PM9313 datasheet(62/343 Pages) PMC

62 / 343 page

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

PM9311/2/3/5 ETT1™ CHIP SET

PMC-2000164

ISSUE 3

ENHANCED TT1™ SWITCH FABRIC

Released

Data Sheet

PMC-Sierra, Inc.

The TDM service is inherently a multicast service. The egress ETT1 must therefore support the ability for a

TDM cell to go to any combination of the four subports within a port. A four-bit field in every TDM table

entry provides the multicast fanout for each TDM cell that is received at the egress port. The EPP keeps

track of this fanout information and sends the TDM cell to each subport that is a member of the fanout.

Figure 28 illustrates how the EPP uses the TDM table to determine the source port of a TDM cell, as well

as the local subport multicast fanout.

Figure 28. The oEPP Must Treat the Transferred TDM Cell as a Multicast Cell

The output TDM cell queue does not need to be large as TDM cells are always forwarded to the output

linecards at the highest priority, and the TDM queue is never backpressured. The size of this queue does,

however, restrict the possible TDM table configuration. The following constraints are required to prevent

dropped TDM cells:

•

In a TDM table time slot, an input port can not send more than one cell and an output port can not

receive more than one cell.

•

Subport mode: The TDM Reservation Table can specify the same ingress subport only once every

four time slots.

•

Subport mode: The TDM Reservation Table can not specify the same egress subport more than

48 time slots within a moving window of 192 time slots. This constraint is caused by the TDM

output queue.

Current TDM Slot Time

TDM Reservation Table

991

Inputport= 12

output vector

= 0101

Cell from Crossbar

To Scheduler

0001

0111

0101

Output TDM Cell Queue

(multicast fanout)

PM9313 Datasheet(PDF) 62 Page - PMC-Sierra, Inc

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