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Example: Configuring Transmission Rate with Intelligent Oversubscription on SONET/SDH OC48/STM16 IQE PICs

This example shows how to configure transmission rates on a sonet interface for eight forwarding classes with transmission rate values that exceed 100 percent, causing the interface to be in an oversubscribed state.


This example requires the following hardware and software components:

  • Networking devices using a SONET/SDH OC48/STM16 IQE PIC.

  • Junos OS Release 12.2 or later running on the devices.

Before you begin:

  1. Configure the device interfaces.

  2. Enable class-of-service (CoS) queuing, scheduling, and shaping on the device interfaces.

Overview and Topology

Junos OS Release 12.2 and later support oversubscribing the available bandwidth on a SONET/SDH OC48/STM16 IQE PIC up to 300 percent. This optimization is achieved by creating an additional priority group for all queues specified for low priority, and the sum of transmission rates for all the low priority queues adding up to 100 percent, independent of the transmission rate configured for all other queues.

Previously, the SONET/SDH OC48/STM16 IQE PIC supported a maximum bandwidth optimization by oversubscribing the available bandwidth up to 200 percent, by excluding the transmission rate percentage specified for the Strict-High queue from the total 100 percent transmission rate. Therefore, the transmission rate percentage for all the non-Strict-High queues added up to 100 percent. This computation was done after the internal mapping of the excess priority or the excess rate.

As an enhancement to the intelligent oversubscription feature on SONET/SDH OC48/STM16 IQE PICs, support for maximum bandwidth optimization is increased to 300 percent.

When the sum of transmission rates for all queues exceeds 100 percent, the interface is in an oversubscribed state. At the time of oversubscription, the queues are split into three priority groups with the intelligent oversubscription feature enhancement:

  • Strict-High

  • High, Medium-High, and Medium-Low

  • Low

Each of the above priority groups can be configured to have a transmission rate oversubscription up to 100 percent. The transmission rate oversubscription value can be expressed as a percentage of the CIR or PIR value or as an absolute value.


The remainder option is not supported on an oversubscribed SONET/SDH OC48/STM16 IQE PIC. When the sum of the transmission rates for all queues exceeds 100 percent, and if one or more queues are configured with the remainder option, a syslog error message is generated and the configuration is ignored.

In this example, Router R0 is the route on which the CoS options are configured. Routers R1 and R2 are directly connected to R0 and send traffic to R0.

Figure 1: Example topology Example topology


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.



Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode. To configure the R0 router:

  1. Configure an IP Precedence classifier to classify incoming packets based on the code point values.

  2. Define the classification of code point values to a forwarding class, and configure code point values to classify to loss priority Low.

  3. Define mapping of forwarding classes to queue numbers.

  4. Configure traffic shaping and scheduling profiles.

  5. Apply the class-of-service options to interfaces.

  6. Configure eight packet schedulers with scheduling priority and transmission rates.

  7. Define mapping of forwarding classes to packet schedulers.


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

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


Confirm that the configuration is working properly.

Verifying Queue Transmission Rate Oversubscription


Verify that the SONET/SDH OC48/STM16 IQE PIC supports 300 percent oversubscription.


Configure the queue transmission rates such that they are oversubscribed up to 300 percent.

The sum of transmission rates of all queues can be less than or equal to 300 percent. The sum of transmission rates of all queues in each priority group should be less than or equal to 100 percent.

In this example, Router R0 interfaces have been oversubscribed by 150 percent of the available bandwidth. The sum of transmission rates of all the queues in each of the priority groups are:

  • Strict-High—(q0) 25%

  • High, Medium-High, Medium-Low—(q1, q2, q3, and q4) 80%

  • Low—(q5, q6, and q7) 45%

When the sum of transmission rates of all queues in any of the priority groups exceeds 100 percent, the commit fails.

For example, if the transmission rate of q1 is 30 percent, the sum of the transmission rates of all queues (q1, q2, q3, and q4) in the High-Medium priority group is 110 percent. At the time of commit, the following error is displayed:


When the sum of transmission rates of all queues exceeds 100 percent, a new priority group is created for all Low priority queues. The queue transmission rates in the Low priority group can add up to 100 percent.