zl50415 Zarlink Semiconductor, zl50415 Datasheet - Page 34

• Manufacturer Part Number: zl50415
• Description: Managed 16-port 10/100 M + 2-port 1 G Ethernet Switch
• Manufacturer: Zarlink Semiconductor

QOSC40 [7:6] and QOSC48 [7:6] select these modes for the first and second gigabit ports, respectively.
The default configuration for a 10/100 Mbps 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 1 Gbps port, we have a default
of six delay-bounded queues and two best-effort queues. The delay bounds for a 1 Gbps 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. Best effort traffic is only served when
there is no delay-bounded traffic to be served. For a 1 Gbps port where there are two best-effort queues P1 has
strict priority over P0.
We have a second configuration for a 10/100 Mbps 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 a adverse effect on all other classes’ performance.
For a 1 Gbps 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.
The third configuration for a 10/100 Mbps port contains one strict priority queue and three queues receiving a
bandwidth partition via WFQ. As in the second configuration, strict priority traffic needs to be carefully controlled. In
the fourth configuration all queues are served using a WFQ service discipline.
7.3
In the absence of a sophisticated QoS server and signaling protocol, the ZL50418 may not know the mix of
incoming traffic ahead of time. To cope with this uncertainty, our delay assurance algorithm dynamically adjusts its
scheduling and dropping criteria, guided by the queue occupancies and the due dates of their head-of-line (HOL)
QOSC32 [7:6]_CREDIT_C20
QOSC36 [7:6]_CREDIT_C30
Op1 (default)
Op2
Op3
Op4
Op1 (default)
Op2
Op3
Op4
Delay Bound
Table 8 - Four QoS Configurations for a 10/100 Mbps Port
Table 9 - Four QoS Configurations for a Gigabit Port
Delay Bound
SP
SP
WFQ
Delay Bound
SP
SP
WFQ
P7
P3
P6
Zarlink Semiconductor Inc.
Delay Bound
WFQ
Delay Bound
WFQ
ZL50418
P5
34
P2
P4
P3
P1
P2
BE
BE
BE
BE
P1
P0
Data Sheet
P0