The second model of bandwidth allocation on an egress access port is to directly associate a service or subscriber or multiservice site policer or queue to a port-level scheduler. This model allows the port scheduler hierarchy to allocate bandwidth on a per class or priority basis to each service or subscriber or multiservice site policer or queue. This allows the provider to manage the available egress port bandwidth on a service tier basis ensuring that during egress port congestion, a deterministic behavior is possible from an aggregate perspective. While this provides an aggregate bandwidth allocation model, it does not inhibit per-service or per-subscriber or multiservice site queuing. Figure: Direct service or subscriber or multiservice site association to port scheduler model shows the single, port scheduler policy model.
Figure: Direct service or subscriber or multiservice site association to port scheduler model also shows the optional aggregate rate limiter at the SAP, multiservice site or subscriber or multiservice site level. The aggregate rate limiter is used to define a maximum aggregate bandwidth at which the child queues and policers, if used, can operate. While the port-level scheduler is allocating bandwidth to each child queue, the current sum of the bandwidth for the service or subscriber or multiservice site is monitored. When the aggregate rate limit is reached, no more bandwidth is allocated to the children associated with the SAP, multiservice site, or subscriber or multiservice site. Aggregate rate limiting is restricted to the single scheduler policy model and is mutually exclusive to defining SAP, multiservice site, or subscriber or multiservice site scheduling policies.
The benefit of the single scheduler policy model is that the bandwidth is allocated per priority for all queues associated with the egress port. This allows a provider to preferentially allocate bandwidth to higher priority classes of service independent of service or subscriber or multiservice site instance. In many cases, a subscriber can purchase multiple services from a single site (VoIP, HSI, Video) and each service can have a higher premium value relative to other service types. If a subscriber has purchased a premium service class, that service class should get bandwidth before another subscriber’s best effort service class. When combined with the aggregate rate limit feature, the single port-level scheduler policy model provides a per-service instance or per-subscriber instance aggregate SLA and a class-based port bandwidth allocation function.
