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Understanding CoS Traffic Control Profiles

A traffic control profile defines the output bandwidth and scheduling characteristics of forwarding class sets (priority groups). The forwarding classes (queues) mapped to a forwarding class set share the bandwidth that you assign to the forwarding class set in the traffic control profile.

This two-tier hierarchical scheduling architecture provides flexibility in allocating resources among queues and:

  • Assigns a portion of port bandwidth to a priority group. You define the port resources for the priority group in a traffic control profile.
  • Allocates priority group bandwidth among the queues that belong to the priority group. A scheduler map attached to the traffic control profile defines the amount of the priority group’s resources that each queue can use.

Attaching a priority group and traffic control profile to a port defines the hierarchical scheduling properties of the group and the queues that belong to the group.

The ability to create priority groups supports enhanced transmission selection (ETS, described in IEEE 802.1Qaz). When a priority group does not use its allocated port bandwidth, ETS shares the excess port bandwidth among other priority groups on the port in proportion to their guaranteed minimum bandwidth (guaranteed rate). This utilizes the port bandwidth better than scheduling schemes that require setting strict priorities that reserve bandwidth for all groups whether it is needed or not. ETS allows traffic groups that need extra bandwidth to use it if the bandwidth is available, while preserving the ability to specify the minimum guaranteed bandwidth for traffic groups.

Traffic control profiles define the following CoS properties for priority groups:

  • Minimum guaranteed bandwidth—Also known as the committed information rate (CIR). This is the minimum amount of port bandwidth the priority group receives. Priorities in the priority group receive their minimum guaranteed bandwidth as a portion of the priority group’s minimum guaranteed bandwidth. The guaranteed-rate statement defines the minimum guaranteed bandwidth.

    Note: You cannot apply a traffic control profile with a minimum guaranteed bandwidth to a priority group that includes strict-high priority queues.

  • Shared excess (extra) bandwidth—When the priority groups on a port do not consume the full amount of bandwidth allocated to them or there is unallocated link bandwidth available, priority groups can contend for that extra bandwidth if they need it. Priorities in the priority group contend for extra bandwidth as a portion of the priority group’s extra bandwidth. The amount of extra bandwidth for which a priority group can contend is proportional to the priority group’s guaranteed minimum bandwidth (guaranteed rate).
  • Maximum bandwidth—Also known as peak information rate (PIR). This is the maximum amount of port bandwidth the priority group receives. Priorities in the priority group receive their maximum bandwidth as a portion of the priority group’s maximum bandwidth. The shaping-rate statement defines the maximum bandwidth.
  • Queue scheduling—Each traffic control profile includes a scheduler map. The scheduler map maps priorities (forwarding classes) to schedulers to define the scheduling characteristics of the individual priorities in the priority group. The resources scheduled for each priority represent portions of the resources that the traffic control profile schedules for the entire priority group, not portions of the total link bandwidth. The scheduler-maps statement defines the mapping of forwarding classes to schedulers.
 

Related Documentation

 

Published: 2014-07-23

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