Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
1.3.3.1 Virtual Output Queues
Ideally, the EPP/DS would have a separate VOQ which would correspond to each of the request counters.
This would mean that congestion on one VOQ would not impact any other VOQ on the same OC-48c or
any VOQs on different OC-48c channels.
In practice, the EPP is constrained by the amount of cell buffering available in the ETT1 Dataslice device
(which contains the actual cell buffers). Consequently, all four request counters that correspond to a single
output channel share a single queue, as shown in Figure 14.
The EPP only manages a single queue for each of the output channels (whether the output channel is
OC-48c or OC-192c). If the EPP is connected to four OC-48c inputs, then those four OC-48c linecards
must share the single queue used for each output. The four dotted arrows in Figure 14 show that the four
request counters for output (0,0) all map to the same VOQ for output (0,0).
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
37
PMC [ PMC-SIERRA, INC ]
