Configure Hierarchical Scheduling

Configure Schedulers

1. In Director view:
   1. Select the Configuration tab in the top menu bar.
   2. Select Template > Device Templates in the left menu bar.
   3. Select an organization in the Organization field.
   4. Select a template in the main pane. The view changes to Template view.
2. Select Configuration > Networking > NPU > Class of Service > Schedulers in the left menu bar.
   
   
3. Click the  Add icon. The Add Scheduler screen displays. Enter information for the following fields.
   
   
    

   Field	Description
   Name (Required)	Enter a name for the scheduler.
   Description	(Optional) Enter a text description of the scheduler.
   Mode (Required)	Select a scheduler mode. The options are: SP—Strict Priority WRR—Weighted Round Robin DWR— Deficit Weighted Round Robin
   Weight	(For WRR and DWR mode only.) Set the transmission rate of data packets. SP—Not configurable. The SP weight is 0.  WRR—Weighted Round Robin Range: 1 through 100 DWR— Deficit Weighted Round Robin Range: 1 through 100
   Shaping Rate (Group of Fields)
   Scheduler Transmit Rate (PIR) Kbps	Enter the Peak Information Rate (PIR). PIR is the maximum rate of traffic that can pass through an interface, in kilobits per second (Kbps). The PIR value must be equal to or greater than the CIR value. Range: 0 through 4294967295 Kbps Default: None
   Scheduler Committed Rate (CIR) Kbps	Enter the Committed Information Rate (CIR) in kilobits per second (Kbps). CIR is the average rate of traffic that can pass through an interface. Range: 0 through 4294967295 Kbps Default: None

Configure Scheduler Maps

1. In Director view:
   1. Select the Configuration tab in the top menu bar.
   2. Select Templates > Device Templates in the left menu bar.
   3. Select an organization in the Organization field.
   4. Select a template in the main pane. The view changes to Template view.
2. Select Configuration > Networking > NPU > Class of Service > Scheduler Maps in the left menu bar.
   
   
    
3. Click the  Add icon. The Add Scheduler Map screen displays. Enter information for the following fields.
   
   
    

   Field	Description
   Name (Required)	Enter a name for the scheduler map.
   Description	(Optional) Enter a text description of the scheduler map.
   Level	Select a child scheduler-map level from the drop-down list. The options are: 0 (Set) 1 (Group) 2 (CoS)
   Child Scheduler	Select a child scheduler from the drop-down list.
   Node ID	Enter the node ID for the scheduler.
   Scheduler	Select a scheduler from the drop-down list.

4. Click OK.

Attach a Scheduler Map to an Interface 

1. In Director view:
   1. Select the Configuration tab in the top menu bar.
   2. Select Templates > Device Templates in the left menu bar.
   3. Select an organization in the Organization field.
   4. Select a template in the main pane. The view changes to Template view.
2. Select Configuration > Networking > NPU > Class of Service > Interface/Network in the left menu bar.
   
   
    
3. Select the Interface horizontal sub-tab, then click the  Add icon. The Add Interface screen displays. Enter information for the following fields.
   
   
    

   Field	Description
   Name (Required)	Select the name of an interface.
   Description	(Optional) Enter a text description for the interface or network.
   DSCP Rewrite Rule	(Available only for VNI interfaces, TVI interfaces, and network associations.) Select the Differentiated Services Code Point (DSCP) rewrite rule to use for the egress traffic, which rewrites the DSCP code points of packets before forwarding the packets.
   802.1p Rewrite Rule	Select the 802.1p rule to use for the egress traffic, which rewrites the 802.1p code points of Ethernet packets before forwarding the packets.
   DSCP Classifier Rule	Select the DSCP classifier rule to use, which classifies traffic into forwarding classes and assigns loss priorities to the traffic based on DSCP bits.
   802.1p Classifier Rule	Select the 802.1p classifier rule to use, which classifies Ethernet traffic into forwarding classes and assigns loss priorities to the traffic based on 802.1p code point bits.
   Scheduler Map	Select the scheduler map to use for the egress traffic.
   Shaping Rate (Kbps)	Enter the shaping rate, in Kbps. Range: 8 through 200000000 Kbps Default: None
   Burst Size (Bytes)	Enter the burst size, in bytes. Range: 256 through 100000000 bytes Default: Depends on the link speed of the underlying interface. For example, if you connect two 1-GB interfaces, the burst size is 125000 bytes. If you connect a 1-GB interface to a 100-MB interface, the link speed is autonegotiated to 100 MB and the burst size is automatically set to 12500 bytes, and if you connect a 1-GB to a 10-MB interface, the burst size is automatically set to 1250 bytes. For most cases, it is recommended that you do not change the interface's burst size. However, you might consider changing it when the interface has autonegotiated a smaller burst size, but you know that the link can handle a larger higher burst. For example, if a 1-GB interface has autonegotiated to 10 MB, and if you know that the hardware can handle a burst of 125000 bytes and that the other side of the line can handle that much incoming burst, you could configure a larger burst.

4. Click OK.

Example 1: Strict Priority (SP) for Voice

The objective of this example is to provide absolute priority to voice traffic, ensuring lowest latency and jitter for real-time applications. It is recommended to use SP when voice traffic must always be served first, regardless of other flows.

• Configuration:
  • Voice queue (q4) is configured as Strict Priority (SP).
  • Video (q6) and default (q0) use WRR scheduling with lower weights.
• Example Mapping:
  
  
   
• Behavior:
  • SP ensures that voice traffic (q4) is always serviced before any other queue as long as it has traffic to send.
  • Guarantees minimal delay and jitter for voice but can starve lower-priority queues (video and default) under high voice load.
  • Best suited for critical real-time services with low-bandwidth but strict latency requirements.
  • Pros: Absolute priority for voice.
  • Cons: Risk of starvation for other queues during congestion.

Example 2: WRR with High Weight for Voice

The objective of this example is to use WRR weights to achieve prioritization while maintaining fairness and preventing starvation. It is recommended to use WRR with high weights for priority with fairness.

• Configuration: All traffic classes use WRR, with weights reflecting their relative importance.
• Example Mapping:
  
  

 Behavior:

• WRR serves queues proportionally to their assigned weights.
• Voice traffic (q4) is scheduled most frequently, but video and default traffic still receive service.
• Suitable for networks where voice is important but not critical enough for strict priority.
• Pros: Maintains fairness; no starvation.
• Cons: Voice latency may slightly increase under heavy load compared to SP mode.

Example 3: WRR + Shaping (CIR/PIR)

The objective of this example is to combine WRR scheduling with CIR/PIR shaping to enforce guaranteed minimum rates while maintaining fairness under congestion. It is recommended to use WRR with shaping for guaranteed bandwidth allocation and optimal fairness under congestion for balanced QoS.

• Configuration: All traffic classes use WRR, with weights and CIR/PIR, reflecting their relative importance.
• Example Mapping:
  
  

If only weights are defined without shaping parameters (CIR/PIR):

• WRR schedules traffic based purely on relative weights.
• Under congestion, high-weight queues (like voice) can consume most of the available bandwidth, leaving little or no capacity for others.
• This can cause bandwidth starvation for low-weight queues (e.g., q0).

Combining WRR with shaping provides a more balanced and controlled behavior.

Supported Software Information

Releases 23.1.2 and later support all content described in this article.

Additional Information

Configure CoS for SD-LAN