Quality of Service Overview
February 22, 2008
Page 7 of 29
Figure 4 Hybrid Queuing Packet Behavior
Rate Limiting
Rate
limiting
is
used
to
control
the
rate
of
traffic
entering
(inbound)
and/or
leaving
(outbound)
a
switch
per
CoS.
Rate
limiting
allows
for
the
throttling
of
traffic
flows
that
consume
available
bandwidth,
in
the
process
providing
room
for
other
flows.
Rate
limiting
guarantees
the
availability
of
bandwidth
for
other
traffic
by
preventing
the
rate
limited
traffic
from
consuming
more
than
the
assigned
amount
of
a
network’s
resources.
Rate
limiting
accomplishes
this
by
setting
a
cap
on
the
bandwidth
utilization
of
specific
types
of
both
inbound
and
outbound
traffic.
When
a
rate
limit
has
been
exceeded,
the
CoS
can
be
configured
to
perform
one
or
all
of
the
following:
record
a
Syslog
message,
send
an
SNMP
trap
to
inform
the
administrator,
and
automatically
disable
the
port.
Figure 5
illustrates
how
bursty
traffic
is
clipped
above
the
assigned
threshold
with
rate
limiting
applied.
