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Example: Configuring Excess Rate for PTX Series Packet Transport Routers

You can configure excess rate to customize the distribution of available excess bandwidth among the queues for PTX Series Packet Transport Routers. When excess rate is not configured, the excess bandwidth available is distributed in proportion to the transmit rates allocated to the queues.

Requirements

This example uses the following hardware and software components:

  • One PTX Series Packet Transport Router
  • Junos OS Release 12.1X48R2 or later

Overview

This set of examples illustrates how you configure schedulers for the PTX Series Packet Transport Router to distribute the remaining bandwidth (excess rate) among the configured queues.

When you configure excess rate, use the following guidelines:

  • The transmit-rate statements of the configured schedulers can add up to at most 100%.
  • All queues on the PTX Series Packet Transport Router have the same excess priority. Excess priority configuration is not supported.
  • If a strict-high priority queue is configured and is rate-limited, this queue gets the rate-limited bandwidth first. Then the configured transmit-rate value of other queues is met (regardless of queue priority), and finally the excess bandwidth is distributed in proportion to the configured excess-rate values.

    Note: We recommend that you configure rate limit on strict-high queues because the other queues may not meet their guaranteed bandwidths. See transmit-rate.

Configuration

To configure excess rate, perform one or more of these tasks:

Configuring Schedulers Without Specifying Excess Rate

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

set class-of-schedule schedulers sched_queue_0 transmit-rate percent 20set class-of-schedule schedulers sched_queue_1 transmit-rate percent 40set class-of-schedule schedulers sched_queue_2 transmit-rate percent 10set class-of-schedule schedulers sched_queue_3 transmit-rate percent 10

Step-by-Step Procedure

In this example, four queues are configured and each associated scheduler is assigned the indicated transmit rate. Across the four queues, the transmit rate totals to 80%. No excess rate is configured. Assuming that each queue has loads greater than or equal to the configured transmit rate, the remaining 20% of the bandwidth is distributed in proportion to the configured transmit rates (20:40:10:10):

  • sched_queue_0—5% (20% of the guaranteed rate plus 5% of the remaining bandwidth is 25%)
  • sched_queue_1—10% (40% of the guaranteed rate plus 10% of the remaining bandwidth is 50%)
  • sched_queue_2—2.5% (10% of the guaranteed rate plus 2.5% of the remaining bandwidth is 12.5%)
  • sched_queue_3—2.5% (10% of the guaranteed rate plus 2.5% of the remaining bandwidth is 12.5%)

The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure the schedulers:

  1. Create the scheduler for queue 0:
    [edit class-of-schedule]user@host# set schedulers sched_queue_0 transmit-rate percent 20
  2. Create the scheduler for queue 1:
    [edit class-of-schedule]user@host# set schedulers sched_queue_1 transmit-rate percent 40
  3. Create the scheduler for queue 2:
    [edit class-of-schedule]user@host# set schedulers sched_queue_2 transmit-rate percent 10
  4. Create the scheduler for queue 3:
    [edit class-of-schedule]user@host# set schedulers sched_queue_3 transmit-rate percent 10

Results

From configuration mode, confirm your configuration by entering the show class-of-service schedulers command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

sched_queue_0 {transmit-rate percent 20;}sched_queue_1 {transmit-rate percent 40;}sched_queue_2 {transmit-rate percent 10;}sched_queue_3 {transmit-rate percent 10;}

If you are done configuring the device, enter commit from configuration mode.

Configuring Schedulers by Specifying Excess Rate

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

set class-of-schedule schedulers sched_queue_0 transmit-rate percent 25set class-of-schedule schedulers sched_queue_0 excess-rate percent 25set class-of-schedule schedulers sched_queue_1 transmit-rate percent 25set class-of-schedule schedulers sched_queue_1 excess-rate percent 50set class-of-schedule schedulers sched_queue_2 transmit-rate percent 25set class-of-schedule schedulers sched_queue_3 transmit-rate percent 25

Step-by-Step Procedure

In this example, four schedulers are configured and each is assigned a transmit rate of 25%. Queue 0 is configured with 40% and queue 1 with 60% of the excess rate. If the offered load through queue 2 is only 10%, the remaining bandwidth is distributed as: queue excess rate / total excess rate * remaining bandwidth percentage. If a queue has transmit rate configured but not excess rate, the excess rate for that queue is 1. In this example, the excess rate ratio is 25:50:1:1, which yields the following distribution of the 15% remaining bandwidth from queue 2:

  • sched_queue_0—4.93% (25 / 76 * 15%)
  • sched_queue_1—9.87% (50 / 76 * 15%)
  • sched_queue_3—0.197% (1 / 76 * 15%)

When the offered load on queue 2 increases to 25% or greater, the other queues get only their configured transmit rates.

The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure the schedulers:

  1. Create the scheduler for queue 0:
    [edit class-of-schedule]user@host# set schedulers sched_queue_0 transmit-rate percent 25user@host# set schedulers sched_queue_0 excess-rate percent 25
  2. Create the scheduler for queue 1:
    [edit class-of-schedule]user@host# set schedulers sched_queue_1 transmit-rate percent 25user@host# set schedulers sched_queue_1 excess-rate percent 50
  3. Create the scheduler for queue 2:
    [edit class-of-schedule]user@host# set schedulers sched_queue_2 transmit-rate percent 25
  4. Create the scheduler for queue 3:
    [edit class-of-schedule]user@host# set schedulers sched_queue_3 transmit-rate percent 25

Results

From configuration mode, confirm your configuration by entering the show class-of-service schedulers command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

sched_queue_0 {transmit-rate percent 25;excess-rate percent 25;}sched_queue_1 {transmit-rate percent 25;excess-rate percent 50;}sched_queue_2 {transmit-rate percent 25;}sched_queue_3 {transmit-rate percent 25;}

If you are done configuring the device, enter commit from configuration mode.

Configuring Schedulers to Control Excess Rate for Non-High Priority Queues

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

set class-of-schedule schedulers sched_queue_0 transmit-rate percent 90set class-of-schedule schedulers sched_queue_0 priority highset class-of-schedule schedulers sched_queue_1 transmit-rate percent 10set class-of-schedule schedulers sched_queue_1 priority lowset class-of-schedule schedulers sched_queue_2 excess-rate percent 10set class-of-schedule schedulers sched_queue_3 excess-rate percent 30

Step-by-Step Procedure

In this example, the scheduler for queue 0 is configured to transmit up to 90% of traffic if there is enough offered load. When the traffic to queue 0 is less than 90%, excess rate is configured to distribute the remaining bandwidth in the ratio 1:1:10:30 (when the offered load on queue 1 is greater than 10%), which yields the following distribution of the remaining bandwidth from queue 0:

  • sched_queue_1—0.0244 * x% (1 / 41 * remaining bandwidth (x)%)
  • sched_queue_2—0.244 * x% (10 / 41 * remaining bandwidth (x)%)
  • sched_queue_3—0.732 * x% (30 / 41 * remaining bandwidth (x)%)

Note: Although the transmit-rate values on queues can add up to at most 100%, the excess-rate value does not have this restriction because it is a ratio.

The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure the schedulers:

  1. Create the scheduler for queue 0:
    [edit class-of-schedule]user@host# set schedulers sched_queue_0 transmit-rate percent 90user@host# set schedulers sched_queue_0 priority high
  2. Create the scheduler for queue 1:
    [edit class-of-schedule]user@host# set schedulers sched_queue_1 transmit-rate percent 10user@host# set schedulers sched_queue_1 priority low
  3. Create the scheduler for queue 2:
    [edit class-of-schedule]user@host# set schedulers sched_queue_2 excess-rate percent 10
  4. Create the scheduler for queue 3:
    [edit class-of-schedule]user@host# set schedulers sched_queue_3 excess-rate percent 30

Results

From configuration mode, confirm your configuration by entering the show class-of-service schedulers command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

sched_queue_0 {transmit-rate percent 90;priority high;}sched_queue_1 {transmit-rate percent 10;priority low;}sched_queue_2 {excess-rate percent 10;}sched_queue_3 {excess-rate percent 30;}

If you are done configuring the device, enter commit from configuration mode.

Verification

Verifying the Excess Rate Configuration

Purpose

Verify that the excess rate configuration is producing the results you expect.

Action

From operational mode, enter the show interfaces queue interface command for the physical interface to verify.

Meaning

The show command output lists the traffic by queue and forwarding class names. Verify that the Bytes field for active queues on the specified physical interface match the proportions you expect from the excess rate configuration.

 

Related Documentation

 

Published: 2013-07-18

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