Fairness
Fairness algorithms are also 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
ring capacity and get high throughput in these instances. Secondly, it ensures that no
service is ever starved of bandwidth. Network managers can always reserve some portion
of the ring for Best Effort traffic. These two facts mean that network owners with
RPR transport equipment can overbook their networks to a much greater extend and
enjoy much greater revenue as a result.
The 802.3 Ethernet MAC has no comparable mechanisms. There is no signaling
among devices to understand the congestion state of other switches on the network.
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