Chapter 20: Quality of Service (QoS) Commands

 

 

A new DSCP value can be set at all three levels:

 

flow group, traffic class, and policy. A DSCP value

 

specified in a flow group overrides a DSCP value

 

specified at the traffic class or policy level. A

 

DSCP value specified at the traffic class level is

 

used only if no value has been specified at the

 

flow group level. It will override any value set at

 

the policy level.

maxbandwidth

Specifies the maximum bandwidth available

 

to the traffic class. This parameter determines

 

the maximum rate at which the ingress port

 

accepts data belonging to this traffic class

 

before either dropping or remarking occurs,

 

as specified with the EXCEEDACTION

 

parameter. If the sum of the maximum

 

bandwidth for all traffic classes on a policy

 

exceeds the (ingress) bandwidth of the port

 

to which the policy is assigned, the

 

bandwidth for the port takes precedence and

 

the port discards packets before they can be

 

classified. The range is 0 to 1016 Mbps.

 

The value for this parameter is rounded up to

 

the nearest Mbps value when this traffic class

 

is assigned to a policy on a 10/100 port, and

 

up to the nearest 8 Mbps value when

 

assigned to a policy on a gigabit port (for

 

example, on a gigabit port, 1 Mbps is rounded

 

to 8 Mbps, and 9 is rounded to 16).

burstsize

Specifies the size of a token bucket for the

 

traffic class. The token bucket is used in

 

situations where you have set a maximum

 

bandwidth for a class, but where traffic

 

activity may periodically exceed the

 

maximum. A token bucket can provide a

 

buffer for those periods where the maximum

 

bandwidth is exceeded.

 

Tokens are added to the bucket at the same

 

rate as the traffic class’ maximum bandwidth,

 

set with the MAXBANDWIDTH parameter. For

 

example, a maximum bandwidth of 50 Mbps

 

adds tokens to the bucket at that rate.

 

If the amount of the traffic flow matches the

 

maximum bandwidth, no traffic is dropped

 

because the number of tokens added to the

 

bucket matches the number being used by

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Allied Telesis management software layer 2+ fast ethernet switches Flow group, traffic class, and policy. a Dscp value