ClassB is useful for services
that require a guaranteed bandwidth component, but have also the ability to accesses
more resources when available.
ClassC ClassC service provides a best-effort traffic service with no allocated or
guaranteed data rate and no bounds on end-to-end delay or jitter. ClassC traffic is always
subject to the fairness algorithm. In a single-queue implementation, classC traffic
moves through the primary transit path. In a dual-queue implementation, classC traffic
moves through the secondary transit path.
334 Chapter 12
The MAC Reference Model
As illustrated in Figure 12.3, the MAC is comprised of the MAC control sublayer and
the MAC datapath sublayer. The MAC datapath sublayer is comprised of the ringlet
selection entity and the datapaths for the two ringlets. These components and their
interconnections are illustrated in Figure 12.3 within the context of a single station
view of the MAC architecture.
Figure 12.3 also shows the activities implemented by each block within the MAC. The
main activities are further described in the following paragraphs.
Fairness Bandwidth management is done to maintain fairness for fairness eligible
frames (those without or beyond allocated bandwidth), with mechanisms to assure
that all stations receive their fair share of ring capacity across the links being used by
the stations, where the fair share is not necessarily the same for all stations.
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