Quality of Service Overview
February 22, 2008
Page 3 of 29
•
Priority
Transmit
Queue
(TxQ)
with
configurable
forwarding
behavior
•
In
‐
bound
and/or
outbound
rate
Limiter
(IRL)
per
transmit
queue
•
Outbound
rate
shaper
per
transmit
queue
The
CoS
configuration
for
each
service
can
be
easily
viewed
using
the
CoS
setting
tables.
Ports
are
bundled
into
port
groups
with
the
group
assigned
to
a
CoS,
significantly
cutting
down
on
operational
overhead
and
complexity.
CoS Priority and ToS Rewrite
The
two
parameters
configurable
for
CoS
priority
are
802.1p
and
Type
of
Service
(ToS).
Each
CoS
can
be
mapped
to
an
802.1p
priority
and
a
ToS
rewrite
value.
The
802.1p
parameter
is:
•
A
subset
of
ToS
with
values
0–7
(upper
3
bits
of
the
8
bit
ToS
field)
•
Supported
in
both
layer
2
and
layer
3
The
ToS
parameter
is:
•
An
8
‐
bit
field
with
values
0–255
•
Supported
in
layer
3
only
•
Also
referred
to
as
the
Differentiated
Services
Code
Point
(DSCP)
when
limited
to
the
lower
5
bits
of
the
field
Figure 1
displays
the
relationship
between
your
application,
priority
level,
802.1p,
and
ToS
assignments
(shown
here
using
DSCP
terminology).
QoS
priority/ToS
configuration:
•
Derives
its
characteristic
requirements
from
the
end
‐
system
application.
•
Is
configured
on
the
edge
device
the
application
is
connected
to
•
Is
propagated
through
the
network
in
the
protocol
packet
header
