Allied Telesis AT-S62 User Manual
Page 292
Chapter 17: Class of Service
Section II: Advanced Operations
292
❑ Strict priority
❑ Weighted round robin priority
Note
Scheduling is set at the switch level. You cannot set this on a per-
port basis.
Strict Priority Scheduling
With this type of scheduling, a port transmits all packets out of higher
priority queues before transmitting any from the lower priority queues.
For instance, as long as there are packets in Q3 it does not handle any
packets in Q2.
The value to this type of scheduling is that high priority packets are
always handled before low priority packets.
The problem with this method is that some low priority packets might
never be transmitted out the port because a port might never get to the
low priority queues. A port handling a large volume of high priority
traffic may be so busy transmitting that traffic that it never has an
opportunity to get to any packets that are stored in its low priority
queues.
Weighted Round Robin Priority Scheduling
The weighted round robin scheduling method functions as its name
implies. The port transmits a set number of packets from each queue, in
a round robin fashion, so that each has a chance to transmit traffic. This
method guarantees that every queue receives some attention from the
port for transmitting packets.
To use this scheduling method, you need to specify the maximum
number of packets a port should transmit from a queue before moving
to the next queue. This is referred to as specifying the “weight” of a
queue. In all likelihood, you will want to give greater weight to the
packets in the higher priority queues over the lower queues.
Table 9 Example of Weighted Round Robin Priority
Port Egress Queue
Maximum Number of
Packets
Q3
15