Shaping hierarchy

The following describes the seven tiers of hierarchical shaping on HSQ:

• First shaping tier:

  This is the rate control tier. At the bottom of the shaping hierarchy is a queue that represents the basic entity from which a packet is extracted and sent out of the port by the port scheduler. At the SPI level, a queue can be attached either to a scheduler class or to a WRR group (but not to both simultaneously). Accordingly, the following shapers are supported at the bottom (first) tier:

  • Queue shaper — If a queue is directly attached to a scheduler class.

  • WRR group shaper – If a queue (possibly along with other queues) is attached to one of the two WRR groups at the SPI level. In this case, the queue shaper is ignored.

• Second shaping tier:

  This tier continues to operate at the SPI level. Eight queues form a queue set which is always allocated per SPI and the entire queue set can be shaped to an aggregate rate. In the ESM context, this tier is referred to as the SPI shaping tier. Depending on the SLA mode of operation, this tier can represent a subscriber aggregate rate (in a single SLA mode) or the aggregate rate for a subset of services within a subscriber (in an expanded SLA mode).

• Third shaping tier:

  Multiple SPIs within a single subscriber (supported only in expanded SLA mode) can be attached to a primary shaper which controls subscriber’s aggregate rate. The aggregate rate of the primary shaper is the third shaping tier.

• Fourth shaping tier:

  This tier is enforced within the context of the secondary shaper. The secondary shaper represents an aggregation of subscribers, for example, a group of subscribers that are attached to the same aggregation node (DSLAM or OLT).

  Each scheduling class at the secondary shaper can be individually shaped.

• Fifth shaping tier:

  This tier is the aggregate rate of the secondary shaper.

• Sixth shaping tier:

  Sixth and seventh shaping tier are at the port level.

  At the port level, scheduling classes can be either:

  • individually shaped

  • collapsed into a single WRR group, in which the collection of scheduling classes (a WRR group) is shaped.

  • These two possibilities (individual or group shaping) are mutually exclusive by configuration, and whichever is chosen represents the sixth shaping tier.

• Seventh shaping tier:

  This tier is the aggregate shaping rate of the physical port.