Per-Unit Scheduling and Hierarchical Scheduling for MPC Interfaces

Limited Scale Per-Unit Scheduling MPCs

Per-unit scheduling features on a limited scale are supported for interfaces hosted on some MPCs that do not have a dedicated queuing chip.

On MPCs that support per-unit scheduling, the following scheduling capabilities are available:

• Four or eight egress queues per unit.

• Delay buffer capacities of 100 ms by default, and up to 200 ms maximum delay.

• Rate shaping of the ports and their queues.

• Guaranteed rate enforced at the queues.

The per-unit scheduling features also support pre-classification of incoming packets to protect high priority packets in the event of congestion. Such features include ingress DSCP rewrite and per-VLAN classification, ingress and egress policing, and rewrites.

Hierarchical Scheduling MPCs

MPCs that provide a dedicated queuing chip support hierarchical scheduling.

Hierarchical scheduling MPCs support all per-unit scheduling functionality plus fine-grained queuing abilities over four or five levels of hierarchical scheduling:

• Hierarchical scheduling with ports, interface sets, and logical interfaces.

• Shaping—Committed Information Rate (CIR) and a peak information rate (PIR)—at all scheduling levels, including queues.

• Three normal- priority levels and two excess- priority levels configurable at all scheduling levels, including queues.

• Per-priority shaping of traffic at Level 1 or Level 2.

• Shaping for unconfigured customer VLANs (C-VLANs) and for service VLANs (S-VLANs).

Scheduler Node Levels for Per-Unit Scheduling MPCs

For an interface hosted on a per-unit scheduling MPC, each logical interface has its own dedicated level 3 node, and all logical interfaces share a common level 2 node (one per port).

Figure 1 illustrates scheduler node levels for an interface hosted on a per-unit queuing MPC.

Figure 1: Scheduler Node Levels for Per-Unit Scheduling MPCs

For interfaces hosted on per-unit scheduling MPCs, the level 2 node is always a dummy node.

Scheduler Node Levels for Hierarchical Scheduling MPCs

The queuing model used by interfaces hosted on hierarchical scheduling MPCs supports up to five levels of scheduler nodes: the queue itself (level 5), session logical interface (ppp or dhcp) (level 4), customer VLAN (C-VLAN) (level 3), the interface set or service VLAN (S-VLAN) collection (level 2), and the physical interface or port (level 1).

Figure 2 illustrates the scheduler node levels for an interface hosted on a hierarchical scheduling MIC or MPC.

Figure 2: Scheduler Node Levels for Interfaces on Hierarchical Scheduling MPCs

The figure depicts scheduler nodes for an interface that does not include interface sets and for which traffic control profiles are applied to the logical interfaces only.