shown
in the tables below. For 10/100 M ports, the following registers select these modes:
Table 8 - Four QoS Configurations for a 10/100 M Port
QOSC40 [7:6] and QOSC48 [7:6] select these modes for the first and second Gigabit ports, respectively.
Table 9 - Four QoS Configurations for a Gigabit Port
The default configuration for a 10/100 M port is three delay-bounded queues and one best-effort queue. The delay
bounds per class are 0,8 ms for P3, 3.2 ms for P2, and 12.8 ms for P1. For a Gigabit port, we have a default of six
delay-bounded queues and two best-effort queues. The delay bounds for a Gigabit port are 0.16 ms for P7 and P6,
0.32 ms for P5, 0.64 ms for P4, 1.28 ms for P3, and 2.56 ms for P2. For a Gigabit port, where there are two best-
effort queues, P1 has strict priority over P0. Best effort traffic is only served when there is no delay-bounded traffic
to be served.
We have a second configuration for a 10/100 M port in which there is one strict priority queue, two delay bounded
queues and one best effort queue. The delay bounds per class are 3.2 ms for P2 and 12.8 ms for P1. If the user is
to choose this configuration, it is important that P3 (SP) traffic be either policed or implicitly bounded (e.g., if the
incoming P3 traffic is very light and predictably patterned). Strict priority traffic, if not admission-controlled at a prior
stage to the ZL50418, can have an adverse effect on all other classes’ performance. For a Gigabit port, P7 and P6
are both SP classes and P7 has strict priority over P6. In this case, the delay bounds per class are 0.32 ms for P5,
0.64 ms for P4, 1.28 ms for P3, and 2.56 ms for P2.
QOSC24 [7:6]_CREDIT_C00
QOSC28 [7:6]_CREDIT_C10
QOSC32 [7:6]_CREDIT_C20
QOSC36 [7:6]_CREDIT_C30
P3
P2
P1
P0
Op1 (default)
Delay Bound
BE
Op2
SP
Delay Bound
BE
Op3
SP
WFQ
Op4
WFQ
P7
P6
P5
P4
P3
P2
P1
P0
Op1 (default)
Delay Bound
BE
Op2
SP
Delay Bound
BE
Op3
SP
WFQ
Op4
WFQ