Supported Platforms
Understanding Fine-Grained Queuing for Hierarchical Scheduling
This topic covers the following information:
CoS Scheduling with MIC and MPC Interfaces
Interfaces hosted on Modular Interface Card (MIC) and Modular Port Concentrator (MPC) line cards in MX Series 3D Universal Edge Routers support two types of class-of-service (CoS) queuing and scheduling, depending on MIC or MPC type:
Port-based Queuing MPCs
Port-level CoS features are available for interfaces hosted on MPCs that don’t have a dedicated queueing chip, specifically the MPC1, MPC2, and MPC3 line cards and on the fixed-configuration 16-port 10-Gigabit Ethernet MPC in MX240, MX480, MX960, MX2010, and MX2020 routers.
On port-based queuing MPCs, the following port-based queuing capabilities are available:
- Up to 8 egress queues per port.
- Delay buffer capacities for 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.
Port-based queuing MPCs 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 Queuing MICs and MPCs
Hierarchical CoS features are available for interfaces hosted on MICs in MPC1 Q, MPC2 Q, and MPC2 EQ line cards in MX240, MX480, MX960, MX2010, and MX2020 routers and for interfaces hosted on 2-port or 4-port 10-Gigabit Ethernet MICs in MX5, MX10, MX40, or MX80 modular chassis routers. These MICs and MPCs provide a dedicated queuing chip that supports hierarchical queuing.
Hierarchical queuing MICs and MPCs support all port-level CoS functionality plus fine-grained queuing abilities over four 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 VLAN (S-VLANs).
Hierarchical Scheduling with Hierarchical Queuing MICs and MPCs
Whereas standard CoS scheduling is based on the scheduling and queuing characteristics of a router’s egress ports and their queues, hierarchical CoS scheduling is based on the scheduling and queuing characteristics that span a hierarchy of scheduler nodes over a port. The hierarchy begins at Level 1, a root node at the physical interface (port) level of the CLI hierarchy and terminates at Level 4, a leaf node at the queue level. Between the root and leaf nodes of any scheduler hierarchy are one or more internal nodes, which are non-root nodes that have other nodes as “children” in the hierarchy.
Whereas you configure standard CoS scheduling by applying a scheduler map to each egress port to specify a forwarding class and a queue priority level, you configure hierarchical CoS scheduling with additional parameters. To configure hierarchical CoS scheduling, you apply a scheduler map to the queue level (Level 4) of a scheduler hierarchy, and you can apply a different traffic control profile at each of the other levels. A traffic control profile specifies not only a scheduler map (forwarding class and queue priority level) but also optional shaping rate (PIR), guaranteed transmit rate (CIR), burst rate, delay buffer rate, and drop profile.
Table 1 illustrates the possible combinations of scheduler nodes and their corresponding node level designations in a hierarchical scheduling environment.
Table 1: Node Levels Designations in Hierarchical Scheduling
Scheduler Configuration for Hierarchical CoS | Hierarchical CoS Scheduler Nodes | |||
|---|---|---|---|---|
Root Node | Internal (Non-Leaf) Nodes | Leaf Node | ||
Level 1 | Level 2 | Level 3 | Level 4 | |
One or more traffic control profiles configured on logical interfaces, but no interface-sets configured. | Physical interface | — | One or more logical interfaces | One or more queues |
Interface-sets (collections of logical interfaces) configured, but no traffic-control profiles configured on logical interfaces. | Physical interface | — | Interface-set | One or more queues |
Fully configured scheduler nodes: | Physical interface | Interface-set | One or more logical interfaces | One or more queues |
For example, if an interface-set statement is configured with logical interfaces (such as unit 0 and unit 2) and a queue, then the interface-set is an internal node at Level 2 of the scheduler node hierarchy. However, if there are no traffic control profiles configured on logical interfaces, then the interface set is at Level 3 of the hierarchy.
