Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
In the ideal scenario, each oEPP would have a separate virtual input queue for every (possibly 128) input
channel. However, the same restriction applies, limiting the oEPP to just 32 queues per output OC-48c
(and per priority). Figure 16 shows the virtual input queues in each oEPP when attached to four OC-48c
ports.
Each virtual input queue maps back to a single virtual output queue in one of the iEPPs. In abstract terms,
the virtual input queue is simply an extension of the appropriate virtual output queue.
Each output OC-48c channel within the oEPP has its own set of unicast virtual input queues. If an output
queue (virtual input queue) is backpressured, then this will push back to the appropriate virtual output
queue. However, each virtual output queue is shared by the four input OC-48c channels within that iEPP,
so backpressuring a virtual output queue has the effect of asserting backpressure to all four OC-48c’s on
the same iEPP.
The oEPP has an Output Scheduler process which determines which cell should be forwarded to the
egress linecards.
42
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
