Overview

If the user enables the multi-class option under an MLPPP bundle, the XMA or MDA egress data path provides a queue for each of the four classes of MLPPP. The user configures the required number of MLPPP classes to use on a bundle. The forwarding class of the packet, as determined by the ingress QoS classification, is used to determine the MLPPP class for the packet and, therefore, in which of the four egress XMA or MDA queues to store the packet. The mapping of forwarding class to MLPPP class is a function of the user configurable number of MLPPP classes. The default mapping for a 4-class, 3-class, and 2-class MLPPP bundle is described in Table: Default packet forwarding class to MLPPP class mapping .

Table: Packet forwarding class to MLPPP class mapping describes a different mapping enabled when the user applies one of three predefined egress QoS profiles in the 4-class bundle configuration only.

The MLPPP class queue parameters and its scheduling parameters are also configured by applying one of the three predefined egress QoS profiles to an MLPPP bundle.

Table: MLPPP class queue threshold parameters and Figure: MLPPP class queue thresholds for in-profile and out-of-profile packets describe the class queue threshold parameters. Packets marked with a high drop precedence, such as out-of-profile, by the service or network ingress QoS policy are discarded when any class queue reaches the OOP threshold. Packets with a low drop precedence marking, such as in-profile, are discarded when any class queue reaches the max threshold.

Figure: MLPPP class queue thresholds for in-profile and out-of-profile packets

Table: MLPPP class queue scheduling parameters and Figure: MLPPP class queue scheduling scheme describe the class queue scheduling parameters.

Figure: MLPPP class queue scheduling scheme

All queue threshold and queue scheduling parameters are adjusted to the available bundle rate. If a member link goes down or a new member link is added to the bundle, the scheduling parameters MIR, W1, W2, W3, as well as the per class queue thresholds OOP and Max, are automatically adjusted to maintain the same values.

Class 0 queue is serviced at MLPPP at available bundle rate. Class 1 queue is guaranteed a minimum service rate but is allowed to share additional bandwidth with class 2 and 3 queues based on the configuration of WRR weight W1.

Class 2 and 3 queues can be given bandwidth guarantee by limiting MIR of class 1 queue to less than 100% and by setting the WRR weights W1, W2, and W3 to achieve the needed bandwidth distribution among all three class queues.

There is one queue per bundle member link to carry link control packets, such as LCP: PPP, and which are serviced with strict priority over the 4 class queues (not shown).

In the default 2-class, 3-class, and 4-class egress QoS profile, the class queues are serviced with strict priority in ascending order of class number.