
PMC-Sierra, Inc.
PM73488 QSE
L
PMC-980616
Issue 3
5 Gbit/s ATMSwitch Fabric Element
Released
Datasheet
34
To overcome the inefficiencies caused by collision in the network, the fabric must be run at a rate greater than line
rate. The speedup factor is the minimum rate necessary to guarantee that the network is no longer the system bottle-
neck. Note that in this case, the network efficiently moves data from the input to the output buffers, and the switch
performs similar to a purely output buffered switch.
2.8.2
Network Definition
A large range of switch fabrics can be described as follows: w
ith the following notation: “p” refers to the number of
fabric planes, and “x,” “y,” and “z” refer to the routing tag size necessary to make routing decisions in the Banyan
section of the network to route cells to the correct output port. This is summarized as follows:
(z)xp —
(y,z)xp — 3-stage network
1-stage network
Hence, the (3)
×
1 network shown in Figure 20 refers to a single switch stage, and three routing bits are required to
select from one of the eight output port groupings. (Recall that the QSE has 32 output ports that can be configured in
groups of 1, 2, 4, 8, 16, or 32. In Figure 20, they are configured in groups of four. The input and output buffers pro-
vided by the QRT have four input ports and four output ports to the switch fabric, and are logically broken into the
input half of the QRT (IRT) and output half of the QRT (ORT) for convenience.
The (5)
×
4 network shown in Figure 21 is an example of a network with four parallel planes. It demonstrates the flex-
ibility allowed because the QRT has four input and output ports. In this case, randomization is performed in the IRT.
Figure 20. (3) x 1 - 5 Gbps System
Figure 21. (5) x 4 - 20 Gbps System
x4
622 Mbps
UTOPIA
622 Mbps
UTOPIA
QSE
ORT
IRT
x 4
x 4
x4
x 1
622 Mbps
UTOPIA
622 Mbps
UTOPIA
QSE
ORT
IRT
x 4
x 4
x 1
Randomizer