Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

 
 

CoS Features and Limitations on vMX

vMX has the following limitations for CoS support:

  • Schedulers support only the transmit-rate and excess-rate statements. Only weights are supported at the queue level, so transmission rate and excess rate are used for calculating queue weights.

    • If transmit-rate percent is configured at the queue level, then configure guaranteed rate at the VLAN level.

      Note:

      Guaranteed rate is not supported, but it is used to calculate queue weights.

    • If you only configure transmit rate, queue weights are calculated based on the transmission rate.

    • If you only configure excess rate, queue weights are calculated based on the excess rate.

    • If you configure both transmit rate and excess rate, queue weights are calculated based on the excess rate.

    • If you configure the excess rate for one queue, the excess rate is expected for all the queues to compute the weights. If the excess rate is not configured, the default weight of 1 is used.

      Note:

      To get the expected behavior, you must configure the excess rate for all queues.

  • Traffic control profiles support only the shaping-rate and scheduler-map statements.

    If a traffic control profile has a default scheduler map, you must configure the guaranteed rate.

  • For high- and medium-priority traffic classes, the transmission rate is the shaping rate.

  • For low-priority queues, the shaping rate for the VLAN is used for the queue. As a result, the low-priority queues can burst up to the configured shaping rate for the VLAN. The transmission rate is used as the WRR weight when there is more than one queue configured for a given priority.

Some considerations for the high- and medium-priority traffic classes:

  • All excess traffic from the traffic classes for high- and medium-priority queues are discarded as tail drops.

  • For high- and medium-priority traffic classes, the transmission rate is the shaping rate.

    If the transmission rate is not configured and the shaping rate is configured, then the queue weight is calculated based upon the configured shaping rate.

    If you configure the transmission rate for both queues of the same traffic class, the shaping rate of the traffic class is the sum of the individual transmission rates of the queues for that traffic class.

  • If a queue is not configured, its transmission rate is set to zero.

    If no queues are configured, the shaping rate of the VLAN is applied to the traffic class as the transmission rate.

  • If any of the queues in the traffic class is configured, the shaping rate of the VLAN is set to the guaranteed rate of the configured queue. If a queue is not configured, the guaranteed rate is set to zero by default.

  • If the sum of the rates of the individual queues in a traffic class exceeds the shaping rate of the VLAN, the shaping rate of the VLAN is used as the shaping rate of the traffic class.

Weighted Round-Robin of Subscriber Traffic on a Port Limitations

The following list describes the limitations for WRR:

  • A discrepancy in the delay-buffer rate values among the VLANs belonging to the same level 2 scheduler node can cause the WRR to work incorrectly.

  • WRR does not work correctly if the ratio of the shaping rate is greater than 100 among all the subscribers.

  • The number of level 2 scheduler nodes and the number of subscribers per level 2 scheduler node must be equal to 32,000 for it to work correctly.

  • Any modification to the level 2 scheduler node configuration requires an FPC reset.

Related Documentation