Configuring Low-CDV Mode for Per-Port Queuing on ATM Interfaces
In low-CDV mode, the HRR scheduler and the SAR scheduler operate in concert. In low-CDV QoS port mode, QoS automatically configures the shaping rate of the VPs, VCs, or both based on the QoS profile and the scheduler profile. Therefore, the QoS shaping mode must be set to the cell mode. In low-CDV mode, the SAR scheduler converts frame-atomic bursts of cells to CDVT-conformant streams of interleaved cells. There is no VC backpressure, and the port backpressure is loose, so several megabytes of cells can reside in the SAR buffer pool.
When you configure low-CDV mode:
- QoS synchronizes the shaping rates for VPs and VCs in the HRR and SAR schedulers.
- VC backpressure is disabled.
- Port backpressure is set to default thresholds of 6 MB per OC3 port and 24 MB per OC12 port.
- SAR scheduler performs more buffering than in low-latency mode.
- Use cell QoS shaping mode.
This procedure creates the low-CDV mode with per-VP CDVT configuration shown in Figure 1. Figure 2 shows low-CDV mode with per-VC CDVT.
Figure 1: Low-CDV Mode (per-VP CDVT)
Figure 2: Low-CDV Mode (per-VC CDVT)
To configure low-CDV mode with a strict-priority queue and a best-effort queue:
- Configure the traffic class.
- host1(config)#traffic-class strict
- host1(config-traffic-class)#exit
- 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
- Define the scheduler profiles for the traffic-class group.
- host1(config)#scheduler-profile strict
- host1(config-scheduler-profile)#strict-priority
- host1(config-scheduler-profile)#exit
- host1(config)#scheduler-profile 500k
- host1(config-scheduler-profile)#shaping-rate 500000
- host1(config-scheduler-profile)#exit
- host1(config)#scheduler-profile 1m
- host1(config-scheduler-profile)#shaping-rate 1000000
- host1(config-scheduler-profile)#exit
- host1(config)#scheduler-profile 2m
- host1(config-scheduler-profile)#shaping-rate 2000000
- host1(config-scheduler-profile)#exit
- Configure per-VC CDVT by configuring QoS profile with
ATM VC queues.
- host1(config)#qos-profile low-cdv-q-p
- host1(config-qos-profile)#atm-vc node scheduler-profile 1m
- host1(config-qos-profile)#atm-vp node scheduler-profile 2m
- 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 scheduler-profile 500k
- host1(config-qos-profile)#exit
- Configure per-VP CDVT using shapeless VP tunnels that
are used when the QoS application controls SAR scheduler shaping and
set the QoS port mode to low CDV.
- host1(config)#interface atm 2/0
- host1(config-if)#atm vp-tunnel 0 0
- host1(config-if)#atm vp-tunnel 1 0
- host1(config-if)#qos-mode-port low-cdv
- host1(config-if)#qos-profile low-cdv-q-p
- host1(config-subif)#interface atm 2/0.5
- host1(config-subif)#atm pvc 5 0 5 aal5snap
- host1(config-subif)#interface atm 2/0.6
- host1(config-subif)#atm pvc 6 0 6 aal5snap
- host1(config-subif)#interface atm 2/0.7
- host1(config-subif)#atm pvc 7 1 7 aal5snap
- host1(config-subif)#interface atm 2/0.8
- host1(config-subif)#atm pvc 8 1 8 aal5snap
Tip: For ATM interfaces on ERX-7xx models, ERX-14xx models, and the ERX-310 router, you must specify port 0.
Configuring an ATM VP tunnel sets a shaping rate in the SAR scheduler. Before configuring an ATM VP tunnel, there must be no PVCs with the same VPI that you are about to configure. Before using the atm vp-tunnel command, remove any PVCs from the configuration. You can reconfigure the PVCs after configuring the shapeless VP tunnel.
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)