xStack DGS/DXS-3300 Series Layer 3 Stackable Gigabit Ethernet Switch CLI Manual
102
config scheduling
Purpose
Used to configure traffic scheduling for each of the Switch’s hardware
priority classes.
Syntax
config scheduling <class_id 0-6> {max_packet <value 0-15>}
Description
The Switch contains seven hardware classes of service per device. The
Switch’s default settings draw down seven hardware classes of service in
order, from the highest priority class (Class 6) to the lowest priority class
(Class 0). Starting with the highest priority class (Class 6), the highest
priority class will transmit all of the packets and empty its buffer before
allowing the next lower priority class to transmit its packets. The next
highest priority class will empty before proceeding to the next class and so
on. Lower priority classes are allowed to transmit only if the higher priority
classes in the buffer are completely emptied. Packets in the higher priority
classes are always emptied before any in the lower priority classes.
The default settings for QoS scheduling employ this strict priority scheme to
empty priority classes.
The
config scheduling
command can be used to specify the weighted
round-robin (
WRR
) rotation by which these seven hardware priority classes
of service are reduced. To use a weighted round-robin (
WRR
) scheme, the
max_packets
parameters must not have a value of zero (
0
). (See
Combination Queue
below.)
The
max_packet
parameter allows the user to specify the maximum
number of packets a given priority class can transmit per weighted round-
robin (
WRR
) scheduling cycle. This provides for a controllable CoS
behavior while allowing for other classes to empty as well. A value between
0 and 15 packets can be specified per priority queue.
Entering a
0
into the
<value 0-15>
field of the
max_packet
parameter
allows for the creation of a
Combination Queue
for the forwarding of
packets. This
Combination Queue
allows for a combination of strict and
weight-fair (weighted round-robin
“
WRR
”
) scheduling. Priority classes that
have a
0
in the
max_packet
field will forward packets with strict priority
scheduling. The remaining classes, that do not have a
0
in their
max_packet
field, will follow a weighted round-robin (
WRR
) method of
forwarding packets — as long as the priority classes with a
0
in their
max_packet
field are empty. When a packet arrives in a priority class with a
0
in its
max_packet
field, this class will automatically begin forwarding
packets until it is empty. Once a priority class with a
0
in its
max_packet
field is empty, the remaining priority classes will reset the weighted round-
robin (
WRR
) cycle of forwarding packets, starting with the highest available
priority class. Priority classes with an equal level of priority and equal
entries in their
max_packet
field will empty their fields based on hardware
priority scheduling.
Parameters
<class_id 0-6>
−
Specifies which of the seven hardware priority classes to
which the
config scheduling
command will be applied. The seven priority
classes are identified by number
−
from 0 to 6
−
with queue 6 being the
highest priority.
max_packet <value 0-15>
−
Specifies the maximum number of packets the
above specified priority class will be allowed to transmit per weighted
round-robin (
WRR
) cycle. A value between 0 and 15 packets can be
specified. A zero (
0
) denotes strict priority scheduling for that priority class.
Restrictions Only
administrator-level users can issue this command.
