Configuring the Scheduler Buffer Size

To control congestion at the output stage, you can configure the delay-buffer bandwidth. The delay-buffer bandwidth provides packet buffer space to absorb burst traffic up to the specified duration of delay. Once the specified delay buffer becomes full, packets with 100 percent drop probability are dropped from the head of the buffer.

The default scheduler transmission rate for queues 0 through 7 are 95, 0, 0, 5, 0, 0, 0, and 0 percent of the total available bandwidth.

The default buffer size percentages for queues 0 through 7 are 95, 0, 0, 5, 0, 0, 0, and 0 percent of the total available buffer. The total available buffer per queue differs by PIC type, as shown in Table 29.

To configure the buffer size, include the buffer-size statement at the [edit class-of-service schedulers scheduler-name] hierarchy level:

For each scheduler, you can configure the buffer size as one of the following:

• A percentage of the total buffer. The total buffer per queue is based on microseconds and differs by platform type, as shown in Table 29.
• The remaining buffer available. The remainder is the buffer percentage that is not assigned to other queues. For example, if you assign 40 percent of the delay buffer to queue 0, allow queue 3 to keep the default allotment of 5 percent, and assign the remainder to queue 7, then queue 7 uses approximately 55 percent of the delay buffer.
• A temporal value, in microseconds. For the temporal setting, the queuing algorithm starts dropping packets when it queues more than a computed number of bytes. This maximum is computed by multiplying the logical interface speed by the configured temporal value. The buffer size temporal value per queue differs by platform type, as shown in Table 29.

For information about configuring large buffer sizes on IQ PICs, see Configuring Large Delay Buffers for Slower Interfaces.

Table 29: Buffer Size Temporal Value Ranges by Platform Type

For more information about configuring delay buffers, see the following subtopics:

• Configuring Large Delay Buffers for Slower Interfaces
• Enabling and Disabling the Memory Allocation Dynamic per Queue

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