Manual

139

User Guide

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corresponding priority levels. Non-IP Datagrams with 802.1Q tags are mapped to differ-

ent priority levels based on the 802.1P Priority mode. Any untagged Non-IP Datagrams

are Mapped based on the Port Priority mode.

Priority Schedule Mode

When the Network is congested, packets compete for resources. This is solved using

Queue Scheduling. The Switch implements four Scheduling Queues, TC0, TC1, TC2 and

TC3. TC0 has the lowest priority while TC3 has the highest priority. The Switch pro-

vides four Priority Schedule Modes: SP (Strict Priority), WRR (Weighted Round Robin),

SP+WRR (Strict Priority+Weighted Round Robin) and Equ (Equal).

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SP-Mode (Strict-Priority Mode): In this mode, the Queue with highest priority will oc-

cupy all available bandwidth. Packets in the Queue with Lower Priority are sent only

when the Queue with Higher Priority is empty. The Switch has four Egress Queues

TC0, TC1, TC2 and TC3. In SP mode their Priorities increase in order. TC3 has the

Highest Priority. A disadvantage of SP-Mode is that if there are packets in the queues

with Higher Priority for long periods of time during congestion, the packets in the

queues with Lower Priority will expire because they are not forwarded. This requires

the Low Priority packets to be resent, further congesting the Network.

Figure 9-4 SP-Mode