The LINK_RATE represents
the capacity of the ringlet and fa represents the fraction of capacity consumed
by higher-precedence (classA and classB-CIR) allocated traffic. The objective of the
fairness algorithm is to compute a fairRate applied to the contributing stations such
that the following goals are met:
?– bi/wi ?‰¤ fairRate: Contributing stations maximize their weight-adjusted rate without
exceeding the fairRate.
?– b1+??¦+b6 ?‰¤ LINK_RATE(1-fa): The sum of fairness eligible traffic transmitted by
the congested station maximizes use of available capacity without exceeding that
capacity.
In order to meet the condition bi/wi ?‰¤ fairRate at each contributing station (S1??“S6), the
fairRate computed by the congested station is propagated hop by hop in the upstream
direction, by fairness frames transmitted regularly, making the value known to each of
the contributing stations.
The propagation of the fairRate is known as rate advertisement. Figure 12.5 illustrates
the path of an advertisement propagated on ringlet1 in order to control congestion on
ringlet0. The advertisement carries the identity of the ringlet on which it is transmitted
(i.
Pages:
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774