Configuring Schedulers

You use schedulers to configure transmission scheduling and rate control parameters. Schedulers define the priority, bandwidth, delay buffer size, rate control status, and RED drop profiles to be applied to a particular class of traffic.

You associate the schedulers with forwarding classes by means of scheduler maps. You can then associate each scheduler map with an interface, thereby configuring the hardware queues, packet schedulers, and RED processes that operate according to this mapping.

A scheduler configuration block specifies the buffer size, bandwidth, and priority for a queue. It also specifies the RED drop profile for packets that fall within specification and out of specification.

Physical interfaces (for example, t3-0/0/0, t3-0/0/0:0, and ge-0/0/0) support scheduling with any encapsulation type pertinent to that physical interface. For a single port, you cannot apply scheduling to the physical interface if you have applied scheduling to one or more of the associated logical interfaces.

Logical interfaces (for example, t3-0/0/0 unit 0 and ge-0/0/0 unit 0) support scheduling on data link connection identifiers (DLCIs) or VLANs only.

In the JUNOS software implementation, the term logical interfaces generally refers to interfaces you configure by including the unit statement at the [edit interfaces interface-name] hierarchy level. Logical interfaces have the .logical descriptor at the end of the interface name, as in ge-0/0/0.1 or t1-0/0/0:0.1, where the logical unit number is 1.

Although channelized interfaces are generally thought of as logical or virtual, the JUNOS software sees T3, T1, and NxDS0 interfaces within a channelized IQ PIC as physical interfaces. For example, both t3-0/0/0 and t3-0/0/0:1 are treated as physical interfaces by the JUNOS software. In contrast, t3-0/0/0.2 and t3-0/0/0:1.2 are considered logical interfaces because they have the .2 at the end of the interface names.

Within the [edit class-of-service] hierarchy level, you cannot use the .logical descriptor when you assign properties to logical interfaces. Instead, you must include the unit statement in the configuration. For example:

[edit class-of-service]

user@host# set interfaces t3-0/0/0 unit 0 scheduler-map map1

To configure class-of-service (CoS) schedulers, you can include the following statements at the [edit class-of-service] hierarchy level of the configuration:

class-of-service {

    interfaces {

        interface-name {

            scheduler-map map-name;

            scheduler-map-chassis map-name;

            unit logical-unit-number {

                scheduler-map map-name;

                shaping-rate rate;

            }

        }

    }

    fabric {

        scheduler-map {

            priority (high | low) scheduler scheduler-name;

        }

    }

    scheduler-maps {

        map-name {

            forwarding-class class-name scheduler scheduler-name;

        }

    }

    schedulers {

        scheduler-name {

            buffer-size (percent percentage | remainder | temporal microseconds);

            drop-profile-map loss-priority (any | high | medium | low) 
                     protocol (any | non-tcp | tcp) drop-profile profile-name;

            priority priority-level;

            transmit-rate (rate | percent percentage | remainder) <exact>;

        }

    }

}

This chapter discusses the following topics:

• Default Scheduler
• Configuring the Scheduler Buffer Size
• Configuring the Scheduler Drop Profile
• Configuring Priority Scheduling
• Configuring the Scheduler Transmission Rate
• Configuring the Scheduler Map
• Associating the Scheduler Map with an Output Interface
• Scheduling Packet Forwarding Component Queues
• Associating a Scheduler Map with a DLCI or VLAN
• Associating a Scheduler with a Fabric Priority