The subclassA1partition
is more efficient, but limited by the sizes of secondary transit queue.
ClassA traffic is not subject to the fairness algorithm at ingress to the ring or when
transiting through the ring. ClassA traffic has precedence over classB and classC
traffic at ingress to the ring, and during transit through the ring (for dual-queue stations).
ClassA traffic moves through the primary transit path in each station as it
propagates around the ring, as a result a classA frame in transit can be preempted
only by a frame that started transmission into the ring before the classA arrived to
the transit station.
Description and operation of the primary and secondary transit paths, and descriptions
of single-queue and dual-queue models, are provided later on in this paper.
ClassB ClassB service provides an allocated, guaranteed data rate, bounded endto-
end delay and jitter for the traffic within the allocated rate; and access to additional
best effort data transmission that is not allocated, guaranteed, or bounded, and is subject
to the fairness algorithm. Within this class, the MAC uses fairness eligibility markings
to differentiate the committed information rate portion of classB (classB-CIR) and
the excess information rate portion of classB (classB-EIR).
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