11-7
Cisco ONS 15310-CL and Cisco ONS 15310-MA Ethernet Card Software Feature and Configuration Guide R8.5
78-18133-01
Chapter 11 Configuring Quality of Service on the ML-Series Card
ML-Series QoS
Weights are assigned to each queue as a result of the service provisioning process. When coupled with
policing and policy mapping provisioning, these weights and the WDRR scheduling process ensure that
QoS commitments are provided to each service flow.
Figure 11-5 illustrates the ML-Series card’s queuing and scheduling.
Figure 11-5 Queuing and Scheduling Model
The weighting structure allows traffic to be scheduled at 1/2048 of t he port rate. This equates to
approximately 49 kbps for traffic exiting a FastEthernet port.
The unicast queues are created as the output service policy implementation on the egress ports. Each
unicast queue is assigned with a committed bandwidth and the weight of th e queue is determined by the
normalization of committed bandwidth of all defined unicast queues for that port. The traffic beyond the
committed bandwidth on any queue is treated by the scheduler according to the relative weight of the
queue.
The LLQ is created as the output service policy implementation on the egress ports. Each LLQ is
assigned with a committed bandwidth of 100 percent and is served with lower latency. To limit the
bandwidth usage by the LLQ, a strict policer needs to be implement ed on the ingress for the LLQ traffic
classes.
The DE allows some packets to be treated as committed and some as discard-eligible on the scheduler.
For the Ethernet frames, the CoS (IEEE 802.1p) bits are used to identify committed and discard eligible
packets, where the RPR-CoS and the DE bits are used for RPR tra ffic. When congestion occurs and a
queue begins to fill, the DE packets hit a lower tail-drop threshold than the committed packets.
Committed packets are not dropped until the total committed load exceeds the interface output. The
tail-drop thresholds adjust dynamically in the card to ma ximize use of the shared buffer pool while
guaranteeing fairness under all conditions.
Control Packets and L2 Tunneled Protocols
The control packets originated by the ML-Series card have a higher priority than data packets. The
external Layer 2 and Layer 3 control packets are handled as data packets and assigned to broadcast
queues. Bridge protocol data unit (BPDU) prioritization in the M L-Series card gives Layer 2-tunneled
BPDU sent out the multicast/broadcast queue a higher discard value and therefore a higher priority than
than other packets in the multicast/broadcast queue. The Ethernet CoS (IEEE 802.1p) for
Layer 2-tunneled protocols can be assigned by the ML-Series card.
96502
Low Latency Queues
Weighted
Deficit
Round
Robin
Unicast Queues
Weighted
Deficit
Round
Robin
Weighted
Deficit
Round
Robin
Multi/Broadcast Queues
Weighted
Deficit
Round
Robin
Queues assigned by
"Priority" Command for
associated Classification
for Scheduling
Queues assigned by
"Bandwith" Command for
associated Classification
for Scheduling
Queues automatically
assigned