Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Figure 3. Two Port Configuration of a ETT1 Switch
1,3
2
6
7
Crossbar
5
Input Data Slice
Output Data Slice
5
6
5,7
1,3
2,3
5
7
7
Flow Control
Crossbar
Output EPP
Input EPP
4
3
4
Scheduler
6,7
data cell flow
control flow
Figure 3 shows a two-port configuration of a ETT1 switch. Only the ingress queues of the left hand port
and the egress queues of the right hand port are shown. The port has one EPP and either six or seven DS
devices. The DS contains the cell queue memory and also has the Serdes interface to the linecard. A
single cell is “sliced” across all of the Dataslice devices, each of which can manage two slices. The EPP is
the port controller, and determines where cells should be stored in the DS memories. Multiple Crossbar
devices make up a full Crossbar. A single Scheduler device can arbitrate for the entire core.
A cell traverses the switch core in the following sequence of events:
1. A cell request arrives at the ingress port, and is passed to the EPP. The EPP adds the request to
any other outstanding cell requests for the same queue.
2. At some later time, the EPP issues a grant/credit to the source linecard, requesting an actual cell
for a specific queue. The linecard must respond with the cell within a short period of time.
3. The cell arrives at the ingress port and the LCS header is passed to the EPP. The EPP
determines the destination queue from the LCS header, and then tells the Dataslices where to
store the cell (each Dataslice stores part of the cell). The EPP also informs the Scheduler that a
new cell has arrived and so the Scheduler should add it to the list of cells waiting to be forwarded
through the Crossbar. The EPP modifies the LCS label by replacing the destination port with the
source port, so the egress port and linecard can see which port sent the cell.
4. The Scheduler arbitrates among all queued cells and sends a grant to those ports that can forward
a cell. The Scheduler also sends a routing tag to each of the destination (egress) ports; this tag
20
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
