Overview
512 Quality of Service Guide
provides an aggregate bandwidth allocation model, it does not inhibit per service or per
subscriber or multi-service site queuing. Figure 23 demonstrates the single, port scheduler
policy model.
Figure 23 also demonstrates the optional aggregate rate limiter at the SAP, multi-service site
or subscriber or multi-service site level. The aggregate rate limiter is used to define a
maximum aggregate bandwidth at which the child queues 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 multi-service site is monitored. Once the aggregate rate limit is
reached, no more bandwidth is allocated to the children associated with the SAP, multi-
service site, or subscriber or multi-service site. Aggregate rate limiting is restricted to the
single scheduler policy model and is mutually exclusive to defining SAP, multi-service site,
or subscriber or multi-service 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 multi-
service site instance. In many cases on the 7750 SR, 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.
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