JUNOSe 9.1.x Quality of Service Configuration Guide > Configuring an Integrated Scheduler to Provide QoS for ATM > Configuring Low-Latency Mode for Per-Port Queuing on ATM Interfaces

Configuring Low-Latency Mode for Per-Port Queuing on ATM Interfaces

In low-latency mode, the SAR scheduler backpressures the HRR scheduler per physical port; each physical port buffers only a few kilobytes.

When you configure low-latency mode:

• VC backpressure is disabled.
• Port backpressure is enabled as aggressive.
• SAR scheduler performs minimal buffering.
• HRR scheduler is dominant.

This procedure creates the low-latency mode configuration shown in Figure 45.

Figure 45: Low-Latency Mode

To configure low-latency mode with a strict-priority queue and a best-effort queue:

1. Configure the traffic class.

host1(config)#traffic-class strict 

host1(config-traffic-class)#exit 

2. Set the traffic class in the traffic-class group.

host1(config)#traffic-class-group strict

host1(config-traffic-class-group)#traffic-class strict

host1(config-traffic-class-group)#exit

3. Define the scheduler profile for the traffic-class group.

host1(config)#scheduler-profile strict

host1(config-scheduler-profile)#strict-priority

host1(config-scheduler-profile)#exit

4. Configure the QoS profile with two ATM VC queues.

host1(config)#qos-profile low-latency-q-p

host1(config-qos-profile)#atm-vc node

host1(config-qos-profile)#atm-vc queue traffic-class best-effort

host1(config-qos-profile)#atm group strict scheduler-profile strict

host1(config-qos-profile)#atm-vc queue traffic-class strict

host1(config-qos-profile)#exit

5. From the desired port, set the QoS port mode to low latency.

host1(config)#interface atm 2/0

host1(config-if)#qos-mode-port low-latency

host1(config-if)#qos-profile low-latency-q-p

TIP: For ATM interfaces on ERX-7xx models, ERX-14xx models, and the ERX-310 router, you must specify port 0.

The qos-mode-port command:

• Excludes non-UBR ATM QoS services on any VC on the ATM module; for example, PCR, nrtVBR, and CBR
• Cannot be used if shaping is currently configured on the SAR scheduler
• Cannot be used with ATM VP tunnels with nonzero rates; however, can be used with tunnels with rates of zero (shapeless tunnels).

Related Topics

• Per-Packet Queuing on the SAR Scheduler Overview
• Guidelines for Configuring QoS over ATM
• interface atm command
• qos-mode-port command
• qos-profile command