2 Dual ring structure and conventions
ringlet0
ringlet1
S1 S2 S3 S4 S5 S6 S7 S8 S9
West East Span Links
Resilient Packet Ring (RPR) 333
The MAC provides two types of frame transmission services: Strict and Relaxed
Strict The Strict transmission service guarantees that all delivered data units are not
duplicated nor reordered, at the expense of discarding more data frames than in the
Relaxed mode.
Relaxed The Relaxed transmission service has the same guarantees as the Strict service,
except while recovering from failures in the ring in which case a negligible amount
of reorder or duplication can occur.
Since Relaxed mode is more effective than Strict mode, its use is recommended when
possible.
To support services with different quality of service demands, the MAC supports
three classes of service (CoS) into which the services may be mapped by the MAC client
according to their specific quality of service requirements.
ClassA ClassA service provides an allocated, guaranteed data rate and a low end-to-end
delay and jitter bound; as such classA can be used to support services such as TDM pseudo
wire emulation. Within this class, the MAC uses two internal subclasses, subclassA0 for
reserved bandwidth and subclassA1 for reclaimable bandwidth.
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