Basic QoS functional description

The handling has impact on the frame on ingress:

  • Give frame classified Priority.

  • Give frame classified DPL (Drop Precedence Level).

  • Give frame classified PCP.

  • Give frame classified DEI.

The handling has impact on the frame on egress:

  • Scheduling the frame

  • Shaping the frame

  • Give the PCP and DEI value in the VLAN tag.

The consequences of frame classified values are generally described in the Frame Metadata section.

1. Bridge device Default Configuration.

Default classified Priority, DPL, PCP and DEI can be configured per bridge device. The default PCP and DEI are only relevant for frames that are classified as untagged.

The ingress default value can be given by this command:

qos i_def eth0 --prio 5 --pcp 5 --dei 1 --dpl 1

The parameters:

  • eth0 - The device is eth0

  • prio - The default priority value.

  • pcp - The default PCP value.

  • dei - The default DEI value.

  • dpl - The default Drop Precedence Level value.

A frame will get default PCP and DEI classified values.
A tagged frame will get Tag PCP and DEI as classified PCP and DEI values.

2. Frame DSCP value to Prio/DPL mapping.

A global table mapping the trusted DSCP value of an IP frame to the classified Priority and DPL can be configured. Per port it can be configured if mapping of DSCP should happen or not.

A trusted DSCP value can be inserted in the table by this command:

qos i_dscp_map 22 --enable 1 --prio 5 --dpl 1

The parameters:

  • 22 - The inserted trusted DSCP value is 22.

  • enable 1 - The DSCP value is enabled in the table.

  • prio - The mapped to priority value.

  • dpl - The mapped to Drop Precedence Level value.

This is overwriting the default classified values.

A trusted DSCP value can be removed from the table by this command:

qos i_dscp_map 22 --enable 0

The parameters:

  • 22 - The removed trusted DSCP value is 22.

  • enable 0 - The DSCP value is removed from the table.

3. Tag PCP/DEI to Prio/DPL mapping.

A table per bridge device, mapping the PCP and DEI values from a tagged ingress frame to classified Priority and DPL, can be configured.

The ingress tag mapping table can be given by this command:

qos i_tag_map eth0 --prio 0123456701234567 --dpl 0000000011111111

The parameters:

  • eth0 - The device is eth0

  • prio - The map of TAG PCP,DEI to Priority. PCP(0-7)/DEI(0) and PCP(0-7)/DEI(1)

  • dpl - The map of TAG PCP,DEI to (color)DPL. PCP(0-7)/DEI(0) and PCP(0-7)/DEI(1)

The above command configures what is default:
PCP 0-7 is mapping to Prio 0-7 for both DEI 0 and 1.
PCP 0-7 is mapping to DPL 0 for DEI 0 and DPL 1 for DEI 1.

qos i_tag_map eth0 --prio 22244477111333666 --dpl 1111111100000000

The above command configures:
PCP 0-2 is mapping to Prio 2 for DEI 0,
PCP 3-5 is mapping to Prio 4 for DEI 0,
PCP 6-7 is mapping to Prio 7 for DEI 0,
PCP 0-2 is mapping to Prio 1 for DEI 1,
PCP 3-5 is mapping to Prio 3 for DEI 1,
PCP 6-7 is mapping to Prio 6 for DEI 1,
PCP 0-7 is mapping to DPL 1 for DEI 0 and DPL 0 for DEI 1.

4. Ingress mode.

The ingress mode per bridge device can be configured.
The ingress mode determines how the frame classified Priority and DPL values are given.
The ingress mode can be given by this command:

qos i_mode eth0 --tag 0 --dscp 0

The parameters:

  • eth0 - The device is eth0

  • tag - Mapping of TAG PCP/DEI is disabled.

  • dscp - Mapping of trusted DSCP is disabled.

The above command gives frame the default Prio/DPL values for the device as both mapping types are disabled.

qos i_mode eth0 --tag 1 --dscp 0

The above command gives frames the tag PCP/DEI mapped to classified Prio/DPL values.

qos i_mode eth0 --tag 1 --dscp 1

The above command gives frames the tag PCP/DEI mapped to classified Prio/DPL values. Any IP frame with a DSCP value matching an entry in the global DSCP mapping table will get classified Prio/DPL values from the DSCP mapping table.