3Com 4007, Руководство по внедрению, Страница: 585 / 684

QoS Controls 585
Specifying Rate Limits A rate limit restricts the amount of input bandwidth that is used by
incoming classified traffic (optionally, on a per-port basis). When you
define a control, you can specify one of three rate limits:
■
None — No rate limit
■
ReceivePort — Imposes a separate limit on each receive port
■
Aggregate — Imposes limits on groups of receive ports. This rate
limit type can only be applied to flow classifiers.
Your choice of rate limit determines how much additional information
you need to supply. The default rate limit is
none
, which means that there
is no rate limit applied to the classifier. If you specify a rate limit of
none
,
you have a small subset of options to specify. You select a service level
and loss-eligibility status for conforming packets (packets that are below
the rate limit), decide if you want to apply an IEEE 802.1p priority tag
value to forwarded frames (for service levels other than drop), and specify
the classifiers with which you want to associate the control.
If you specify a rate limit of
receivePort
or
aggregate
, you have many
additional options. After you specify a service level and loss-eligibility
status for conforming packets, you can also specify a service level for
nonconforming excess packets (packets that exceed the specified rate
limit), whether the nonconforming excess are loss eligible, how the rate
limit for receive ports should be expressed, the rate-limit value, a burst
size, and the receive ports for which you want to enable the rate limit.
(The rate limit sets a bandwidth limit for a specific set of ports. You can
specify multiple rate-limit values for different subsets of ports. As with
any rate limit type, you can additionally specify an IEEE 802.1p priority tag
value on forwarded frames.)
When you specify how a receivePort or aggregate rate limit is expressed,
you can select a percentage of port bandwidth or KBps:
■
For KBps as a rate limit (the default), specify the value for the rate limit
in KBps (
0 through 65434 ).
■
For a percentage for the rate limit, specify the percentage in the range
of from
0 through 100 percent. These numbers are rounded to the
nearest 16 KB. A value of 0 makes all packets nonconforming excess
packets. The Multilayer Switching Module drops these packets only if
the service level for excess packets is set to
drop
.