1 Quality of Service Options in RPR
Resilient Packet Ring (RPR) 335
A station deploying a dual transit queue MAC is congested when occupancy of the
secondary transit queue (STQ) is excessive. A station deploying a single transit queue
MAC is congested when the rate of transmission is excessive relative to the capacity of
the transmission link or traffic is delayed excessively while awaiting transmission.
Figure 12.4 shows a congested station (S6) and the set of contiguous stations (S1 to
S6) contributing to the congestion at S6.
Each contributing station is associated with a rate (bi) at which it adds fairness
eligible traffic crossing the outbound link of the congested station S6. The rate, bi, is
scaled by an administrative weight (wi) that allows a station to add at a rate higher or
Figure 12.3 Single station view of MAC architecture
MAC client
MA control.request MA control.indication
MAC service interface
MA_data.request MA_data.indication
MAC client
Control interface
Fairness algorithm
Protection
Topology
OAM
Frame send/receive
Ringlet selection
Ringlet selection
Flood selection
Extended frame selection
Ringlet1 datapath
Encapsulation/decasulation
Shaping
Staging and queuing
Copying and routing
Stripping
Transit west/receive east
Ringlet0 datapath
Encapsulation/decapsulation
Shaping
Staging and queuing
Copying and routing
Stripping
Transit west/receive east
PHY service interface
East PHY West PHY
336 Chapter 12
lower than other stations without violating fairness principles.
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