It can be inferred that no single contributing station, S1, S2, or
S3, is contributing (i.e., adding fairness eligible traffic transiting S6) at a rate greater
than 4 units since it is known that the sum of this traffic is not greater than 4 units.
Propagation of the fairRate of 5 units beyond station S4 would, therefore, not reduce the
contributing rate of any station upstream of S4. S4 advertises the value FULL_RATE
indicating to upstream stations that their contributing rates need not be restricted.
As illustrated in the preceding examples, a station can advertise one of three possible
values to its upstream neighbor.
?– Its locally computed fairRate.
?– The fairRate advertised by its downstream neighbor.
?– The value FULL_RATE indicating that upstream stations are not contributing to
downstream congestion.
Figure 12.7 Local fairRate more restrictive than received fairRate
S0 S1 S2 S3 S4 S6 S7 S8 S5
Fairrate = 20 Fairrate = 10
10 10 10 10 10
Advertised fairrate
Figure 12.8 Advertising the FULL_RATE
S0 S1 S2 S3 S4 S6 S7 S8 S5
Fairrate = 5 Fairrate = 10
Full Full Full 5 5
Advertised fairrate
Resilient Packet Ring (RPR) 339
An advertisement carries the identity of its station of origin.
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