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Page 29 | AlliedWare Plus™ OS: Overview of QoS
The first of these numbers is the percentage limit for queue 0, the second number is the limit
for queue
1
, and so on.
For example, to give queue 0 less of the buffer space and queues 3 and 4 more, you could use
the command:
wrr-queue queue-limit 6 12 12 17 17 12 12 12
You can use this command to configure queues that are members of the strict-priority group
of queues, even though it begins with the keyword wrr-queue.
Viewing
queue
settings
To see the configured settings for each queue, use the command:
awplus#sh mls qos interface
Egress bandwidth limiting
The total bandwidth that can be transmitted from a set of egress queues on a port is
configurable using the interface mode command:
awplus(config-if)#egress-rate-limit <bandwidth-limit>
This means that the maximum bandwidth is not necessarily set for the port as a whole, but
for a set of the egress queues on the port.
The bandwidth limits can only be specified in multiples of 650 kbps. Whatever value you
configure will be rounded up to the nearest multiple of 650 kbps.
It is important to understand the relationship between a queue’s wrr-queue egress-rate-
limit command and a port’s egress-rate-limit command. These two commands actually
control two different aspects of the egress scheduling process.
The model to consider is this: the process of putting packets onto the wire “pulls” packets
out of egress queues and puts them out the port. However, the queues can resist a “pull” and
effectively tell the “pulling” process, “sorry, I have hit my bandwidth limit and cannot give you
any packets right now”.
The port’s egress-rate-limit command sets the rate at which the port “pulls” packets from
the egress queues. The queue’s wrr-queue egress-rate-limit command sets the rate at
which a queue will allow packets to be pulled out of it.
Therefore, the port’s egress-rate-limit command sets the maximum rate at which data can
leave the port.
The queue’s wrr-queue egress-rate-limit command can do two things:
z ensure that data is able to leave some queues more quickly than others.
z possibly set a maximum limit on the egress rate from the port. If the sum of the egress
rates on all the queues is less than the total egress limit set by the port’s egress-rate-
limit command, then in fact the maximum rate at which packets can exit the port will be
the sum of the egress rates on the queues.