
PMC-Sierra, Inc.
PM73488 QSE
L
PMC-980616
Issue 3
5 Gbit/s ATMSwitch Fabric Element
Released
Datasheet
25
2
THEORY OF OPERATION
Multiple PM73488 QSEs can be combined to build a scalable switch fabric. The QSE switches data in the form of
118 nibble cells. The QSE has 32-input ports and 32 output ports, each containing a nibble-wide data interface, an
SOC signal, and a backpressure/data-acknowledge signal.
Groups of 1, 2, 4, 8, 16, or 32 ports can be internally configured to act as a single aggregate port (also called gang) for
unicast traffic. For multicast traffic, inputs and outputs can be grouped together in groups of 1, 2, or 4 ports. The input
multicast grouping mode, output multicast grouping mode, and the unicast grouping modes do not need to be the
same. Also, the QSE can be configured as a single 32 input
×
32 output switch
The cell flow through the QSE has two separate data paths; one path for unicast cells and another path for multicast
cells. Unicast cells are routed from one end of the switch fabric to the other end in a single cell time. In other words,
no unicast cells are ever stored in the switch fabric. Unicast cells are stored only at the ingress and egress of the
switch fabric. Multicast cells are routed in a store-and-forward manner. Each QSE can store up to 64 multicast cells.
The QRT used as an interface to a switch fabric constructed with QSEs allows the construction of an ATM switch up
to 160 Gbps.
A diagram of the QSE cell flow is shown in Figure 13. The unicast cell flow contains a routing stage that uses routing
information from the cell header to determine the output group. The multicast cell flow contains an interface to an
external SSRAM that contains the Multicast Port Vector (MPV) information for routing cells to multiple output
groups.
Figure 13. Basic QSE Flow
External SSRAM
Arbiter
Unicast Routing and
Distribution Path
Multicast
Path
Phase Aligners
and
Receive SE_D_IN
and SE_SOC_IN
Data
Drivers
Phase Aligners
and Receive
BP_ACK_IN
BP_ACK
Drivers
Forward Cell Flow
Backpressure/Ack Flow
Miscellaneous Signals