QoS Ports and Queues Configuring QoS
page 30-24 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
QoS Ports and Queues
Queue parameters may be modified on a port basis. When a flow coming into the switch matches a policy,
it is queued based on:
• Parameters given in the policy action (specified by the policy action command) with either of the
following keywords: priority, maximum bandwidth, or maximum depth.
• Port settings configured through the qos port command.
Shared Queues
Eight priority queues are available at startup for each port. Flows always share queues; however, when a
shared action is specified in policies, the policies will use the same values to implement maximum band-
width.
Note that the OmniSwitch 6800 also has eight priority queues per port but that two of these queues are
reserved for internal use and are not available.
Prioritizing and Queue Mapping
QoS prioritizes packets by placing them in a higher priority egress queue. As previously mentioned, there
are eight egress queues available for each port. In addition, there are different queuing algorithms avail-
able for egressing packets of different priorities. The algorithm used is determined by the servicing mode
that is active for the egress port. See “Configuring the Servicing Mode for a Port” on page 30-26 for more
information.
The egress priority of a packet is determined as follows:
1 If a packet matches a QoS policy rule that sets a priority value, the egress priority for the packet is set
using the value specified in the rule.
2 If a packet ingressing on a trusted port does not match any QoS policy rule that sets the priority, then
the egress priority for the packet is set using the existing DSCP value (IP packets), the existing 802.1p
value (non-IP packets), or the default classification priority value for the port. See “Configuring Trusted
Ports” on page 30-28 for more information.
3 The egress priority for a packet ingressing on a VLAN Stacking port (a trusted port) is set using the
existing 802.1p value or configured through an associated VLAN Stacking service.
4 If a packet ingressing on an untrusted port does not match any QoS rule that sets the priority, then the
egress priority for the packet is set using the default 802.1p value configured for the port on which the
packet was received. See “Configuring the Egress Queue Minimum/Maximum Bandwidth” on page 30-27
for more information.
5 Note that the 802.1p bit for tagged packets ingressing on untrusted ports is set with the default 802.1p
value, which is configured using the qos port default 802.1p command. If the packet is untagged,
however, then the DSCP bit is set with the default DSCP value, which is configured using the qos port
default dscp command.
Use the following table to see how packets are directed to the appropriate queues:
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