Shared-Queue QoS Policies
Quality of Service Guide 643
When multiple hardware queues represent a single logical service queue, the system
automatically monitors the offered load and forwarding rate of each hardware queue. Based
on the monitored state of each hardware queue, the system imposes an individual CIR and
PIR rate for each queue that provides an overall aggregate CIR and PIR reflective of what is
provisioned on the service queue.
Figure 36: Unicast Service Queue Mapping to Multiple Destination Based Hardware Queues
Ingress Shared Queuing
To avoid the hardware queue expansion issues associated with normal service based queuing,
the system allows an ingress logical service queue to map to a single hardware queue when
shared queuing is enabled. Shared queuing uses two passes through the ingress forwarding
plane to separate ingress per service queuing from the destination switch fabric queuing. In
the case of shared queuing, ingress unicast service queues are created one-for-one relative to
hardware queues. Each hardware queue representing a service queue is mapped to a special
destination in the traffic manager that ‘forwards’ the packet back to the ingress forwarding
plane allowing a second pass through the traffic manager. In the second pass, the packet is
placed into a ‘shared’ queue for the destination forwarding plane. The shared queues are used
by all services configured for shared queuing.
Multicast
Queue
Unicast
Queue
Hardware
Queue
Hardware
Queue
Hardware
Queue
Hardware
Queue
Hardware
Queue
SF Egress
MDA 1
SF Egress
MDA 2
SF Egress
MDA 3
SF Egress
MDA n
Switch Fabric
Multipoint Service Queue is
representated by a single
Hardware Queue (Single Pass)
Unicast Service Queue is
representated by Multiple SF
Destination Hardware Queues
Backpressure through
Switch Fabric based
on Class
IOM monitors individual destination
Hardware Queues based on offered
Load and Forwarded Rate determine
each Queues Operating Parameters
(CIR, PIR...) relative to the Service Queue
Fig_22
Unicast
Multicast
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