Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
The output multicast fanout table (EOTIBM in the EPP) is only used if the port is in quad OC-48c mode. In
quad OC-48c mode a multicast cell arrives at the oEPP via the crossbar. The oEPP must determine what
combination of the four OC-48c ports that this multicast cell should be forwarded to (15 possible
combinations assuming it goes to at least one of the ports). The oEPP has the multicast tag (12 bits) from
the label, but that is not sufficient. It is not sufficient because the multicast tags are managed
independently across all ports: each iEPP has its own EITIBM and so a given 12 bit multicast tag might be
used to specify different multicast fanouts for two different iEPPs. To resolve the ambiguity, the oEPP must
also include the source port number with the 12 bit multicast tag, and combines the 5 bit source port with
the 12 bit multicast tag to produce a 17 bit tag that is unique across the entire fabric. This can then be used
to index into a table of 4-bit entries as shown in Figure 22.
Figure 22. OITIBM structure
oEPP
Output Multicast
Fanout Table EOTIBM
0
Multicast tag [11:0]
Source port[4:0]
17
131071
To Output
Scheduler
4
3
0
1 bit for each of the four local OC-48c ports
The index is the combination of {Multicast_tag, source_port}, so that the source port forms the least
significant bits of the address (index). Each entry has four bits such that bit 0 corresponds to subport 0 and
bit 3 corresponds to subport 3.
1.3.5 Combinations of OC-192c and Quad OC-48c Linecards
A switch might contain both OC-192c ports and quad OC-48c ports. Each port card must be configured
with information about all of the cards. The number of ingress queues is a function of this mix of ports:
given n quad OC-48c ports and m OC-192c ports, then each port will have U unicast queues, where:
U = 4 priorities * n * 4 egress subports + 4 priorities * m
So if n = 32 and m = 0 then U = 512.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
49
PMC [ PMC-SIERRA, INC ]
