Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Figure 19. Each iEPP has a Single Virtual Output Queue for Multicast Cells
m
iEPP
Priority 0
OC-48c 0
OC-48c 1
OC-48c 2
OC-48c 3
OC-48c 0
OC-48c 1
2
m
5
multicast cells
m
0
OC-48c 2
OC-48c 3
m
4
As before, this single queue is not a limitation unless backpressure is asserted to the queue, in which case
all four OC-48c subports are backpressured for all multicast cells from this port at this priority.
ETT1 uses a multicast tag in the LCS header to identify the multicast group that this cell should go to. The
iEPP then maps the tag into a port vector with one bit per port. This port vector is then passed to the
Scheduler to indicate the list of ports that should receive this multicast cell. Again, the Scheduler only
recognizes 32 ports and not 128 OC-48c subports; at the input side, a multicast cell destined for any one of
output ports (0,0), (0,1), (0,2) or (0,3) would simply be forwarded to the oEPP at port 0.
The oEPP receives the multicast cell, together with its tag. It then maps the (tag, source_port) into a new
4-bit vector that identifies what combination of the four subports should receive this multicast cell.
Figure 20 shows the entire process.
Figure 20. Multicast Cell Processing
iEPP
oEPP
multicast
multicast
Crossbar
Output Multicast
Fanout Table
Input Multicast
Fanout Table
src
prt
tag
tag
17
12
4
Output Scheduler
Scheduler
32
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
47
PMC [ PMC-SIERRA, INC ]
