To overcome these issues, fairness algorithms are built into the RPR protocol. These
messages are part of the RPR header and tell the MAC how to treat each packet. The
various classes and sub classes can be used to create any service profiles appropriate
for any application. High priority, guaranteed traffic is never subject to fairness. High
priority traffic always gets the bandwidth assigned to it, always receives priority on the
ring and is therefore never subject to delay or delay variation. The fairness algorithm
ensures weighted dynamic distribution of available link bandwidths to source stations
using those links.
This feature enables two real benefits. One, it allows users to burst into any unused
network capacity and get high throughput in these instances. Secondly, it ensures
that no service is ever starved of bandwidth, since some network managers can always
reserve a portion of the ring bandwidth for Best Effort traffic.
RPR is the only standardized packet-based Layer 2 mechanism for ring topologies
that provides both the resilience and jitter/delay control necessary for the voice and
video services increasingly desired by telecommunications subscribers.
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