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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 (which are mapped to output queues) that belong to a forwarding class set (fc-set) share the bandwidth that you assign to the fc-set in the traffic control profile.

This two-tier hierarchical scheduling architecture provides flexibility in allocating resources among forwarding classes, and also:

  • Assigns a portion of port bandwidth to an fc-set. You define the port resources for the fc-set in a traffic control profile.

  • Allocates fc-set bandwidth among the forwarding classes (queues) that belong to the fc-set. A scheduler map attached to the traffic control profile defines the amount of the fc-set’s resources that each forwarding class can use.

Attaching an fc-set and a traffic control profile to a port defines the hierarchical scheduling properties of the group and the forwarding classes that belong to the group.

The ability to create fc-sets supports enhanced transmission selection (ETS), which is described in IEEE 802.1Qaz. When an fc-set does not use its allocated port bandwidth, ETS shares the excess port bandwidth among other fc-sets on the port in proportion to their guaranteed minimum bandwidth (guaranteed rate). This utilizes the port bandwidth better than scheduling schemes that reserve bandwidth for groups even if that bandwidth is not used. ETS shares unused port bandwidth, so traffic groups that need extra bandwidth can 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 fc-sets:

  • 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 forwarding classes (priorities) to schedulers to define the scheduling characteristics of the individual forwarding classes in the fc-set. The resources scheduled for each forwarding class represent portions of the resources that the traffic control profile schedules for the entire fc-set, not portions of the total link bandwidth. The scheduler-maps statement defines the mapping of forwarding classes to schedulers.

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